Yes and no. If the conductors in an ungrounded bipolar system (there are ungrounded systems which are not bipolar and therefore are not different from conventional systems WRT equipment grounding) from the upper array are kept separate from those of the lower array all the way back to the inverter, then the voltage between the positive conductor of the positive array and the negative conductor of the lower array is not an issue.Yes you do. The definition of to "voltage to ground" in an ungrounded system is the potential between conductors of the circuit...
... positive conductor of the upper array, I meant to say....positive conductor of the positive array...
Some of this does not make sense. Please give an example of "ungrounded systems which are not bipolar". One guess is tripolar with an ungrounded center tap (not ungrounded after all).
I do not see how " If the conductors in an ungrounded bipolar system (......) from the upper array are kept separate from those of the lower array all the way back to the inverter, then the voltage between the positive conductor of the positive array and the negative conductor of the lower array is not an issue."
If one end of a high voltage string that is ungrounded becomes grounded due to a fault, the opposite end has full voltage with respect to ground. Cannot use 600V wire in a 1000V bipolar system. It may be good practice to use separate conduits as suggested by several inverter manufacturers as it reduces the voltage stress on wire insulation. After all, we are trying to instal PV systems that will still be safe in 25 years or more. The full voltage is an issue.
Yes you do. The definition of to "voltage to ground" in an ungrounded system is the potential between conductors of the circuit...
THanks, Shortcircuit2.
I did not know the potential between conductors is what counts here. (my systems are not bipolar. e.g. SMA SB3000TL)
I will continue to use grounding bushings, the bane of my professional life. :weeping:
Also, thanks all. The bipolar issue is not one i face.
Voltage to Ground. For grounded circuits, the voltage between the given conductor and that point or conductor of the circuit that is grounded; for ungrounded circuits, the greatest voltage between the given conductor and any other conductor of the circuit.
Do i need to use grounding bushings on metal conduit in a transformerless system when going into eccentric/concentric knockouts on boxes?
250.97 says yes, if over "250 V to ground."
Well, i have up to 600 V line to line, but to ground?
I don't have my codebook at home, but could you cite that article? I think that in AE bipolar inverters (the former Solaron line), the only time the array is center grounded is when the inverter is off. Caveat: that's from memory; I haven't designed a system around one in a while and the manual is at work.As for the bipolar PV circuit with a grounded neutral (the only type of bipolar PV circuit allowed by the NEC)...
I don't have my codebook at home, but could you cite that article? I think that in AE bipolar inverters (the former Solaron line), the only time the array is center grounded is when the inverter is off. Caveat: that's from memory; I haven't designed a system around one in a while and the manual is at work.
Especially on the internet, it takes a Big Man...690.41
But now that I look at it again, the exception (systems complying with 690.35) applies to all types of systems, so I was wrong.
"Missed it by that much...."Article 100:Some parts of the NEC may require they be kept separate if the voltage to ground is above 600V, but the definition quoted above refers to the circuit not the raceway.