NEC 2014 section 705.95(B)

[hhsting]

Attached sketch shows (2) Solaredge SE43.2kUS three phase inverter for 208V grid and (2) Solaredge SE14.4kUS three phase inverter for 120/208V grid.

I have feeders from AC side of inverters labeled F1, F2, F3, F4 go to AC panelboard PV-1. There are No other loads PV-1 panel. From PV-1 panel feeder F5 goes to AC fused disco which then connects to grid and also to building loads.

NEC 2014 section 705.95(B) is confusing conductors used solely for instrumentation, voltage detection, or phase detection. Would conductors labeled F1, F2, F3, F4, F5 considered used solely for instrumentation, voltage detection, or phase detection and fall under NEC 2014 Section 705.95(B) or not?

 

[jaggedben]

705.95(B) is for neutrals only. It would apply all of the neutrals you've mentioned if the inverter only uses the neutral for instrumentation, voltage detection, or phase detection.

(Why start a new thread?)

 

[Carultch]

Attached sketch shows (2) Solaredge SE43.2kUS three phase inverter for 208V grid and (2) Solaredge SE14.4kUS three phase inverter for 120/208V grid.

I have feeders from AC side of inverters labeled F1, F2, F3, F4 go to AC panelboard PV-1. There are No other loads PV-1 panel. From PV-1 panel feeder F5 goes to AC fused disco which then connects to grid and also to building loads.

NEC 2014 section 705.95(B) is confusing conductors used solely for instrumentation, voltage detection, or phase detection. Would conductors labeled F1, F2, F3, F4, F5 considered used solely for instrumentation, voltage detection, or phase detection and fall under NEC 2014 Section 705.95(B) or not?

705.95(B) is now in 705.28, for the 2020 NEC. The rule in the 2020 NEC is a little more nuanced than the previous 705.95(B), because it accounts for the possibility of supply-side conductors, or transformer secondary conductors, that have a different "EGC"-sizing algorithm than 250.122. Most of the time, you would match the EGC sized per 250.122, if you were following this rule.

I put "EGC" in quotes, because a different term applies when it isn't in a feeder/branch circuit that is behind an OCPD. In any case, it is the sizing algorithm of the green-or-bare conductor, that governs the lower limit on the size of the no-load or negligible load neutral. Could be an EGC is sized by 250.122, an SDSBJ per 250.30 or an SSBJ per 250.102. If there is a significant neutral current in excess of the EGC size's ampacity, it would have to at least as large as is needed for the current.

It generally applies to neutral conductors of 3-phase inverters, and the feeders that supply combining panelboards for them, but only when the inverter in question qualifies. It is common that such an inverter only uses the neutral as a reference point for voltage and frequency measurements, or it might use the neutral to operate its internal power supply, and therefore put an insignificant current on the neutral only. An example that wouldn't qualify, is an inverter that selectively operates its three Y-connected power stages based on DC power available to it. As a result, it will output an unbalanced source that will use its neutral for carrying the full load equal to the one or two power stages that operate. I'm not aware of any currently-available inverter that does this, but my go-to example is the Fronius IG Plus 12kW inverters from the early 2010's.