Single-Phase 3-Wire panelboard supplied by a 2-Wire Source?

[anon23]

Does the NEC code allow for a single-phase 3-wire panelboard meant for 120/240VAC to be supplied by a single-phase 2-wire 120VAC source by jumpering both the A and B bus together if only 120VAC is needed?

 

[Dennis Alwon]

Does the NEC code allow for a single-phase 3-wire panelboard meant for 120/240VAC to be supplied by a single-phase 2-wire 120VAC source by jumpering both the A and B bus together if only 120VAC is needed?

The Nec is silent on that and it has been done many times. An inspector should not be concerned, imo however they could cite 110.3(B). Ask first.

 

[jumper]

I got no problem with it as long as you do not jumper off a lug listed for 1 conductor. Polaris type connections or split bolts are usually needed.

 

[hardworkingstiff]

I got no problem with it as long as you do not jumper off a lug listed for 1 conductor. Polaris type connections or split bolts are usually needed.

How would you rule if you saw a panel that had A-phase fed with 120-volts and B-phase fed with a neutral (in a gas station so 2-pole breakers could be used in place of switched neutral breakers)?

 

[kwired]

How would you rule if you saw a panel that had A-phase fed with 120-volts and B-phase fed with a neutral (in a gas station so 2-pole breakers could be used in place of switched neutral breakers)?

I would say "how creative" then I would ask why not just get the switched neutral breakers? Most of the time you are begging just to get space to allow for 110.26 compliance in the first place in these places. So the panel in question is probably not the panel that contains the service disconnect and also is not a major distribution panel so that means it is some small panel that possibly needs even more space that is at a premium, plus labor to put it all together - switched neutral breakers are not that expensive. A lot of new equipment is 208/240 volt anyway.

 

[hardworkingstiff]

Most of the gas stations I see now require all of the dispensers to be on the same phase. Most of the time a sub panel is set with a contactor or shunt trip breaker (controlled by E-stop switch/s) to kill the power to the equipment. The SWN breakers are about twice as much as 2-pole breakers.

There may be an issue in that the power for the 208-240V submerged pumps would need to come out of the main panel and the E-stop would depend on the control power from the dispensers dropping out the coil of the power relay for the feed to the sub pump. I understand some people don't like that.

 

[kwired]

Most of the gas stations I see now require all of the dispensers to be on the same phase. Most of the time a sub panel is set with a contactor or shunt trip breaker (controlled by E-stop switch/s) to kill the power to the equipment. The SWN breakers are about twice as much as 2-pole breakers.

There may be an issue in that the power for the 208-240V submerged pumps would need to come out of the main panel and the E-stop would depend on the control power from the dispensers dropping out the coil of the power relay for the feed to the sub pump. I understand some people don't like that.

Do you put each dispenser on its own circuit? If the pump is remote type, the load of dispensers is not that much.

I have to admit I have not done retail type fuel dispensers in a long time, maybe 15 years, so I don't necessarily know what current practices may be.

 

[hardworkingstiff]

Do you put each dispenser on its own circuit?

Yes, in order to meet 514.11 without interrupting the other dispensers.

If the pump is remote type, the load of dispensers is not that much.

The manufacturers require each dispenser to be on a separate circuit.

I have to admit I have not done retail type fuel dispensers in a long time, maybe 15 years, so I don't necessarily know what current practices may be.

It's been a while for me too, so I might be out of date too.