220v Extension Cord for New G1023SL

[Rob Russell]

Tod,

Yes, I'm suggesting pulling a 120v circuit from the 240v circuit. It's fine if done properly.

When wired as a branch circuit where you have 2 hot legs (with 240v between the hot legs) and a common neutral, that's called a multi-wire circuit. IMO, the NEC is actually a bit lax on this type of circuit. All it requires is a common disconnect if both hot legs are used on a single device, i.e. if you "split-wired" a receptacle so the top outlet is leg A and the bottom outlet is leg B. It would be NEC-compliant to actually have a pair of single pole breakers to feed the 2 hot legs as long as you didn't use both legs on the same device, for example if you alternated receptacles - duplex receptacle #1 on leg A, then duplex receptacle#2 on leg B,duplex receptacle #3 back on leg A, etc. Personally - I wouldn't do it that way. All the multiwire circuits I've run in our house used a 2-pole common trip breaker. If 1/2 of the circuit causes a trip - both halves are going down.

I'm guessing that there has always been a bugaboo about pulling a 120v circuit from a 240v circuit because of 2 things - lack of a 2-pole common trip breaker and lack of a proper neutral. It would be flat wrong and dangerous to create a 120v circuit from a 240v circuit by using the equipment grounding conductor as the neutral. It would likely work, which is why people did it, but it effectively makes the equipment grounding conductor a live current-carrying conductor and that's a potentially deadly situation.

Rob

[Frank Chaffee]

Hank,
If I may ask of the knowledgeable responders to your original question,
For the purpose of understanding circuitry of duo voltage runs,
I can see how two 120V hot legs 180° out of phase can share a neutral wire in a 240V circuit, but I do not understand how that same neutral wire can also serve a separate 120V circuit that could be used simultaneously.
HELP!
Rob, you may have already explained the situation I am confused about, but, and I apologize, I still don’t understand.
Frank

[Rob Russell]

Frank,

A 240v single-phase circuit doesn't use a neutral. The circuit actually only needs the 2 hot legs to run, although any 240v circuit will include an equipment grounding conductor as a "safety ground".

Here's an example of a 20 amp, 240v circuit, with neutral to provide for 120v loads.
- assume that you've put in 120v outlets for both hot legs.
- assume a 10 amp, 240v motor load
- assume a 5 amp, 120v load running on leg A (let's say running a small power feeder)
- assume a 3 amp, 120v load running on leg B (I'm stretching here - maybe a mini-vacuum pump to run a vacuum hold-down).

The net current returning on the neutral would be 2 amps. The calculation would be (0 amps from the 240v motor + 5 amps from leg A - 3 amps from leg B), giving 2 amps.

The reason for this is what you've already pointed out - that the 2 hot legs are exactly 180 degrees out of phase. On a 240v motor, the amount of amperage drawn through each leg is equal, so the 2 legs cancel each other out. On the 120v legs, you need a neutral for the current to return.

If you had 2 equal, 120v loads running on opposite legs, the currents running through the neutral would be just like a 240v motor - they would cancel each other out. Normally on a multiwire circuit, the amount of current that will flow back through the neutral will be the unbalanced load between the 2 hot legs.

It's important to note that on a "normal" 120v circuit (i.e. not 1/2 of a "multi-wire circuit" with a shared neutral between 2 hot legs), the neutral carries the same amount of current as the hot leg. If you put an ammeter on the neutral when you were running a router that's drawing 12 amps, you'd see 12 amps flowing back through the neutral to your electrical panel.

Rob
Addy protocol: not a licensed electrician

[J. Greg Jones]

This thread has been very interesting and has given me some ideas for getting 240v into my garage. One thought that I have is that my laundry room with 240v for the dryer is on the interior/garage wall, just where I would like a 240v outlet to be in the garage. The dryer is fed with a 30 amp, 240v circuit. Would it be possible, safe, and within code, to junction off the existing 30 amp, 240v circuit and put in a 240v receptacle and (1) split-wired 20A/125V duplex receptacle like what Rob describes above?

[Mike Cutler]

This thread has been very interesting and has given me some ideas for getting 240v into my garage. One thought that I have is that my laundry room with 240v for the dryer is on the interior/garage wall, just where I would like a 240v outlet to be in the garage. The dryer is fed with a 30 amp, 240v circuit. Would it be possible, safe, and within code, to junction off the existing 30 amp, 240v circuit and put in a 240v receptacle and (1) split-wired 20A/125V duplex receptacle like what Rob describes above?

Greg.

It is always possible to do this. It can be safe also, assuming that the dryer would not be in use. I don't believe that it is allowed per code though.
When we put in our laundry room. The 220 for the dryer, the 115 for the washer, and the 115 for the convenience recpeptacle all(each) had to have their own dedicated breaker. This was in Connecticut in 1993. It may be different now, but I don't think so.

[Mike Evertsen]

are you sure you got the right plug because both of my grizzly machines my grizzly DC and my unisaw have plugs like this one

[Rob Russell]

Greg,

The answer to your question is maybe. Is your dryer fed by a 3-wire or 4-wire circuit? If the answer is 3, then you need to rewire the circuit because it's an older circuit and doesn't have an equipment grounding conductor. I'm saying 4-wire vs. 4-prong plug on your dryer because a creative electrician (read unknowing homeowner) could have put a 4-prong receptacle in and incorrectly used a 3-wire circuit to feed it. If your dryer plug is only 3-prong, it's almost a certainty that you have to rewire the circuit. If it's got a 4-prong plug, I'd kill power to the circuit and check either the receptacle or the breaker panel to ensure that it really is a 4-wire circuit.

The code used to allow new 3-wire circuits for 240v ranges and dryers. The neutral was needed because of the 120v loads like lights or clocks. The frame of the dryer/range was also bonded with the neutral, so the neutral served as the equipment grounding conductor, which isn't right. The code currently requires 4-wire circuits for dryers/ranges, but existing circuits are grand-fathered in as an exception. The NEC article on this, if you care to read it, is 250.140.

So - if you have a 4-wire circuit, you can do what you want to do.

Mike,

The code would currently require at least 2 and possibly 3 circuits to have a 240v dryer and (2) 120v circuits in a laundry. I'm not aware of any prohibition in the NEC that says you can't run a 240v circuit for the dryer and pull a 120v circuit off of that. What the code does require is a dedicated 20 amp, 120v "laundry circuit" for the washing machine. Since most electricians are not going to pull a 120v circuit off of the dryer circuit, they'll install (1) 240v circuit for the dryer, (1) 20A/120v laundry circuit and optionally (1) 15A or 20A, 120v convenience circuit in the laundry room. The latter is what I did when I wired the laundry room in our addition. Note that, if you have a sink in the laundry room, any convenience receptacle within 6 feet of the sink must be GFI-protected. There's talk about the laundry circuit needing GFI protoection too, but that would be a change in the 2008 code if it's accepted.

Rob

[Rob Russell]

Mike Evertsen,

That plug looks like a 250v/15A plug to me. We're talking about dryer plugs which are a whole lot bigger and have a whole lot different configuration.

This link shows the plug configurations - http://www.leviton.com/sections/techsupp/nema.htm.

Rob

[Mike Cutler]

Rob.

When we put in our laundry room, it kinda threw everyone for a loop.
Our washer and dryer are Asko's from Sweden. The Washer runs off of 115 and 220, it has an on demand hot water heater built into it. It also plugged into the back of the dryer, which is plugged into the 240.

I remember asking why I had to put in two dedicated 115's when the washer plugged into the dryer, and I would never need the third, and have never used the other 115 receptacle.
Bottom line, that was what had to be there. No use fightin' city hall eh..

This is also why I know about the "laundry breaker". The 115 is paralleled off of the 220, it's just done at the breaker is all. A single 220 space, supplies 1-220 breaker, and 2 115's. Pretty slick.

Moral to this story. Don't be the first person on the block to have some new fangled swedish washer/dryer in 1993. .

I always advise to bring in a local liscense. They know what the building inspector wants to see, and they do it for a living, everyday.

PS. I argued a liitle more about running Hot and Cold water to a washer that didn't use hot water. I lost that battle too.

[Rob Russell]

... I remember asking why I had to put in two dedicated 115's when the washer plugged into the dryer, and I would never need the third, and have never used the other 115 receptacle.
Bottom line, that was what had to be there. No use fightin' city hall eh..

You might not have needed the circuits, but the next homeowner could have because they didn't have a fancy-pants Swedish washer/dryer. The town was just making sure that the laundry was installed to meet the then current, local, adoption of the NEC.