2-Pole Main Breaker vs 4-Pole Main Breaker?

[Garbluck]

Seems that the Jurisdictions in the Las Vegas area are going to require:
that no PV systems can be interconnected on the load side of a center-fed panelboard
Unless: The panelboard's Main breaker is 4 Pole

I don't understand the reasoning behind this, so my question in the title stands:

What's the difference between a main breaker that is 2 pole vs 4 pole?

 

[jtopham26]

4 pole means it's 3 phase with a switched neutral making it a separatey derived system

 

[Garbluck]

4 pole means it's 3 phase with a switched neutral making it a separatey derived system

What does this mean for the interconnected PV system? It appears 3 phase is more common and practical?

 

[Carultch]

Seems that the Jurisdictions in the Las Vegas area are going to require:
that no PV systems can be interconnected on the load side of a center-fed panelboard
Unless: The panelboard's Main breaker is 4 Pole

I don't understand the reasoning behind this, so my question in the title stands:

What's the difference between a main breaker that is 2 pole vs 4 pole?

Could this be single phase, with two of the breaker poles protecting the upper half, and the other two protecting the lower half?

In that case, I see the rationale behind this. Both busbar halves have to be protected, from the other busbar half backfeeding it.



I thought that exotic situations like this were supposed to be allowed under "engineering supervision", that accounts for a specific list of studies about the potential issues within the panelboard.

 

[Garbluck]

Could this be single phase, with two of the breaker poles protecting the upper half, and the other two protecting the lower half?

In that case, I see the rationale behind this. Both busbar halves have to be protected, from the other busbar half backfeeding it.

I thought that exotic situations like this were supposed to be allowed under "engineering supervision", that accounts for a specific list of studies about the potential issues within the panelboard.

I haven't run into much of an "exotic situation" behind the Center-fed panelboards I deal with. I see the point there, to ensure that both busbars are protected. Sometimes i see a 4-pole Main (mostly 200A or 225A), other times i see a normal 2-pole (125A or 100A). If we have to upgrade these smaller ampere panelboards, there's no way we can keep business in the Vegas area.

 

[Carultch]

I haven't run into much of an "exotic situation" behind the Center-fed panelboards I deal with. I see the point there, to ensure that both busbars are protected. Sometimes i see a 4-pole Main (mostly 200A or 225A), other times i see a normal 2-pole (125A or 100A). If we have to upgrade these smaller ampere panelboards, there's no way we can keep business in the Vegas area.

I'm saying that it is exotic, because you aren't given a specific procedure on how to handle center-fed panels in the NEC.
In the NEC2014, they added a rule that says with engineering supervision, interconnection strategies can be solved for situations not covered with a specific calculation. And center-fed panels is one example.

 

[ggunn]

4 pole means it's 3 phase with a switched neutral making it a separatey derived system

I don't think so. I think it's more likely that the upper and lower busbars are isolated from each other and there is a 2 pole breaker for each half. The OP said the main breaker must be 4 pole, not the backfed breaker.

 

[jtopham26]

I don't think so. I think it's more likely that the upper and lower busbars are isolated from each other and there is a 2 pole breaker for each half. The OP said the main breaker must be 4 pole, not the backfed breaker.

Thanks, I was completely in the wrong ballpark.

I read an interesting article: http://www.nmsu.edu/~tdi/pdf-resources/IAEI Jul-Aug 2014.pdf

Basicially it's now a 100% rule rather than 120% rule.

It also requires engineering supervision in 2014... this is really what breaks the deal rather than disallowing line side taps IMO.

if a 4 pole breaker is used and the two buses are not connected i believe the situation lets you use the 120% rule again... correct me if I am wrong

Are these center fed panels more common on the west coast? I never see them in the northeast

 

[Zee]

Yes, I agree:
If two separate busbars are fed by a 4 pole breaker (which in essence is a pair of separate 2pole breakers with handles tied)....then it really is a split service, AKA a main with two main disconnects feeding two busbars.

In effect, this may physically look like a center fed panel......but electrically it is not. In which case 120% rule should apply.
Am i right here? Not sure if i've ever seen such a setup.

Also, bear in mind for "true centerfed" situations: reducing the main brkr may be feasible, and can keep you in biz, and still meet the 100% requirement.

 

[Carultch]

In effect, this may physically look like a center fed panel......but electrically it is not. In which case 120% rule should apply.

Excellent explanation. I completely agree.


By the way, what exactly counts as "engineering supervision"?

Suppose I am a staff engineer at my company, with an engineering background and knowledge of the code, but no formal license. I perform the required calculation(s), explain and review them with my licensed Professional Engineer. And finally seal a stamped report of this calculation with his stamp on it.

Is that what they mean by this term?

 

[Smart $]

...


By the way, what exactly counts as "engineering supervision"?

Suppose I am a staff engineer at my company, with an engineering background and knowledge of the code, but no formal license. I perform the required calculation(s), explain and review them with my licensed Professional Engineer. And finally seal a stamped report of this calculation with his stamp on it.

Is that what they mean by this term?

I'd say every AHJ would approve that as engineering supervision.

 

[electricalist]

 

[Sierrasparky]

I was looking for the for a picture like that. I don't see how that would be better than a 2 pole. Me however I used to try and only get the two pole units because they were usually a larger frame.

 

[Garbluck]

I don't think so. I think it's more likely that the upper and lower busbars are isolated from each other and there is a 2 pole breaker for each half. The OP said the main breaker must be 4 pole, not the backfed breaker.

From further research and thinking, I believe this is the answer to my situation. Thanks for shining some light on the situation!

Sounds like the jurisdictions here won't even let us use the 100% rule on a centerfed, and that rule might get shifted to these 4 poles. It's already very rare that a resident will use only the loads on the opposite ends, while using none of the loads on the PV breaker end...

 

[Garbluck]

Also, bear in mind for "true centerfed" situations: reducing the main brkr may be feasible, and can keep you in biz, and still meet the 100% requirement.

We're very aware of De-rating main breakers, it's a life saver! The biggest problems are the smaller rated panelboards (125A bus/ centerfed 100A main), the jurisdictions don't allow us to derate below 100A.

 

[jaggedben]

Attached is a picture of a fairly common Square D panel that is what I thought was meant by 4-pole breaker. But there's only one set of busbars, as the diagram makes clear.

It makes no sense whatsoever to treat these differently than other panels. Nor is it at all justifiable to prohibit PV on centerfed panels if the sums are within 100%. It's a real shame that the AHJs in question here seem to be making up their own completely nonsensical rules.

 

[Carultch]

It's a real shame that the AHJs in question here seem to be making up their own completely nonsensical rules.

I thought the purpose of the AHJ is to provide an interpretation of the code, where the code is subjective and requires an opinion. Not to make up their own rules.