705.12(C)

[Pharon]

Regarding the output connection point of a utility-interactive inverter, Article 705.12 says we must comply with (A), (B), (C), or (D).

We can connect to the supply side of the service disconnecting means as long as it does not exceed the rating of the service, per 705.12(A), or we can connect to the load side as long as the sum of the OCPD protecting the busbar plus the inverter OCPD do not exceed 120% of the busbar rating, per 705.12(D), plus some other things (marking, suitable for backfeed, etc.).

705.12(B) refers us to Article 685, which deals with integrated electrical systems, which are unitized segment of an industrial wiring system. For argument's sake, let's assume this section does not apply for now.

But what about 705.12(C)? If I'm reading this correctly, it basically says that as long as you have inverter(s) that exceed 100kW, then you are not bound by the restrictions of (D) when you connect to the load side, as long as you have qualified personnel, safeguards, etc. in place -- is that correct?

Because that doesn't make any sense to me. Would't you still have all of the same busbar overloading concerns that mandate the requirements of (D)? What am I missing here?

 

[GoldDigger]

The 120% rule only comes into play when you have the possibility that someone will connect loads in the panel that draw more current during normal operation than the main breaker should allow.
In a supervised environment with qualified personnel it is less likely that will happen.

 

[Pharon]

Okay, but what qualifies as a supervised environment? Unless someone is monitoring the amperage of that bus 24/7, and getting alarms when the current exceeds the upper threshold, that scenario could take place no matter how many qualified personnel are present.

 

[jaggedben]

The section is clearly written with the intention of applying to large facilities where parts of the distribution on the load side of the legal service point may resemble a utility distribution system as much as typical premises wiring. Note the condition about services over 1000V.

e.g. college campuses, airports, stadiums...Facilities that would have at least one full-time facilities maintenance employee, or more likely several levels of such employees, possibly even a full-time electrical engineer. Facilities where high current electrical equipment is locked up. That's what would constitute a 'supervised environment'.

Interconnecting may not involve typical busbars at all, but connecting directly to transformers or some other type of distribution.
Presumably on systems over 100kW, an electrical engineer, or a few, would evaluate any overload concerns.

Note that 'Qualified Person' is defined in article 100. The rest is up to the AHJ to interpret, but I think the intention of the section is to allow some leeway for large, very organized facilities, where nobody is going to be allowed to do any subsequent work without passing through the facility's own bureaucracy.