#295000 - 10/03/2007 17:52
Home electrical wiring question...
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carpal tunnel
Registered: 13/02/2002
Posts: 3212
Loc: Portland, OR
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My google fu is weak today...
We just bought a new washer and dryer. The dryer installation manual says that it needs a separate 30 amp circuit, and the dryer has a 3-prong 30 amp plug (with the L shaped neutral/ground). The apartment, however, has a 50 amp circuit for the dryer, with a corresponding 3 prong receptacle.
If I understand things correctly, that means that the dryer needs to be on a separate circuit that has a minimum of 30 amps available, since the amperage rating of a circuit is based on the total watt load, correct? My
plan is to just replace the receptacle with one that fits the dryer plug. Before I actually do this, can anyone suggest why it's not a good idea, and that I'll just fry either myself, or the dryer, if I do?
I suppose a better option would be to find a cord with a 50 amp plug, and replace the power cord on the dryer -- then I wouldn't need to mess with the apartment's electrical at all. Receptacles are easier to source than spare power cords, however...
Cheers,
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#295001 - 10/03/2007 18:16
Re: Home electrical wiring question...
[Re: canuckInOR]
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enthusiast
Registered: 18/03/2002
Posts: 225
Loc: San Diego, California USA
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Let's see if I can help shed some light.... Your new dryer needs a 30 amp 240 volt circuit as a minimum. A larger capacity circuit would be okay, as long as the wall receptacle matches the plug from the dryer. Usually different amp rated circuits have different NEMA receptacles (link below). The amperage rating of a circuit is based mainly on the current capacity of the wire used to wire the circuit from the panel to the receptacle. The breaker size is chosen to protect the wire so it doesn't melt if it is overloaded or shorted. At a minimum, #6 wire is needed for a 50 amp circuit. It sounds from your description that you have a 50 amp 240 volt dryer circuit available in your apartment? Are those hot wires #6 copper? If they're smaller than #6, then the breaker could be incorrectly sized. But we'll assume that the breaker size and wire size is correct. It sounds like your dryer cord doesn't match the receptacle already on the wall? Here's a chart that shows the various configurations: http://nooutage.com/nema_configurations.htmDoes your dryer cord match up to the 5-30R receptacle in the 30 amp section? If so, what configuration is the receptacle on the wall? Maybe you could post a photo or two and that would help identify things.... I think you're on the right track.... Randy
_________________________
Happy owner of 2 Centrals, 2 Empegs Mk2a 160GB, 1 Empeg Mk2a 60 GB, a Rio Riot, 4 Rio Receivers, and two 1GB iPod Shuffles...
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#295002 - 10/03/2007 18:53
Re: Home electrical wiring question...
[Re: The Central Guy]
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carpal tunnel
Registered: 13/02/2002
Posts: 3212
Loc: Portland, OR
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Blessed be the all knowing empeg bbs members.  Quote:
The amperage rating of a circuit is based mainly on the current capacity of the wire used to wire the circuit from the panel to the receptacle. The breaker size is chosen to protect the wire so it doesn't melt if it is overloaded or shorted. At a minimum, #6 wire is needed for a 50 amp circuit.
Ah, that's good information about how a breaker size is chosen.
Quote:
It sounds from your description that you have a 50 amp 240 volt dryer circuit available in your apartment?
The plug on the old dryer was marked 50 amps, and that's what the guy who was supposed to install the appliances told us.
Quote:
Are those hot wires #6 copper? If they're smaller than #6, then the breaker could be incorrectly sized. But we'll assume that the breaker size and wire size is correct.
I'm assuming that the wiring is correct, but I haven't actually pulled the receptacle cover off to look.
Quote:
It sounds like your dryer cord doesn't match the receptacle already on the wall?
That's correct.
Quote:
Here's a chart that shows the various configurations:
http://nooutage.com/nema_configurations.htm
Does your dryer cord match up to the 5-30R receptacle in the 30 amp section? If so, what configuration is the receptacle on the wall? Maybe you could post a photo or two and that would help identify things....
Neither plug, nor receptacle are on that chart. The plug is definitely 10-30P, and the receptacle is 10-50R, based on this chart. It's marked 50A-125/250V, but doesn't have the NEMA code on it.
I don't have a camera handy... 
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#295003 - 10/03/2007 19:24
Re: Home electrical wiring question...
[Re: canuckInOR]
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carpal tunnel
Registered: 17/12/2000
Posts: 2665
Loc: Manteca, California
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If you are going to replace the receptacle then, the breaker should also be replaced with a 30amp version. Most likely for the best.
_________________________
Glenn
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#295004 - 10/03/2007 20:20
Re: Home electrical wiring question...
[Re: canuckInOR]
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carpal tunnel
Registered: 29/08/2000
Posts: 14482
Loc: Canada
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Quote:
I suppose a better option would be to find a cord with a 50 amp plug, and replace the power cord on the dryer -- then I wouldn't need to mess with the apartment's electrical at all. Receptacles are easier to source than spare power cords, however...
You know the Right Answer(tm): use a 30amp breaker.
The dryer's wiring is all done assuming a 30amp (max) protected circuit. Allowing more than 30amps sustained current could create a fire hazard in the event of a dryer malfunction.
Cheers
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#295005 - 11/03/2007 01:57
Re: Home electrical wiring question...
[Re: mlord]
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carpal tunnel
Registered: 19/01/2002
Posts: 3583
Loc: Columbus, OH
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Also, since noone else has pointed it out, you don't have to replace either the receptacle or the pigtail (cord). Run down to Home Depot and get a receptacle that matches your dryer plug and a plug that matches your apartment and a small piece of wire and make an adapter. Combined with the correct breaker as Mark pointed out, This would be a great solution. Plus you can hang on to it when you move so that you can use either kind of receptacle at the next place. Then again, it's probably just as easy if not easier to change the pigtail on your dryer to match. It's just screw terminals on most dryers.
_________________________
~ John
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#295006 - 11/03/2007 07:44
Re: Home electrical wiring question...
[Re: JBjorgen]
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pooh-bah
Registered: 20/01/2002
Posts: 2085
Loc: New Orleans, LA
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Having just rewired my house, I feel the need to chime in. Everything said so far is absolutely correct. There is NOTHING wrong with having wire that is too big for your circuit. You MUST change your breaker to a 30A. It will WORK with a 50, but as others have stated, it will be a fire hazard. I will say, are you SURE your dryer is looking for 30A only? That seems awfully low for a dryer, unless it's a very small one. Keep in mind, a 30A 220 breaker is two 15's tied together. I've never heard of a 50A 220 circuit (in fact, I've never seen a 25A breaker.) If there is only 1 50A, then what you have is 110, not 220. Keep in mind, this is all true in the states. I have no idea which side of the pond you're on, and have no clue as to how things work in Europe. One other thing to watch out for is that since a 30A won't need the same size wire as a 50A, there's a decent chance the wire won't fit into your breaker without trimming some of the wires off first. (Wire of that gauge is usually stranded so it can be bent without tools.)
Last but not least, check the voltage on the panel with a meter to make sure it's off before you work in your panel. My electrician friend who helped me rewire almost taught his assistant this lesson the hard way at my house. We pulled the meter, the assistant starts to pull a breaker. Jim says "Did you check the power to make sure it's off?" The assistant looks at him like he's nuts, but pulls out his meter. Checks the voltage across the panel, and reads 220. Keep in mind that the power meter is sitting on the ground at our feet. Turns out that in MY house, for some unknown reason, a commercial meter pan was used, rather than residential. In a commercial pan, when you pull the lever to release the meter, there are these bars that slide into contact completing the circuit behind the meter pan. That way, the power company can do whatever they need to do to a meter without interrupting power to the business. Scary. He coulda, and I woulda, been toast. Hurting at the least.
-=edit=-
Of course, after 2 seconds of research, 25 and 50A breakers are quite common, I've just never seen one.
Edited by lectric (11/03/2007 07:50)
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#295007 - 11/03/2007 13:04
Re: Home electrical wiring question...
[Re: lectric]
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old hand
Registered: 01/10/2002
Posts: 1033
Loc: Fullerton, Calif.
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Quote:
Keep in mind, a 30A 220 breaker is two 15's tied together.
A 30 amp 220v breaker (at least here in the states, probably in the EU as well) is two 30 amp single pole breakers tied together.
While it is true that you can get 30 amps of 120v out of a 2 pole 15 amp breaker, that's at 120v... the two loads will balance each other and become a single 15 amp 220 volt load with no current flow on the neutral. A 220volt load like a drier doesn't use the neutral, so if it's 30 amps on one leg, it's 30 on the other. The breaker must be a double 30 amp.
Quote:
If there is only 1 50A, then what you have is 110, not 220.
Probably, you will never find a 50 amp 120v circuit. The largest allowed in the states is 30 amp. Older houses have 15 amp circuits, newer have 20.
My house has one 70 amp circuit to the garage... but that was my doing...
Quote:
One other thing to watch out for is that since a 30A won't need the same size wire as a 50A, there's a decent chance the wire won't fit into your breaker without trimming some of the wires off first. (Wire of that gauge is usually stranded so it can be bent without tools.)
Don't do this please... Most breakers up to 50 amps are all made in the same housing with the same terminals, so the 50 amp wire will fit the 30 amp breaker.
Also, don't bend the wire with pliers. The minimum bend radius of any wire is usually 8x the wire diameter. I've seen a lot of places where the wires were bent into pretty 90 degree sharp angles with pliers (I used to do this as a teen wiring things). Especially in solid core wire, this breaks, or nearly breaks, the core.
Also, a 50 amp circuit may be using a #8 wire, depending on the age of the installation. Probably, since this is a house installation, it will be a solid core. This is still easily bent by hand.
Wires are rated for amperage by the temperature that their insulation can withstand. There are new insulation materials constatly coming out, so that years ago you would have had to use a #6 for the 50 amp circuit, but newer wires could be only a #8. Most wire/current selection charts are simple things and use the most conservative figures. In any case, both 6 and 8 are fine for your 30 amps.
Quote:
Last but not least, check the voltage on the panel with a meter to make sure it's off before you work in your panel.
Always good advice, tho I replace breakers with the power on...
Quote:
We pulled the meter, the assistant starts to pull a breaker. Jim says "Did you check the power to make sure it's off?" The assistant looks at him like he's nuts, but pulls out his meter. Checks the voltage across the panel, and reads 220.
I have seen houses where someone has jumpered one leg of the power meter to same money. It's amazing the stuff that goes on in house wiring...
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#295008 - 11/03/2007 13:08
Re: Home electrical wiring question...
[Re: JBjorgen]
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old hand
Registered: 01/10/2002
Posts: 1033
Loc: Fullerton, Calif.
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Quote:
Also, since noone else has pointed it out, you don't have to replace either the receptacle or the pigtail (cord). Run down to Home Depot and get a receptacle that matches your dryer plug and a plug that matches your apartment and a small piece of wire and make an adapter. Combined with the correct breaker as Mark pointed out, This would be a great solution. Plus you can hang on to it when you move so that you can use either kind of receptacle at the next place. Then again, it's probably just as easy if not easier to change the pigtail on your dryer to match. It's just screw terminals on most dryers.
It's even easier still to just change the receptacle. It's easier to open the junction box than the drier. Probably only $10 for the receptacle, I would suspect the pigtail would be more.
Generally speaking, less connections is better than more.
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#295009 - 11/03/2007 20:32
Re: Home electrical wiring question...
[Re: larry818]
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carpal tunnel
Registered: 17/12/2000
Posts: 2665
Loc: Manteca, California
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General consensus seems to be replace both the breaker and receptacle. Yet this is in an apartment. So mods might be out of order.
_________________________
Glenn
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#295010 - 12/03/2007 02:40
Re: Home electrical wiring question...
[Re: gbeer]
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addict
Registered: 23/01/2002
Posts: 506
Loc: The Great Pacific NorthWest
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Most everything has been explained here. The wire is rated for current capacity based on insulation type but also wire type, aluminum or copper, per NEC 310-16. We won't go into variations of this based on how the wire is used, direct burial, in free air, or in conduit, or derating based on the number of current carrying wires in conduit as these items don't apply. One item that was missed is that the circuit is based on ALL components. This includes the tempurature rating of the terminations. You must use whatever component has the LOWEST temperature rating as the means of determining what chart to use. Just replace the breaker and the recepticle with UL rated components that have the correct amperage ratings for your dryer and you will not only be safe but following the NEC. IF the wire is aluminum you need to apply a de-oxidizing compound to the wire were you make it up at the breaker and at the recepticle. If it is copper you don't.
_________________________
No matter where you might be, there you are.
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#295011 - 12/03/2007 09:31
Re: Home electrical wiring question...
[Re: Neutrino]
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old hand
Registered: 14/08/2001
Posts: 886
Loc: London, UK
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Man - is wiring as complicated and difficult as healthcare is in the US??
_________________________
Mk2a RioCar 120Gb - now sold to the owner of my old car
Rio Karma - now on ebay...
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#295012 - 12/03/2007 09:43
Re: Home electrical wiring question...
[Re: furtive]
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carpal tunnel
Registered: 24/12/2001
Posts: 5528
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Uhh. Super complicated! In the UK we just plug the dryer into a normal 13A wall socket. At least the one I've got does. The only thing with a special dedicated circuit is the oven/hob...
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#295013 - 12/03/2007 13:39
Re: Home electrical wiring question...
[Re: tman]
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carpal tunnel
Registered: 25/12/2000
Posts: 16706
Loc: Raleigh, NC US
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Yeah, but your standard voltage is 220, whereas ours is 110. Our dryers require 220. It's usually the only non-standard outlet in the home. I'm sure the oven requires 220 as well, but I think they're usually hard-wired, not plugged in.
_________________________
Bitt Faulk
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#295014 - 12/03/2007 13:48
Re: Home electrical wiring question...
[Re: wfaulk]
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carpal tunnel
Registered: 29/08/2000
Posts: 14482
Loc: Canada
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Quote:
Yeah, but your standard voltage is 220, whereas ours is 110. Our dryers require 220. It's usually the only non-standard outlet in the home. I'm sure the oven requires 220 as well, but I think they're usually hard-wired, not plugged in.
I think most locales now require outlet/plug for new electric stove connections, too.
Cheers
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#295015 - 12/03/2007 18:24
Re: Home electrical wiring question...
[Re: Neutrino]
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carpal tunnel
Registered: 13/02/2002
Posts: 3212
Loc: Portland, OR
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Quote:
If the wire is aluminum you need to apply a de-oxidizing compound to the wire were you make it up at the breaker and at the recepticle. If it is copper you don't.
Ah, that's a good bit of knowledge.
A little more information... right now, we're in a rental (we'll be house-hunting before the year is out). I'm not excited about paying for renovations to someone else's apartment -- hence the post asking for the best course of action. Our need to do laundry, and the land-lady's sense of timeliness, are not in accord, or I'd just have her call an electrician. When we move out, I plan on returning everything to its original state.
I've replaced the receptacle (cost $5). The wiring is the multi-strand aluminum stuff. I did not trim the ends to fit, since, as was suggested, the back end of the receptacles were identical -- there was no need, and it seems like a foolish thing to do, anyway. What happens if the de-oxidizing compound isn't applied (or, in other words, do I really need to pull the dryer back out, and open the receptacle up again)? The wire was still nice and shiny...
I haven't replaced the breaker, but will do that as soon as I can make it to the hardware store again -- probably tonight, but "lost cat" issues have put electrical issues on the back burner for now.
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#295016 - 12/03/2007 18:35
Re: Home electrical wiring question...
[Re: canuckInOR]
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carpal tunnel
Registered: 29/08/2000
Posts: 14482
Loc: Canada
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Quote:
I've replaced the receptacle (cost $5). The wiring is the multi-strand aluminum stuff.
Apparently, a lot of houses burned down because of aluminum wiring. So, double check that receptacle. It should specify "Al" safe on it somewhere, instead of "Al" crossed-out.
Cheers
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#295017 - 12/03/2007 18:57
Re: Home electrical wiring question...
[Re: canuckInOR]
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addict
Registered: 23/01/2002
Posts: 506
Loc: The Great Pacific NorthWest
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I'm sorry to say but, yes, you should pull out the dryer and apply the de-oxidizing compound. Aluminum will oxidize without it. Over time, exposed to the oxygen in the air, it will form a white powder over the conductors which will cause the electrical connection to degrade. This in turn will cause resistance at the termination to increase which will cause your worst enemy, heat. Aluminum has a higher coefficient of expansion than copper. As the termination heats and cools, the problem will continue to get worse. Eventually there will be a failure. As Mark suggests you should check the receptacle for an AL / CU marking. I would expect that it will be all right. A UL listed receptacle will almost certainly have this. Also to stay within NEC guidelines you MUST use UL listed components. Lastly, please, go get the correct breaker. It is the one component that guards the rest of the system and places it in compliance with the code.
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#295018 - 12/03/2007 19:19
Re: Home electrical wiring question...
[Re: mlord]
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carpal tunnel
Registered: 12/11/2001
Posts: 7738
Loc: Toronto, CANADA
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Quote:
I think most locales now require outlet/plug for new electric stove connections, too.
I haven't seen a hard-wired stove/range connection on any of the homes I've lived in that were built in the past 20 years.
I'm deciding right now whether to add an extra 240v outlet (15A) to my new laundry room for the washer or if I'll instead just use a single 240v 30A outlet intended for the dryer with a splitter/adapter that the appliance manufacturer (Miele) sells. Home won't be delivered until November but I have to make my final decisions on extras including wiring in a few weeks.
As an aside I'm also considering getting certified for electrical and general building/home inspection. Still in the initial "thinking about it" stages.
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#295019 - 12/03/2007 20:00
Re: Home electrical wiring question...
[Re: hybrid8]
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pooh-bah
Registered: 12/02/2002
Posts: 2298
Loc: Berkeley, California
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The Miele one costs more than having an electrician do it right the first time, if I recall correctly. Of course, you'll want it wired so you can go back to a 30amp dryer at some point in the future. The Miele washer and dryer are certainly nice appliances, though I'm not convinced they're worth the premium over a good american front loader.
Just to take this even further off topic, we buy all our appliances from our local Sears appliance outlet. It's a massive wearhouse just south of Oakland where all the returns end up. Some things are beat up, some things seem brand new, and they're often half the cost of buying off the shelf.
Matthew
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#295020 - 12/03/2007 20:22
Re: Home electrical wiring question...
[Re: matthew_k]
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carpal tunnel
Registered: 12/11/2001
Posts: 7738
Loc: Toronto, CANADA
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I'm waiting to find out how much the upgrade price is from the builder for the extra 240v outlet. We'll see if it's cheaper than the adapter or not. It won't be cheaper to pay someone to do the electrical install of a completely new circuit afterwards than buying the adapter though. The laundry is on the second floor and the electrical panel is in the basement. I can do it myself, but it's a hassle to route stuff down to the basement. I'm also waiting for Miele to release new Euro-class machines to North America since I'm a little pissed there's no Spin nor Rinse cycles on the current dumbed-down W1215 washer. Got word from Miele Canada they'll be introducing new models this year that "should make you happy."
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#295021 - 12/03/2007 21:15
Re: Home electrical wiring question...
[Re: hybrid8]
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pooh-bah
Registered: 12/02/2002
Posts: 2298
Loc: Berkeley, California
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Quote:
I'm waiting to find out how much the upgrade price is from the builder for the extra 240v outlet.
Isn't the miele splitter simply a nice box with two 15 amp 220V plugs combined into one 30amp plug? It seems like it's just a matter of what outlet(s) they put on the end of the same wire. Of course, I've always assumed putting a 30 apm dryer on the end of a 50 amp fuse was Just Fine, but the find minds above seem to say that's not the case.
Change orders being what they are, they'll probably try and charge an arm and a leg. Be sure to reply "that's outrageous, will you do it for x/2?" when they give you a number. Back when I worked for a network construction firm we'd bid jobs at cost if we had to and make up for it on change orders.
Matthew
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#295022 - 12/03/2007 21:20
Re: Home electrical wiring question...
[Re: matthew_k]
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addict
Registered: 27/10/2002
Posts: 568
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Quote:
The Miele washer and dryer are certainly nice appliances, though I'm not convinced they're worth the premium over a good american front loader.
I can't comment on the quality of 'good american front loaders', but I can testify about the quality of Miele washers/dryers. We tried to use some cheapish washers and driers onboard the vessel, but they lasted about a week before they broke down. The Mieles we have have lasted several years, and they run not quite 24/7, but close. But of course, if you do laundry once or twice a week, a cheaper unit will also last long.
Stig
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#295023 - 13/03/2007 00:20
Re: Home electrical wiring question...
[Re: larry818]
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pooh-bah
Registered: 20/01/2002
Posts: 2085
Loc: New Orleans, LA
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After being corrected by Larry on basically every single point, I feel like an ass. Just to clarify, how does two 30A breakers on different phases equal 30A? Not trying to argue, but it seems that each leg is capable of pulling 30A, independent of the other. In my mind, it would make sense that one would need a 60A recepticle to handle it. But I guess that's all in how it's labled. Is it that each wire can handle 60A? Grrrr.... Now I'm going to have to borrow a meter from work and check for myself to convince myself..
As to the 8:1 bend ratio, how can that even be possible in most (at least, my) circuit panels? I only have 2" or so to go from vertical to horizontal on my wires. This doesn't seem like enough physical space for a 4-6 guage wire. Not to mention the 0 guage mains that turn in almost as little radius.
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#295024 - 13/03/2007 00:33
Re: Home electrical wiring question...
[Re: lectric]
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carpal tunnel
Registered: 17/12/2000
Posts: 2665
Loc: Manteca, California
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Quote:
As to the 8:1 bend ratio, how can that even be possible in most (at least, my) circuit panels? I only have 2" or so to go from vertical to horizontal on my wires. This doesn't seem like enough physical space for a 4-6 guage wire. Not to mention the 0 guage mains that turn in almost as little radius.
It's not so much of a problem where the wire is new. Bending a tight radius once will work but it will harden the wire and subsequent unbend/bends will cause a break from fatigue.
_________________________
Glenn
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#295025 - 13/03/2007 00:37
Re: Home electrical wiring question...
[Re: gbeer]
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pooh-bah
Registered: 20/01/2002
Posts: 2085
Loc: New Orleans, LA
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Well that makes sense. Metal fatigue can certainly be an issue.
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#295026 - 13/03/2007 01:29
Re: Home electrical wiring question...
[Re: lectric]
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enthusiast
Registered: 18/03/2002
Posts: 225
Loc: San Diego, California USA
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Here's a few more tidbits on the subject...
Here in California, and probably other places as well, a typical electrical feed for a house coming from the utility consists of a single phase 240 volt feed coming out of a center-tapped transformer (in my case it is 12,000 volts into the transformer and 240 volts out).
The center tap is considered the neutral and is bonded at the service panel entrance to an earth ground. At downstream subpanels, the ground and neutral connections are separated.
Anyways, each hot wire at the service entrance measures 120V with respect to that center tap neutral. So there is 240 volts between the two outer legs.
Sometimes people will refer to this arrangement as "two phase", but in reality the home is fed by a single phase circuit (in my case, 12kV). The two 120 volt legs are 180 degrees out of phase with respect to each other. If they are loaded equally, there would be no current flow in the neutral...
I hope that helps and doesn't cause too much confusion...
Randy
_________________________
Happy owner of 2 Centrals, 2 Empegs Mk2a 160GB, 1 Empeg Mk2a 60 GB, a Rio Riot, 4 Rio Receivers, and two 1GB iPod Shuffles...
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#295027 - 13/03/2007 03:50
Re: Home electrical wiring question...
[Re: lectric]
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addict
Registered: 23/01/2002
Posts: 506
Loc: The Great Pacific NorthWest
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How can two 30 amp breakers equal 30 amps? Well, 30 amps is 30 amps. Voltage and current are two different aspects of electricity. Using two legs on different phases does not change the amperage but does change the voltage. To put this into an analogy of water, current is the volume and voltage is the pressure. If there is more voltage or more current there is more power. Using a 240 volt 30 amp circuit delivers twice the power of a 120 volt 30 amp circuit but it is still a 30 amp circuit. As the voltage is increased the amount of current needed to do the same work is decreased. This is the reason why power transmission lines run at very high voltages. It's all rather strange but the amount of energy loss is dependent on current not voltage, I2r and all that. This is also why large appliances use 240 volt instead of 120. Everything gets smaller. The breaker size, the wire size, the line loss, etc, but the same amount of power is transmitted. At the facilities that I oversee everything electrical / electronic we use all kinds of voltages from 12470 on down.
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#295028 - 13/03/2007 06:59
Re: Home electrical wiring question...
[Re: lectric]
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old hand
Registered: 01/10/2002
Posts: 1033
Loc: Fullerton, Calif.
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Quote:
Just to clarify, how does two 30A breakers on different phases equal 30A?
Think of a 220volt center tapped transformer. This is, essentially, what feeds USA houses. There is only one phase, but two "legs". Usually the center tap is tied to ground at the house breaker panel and we call it "neutral". For a 30 amp circuit, it would seem that a one pole 30 amp breaker is enough, but since both legs are hot with respect to neutral and ground, both legs must have a breaker. For 220v loads, the 30 amps on both legs is the same 30 amps, it's not additive.
For 110 volt loads, it does appear that the breaker delivers 60 amps, but the loads, if equal, balance on the two legs and becomes a single 220 volt load. Double the voltage, half the amps, so two 30 amp 110 volt loads becomes a single 30 amp 220 volt load.
There did exist here in the states a two-phase electrical system that required four hot wires that all had to be connected correctly to work. It was kind of a precursor to three-phase, that requires only three wires and, for the most part, can be connected in any way. I think the last two-phase electrical distribution system here was decommissioned back in the '70s.
Stepper motors are two phase.
I'm jealous of our EU friends, they get three phase to their houses. I don't even have three phase to my industrial shop...
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Not trying to argue, but it seems that each leg is capable of pulling 30A, independent of the other.
They are not independent. You can get a single 110v load to pull 30 amps and return it on the neutral, but once you start adding 120v loads on the other leg, you lose current flow on the neutral. With two identical 120v loads, there will be no current flow on the neutral. They become a 220v load.
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As to the 8:1 bend ratio, how can that even be possible in most (at least, my) circuit panels? I only have 2" or so to go from vertical to horizontal on my wires. This doesn't seem like enough physical space for a 4-6 gauge wire. Not to mention the 0 gauge mains that turn in almost as little radius.
A #4 is 0.2" diameter, so 8x is only 1.6" radius. Typically, the big feeder wires come from the top and don't bend much getting to the lugs. Of course, this doesn't mean that your particular panel is done this way. Electricians know very little about wires...
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#295029 - 13/03/2007 12:24
Re: Home electrical wiring question...
[Re: lectric]
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carpal tunnel
Registered: 29/08/2000
Posts: 14482
Loc: Canada
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Quote:
how does two 30A breakers on different phases equal 30A?
.
A simpler answer than the others:
A single wire is not capable of powering anything in your house. Everything needs two wires, one for the electricity to arrive on, and another to carry it away again, forming a loop. Without this wire loop (or "circle" or "circuit"), nothing flows, and your lights (or dryer) don't do anything.
Putting two (or three, or four, or ..) 30A breakers in series (meaning: "anywhere in the same loop") with each other has no more effect than just a single 30A breaker. A breaker still "breaks" the circuit when 30A of current flow is exceeded.
The reason your dryer circuit has a pair of breakers, rather than just a single one, is to guard against wiring faults, in case the current finds a different way to complete a loop (like, through your body..). They just want to guarantee that the electric current *must* pass through at least one of the 30A breakers regardless. That's why.
Edited by mlord (13/03/2007 12:26)
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#295030 - 13/03/2007 13:43
Re: Home electrical wiring question...
[Re: mlord]
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pooh-bah
Registered: 20/01/2002
Posts: 2085
Loc: New Orleans, LA
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Bingo.... That makes sense. So when I have a 200A mains breaker, I should only be subtracting the 30A from it, not the 60A. even though there are 2 30A breakers. Counterintuitive, but it makes sense.
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#295031 - 13/03/2007 15:24
Re: Home electrical wiring question...
[Re: lectric]
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carpal tunnel
Registered: 29/08/2000
Posts: 14482
Loc: Canada
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Quote:
Bingo.... That makes sense. So when I have a 200A mains breaker, I should only be subtracting the 30A from it, not the 60A. even though there are 2 30A breakers. Counterintuitive, but it makes sense.
Yup. Where it gets somewhat funny, requiring the more detailed explanations above, is when you add a breaker for a 120VAC circuit.
Those generally only count for "half" against the main panel's 220VAC capacity of 200A.
EDIT: Or rather, each pair of 15A (or 20A or whatever) 120VAC circuits counts as a single unit against the panel capacity. So two 15A 120VAC circuits normally present only a 15A max load on the main panel, assuming one of them is on one leg of the 220VAC, and the second is on the other leg of the 220VAC (which is how "paired/ganged" breakers are normally installed).
-ml
Edited by mlord (13/03/2007 15:27)
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#295032 - 13/03/2007 17:11
Re: Home electrical wiring question...
[Re: Neutrino]
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carpal tunnel
Registered: 13/02/2002
Posts: 3212
Loc: Portland, OR
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I'm sorry to say but, yes, you should pull out the dryer and apply the de-oxidizing compound.
Okay... will do.
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As Mark suggests you should check the receptacle for an AL / CU marking.
Well, since I have to pull the dryer out, anyway. (Truthfully, I haven't tossed the bag the receptacle came in, yet, so I'm sure it's on there somewhere.) I think it's UL listed, but I can check when I get home.
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Lastly, please, go get the correct breaker. It is the one component that guards the rest of the system and places it in compliance with the code.
I did this last night -- or rather, I purchased it last night. I haven't had time to install it, yet. Hopefully tonight...
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#363129 - 13/12/2014 13:26
Re: Home electrical wiring question...
[Re: canuckInOR]
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addict
Registered: 02/08/2004
Posts: 434
Loc: Helsinki, Finland
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I'm bringing this thread back up as I've just got a new washer/dryer installed (well mostly). In the cubby where they are installed there is just one of the three prong 30 amp style plugs (there was a combo unit in there previsouly that just needed one outlet). The dryer plugs into this just fine, but the washer requires a standard US grounded outlet.
I'll be getting an electrician to get a new outlet installed and to make sure that everything checks out. But I was wondering, can some sort of splitter be installed to break that one 30 amp outlet down to one for the dryer and a standard outlet for the washer? A quick internet search didn't bring me anything so I'm guessing that's a no for multiple reasons, but just curious if this was technically possible.
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#363130 - 13/12/2014 14:45
Re: Home electrical wiring question...
[Re: canuckInOR]
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carpal tunnel
Registered: 29/08/2000
Posts: 14482
Loc: Canada
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Technically possible? Absolutely: that 30A outlet has two 120V legs, neutral, and earth-ground. So yes, technically possible.
A Good Idea(tm) though? NO. Absolutely not.
The breaker and wiring for the dryer circuit are for 30A. The 120V outlet for the washer will be a 15A (or perhaps 20A) device -- so the available current (30A) would exceed that device's safety rating.
Various electical codes also forbid it -- the washer and dryer, like most permanent appliances, are typically each required to have their own, dedicated circuits.
Cheers
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#363131 - 13/12/2014 14:54
Re: Home electrical wiring question...
[Re: mlord]
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addict
Registered: 02/08/2004
Posts: 434
Loc: Helsinki, Finland
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Technically possible? Absolutely: that 30A outlet has two 120V legs, neutral, and earth-ground. So yes, technically possible.
A Good Idea(tm) though? NO. Absolutely not.
The breaker and wiring for the dryer circuit are for 30A. The 120V outlet for the washer will be a 15A (or perhaps 20A) device -- so the available current (30A) would exceed that device's safety rating.
Various electical codes also forbid it -- the washer and dryer, like most permanent appliances, are typically each required to have their own, dedicated circuits.
Cheers
Thanks for the info! That's mostly what I had thought. I'll be getting it all wired up the correct way! On that note the outlet is currently a three prong type, I've read on-line (wikipedia!) that it's now considered an obsolete type and replaced by a four prong design. Is it worth it to have that swapped out as well? The installers helpfully left behind that type of cord.
Edited by petteri (13/12/2014 14:54)
Edit Reason: added thanks
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#363132 - 13/12/2014 15:50
Re: Home electrical wiring question...
[Re: canuckInOR]
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carpal tunnel
Registered: 29/08/2000
Posts: 14482
Loc: Canada
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Ahh.. if it's just 3-prong, then there's probably no neutral in the dryer outlet box after all -- so no 120V access there.
If it's working, leave it. Otherwise they might have to run new wiring to it for that fourth prong. Expensive.
EDIT: On the other hand, if/when the current dryer dies, the replacement will most likely demand a 4-prong outlet.. leaving you in the lurch until it gets rewired then.
Cheers
Edited by mlord (13/12/2014 15:52)
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#363133 - 13/12/2014 16:02
Re: Home electrical wiring question...
[Re: mlord]
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addict
Registered: 02/08/2004
Posts: 434
Loc: Helsinki, Finland
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Okay,
I'll see what the electrician finds when he opens up the panel. He may need to run additional wiring in any case as I need a second outlet in that kubby.
There is an outlet on the opposite side of that wall so I'm hopeful that the work entailed will be minimal. I just need to drag the damn washer/dryer out of there so they can access the area, that I hope is the bulk of the work involved.
Wishing that we just had a 220V setup as continental Europe right now, this would have all been plug and play!
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#363134 - 14/12/2014 04:43
Re: Home electrical wiring question...
[Re: petteri]
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pooh-bah
Registered: 02/06/2000
Posts: 1996
Loc: Gothenburg, Sweden
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Wishing that we just had a 220V setup as continental Europe right now, this would have all been plug and play!
Or you might be faced with pretty much the same thing, single-phase vs three-phase... :-)
_________________________
/Michael
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#363135 - 14/12/2014 11:28
Re: Home electrical wiring question...
[Re: mtempsch]
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addict
Registered: 02/08/2004
Posts: 434
Loc: Helsinki, Finland
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Wishing that we just had a 220V setup as continental Europe right now, this would have all been plug and play!
Or you might be faced with pretty much the same thing, single-phase vs three-phase... :-) Oh leave me and my dreams of a European paradise alone! 
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