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

[skorpioskorpio]

Just curious, as I don't really see where this is explicitly defined. Say I want to have one 2 gang box that has a 120V 20 Amp circuit and a 240V 20 Amp circuit present. For safety, and convenience I would run a 3 phase breaker for these 2 circuits. I realize that common trip is not required, although handle ties might be a good idea, 3 phase breakers seem like an easier and perhaps safer way of accomplishing the same thing, as they are commonly available, and if 3 breaker handle ties exist I've never seen one, not that all breakers could even be tied that way between a single pole and a dual pole breaker, but anyway that isn't the real question.

The real question is what would be the grounding requirements for this? I know that if I was to run these 2 circuits in EMT no separate EGC is required but having one is a better practice. I know that if running NM-B, just running two 12/2 cables would be typical, however it results in non obvious color coding in the box where half the wires really should be reidentified. However, what if this was PVC conduit or a non-metallic raceway? Is one 12Ga ground sufficient or does there need to be an EGC return sufficient for a simultaneous fault of both circuits? Or could you feed this box with 12/4 NM-B? There only needs to be a single neutral going to this box, as the 240V doesn't need one. But what about ground?

I assume all non-metallic scenarios would be the same, regardless if it's NM-B or PVC or some non-metallic raceway like wiremold. I see in the NEC where non-metallic is defined, and see where handle tied breaker use is defined when 2 split phase circuits share a neutral, and also the grounding requirements for metallic conduit and raceway. What I do not see defined is the EGC requirements for multiple circuits sharing the same non-metallic path.

 

[infinity]

However, what if this was PVC conduit or a non-metallic raceway? Is one 12Ga ground sufficient or does there need to be an EGC return sufficient for a simultaneous fault of both circuits?

A single EGC sized for the largest of multiple circuits is all that's required in a single raceway.

 

[electrofelon]

Just curious, as I don't really see where this is explicitly defined. Say I want to have one 2 gang box that has a 120V 20 Amp circuit and a 240V 20 Amp circuit present. For safety, and convenience I would run a 3 phase breaker for these 2 circuits. I realize that common trip is not required, although handle ties might be a good idea, 3 phase breakers seem like an easier and perhaps safer way of accomplishing the same thing, as they are commonly available, and if 3 breaker handle ties exist I've never seen one, not that all breakers could even be tied that way between a single pole and a dual pole breaker, but anyway that isn't the real question.

Infinity answered the main question, but just to comment on the above: Personally I would not use a three phase breaker (unless all conductors land on the same yoke). There is a big price jump for a three pole breaker and IMO it is more unsafe to try and force people to turn off other circuits as it can create a further hassle which can result in them working the circuit live.

Eaton has 3 pole handle ties. SQ D does too (QO3HT). I believe siemens does not offer them annoyingly.

 

[marmathsen]

Also if it's a residential type panel, it may not support 3 pole breakers.

Rob G - Seattle

 

[TX+ MASTER#4544]

Just curious, as I don't really see where this is explicitly defined. Say I want to have one 2 gang box that has a 120V 20 Amp circuit and a 240V 20 Amp circuit present. For safety, and convenience I would run a 3 phase breaker for these 2 circuits. I realize that common trip is not required, although handle ties might be a good idea, 3 phase breakers seem like an easier and perhaps safer way of accomplishing the same thing, as they are commonly available, and if 3 breaker handle ties exist I've never seen one, not that all breakers could even be tied that way between a single pole and a dual pole breaker, but anyway that isn't the real question.

The real question is what would be the grounding requirements for this? I know that if I was to run these 2 circuits in EMT no separate EGC is required but having one is a better practice. I know that if running NM-B, just running two 12/2 cables would be typical, however it results in non obvious color coding in the box where half the wires really should be reidentified. However, what if this was PVC conduit or a non-metallic raceway? Is one 12Ga ground sufficient or does there need to be an EGC return sufficient for a simultaneous fault of both circuits? Or could you feed this box with 12/4 NM-B? There only needs to be a single neutral going to this box, as the 240V doesn't need one. But what about ground?

I assume all non-metallic scenarios would be the same, regardless if it's NM-B or PVC or some non-metallic raceway like wiremold. I see in the NEC where non-metallic is defined, and see where handle tied breaker use is defined when 2 split phase circuits share a neutral, and also the grounding requirements for metallic conduit and raceway. What I do not see defined is the EGC requirements for multiple circuits sharing the same non-metallic path.

2023 NEC
Would Section 250.122(C) help you?
What is that "ground" that you mention?
Grounding requirements, EGC?

 

[skorpioskorpio]

Infinity answered the main question, but just to comment on the above: Personally I would not use a three phase breaker (unless all conductors land on the same yoke). There is a big price jump for a three pole breaker and IMO it is more unsafe to try and force people to turn off other circuits as it can create a further hassle which can result in them working the circuit live.

Eaton has 3 pole handle ties. SQ D does too (QO3HT). I believe siemens does not offer them annoyingly.

I believe the handle ties you are referring to are to tie 3 single pole breakers. In the scenario I described, 2 of those breakers are required to be common trip, not just tied, so a tie bar would not be sufficient unless it was specifically designed to accommodate a single pole and a common trip 2 pole. Most 2 pole breakers I've seen cannot accommodate a tie bar as the handles are either not through drilled or they already have a tie bar installed that is not intended to be removed.

It's always been my understanding that a 2 pole breaker can always legally replace a tied pair of single poles, but not the other way around, so not sure why that would not also be true of 3 or even 4 pole breakers, and given that 4 pole breakers even exist, and they do, what purpose would they serve other than for this exact type of scenario.

I didn't really detail the specifics of where I was going with that, well because it wasn't really the question, but what I was referring to is a single 2 gang box or multiple 2 gang boxes in series that have both 120V and 240V outlets in them. If those 2 circuits travel together, and always land in similarly configured boxes, working in those boxes would always have a live circuit present unless both circuits were tripped. In my personal opinion any operational inconvenience would be outweighed by the safety provided by a common trip of both circuits.

 

[electrofelon]

I believe the handle ties you are referring to are to tie 3 single pole breakers. In the scenario I described, 2 of those breakers are required to be common trip, not just tied, so a tie bar would not be sufficient unless it was specifically designed to accommodate a single pole and a common trip 2 pole. Most 2 pole breakers I've seen cannot accommodate a tie bar as the handles are either not through drilled or they already have a tie bar installed that is not intended to be removed.

It's always been my understanding that a 2 pole breaker can always legally replace a tied pair of single poles, but not the other way around, so not sure why that would not also be true of 3 or even 4 pole breakers, and given that 4 pole breakers even exist, and they do, what purpose would they serve other than for this exact type of scenario.

I didn't really detail the specifics of where I was going with that, well because it wasn't really the question, but what I was referring to is a single 2 gang box or multiple 2 gang boxes in series that have both 120V and 240V outlets in them. If those 2 circuits travel together, and always land in similarly configured boxes, working in those boxes would always have a live circuit present unless both circuits were tripped. In my personal opinion any operational inconvenience would be outweighed by the safety provided by a common trip of both circuits.

Yes the line to line circuit would need to be common trip. Whether you need a handle tie depends on if the circuits are on the same device or not.

I have never heard of anybody using handle ties or multi pole breakers for multiple circuits in the same box, but you are free to do so if you choose .

 

[skorpioskorpio]

A single EGC sized for the largest of multiple circuits is all that's required in a single raceway.

I assume by extension that means that 12/4 NM-B would also meet those requirements. Given that 12/2/2 NM-B exists would lead me to believe that must be the case or that product would be pretty much unusable for anything, since it provides 2 circuits and only a single ground wire. I mean it's really the same product as 12/4 with different color coding.

 

[infinity]

I was referring to is a single 2 gang box or multiple 2 gang boxes in series that have both 120V and 240V outlets in them. If those 2 circuits travel together, and always land in similarly configured boxes, working in those boxes would always have a live circuit present unless both circuits were tripped. In my personal opinion any operational inconvenience would be outweighed by the safety provided by a common trip of both circuits.

You're free to handle tie all of the circuits together but as electrofelon stated it is not required. Personally I see no reason to even consider it. If you need to work in the box you can turn off all of the circuits within the box.

 

[roger]

As Tex posted, 250.122(C) has your answer for the EGC.

 

[skorpioskorpio]

Also if it's a residential type panel, it may not support 3 pole breakers.

Rob G - Seattle

I actually wrote 3 "phase", but meant 3 pole, which I know equates to the same thing more or less, but I don't think any common use split phase panel has anything preventing the use of a 3 pole breaker of the same type in it.

 

[skorpioskorpio]

You're free to handle tie all of the circuits together but as electrofelon stated it is not required. Personally I see no reason to even consider it. If you need to work in the box you can turn off all of the circuits within the box.

I know it isn't required.

 

[infinity]

I assume by extension that means that 12/4 NM-B would also meet those requirements. Given that 12/2/2 NM-B exists would lead me to believe that must be the case or that product would be pretty much unusable for anything, since it provides 2 circuits and only a single ground wire. I mean it's really the same product as 12/4 with different color coding.

That's correct they're both 4 conductors with an EGC. The 12/4 can be used for three circuits with a single EGC. There is no limit as to how many circuits can share the same equipment grounding condcutor.

 

[electrofelon]

I actually wrote 3 "phase", but meant 3 pole, which I know equates to the same thing more or less, but I don't think any common use split phase panel has anything preventing the use of a 3 pole breaker of the same type in it.

Yeah I am 99% sure there is no rejection feature for preventing putting a three-pole breaker in a single phase panel. In the case of square D homeline, of course, they don't make three pole breakers, which is an oddity in the industry.

 

[infinity]

Yeah I am 99% sure there is no rejection feature for preventing putting a three-pole breaker in a single phase panel. In the case of square D homeline, of course, they don't make three pole breakers, which is an oddity in the industry.

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

 

[winnie]

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

I might just have to do this I wonder if I can get a 30-30-20 3 pole breaker for my bathroom renovation (tankless booster heater and normal 20A circuit).....

Seriously, to the OP, speaking as one non-electrician engineering type to another: trust the electricians on this. They listen to me when I go though the maths behind some of the things they do, I listen to them when it comes to practical matters of how things should actually go into the wall.

From my own personal experience, there is always a drive to 'do more than code requires' to improve safety. Often this means missing some non-obvious safety requirement, or violating a code that shouldn't apply but no one considered my wacky use case. Go with standard and if you upgrade just upgrade the quality of standard materials used.

-Jonathan

 

[wwhitney]

Yes the line to line circuit would need to be common trip.

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

 

[Fred B]

Eaton has 3 pole handle ties. SQ D does too (QO3HT). I believe siemens does not offer them annoyingly.

Siemens has a 2 pole tandem that will give either a (2 single trip and a common trip "240v") or an actual 2 double pole tandem common trip giving 2 "240v" circuits in one double pole space.

 

[LarryFine]

Siemens has a 2 pole tandem that will give either a (2 single trip and a common trip "240v") or an actual 2 double pole tandem common trip giving 2 "240v" circuits in one double pole space.

I wonder how they internally link the outer pair.

 

[Fred B]

A single EGC sized for the largest of multiple circuits is all that's required in a single raceway.

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