Panelboard Questions

[Little Bill]

Correct, if your MWBC is supplied by a common trip OCPD, then exception 2 applies. That would let one MWBC supply multiple 240V or 120V/240V pieces of equipment.

But if your MWBC supplies only one piece of equipment, exception 1 applies, and there is no requirement for common trip. You can use two single pole breakers with a handle tie to supply a 120V/240V range, say, as long as nothing else is supplied by that MWBC.

If I've overlooked a different code section that would prohibit that installation, please let me know, but it complies with 210.4(C) and 240.15(B).


Not following--anyone working on the equipment is expected to turn off the breaker, and the handle-tie will ensure that both legs are turned off.

Cheers, Wayne

How would a dryer, or stove comply with 240.15(B)(1) when part of it is 240V. It says only line-neutral loads.

(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.

 

[wwhitney]

How would a dryer, or stove comply with 240.15(B)(1) when part of it is 240V. It says only line-neutral loads.

It doesn't, but then again it doesn't have to, as we have 3 other possible options for compliance with 240.15(B). [Sorry I missed the first time you mentioned 240.15(B)(1).]

The base text of 240.15(B) says "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)." The case under discussion complies with 240.15(B)(2), so there is no requirement in 240.15(B) for a common trip OCPD.

Cheers, Wayne

 

[Little Bill]

It doesn't, but then again it doesn't have to, as we have 3 other possible options for compliance with 240.15(B). [Sorry I missed the first time you mentioned 240.15(B)(1).]

The base text of 240.15(B) says "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)." The case under discussion complies with 240.15(B)(2), so there is no requirement in 240.15(B) for a common trip OCPD.

Cheers, Wayne

But (B)(2) says this

(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.

It says line-line, not both. That's talking about 2-pole single phase 240V.

 

[wwhitney]

It says line-line, not both. That's talking about 2-pole single phase 240V.

You're proposing that 240.15(B)(2) applies only to circuits that supply only 2-wire 240V loads? That's a good question, let me think about that.

It occurs to me that there is a possible issue that could be avoided by a rule prohibiting the simultaneous installation of L-N and L-L loads (even within a single piece of equipment, as per 210.4(C) Exception 1) without a common trip OCPD. Namely suppose load A is supplied L1-N and load B is supplied L1-L2, and L1 trips. Now the two loads A and B are in series and supplied L2-N. Each one will see a voltage across it of less than 120V. Can such an undervoltage cause equipment damage or start a fire?

One issue I have with this interpretation of 240.15(B) is that it makes 210.4(C) Exception 1 useless and something that could be deleted. Namely if the "only one utilization equipment" mentioned in the exception is supplied only L-L, then it doesn't need an MWBC, so 210.4 would not apply, and the exception is unnecessary. While if it is 120/240, then this reading of 240.15(B) says common trip is required anyway, so again the exception is useless.

Cheers, Wayne

 

[kwired]

As far back as the early 80s, QO breakers were made in Ireland and Mexico as well as the Lincoln plant.

Are they still assembling QO breakers there? I thought they moved the operation to Mexico but could be wrong on that.

I know back when I went there they were assembled by machines, the machine operator just kept the thing stocked with parts and cleared malfunctions and such but GFCI's were hand assembled, or at least partially hand assembled. Made some sense why they were much higher in price. Don't know if they are still hand assembled. AFCI wasn't a thing yet. My class from trade school toured the plant together.