Duplex Breaker Rating

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Old 04-05-06, 01:04 PM
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Duplex Breaker Rating

I have an existing 240 V dryer circuit with 30 Amp duplex breaker. I want to pig tail a 120 V receptacle in that circuit between the breaker and the dryer receptacle.

1. Is there any reason why I shouldn't do this?
2. Is the 30 Amp duplex breaker rated 15 Amp each leg or 30 Amp each leg?
 
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Old 04-05-06, 01:06 PM
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Yes, there is a very good reason not to do this. Several actually.

Code forbids it.

It is dangerous.

The only thing on your dryer circuit should be your dryer.
 
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Old 04-05-06, 01:48 PM
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OK if it doesn't meet code, but why would it be considered dangerous?

Is a 30 Amp duplex breaker rated 15 Amps each leg, or 30 Amps each leg?
 
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Old 04-05-06, 01:53 PM
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A 30 amp 240 volt breaker is 30 amps at 240 volts. That means 30 amps on each 120 volt side of the circuit.
 
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Old 04-05-06, 05:11 PM
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Originally Posted by fredmorrison
I have an existing 240 V dryer circuit with 30 Amp duplex breaker. I want to pig tail a 120 V receptacle in that circuit between the breaker and the dryer receptacle.

1. Is there any reason why I shouldn't do this?
2. Is the 30 Amp duplex breaker rated 15 Amp each leg or 30 Amp each leg?
You could do that if:

1. The circuit has a separate ground wire. If it doesn't, you cannot just run a 4th wire to add it. The ground has to be in the same cable bundle, or in the same conduit.

2. Remove the 30 amp (NEMA 14-30R) dryer receptacle. Of course that means you can't use the dryer on it. But if you are switching from electric dryer to gas dryer, this may be your intention. A gas dryer generally needs only a 15 amp 120 volt circuit.

3. Replace the breaker with a 20 amp or 15 amp (still 2-pole with one handle) version.

4. Put in 20 amp or 15 amp 120 volt receptacles.

5. Be sure you have no reason to not use a shared neutral circuit. Maybe local AHJ rules and/or insurance requirements rule this out. You may be required to actually have a 30 amp dryer circuit in a laundry room even if you have no intention to use it that way.

6. Anything else I didn't think of.
 
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Old 04-05-06, 06:22 PM
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Thanks all, I will either run a separate circuit for the 120 V receptacle that I need, or get power from another nearby 120 V receptacle.
 
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Old 04-05-06, 08:00 PM
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If your dryer circuit is older, it may have a neutral but no ground wire. This is a problem right away. Regardless, a 240 circuit is intended to have minimal current in the balanced neutral leg. You would unbalance it. If it were the older 3 wire circuit, the dryer cabinet, which is connected to the neutral in the absence of an actual grounding wire, would no longer be at Zero volts with respect to earth. Some voltage level would develop on the unbalanced neutral, so you could get a tingle when touching the dryer.
 
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Old 04-05-06, 08:28 PM
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594tough, that's a very enlightening post.
 
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Old 04-05-06, 10:13 PM
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Originally Posted by 594tough
If your dryer circuit is older, it may have a neutral but no ground wire. This is a problem right away.
Correct.


> Regardless, a 240 circuit is intended to have minimal current in
> the balanced neutral leg.

Untrue.


> You would unbalance it.
Unimportant. A dryer circuit has a lot of neutral current normally if the dryer running. That's the reason for the move to 4-wire connections.


> If it were the older 3 wire circuit, the dryer cabinet,
> which is connected to the neutral in the absence of an
> actual grounding wire, would no longer be at zero volts

Practically untrue. Say it's 0.5V... so what?


> with respect to earth.
There is no point in measuring wrt earth.
What matters is voltage wrt other metallic objects that can be touched at the same time.


> Some voltage level would develop on the unbalanced neutral,
> so you could get a tingle when touching the dryer.

Very, very unlikely.
If this happens, you probably have a defective/deteriorated installation.


Did anyone explain the biggest problem?

You may not hook a 15A receptacle to a 30A breaker.
A dryer breaker is 30A on each leg.

The maximum allowed OCPD for a 15A receptacle is 20A. That's it.

NEC 220.18 isn't completely clear, but afaIk, there is no way to tap a 15A or 20A receptacle off the line with the dryer even with another OCPD.
 
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Old 04-06-06, 05:44 AM
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bolide, I got my original questions answered, but what is the meaning of afaIk?
 
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Old 04-06-06, 07:35 AM
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afaik = as far as I know
 
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Old 04-06-06, 08:11 AM
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Thanks, bolide, for steering the thread back to the very important issue that none of us had mentioned: putting a 15 amp recept. on a 30 amp breaker.


I would still maintain that the reason the code now requires 4 wire for dryers is that while using connecting the chassis to the neutral wire was sort of safe, it was not safe enough. And tapping a receptacle off that line would make it even "less safe".



BUT, again, you have stated the principal and most important reason not to do it. Apologies to the original poster mr. morrison if I distracted you from getting to the bottom of your question!.
 
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Old 04-06-06, 09:00 AM
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Originally Posted by 594tough
I would still maintain that the reason the code now requires 4-wire for dryers is that while using connecting the chassis to the neutral wire was sort of safe, it was not safe enough.
That is very true. The motor and accessories on a dryer are 120V. Only the heating element is 240V.

There is considerable neutral current when a dryer is running. As I have laid out in another thread, if the neutral becomes loose, corroded, or open anywhere from the appliance to the panel, a serious shock hazard arises.
 
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