277/480, 4W panelboard used as 480, 3W

[hmspe]

I have a client who has installed a Siemens P2 series panelboard labeled as 480Y/277v, 3ph, 4W but who did not install a neutral. The Inspector is citing 110.3 and says the installation is improper since the connection is 3W but the label says 4W. I know that this connection is not uncommon, but "people do it all the time" is not going to be an acceptable reply. Is there anything in the Code (2011), in the listing standards, or in the installation instructions (which I do not have available) which would say whether the installation is compliant?

Thanks.

 

[ActionDave]

The label says what the panel is allowed to be used for and is somewhat generic. There is no requirement to bring a neutral past the service if there are no line to neutral loads.

 

[kwired]

Similar topic came up earlier today, my reply in that thread was that the panel and breakers are rated for 480/277 volt systems, where voltage to ground doesn't exceed 277 nominal. You do not have to utilize a neutral, and it serves no purpose if there is no neutral loads (still need grounded conductor if it is the service equipment though).

What this panel is not suitable for is a delta system where you will either have 480 volts to ground or a 415 volts to ground high leg, or even ungrounded delta systems.

 

[Jraef]

Similar topic came up earlier today, my reply in that thread was that the panel and breakers are rated for 480/277 volt systems, where voltage to ground doesn't exceed 277 nominal. You do not have to utilize a neutral, and it serves no purpose if there is no neutral loads (still need grounded conductor if it is the service equipment though).

What this panel is not suitable for is a delta system where you will either have 480 volts to ground or a 415 volts to ground high leg, or even ungrounded delta systems.

Bingo.

Your SERVICE is still 480/277 whether or not you bring the neutral out to the panel. The voltage reference to ground is still 277V no matter where you measure it (+- based on ground differences). This exact same issue comes up with MCCs all the time. It's very rare that anyone actually uses the Neutral in an MCC, so the Neutral bus is hardly ever ordered. But the MCC is still rated as suitable for 480/277V service. From the bus bar standpoint it really makes no difference, in a panelboard or MCC. But where it DOES make a difference might be in the breakers. If it were a 480V Delta panel, the label would (should) preclude the use of "slash rated" breakers. Slash rated means breakers that can ONLY be used on 480/277V services because they are cheaper and not built to withstand the potentially higher mechanical forces involved in an asymmetrical fault (meaning Line to Ground) where the voltage involved in the fault, and thus the energy in it, is possibly at the line-to-line reference.

 

[ActionDave]

What this panel is not suitable for is a delta system where you will either have 480 volts to ground or a 415 volts to ground high leg, or even ungrounded delta systems.

I'm not so sure about this.

Your SERVICE is still 480/277 whether or not you bring the neutral out to the panel. The voltage reference to ground is still 277V no matter where you measure it....

I agree.

....If it were a 480V Delta panel, the label would (should) preclude the use of "slash rated" breakers. .

I fully agree with both of you on the use of slash rated breakers on a high leg or corner ground circuit. I have never heard of a Delta panel though.

Voltage to ground on slash rated or straight rated breakers applies only to the breaker. The rating of the panel applies to bussing voltage level and max amps, does it not?

 

[hmspe]

Thanks to all.

 

[kwired]

I'm not so sure about this.

I agree.


I fully agree with both of you on the use of slash rated breakers on a high leg or corner ground circuit. I have never heard of a Delta panel though.

Voltage to ground on slash rated or straight rated breakers applies only to the breaker. The rating of the panel applies to bussing voltage level and max amps, does it not?

As Jraef mentioned the bus may be just fine, but is possible they don't make any breakers for that panel that aren't 277/480 rated. I am not familiar with Siemens 480 volt panels at all, have been around some GE and mostly Square D. They both have a line that this is pretty much the case, where if you want to use on corner ground or high leg system you are going to have to use a different panel series to be able to find a breaker rated for the application.

 

[Jraef]

I used to work for Siemens andthe P1 panels are indeed made to ONLY accept slash rated breakers. You cannot use them on a delta supply. The bus bar itself is exactly the same as the P2 panels, but the mounting for the breakers is what makes it so that you can't use it on a Delta supply where you need to use 600V rated breakers (which is how they delineate the ones that are not slash rated).

But again, just because you are only running 3 wires to it does not make it a Delta supply. It's still a 4 wire service, of which you are only using the phase conductors. The inspector is wrong.

 

[hmspe]

This is yet another area where the NEC could be clearer. I can cite 2011 215.2(A)(1) as allowing a grounded conductor sized for zero amps unbalanced load (meaning no neutral) for a panel supplying only three phase loads with no neutral connections, but 215.2(A)(2) states, "The size of the feeder circuit grounded conductor shall not be smaller than that required by 250.122..." 215.2(A)(2) could be read to require a neutral in all feeders, even delta. It may not be best practice, but I agree that there is no reason to install a neutral to a panel on a 277/480V system if there is no neutral load, but the actual wording of 215.2(A)(2) in the NEC may make one necessary.

2011 NEC 215.2(A)(2) is interesting. The text was added in the 2005 NEC, but was part of 215.2(A)(1). In the 2011 the text was renumbered to 215(A)(2), but the last line, "Additional minimum sizes shall be as specified in
215.2(A)(2) and (A)(3) under the conditions stipulated.", was not changed to 215.2(A)(3) and (A)(4). The ROPs and ROCs seem to primarily address the grounding conductor, not the grounded conductor, but the title is "Grounded Conductor". I think this section of the NEC needs to be reworked. The typo for the reference to 215.2(A)(2) and (A)(3) is still in the 2014. I find it highly unlikely that 215.2(A)(2) would reference itself for additional requirements.

 

[kwired]

This is yet another area where the NEC could be clearer. I can cite 2011 215.2(A)(1) as allowing a grounded conductor sized for zero amps unbalanced load (meaning no neutral) for a panel supplying only three phase loads with no neutral connections, but 215.2(A)(2) states, "The size of the feeder circuit grounded conductor shall not be smaller than that required by 250.122..." 215.2(A)(2) could be read to require a neutral in all feeders, even delta. It may not be best practice, but I agree that there is no reason to install a neutral to a panel on a 277/480V system if there is no neutral load, but the actual wording of 215.2(A)(2) in the NEC may make one necessary.

2011 NEC 215.2(A)(2) is interesting. The text was added in the 2005 NEC, but was part of 215.2(A)(1). In the 2011 the text was renumbered to 215(A)(2), but the last line, "Additional minimum sizes shall be as specified in
215.2(A)(2) and (A)(3) under the conditions stipulated.", was not changed to 215.2(A)(3) and (A)(4). The ROPs and ROCs seem to primarily address the grounding conductor, not the grounded conductor, but the title is "Grounded Conductor". I think this section of the NEC needs to be reworked. The typo for the reference to 215.2(A)(2) and (A)(3) is still in the 2014. I find it highly unlikely that 215.2(A)(2) would reference itself for additional requirements.

A three wire delta system will not have a neutral.

True 215.2(A)(2) addresses sizing of grounded conductor, but nothing in 215 that I am aware of requires running a grounded conductor.

Grounded conductor of a grounded system is required to be brought to service equipment, but does not need to run beyond that point if there isn't any loads that utilize the grounded conductor.

 

[GoldDigger]

Since there will be no neutral run in the feeder to the panel, it seems reasonable to remove the neutral bus bar so that nobody is tempted to try to use it to connect a line to neutral load.
That or cover it in a durable way.

 

[kwired]

Since there will be no neutral run in the feeder to the panel, it seems reasonable to remove the neutral bus bar so that nobody is tempted to try to use it to connect a line to neutral load.
That or cover it in a durable way.

With 480/277 maybe that chance goes down, but I have run into situations with 120/240 where those not knowing any better will connect a neutral to the EGC bus if that is all that is available.