Using a 2-pole breaker, and only making use of one of the poles

[kwired]

If you know about the history of proposals to add a 'Do Not Add Loads' labeling option to 705.12, it might start to make some sense to you.

Are we dealing with a 705 application?

 

[highlegdelta]

On the only solar project I've done, I had an inspector require the same thing. I just ordered a 12 space 200a panel that was the exact number of spaces I needed

Sent from my SD4930UR using Tapatalk

 

[jaggedben]

Are we dealing with a 705 application?

Yes, see post 10. I asked because I suspected it was a factor. Only reason I know of why anyone would require anything like this.

 

[ggunn]

I'll just say that I am glad that none of the AHJs I deal with have taken this position. 705 now (in 2014) allows us to legitimately use an AC combiner panel for a PV system without having to use the 120% rule counting the OCPD between the panel and the service. It does not say that the panel must not contain empty slots. Inspectors around here evaluate a system on the basis of what it is, not on what someone could do to it later.

 

[Carultch]

I'll just say that I am glad that none of the AHJs I deal with have taken this position. 705 now (in 2014) allows us to legitimately use an AC combiner panel for a PV system without having to use the 120% rule counting the OCPD between the panel and the service. It does not say that the panel must not contain empty slots. Inspectors around here evaluate a system on the basis of what it is, not on what someone could do to it later.

However, the way that it is written, it does require you to accumulate rounding errors, which can be frustrating.

For instance, consider 12 qty inverters at 26.5A of operating current, each needing a 35A breaker. Total 318A of operating current.

If you add up the breakers, that's a total of 420A, which would indicate you'd need a 600A panelboard, because 450A is within this category.
If you simply take the total operating current and multiply by 1.25, that's 397.5A, which would indicate you'd need a 400A panelboard.

Intuitively, there doesn't seem to be a physical reason why you should have to accumulate rounding errors. And accumulating rounding errors can put you in a significantly larger equipment category.

 

[ggunn]

However, the way that it is written, it does require you to accumulate rounding errors, which can be frustrating.

For instance, consider 12 qty inverters at 26.5A of operating current, each needing a 35A breaker. Total 318A of operating current.

If you add up the breakers, that's a total of 420A, which would indicate you'd need a 600A panelboard, because 450A is within this category.
If you simply take the total operating current and multiply by 1.25, that's 397.5A, which would indicate you'd need a 400A panelboard.

Intuitively, there doesn't seem to be a physical reason why you should have to accumulate rounding errors. And accumulating rounding errors can put you in a significantly larger equipment category.

I understand; that exact thing happened to us on an installation; a 400A combiner became a 600A combiner because the breaker ratings summed to 420A.

It is what it is. Maybe next cycle the rule will get relaxed to 125% of inverter output.

 

[GoldDigger]

Just as has been done in [2014] for the special case of applying the 120% rule.