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

[electrofelon]

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

Hmmm why do gremlins keep sneaking in at night and changing the code book from the way it has been for decades?

 

[electrofelon]

So I am still confused, for a single phase grounded system, the only time common trip is required is if there is a neutral as part of the circuit, and when it is NOT a MWBC?

 

[infinity]

So I am still confused, for a single phase grounded system, the only time common trip is required is if there is a neutral as part of the circuit, and when it is NOT a MWBC?

If you had a 3-wire branch circuit to a single applicance such as a dryer you cannot use a handle tie on two single pole breakers. My understanding is that the reason being is that one leg could trip and the dryer wouldn't work but it would still be partially energized on the other leg. By Article 100 definition it could still be called a MWBC.

This entire section(s) needs to be rewritten. There is no reason why it needs to be this confusing.

 

[wwhitney]

If you had a 3-wire branch circuit to a single appliance such as a dryer you cannot use a handle tie on two single pole breakers.

That is still unclear, my reading of 240.15(B)(2) is that you can do that. And see post #28 for some information from the Handbook that agrees.

Cheers, Wayne

 

[wwhitney]

So I am still confused, for a single phase grounded system, the only time common trip is required is if there is a neutral as part of the circuit, and when it is NOT a MWBC?

On a 120/240V system, common trip is not required for 2-wire L-L circuits (and obviously not an issue for 2-wire L-N circuits).

For a 3-wire circuit supplying only L-N loads, common trip is not required. For a 3-wire circuit supplying two or more pieces of equipment, at least one of which is connected L-L, common trip is required by 210.4(C).

There is some debate about whether common trip is required for a 3-wire circuit supplying a single piece of equipment connected L-L-N. It is not by 210.4(C), but it is possible to read 240.15(B)(2) as only applying to 2-wire circuits. Although that reading of 240.15(B)(2) renders 210.4(C) exception 1 pointless.

Cheers, Wayne

 

[Little Bill]

That is still unclear, my reading of 240.15(B)(2) is that you can do that. And see post #28 for some information from the Handbook that agrees.

Cheers, Wayne

Did you skip over post #35? It has commentary from the handbook stating why common trip would be needed.

 

[wwhitney]

Did you skip over post #35? It has commentary from the handbook stating why common trip would be needed.

That commentary is on 210.4(C), and Exception #1 of 210.4(C) applies to an individual branch circuit (just one load), so 210.4(C) does not require common trip in that scenario. The commentary on 240.15(B) excerpted in post #28 references 210.4(C) Exception 1 and agrees with respect to 210.4(C).

The remaining question is about 240.15(B) and whether it requires common trip, in particular whether the phrase "line-to-line connected loads for single-phase circuits" in 240.15(B)(2) means 2-wire loads only, as I believe you read it, or whether it covers 3-wire loads as well, as I am inclined to believe, and as the commentary excerpted in post #28 indicates.

It is worth noting that 240.15(B)(4), which covers 125/250V DC circuits, refers explicitly to "3-wire DC circuits" and so clearly would allow handle ties only for the (very rare) DC version of the circuit under discussion. So I have been pondering whether there is any reason for 240.15(B) to treat DC differently from AC, or whether the language used in 240.15(B)(4) is a clue to what is intended in 240.15(B)(2). I'm not seeing any reason for 240.15(B) to treat DC differently from AC.

So it seems to me 240.15(B) could be rewritten simply as "Circuit breakers supplying any load line-to-line with a voltage to ground in excess of 125V shall open all ungrounded conductors of the circuit both manually and automatically."

Cheers, Wayne