Any Electrical Circuit Breaker Experts Here?

[ZeeOSix]

I've got a question about wiring a spit duplex NEMA 5-20R to a 208v, 20A, 2-pole circuit breaker. I tried searching the internet and couldn't find a direct answer.

In a split duplex like this, each receptacle in the duplex outlet is wired to one side of the 2-pole 208v breaker, which gives two independent 120v single phase outlets in one duplex box. The beauty with this setup is that both outlets on the duplex box get turned off when the breaker is tripped. Each outlet has it's own hot, neutral and ground wire going back to the breaker panel, which makes them independent circuits that are controlled by the same circuit breaker.

So, question is ... can each independent outlet carry 20A if the 2-pole breaker is rated at 20A?

I believe if either one of the independent outlets exceeds the 20A rating of the breaker, then the the breaker would trip and both outlets will be powered off. Is this true?

 

[river_rat]

Yes and yes.

 

[ddean]

I am not a licensed electrician and hopefully one from the US or Canada can chime in. But I know a bit about wiring and might be able to help. In order for this to be a safe installation with a split duplex both neutrals need to be wired separately AND have the tab connecting the two neutrals broken as you have done with the hot tab. This is because if there is an open neutral fault in the wiring with two pairs of outlets pulling over 20A (ie 15A + 10A) combined this will cause the neutral wire to be overloaded although each pole of the breaker is well under tripping threshold.

Back to your question yes each pole of a 2 pole breaker should act independently and trip if the current exceeds its threshold shutting off both poles. Again I am not an electrician and I have not read up on new NEC codes. Note that installation of a setup such as this is against code in many residential applications because of AFCI requirements however since you have a 208V service then you are probably in a commercial or industrial setting.

 

[tomcat27]

I was a journeyman over 20 years ago - theoretically (if you only use one neutral) it would only carry the imbalance between the two loads. (if both cirbuits were pulling 15A they would balance each other out and there would be no current down the neitral) That being said - we never even talked about that implementation in my few years wiring and I am not sure it would pass inspection - as it sounds like trying to use an outlet as a sub panel..... gotta pull out the code book and look....

 

[Carbon]

Originally Posted By: tomcat27
I was a journeyman over 20 years ago - theoretically (if you only use one neutral) it would only carry the imbalance between the two loads. (if both circuits were pulling 15A they would balance each other out and there would be no current down the neutral)

You are thinking of the 240/120 single phase circuits common in US houses.

 

[kb01]

Admittedly, I haven't gotten my coffee yet and was up for most of the night with a crying baby, so maybe I'm not reading the question correctly but...

Couldn't you achieve the same results by running a Multi Wire Branch Circuit and simply sharing the neutral?

In my area, it's fairly common to use a 20 amp double pole breaker and then run 12/3 NM (or MC) to a split receptacle, with a shared neutral, under the kitchen sink that controls both the garbage disposal and dishwasher.

If I recall, even if you don't go the MWBC route, and use two separate runs of 12/2 NM, you always need to use a double pole breaker when dealing with split receptacles.

I just did a quick search and there's info on the above scenarios at this website: http://www.inspectapedia.com/electric/multiwir.htm

(I'm not an electrician but have an old house and have had many dealings with our local electrical inspector when getting my work cleared)

 

[QuadDriver]

sharing the neutral is ok. the current in the neutral is the net of the difference between the outlets.

In the event of an open neutral the neutral of the shared recep should go diretly to the panel. no other circuits on a shared branch - that way if neutral does open up and the double pole breaker does trip, and other breakers tied to that circuit via neutral wont pass current.

just make sure neutral is very very tied to ground at the box. current does not take the shortest path to ground...it takes ALL paths to ground

 

[Al]

I would never do it. I seriously doubt its within code. Besides a receptacle is rated for 15 Amps total (20 amp if its specified "20A") Two circuits - 40 amps.

Also there is an internal difference between a 220V breaker vs a breaker that can carry 2 120 circuits. At least there is in some brands. For instance a 220V Zinsco breaker has the breaker throws tied together with a pin going through them, whereas the same breaker that is built for 2 120 V circuits doesn't have the pin.

Much more sensible idea is to use 2 boxes, the correct breaker..one breaker per circuit/box.

 

[ZeeOSix]

Originally Posted By: Al
I would never do it. I seriously doubt its within code. Besides a receptacle is rated for 15 Amps total (20 amp if its specified "20A") Two circuits - 40 amps.


There is definitely NEC (National Electrical Code) that pertain to doing a split duplex receptacle.

I believe that each pole of a 2-pole 20A breaker will carry 20A independently ... and if either pole of the breaker exceeds 20A then both poles will be tripped.

 

[QuadDriver]

Originally Posted By: Al
I would never do it. I seriously doubt its within code. Besides a receptacle is rated for 15 Amps total (20 amp if its specified "20A") Two circuits - 40 amps.



the recep the OP quoted is indeed rated for 20 amps

 

[kb01]

Originally Posted By: Al
I would never do it. I seriously doubt its within code. Besides a receptacle is rated for 15 Amps total (20 amp if its specified "20A") Two circuits - 40 amps.


Unless code has changed recently, you can put a 15-amp receptacle on a 20-amp circuit (my town is very behind the times in adopting the new NEC). The reasoning is pretty simple. Unless an appliance's plug is designed for a 20-amp receptacle, with one horizontal terminal and one vertical terminal, it wont fit into a 15-amp receptacle. Any plug that can fit into a 15-amp receptacle will draw less than 15-amps (I think technically, draw less than 80% of 15-amps).

If you had a 20-amp appliance, you would need a 20-amp receptacle with the one T-shaped terminal. I don't think I've ever seen a 20-amp/110 volt plug on any appliance but they're apparently out there. For my house, I usually use commercial spec 20-amp receptacles because they seem to be higher quality (and I'm very OCD about this kind of stuff).

A double pole, 20-amp, 220 volt breaker is essentially just two 20-amp/110 volt breakers that are tied together so if one trips, they both do (typically with a spacer to keep them from being installed incorrectly). Both wires connected to the breaker carry 110 volts each.

A split receptacles needs to have this kind of breaker for safety reasons. Otherwise, if one breaker trips, the electrician or HO might unknowingly work on a hot receptacle.

Outside of under kitchen sinks, I haven't seen too many split receptacles on different circuits. The only other time I've seen it has been with a receptacle that has one plug tied into a 3-way switch on a lighting circuit and the other plug tied into the receptacle circuit (I don't know if this is code, since it was a very old installation).

Unless the NEC has changed recently (which is very possible), split receptacles and MWBCs have been very common for a very long time. I'm not an electrician, so take everything I say with a grain of salt (I'm just someone who has experiences with old houses and has been through the permit/rough in/inspection process more times than I can count).

 

[ZeeOSix]

Originally Posted By: kb01

A double pole, 20-amp, 220 volt breaker is essentially just two 20-amp/110 volt breakers that are tied together so if one trips, they both do (typically with a spacer to keep them from being installed incorrectly). Both wires connected to the breaker carry 110 volts each.


Yes, that's a very good description of a 2-pole breaker. It's essentially two single pole breakers that are joined together and have a tied trip lever. At 2-pole, 208v rated breaker can be used to power two independent 120v circuits. If the breaker trips, then BOTH circuits are tripped simultaneously.

Originally Posted By: kb01
A split receptacles needs to have this kind of breaker for safety reasons. Otherwise, if one breaker trips, the electrician or HO might unknowingly work on a hot receptacle.


In my application, I plan on having an independent hot, neutral and ground wire going to each receptacle in the split duplex box. So this configuration will essentially be like having two independent single pole 120v volt breakers that are tied together so if either receptacle gets over loaded the breaker will trip and cut power to BOTH receptacles. Or if a tech needs to work on the equipment connected to this breaker, when he turns off the breaker then ALL power will be turned off to both sides of the spit duplex receptacle.

 

[brianl703]

Originally Posted By: Al
For instance a 220V Zinsco breaker has the breaker throws tied together with a pin going through them, whereas the same breaker that is built for 2 120 V circuits doesn't have the pin.


I'm not sure I'd use Zinsco as an example of anything other than excessively cheap electrical equipment.