Two dedicated 20 AMP Circuits...

[arjo_reich]

My friend hired an electrician to wire two dedicated 20 AMP circuits for his new home theatre in the basement. The electrician completed the work in a way I thought was rather interesting and, since I consider the members on this board to be the professionals, I was wondering if I could get your opinions on his wiring method.

Rather than using two 20 AMP breakers and running two circuits, he installed a double pole 20 AMP and through the EMT he ran two hots - one for each phase - with a common neutral and ground. The first double gang receptacle enclosure takes one hot, the common ground and neutral and the second hot is ran through to the second double gang enclosure. The distance between the two enclosures is about two feet...although I doubt that matters much.

Would you run it the same way? Why do you think he did it like this?

--
My personal opinion is that he did not run two dedicated circuits as the work-order stated and instead ran a single, "double-phased" (is that the correct terminology) circuit.

Thank you in advance,

R. Joe Reich

 

[electricman2]

Re: Two dedicated 20 AMP Circuits...

Done all the time. Its called a multi-wire circuit. Although I would question the use of a double pole breaker. With this arrangement, one circuit can not be opened without the other. Of course he may have a reason to do so.

 

[charlie]

Re: Two dedicated 20 AMP Circuits...

Joe, can you think of any reason that you really need two individual circuits instead of a multi-wire branch circuit?

 

[crankshaft]

Re: Two dedicated 20 AMP Circuits...

210.4 (B) if the multi wire supplies more than one device or equipment on the same yoke you need a 2 pole breaker. or 210.4 (C) if you want to supply more than line to neutral loads you need a 2 pole breaker. exception no.2

 

[arjo_reich]

Re: Two dedicated 20 AMP Circuits...

Originally posted by charlie:
Joe, can you think of any reason that you really need two individual circuits instead of a multi-wire branch circuit?

If it was my setup, because I would want the circuits to trip independantly as they would likely have different purposes, each potentially consuming up two 12-15 AMPs each of continous load.

Of course that's just off the top of my head.

 

[rattus]

Re: Two dedicated 20 AMP Circuits...

Originally posted by electricman2:
Done all the time. Its called a multi-wire circuit. Although I would question the use of a double pole breaker. With this arrangement, one circuit can not be opened without the other. Of course he may have a reason to do so.

It would seem that in a multiwire circuit, it is desirable to open both poles of the breaker at the same time. Some if not all two-pole breakers are coupled such that a tripped breaker trips the other mechanically. This is in addition to the handle tie. Right?

Remove the handle tie, and you can use the individual breakers as disconnects, and the internal coupling still works, but that may violate the code.

[ August 05, 2005, 12:56 PM: Message edited by: rattus ]

 

[bthielen]

Re: Two dedicated 20 AMP Circuits...

I see this as an opportunity to learn something. Would it be permitted to do this using two single pole CBs and 12-3 W/gnd? You would have a multiwire circuit with independent OCPD protection however, if only one circuit breaker tripped, the neutral could still be carrying current from the other circuit.

Would this be a code violation?

Bob

 

[macmikeman]

Re: Two dedicated 20 AMP Circuits...

There is no code violation unless the both "circuits" are terminated on the same yolk as in a split wired receptacle outlet. The both individual circuits must be on opposite "phase" (for lack of better description) of the load center.

 

[luke warmwater]

Re: Two dedicated 20 AMP Circuits...

First-off, he could have used (2) single-pole breakers.
Would you be satisfied with this?

If the work order specifically states 'two dedicated circuts', which to me would mean 'two individual branch circuts', then, IMO, your friend did not get what he paid for.

 

[Jhr]

Re: Two dedicated 20 AMP Circuits...

Ok I'll go one step further, what do you on this forum consider a dedicated circuit.

1) two circuits sharing the same nuetral and same ground on 2 pole breaker .

2) two circuits with separate nuetrals, but sharing the same ground on separate breakers .

3) two circuits with separate nuetrals and separate grounds on separate breakers.

I would say #2 and #3

[ August 05, 2005, 01:58 PM: Message edited by: Jhr ]

 

[charlie b]

Re: Two dedicated 20 AMP Circuits...

Neither. Or either. Or all. Or none. ), the term "dedicated circuit" has to do with the end point of the circuit, not the begining. If a single breaker provides power to a single receptacle, it is "dedicated." It gets tricky when a single breaker supplies one "duplex" receptacle and no other load, but I would still call that "dedicated." In this context, all three of your configurations could be "dedicated circuits," depending only on what is connected at the end point.

 

[allenwayne]

Re: Two dedicated 20 AMP Circuits...

I`m a little fuzzy today
We have discussed the use of multi wire circuits umpthteen times.Yes if on the same yoke a 2 pole is mandated.As far as I am concerned the grounded conductor if not pigtailed IMO the ungrounded conductors should both be opened at the same time

 

[sceepe]

Re: Two dedicated 20 AMP Circuits...

In my way of thinking (Caution: Engineer is trying to think ), the term "dedicated circuit" has to do with the end point of the circuit, not the begining. If a single breaker provides power to a single receptacle, it is "dedicated."

I agree with Charlie

 

[charlie b]

Re: Two dedicated 20 AMP Circuits...

Originally posted by allenwayne:Since then if multi wire both get shut off

All ye who are "young in the trade," and we who are "not so young," take note! When anyone shares a story like this, it becomes your duty to never let it happen to you. There are many who were not fortunate enough to have lived to tell such stories. Don't be one of them.

allenwayne: Many thanks for sharing this story.

 

[bthielen]

Re: Two dedicated 20 AMP Circuits...

sceepe,

What part do you agree with? The warning that we should proceed with caution?

 

[infinity]

Re: Two dedicated 20 AMP Circuits...

Originally posted by allenwayne:Since then if multi wire both get shut off

I would add that in a three phase system all three circuits sharing a neutral get shut off. Many electricians have been injured while working on a dead 277 volt circuit forgetting that the neutral was still supplying two other live circuits. Better to be safe than sorry. Like Allenwayne said shut them all off.

 

[milwaukeesteve]

Re: Two dedicated 20 AMP Circuits...

A multiwire branch circuit, as defined in art 100, is 2 (or 3 in a 3phase system) individual circuits that share a common Neutral or GroundED wire. Do not confuse groundED with groundING. The GroundED conductor is the return path for the Circuit conductor and is a current carrying conductor. The groundING conductor is there to establish ground (if needed) AND there to provide a SAFE path for a FAULT back to the panel. This conductor is only current carrying IF there is a fault.

In a multiwire branch circuit, the 2 individual hot conductors can share the neutral conductor. The reason for this is not explained in the NEC, rather it is a fundamental of Electricity; the fact that the returning currents from 2 different phases will cancel each other out, and not add on each other (unless non linear loads, but don't worry about that for this basement) IF, and it MUST be this way, If the two individual hot conductors are 2 different phases, the neutral conductor will never see more current than either of the individual hot conductors, and that would be when the other hot has no load on it at all, because any current would subtract/cancel the other.
With knowing this, we always keep an eye on our phasing. MWB circuits must stay on opposite phases, and the breakers must stay on opposite busses in the panel.
Generally, (not required by NEC, but very good practice) we install the breakers next to each other in order to group them for better identification for the next person. Taping all 3 conductors is also nice to do.
However, the use of a double pole breaker is wrong, and is only available for such use in non-Line to Neutral loads (210.4(C)(2))
210.7(b) states that where 2 or more circuits supply devices on the same YOKE, then a means to simultaneously disconnect the ungrounded conductors supplying those devices shall be provided...
Note how that does not say "common trip". 240.20(B)(1)individual breakers with or without handle ties....that serve only line to neutral loads.

 

[iwire]

Re: Two dedicated 20 AMP Circuits...

Originally posted by milwaukeesteve:
However, the use of a double pole breaker is wrong, and is only available for such use in non-Line to Neutral loads (210.4(C)(2))
210.7(b) states that where 2 or more circuits supply devices on the same YOKE, then a means to simultaneously disconnect the ungrounded conductors supplying those devices shall be provided...

Wrong?

Poor design maybe but it is not wrong or a code violation to use a common trip breaker.

Originally posted by milwaukeesteve:
IF, and it MUST be this way, If the two individual hot conductors are 2 different phases, the neutral conductor will never see more current than either of the individual hot conductors, and that would be when the other hot has no load on it at all, because any current would subtract/cancel the other.
With knowing this, we always keep an eye on our phasing. MWB circuits must stay on opposite phases, and the breakers must stay on opposite busses in the panel.

Really?

What about doing it this way?



[ August 05, 2005, 04:04 PM: Message edited by: iwire ]

 

[roger]

Re: Two dedicated 20 AMP Circuits...

Steve,

A multiwire branch circuit, as defined in art 100, is 2 (or 3 in a 3phase system) individual circuits that share a common Neutral or GroundED wire.

this is not the definition for Branch-Circuit, Multiwire per article 100 wording.

The word circuits is not in the definition, in reality this is a single circuit.

If you read it again you will notice that it says

"two or more ungrounded conductors that have voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit"

Roger

 

[wbalsam1]

Re: Two dedicated 20 AMP Circuits...

Also note that NEC 2005 at 240.20(B) requires circuit breakers to open all ungrounded conductors of the circuit both manually and automatically. Handle-ties do NOT cause a common trip.