Opinion of Article 705

[marsac]

Your analysis/opinion on NEC 705.40 (&705.42).
You can use a single phase utility interactive inverter in a three phase system if its listing allows.
My understanding is part of UL Std. 1741 is the capability to ?Upon loss of primary source, an electric power production source" (the PV inverter) "shall be automatically disconnected??.? or by exception ?cease exporting power?.

Our jurisdictions position is that both of the above code references requires a single phase PV source when attached to a 3-phase system to cease exporting power when the primary source loses one or all phases. This would include the phase that the single phase PV inverter is not connected to.

We would appreciate your analysis and opinion

 

[dbuckley]

Its a poor, but understandable interpretation, in my opinion.

Lets apply some logic and see where it takes us.

All electricity distribution is three phase, and most electricity consumption (by number of connections) is single phase. Take the common case of dwellings A, B, and C being fed by a phase each. Each dwelling has a PV on the roof. The phase supplying dwelling A fails, whilst dwellings B and C are still supplied with power. Does this mean that dwellings B and C's PV systems somehow should magically know that next door and next-door-but-one are without power and so they should shut down?

Most folks would agree that is a ludicrous interpretation.

But its very closely related to the view your jurisdiction is taking. The intent of the regulation is to prevent the PV (or other SDS) continuing to supply (export) power to a failed supply, to prevent danger to people who may be in contact with the dead supply. If one or two out of three phases are still up, then (a) the danger of contact to the live supply still exists even in the absence of the PV, and (b) because the supply is still live there should be sufficient measures in place to prevent accidental or deliberate contact by persons with that supply.

If this was a required scenario, then for a single phase inverter to get listed to operate on a three phase supply, all inverters would have all three phase terminals, even though only one is required for export. The very lack of these aditional two phase monitoring terminals is strong evidence that both the manufacturers and UL consider it unnecessary.

 

[George Stolz]

Our jurisdictions position is that both of the above code references requires a single phase PV source when attached to a 3-phase system to cease exporting power when the primary source loses one or all phases.

705.42 clearly requires this, IMO.

Looks as though a 3-phase inverter would be required if three single-phase inverters cannot communicate their supply failure to each other.