options for Switched neutral breakers

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Buck Parrish

Senior Member
Location
NC & IN
I don't see anything there prohibiting the use of a 3 bus panel for 120/240V plus neutral, seems like an elegant solution.

Cheers, Wayne
110.3 (C) is all I've got.
I've actually done it. Didn't work out to good. Got turned down, but with a smile. He said nice try looks good, but nope.
But the AHJ could allow it.
 

Buck Parrish

Senior Member
Location
NC & IN
What would have been a compliant installation?
All I'm saying is I don't think it has been UL approved to have the grounded conductor terminated on the lug designed for a hot wire,
Are you following me?
He has a three phase panel. He wants to take the neutral from a single phase and put it on the middle phase of the three phase panel.
He wants to use a three phase breaker on single phase and wants the neutral on the third terminal. I'm referring to 110.3 (C)
So two items, the panel and the breaker would have to have been approved for that install.
 

wwhitney

Senior Member
Location
Berkeley, CA
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Retired
110.3 (C) is all I've got.
I've actually done it. Didn't work out to good. Got turned down, but with a smile. He said nice try looks good, but nope.
Bad call by the inspector.

In an ungrounded system, all circuit conductors will be disconnected by an OCPD, so they will all go to the busbars in a panel. In a grounded system, we usually take advantage of no longer needing to interrupt the grounded circuit conductor, so we use a terminal bar instead of a busbar. But nothing says we have to do that. The listing on a panel may impose a maximum voltage between the busbar and ground, but it certainly doesn't impose a minimum voltage.

240.22(1) tells us we can install OCPD on the grounded conductor when all circuit conductors are simultaneously opened by a common trip OCPD. To me, that says using a busbar for the grounded circuit conductor is allowed.

Cheers, Wayne
 

Buck Parrish

Senior Member
Location
NC & IN
Bad call by the inspector.

In an ungrounded system, all circuit conductors will be disconnected by an OCPD, so they will all go to the busbars in a panel. In a grounded system, we usually take advantage of no longer needing to interrupt the grounded circuit conductor, so we use a terminal bar instead of a busbar. But nothing says we have to do that. The listing on a panel may impose a maximum voltage between the busbar and ground, but it certainly doesn't impose a minimum voltage.

240.22(1) tells us we can install OCPD on the grounded conductor when all circuit conductors are simultaneously opened by a common trip OCPD. To me, that says using a busbar for the grounded circuit conductor is allowed.

Cheers, Wayne
OK , well there you go. Hope the OP is reading that. BTW Wayne, Have you used this option? Just wondering...
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
No, I'm not a practicing electrician. That means I'm often guided by reading the NEC itself, rather than received wisdom. That doesn't mean you won't find an AHJ who doesn't like the idea and isn't convinced by the citation I provided.

Cheers, Wayne
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
240.22(1) tells us we can install OCPD on the grounded conductor when all circuit conductors are simultaneously opened by a common trip OCPD. To me, that says using a busbar for the grounded circuit conductor is allowed.
In addition, 404.2(B) Exception says:
"A switch or circuit breaker shall be permitted to disconnect a grounded circuit conductor where all circuit conductors are disconnected simultaneously ... "
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Of course, those two references just tell you that you can use switched neutral breakers. They don't explicitly tell you that you do it via a regular multi-pole breaker with the neutral on one of the panel busses.

But absent anything specific that prohibits it, it is allowed. I don't believe the product standard for panelboards is going to require a minimum voltage between the busbars and ground, so 110.3(C) is no prohibition.

Cheers, Wayne
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I don't recall ever seeing a panel instruction prohibiting grounded conductors on line terminals.

As long as it's as large as the other feeder conductor(s), it should be fine.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
I don't recall ever seeing a panel instruction prohibiting grounded conductors on line terminals.

As long as it's as large as the other feeder conductor(s), it should be fine.
I would/could use them on a three phase grounded delta system and be perfectly legal. There is no difference other than the application to single phase, however, I would not surprise my AHJ. They may be wrong in their interpretation but way cheaper to have the discussion before the installation.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
I would/could use them on a three phase grounded delta system and be perfectly legal.
Can you use a single phase panel (I should say two bus bar panel) on a three phase grounded delta, with the grounded conductor on the "neutral" bar? If not, why not?

I can see a voltage to ground issue, if single phase panels aren't available with a sufficiently high voltage to ground rating, but I'm curious if there's any other issue. Also, if you wanted to balance your single phase L-L loads evenly, one third (VA wise) of them would need to originate from double pole breakers.

Cheers, Wayne
 

oldsparky52

Senior Member
I have used a contactor to cover the "switched neutral" requirements for C1D1 dispenser circuits. Hot and neutral of the circuit leave the panel and go to L1 and L2 of the contactor and jump to coils of the contactor. The L and N of the dispenser circuit land on the output of the contactor. Turn off the single-pole breaker and the contactor drops out breaking both hot and neutral.

For years I've wanted to try the feeding a panel with L and N and using 2-pole breakers but I never wanted to risk doing it w/out prior approval and I never found an AHJ that would stick their neck out.

Too many lawyers needing work is not good for our society.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
The standard plug on CH 3 phase panel I have on my shelf is 208Y/120 VAC. Can't use that one.
I didn't track down the actual Eaton catalog, but this webpage (near the bottom) says that the CH 3 phase panels are "Three-Phase Four-Wire--208Y/120 Vac or 240 Vac Insulated/Bondable Split Neutral". Not 100% sure what the last part means, but pretty sure it means that 240V between busbars is OK, you're not limited to 208V.


Cheers, Wayne
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
I think it refers to two neutral bars, joined by a removable link, and bonding it/them is optional.
Now that I look at it again, the single phase panels are labeled "Single-Phase Three-Wire--120/240 Vac--Insulated/Bondable Single Neutral".

So the "insulated/bondable" definitely refers to a bonding jumper/screw. But I think that "split neutral" vs "single neutral" probably refers to using one of the bus bars for a grounded conductor.

Cheers, Wayne
 

mannyb

Senior Member
Location
Florida
Occupation
Electrician
You see this at most any gas/fuel station. The panel neutral is switched only for fuel panel. I know CUtler hammer has a 2pole switch neutral breaker where you dont need to modify panel at all. The neutral feeds through breaker similar to AFCI breaker but makes no contact with buss. Just FYI.
 
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