Multiple circuits sharing a ground (Split phase, Non-metallic)

[roger]

And 250.148(A) requires all EGC to be tied together in an enclosure or box.

Actually it does not require egcs associated with circuits passing through unbroken to be tied to others.

 

[skorpioskorpio]

Can you imagine the inspection confusion if you did install a few 3 poles in your home panel.

Yea, well you need to label it entertainingly, like "toaster". Or maybe 2 of these in a single story slab house marked "Elevator A" and "Elevator B", the inspector will be so distracted looking for the elevators, they'll probably stop inspecting anything else.

 

[skorpioskorpio]

I wonder how they internally link the outer pair.

I always kinda wondered that myself, I've seen them and the outer pair tie bar does not look like it would reliably trip both on it's own.

 

[marmathsen]

Not correct for a 2-wire circuit on a 120/240V system. See 240.15(B)(2).

For a 3-wire individual branch circuit for a 120/240V load, I'm unclear whether 240.15(B)(2) applies or not. For a 120/240V load on other than an individual branch circuit, the question is moot because of 210.4(C)--exception 2 is the only way to comply.

Cheers, Wayne

This is something I've been meaning to bring up in the forums. You seem to be interpreting it the same way I am.

Is there any scenario in a 120/240 grounded system that requires a common trip breaker?

240.15(B)(2) says no, and is confirmed by the commentary in the handbook/NFPA Link. Oddly the commentary for 210.4(C) says otherwise.

New to me is that the NEC considers a 3-wire range or dryer circuit to be a Multiwire Branch Circuit. I mistakenly only used that term for 2+ 120 circuits that share a neutral.

Rob G - Seattle

 

[Fred B]

Actually it does not require egcs associated with circuits passing through unbroken to be tied to others.

View attachment 2574919

True but, I don't think the exception applies in most switch or receptacle boxes. Even if only the hots are opened to connect to a switch, the "circuit(s)" do not "pass through". While might be applicable for a pull point box you still need to bond a metal box if method of entry does not create an EGC, Non-metallic boxes of course would be different.

 

[infinity]

Is there any scenario in a 120/240 grounded system that requires a common trip breaker?

240.15(B)(2) says no, and is confirmed by the commentary in the handbook/NFPA Link. Oddly the commentary for 210.4(C) says otherwise.

New to me is that the NEC considers a 3-wire range or dryer circuit to be a Multiwire Branch Circuit. I mistakenly only used that term for 2+ 120 circuits that share a neutral.

An individual branch circuit for a wire or range would require a common trip circuit breaker even if it it also meets the definition of a MWBC. Single pole breakers with a handle tie are not code complaint.

240.15(B) Circuit Breaker as Overcurrent Device.
Circuit breakers shall open all ungrounded conductors of the circuit both manually and automatically unless otherwise permitted in 240.15(B)(1), (B)(2), (B)(3), and (B)(4).
240.15(B)(1) Multiwire Branch Circuits.
Individual single-pole circuit breakers, with identified handle ties, shall be permitted as the protection for each ungrounded conductor of multiwire branch circuits that serve only single-phase line-to-neutral loads.
240.15(B)(2) Grounded Single-Phase Alternating-Current Circuits.
In grounded systems, individual single-pole circuit breakers rated 120/240 volts ac, with identified handle ties, shall be permitted as the protection for each ungrounded conductor for line-to-line connected loads
for single-phase circuits.

 

[roger]

True but, I don't think the exception applies in most switch or receptacle boxes. Even if only the hots are opened to connect to a switch, the "circuit(s)" do not "pass through". While might be applicable for a pull point box you still need to bond a metal box if method of entry does not create an EGC, Non-metallic boxes of course would be different.

It's not an exception, it is the actual code language. The exception in 250.148 is for isolated grounds.

 

[marmathsen]

An individual branch circuit for a wire or range would require a common trip circuit breaker even if it it also meets the definition of a MWBC. Single pole breakers with a handle tie are not code complaint.

This is from the 240.15(B) commentary in NFPA Link.

The exhibit below shows where handle ties are required for single-pole circuit breakers on multiwire branch circuits serving line-to-line loads. The multiwire branch circuits shown in the top and middle diagrams supply a single piece of utilization equipment in accordance with 210.4(C), Exception No. 1. For those branch circuits, common trip operation is permitted but is not required.

 

[infinity]

This is from the 240.15(B) commentary in NFPA Link

What code cycle is this from? Look at the code sections in post #26. How does the commentary in graphics 1 and 2 comply with those sections? 240.15(B) says that the circuit breakers shall open automatically unless it complies with (B)(1) or (B)(2). Handle ties do not provide automatic opening of both ungrounded conductors witn a fault in one of the legs.

 

[marmathsen]

What code cycle is this from?

It's from 2023 NEC but that same verbiage is present in 2020, and 2017.

Look at the code sections in post #26. How does the commentary in graphics 1 and 2 comply with those sections? 240.15(B) says that the circuit breakers shall open automatically unless it complies with (B)(1) or (B)(2). Handle ties do not provide automatic opening of both ungrounded conductors witn a fault in one of the legs.

I think it's interesting that 240.15(B)(1) says "only single-phase line-to-neutral loads", but 240.15(B)(2) doesn't use the term "only". I think it's also key to look at 210.4(C)

210.4(C) Line-to-Neutral Loads.

Multiwire branch circuits shall supply only line-to-neutral loads.
Exception No. 1: A multiwire branch circuit that supplies only one utilization equipment shall be permitted to supply line-to-line loads.
Exception No. 2: A multiwire branch circuit shall be permitted to supply line-to-line loads if all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch-circuit overcurrent device.

Does the phrase "opened simlutaneously by the branch-circuit overcurrent device" in 210.4(C) mean the same thing as "open all ungrounded conductors of the circuit ... automatically" from 240.15(B)? Maybe it does, in which case you are right.

Perhaps I'm mistaken but then the commentary is incorrect. I don't see how that can me misunderstood.

 

[wwhitney]

240.15(B) says that the circuit breakers shall open automatically unless it complies with (B)(1) or (B)(2).

I think the question is whether a 3-wire 120/240 load counts as a "line-to-line connected load", or whether that term implies a 2-wire load. My initial reading was that it does count as a line-to-line connected load, and the commentary from the Handbook excerpted in post #28 agrees. But you and Little Bill (in another thread) seem to read that language as only applying to 2-wire loads.

Is there any scenario in a 120/240 grounded system that requires a common trip breaker?

Yes, any MWBC supplying line-to-line loads that is not an individual branch circuit, per 210.4(C).

Cheers, Wayne

 

[wwhitney]

Does the phrase "opened simlutaneously by the branch-circuit overcurrent device" in 210.4(C) mean the same thing as "open all ungrounded conductors of the circuit ... automatically" from 240.15(B)?

Yes.

Maybe it does, in which case you are right.

Not following: the Handbook example diagrams are individual branch circuits, so they comply with 210.4(C) Exception 1, so the wording of Exception 2 is not relevant.

Cheers, Wayne

 

[infinity]

Does the phrase "opened simlutaneously by the branch-circuit overcurrent device" in 210.4(C) mean the same thing as "open all ungrounded conductors of the circuit ... automatically" from 240.15(B)? Maybe it does, in which case you are right.

IMO no. Simultaneously would be when you use your hand to flip off the single pole breakers that are handle tied together. One movement of the hand simultaneously opens the breaker. If there is a fault in one leg of the handle tied breakers there is no guarantee that the handle tie will automatically open the other single pole breaker(s).

 

[wwhitney]

IMO no. Simultaneously would be when you use your hand to flip off the single pole breakers that are handle tied together.

210.4(B) already requires handle-ties. If 210.4(C) Exception 2 were referring to handle-ties, it would render 210.4(C) meaningless. 210.4(C) Exception 2 is referring to common trip.

The phrase "by the branch-circuit overcurrent device" is referring to automatic operation, not manual operation.

Cheers, Wayne

 

[Little Bill]

Here is commentary from the 2005 handbook
It agrees with my interpretation of needing a common trip on 240V/120V MWBC.

 

[TX+ MASTER#4544]

Actually it does not require egcs associated with circuits passing through unbroken to be tied to others.

View attachment 2574919

TX+MASTER#4544....says....
How many wires are in that box?
All same size?