downsize neutral

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Zee

Senior Member
Location
CA
Does the Code permit me to downsize the neutral on an inverter output circuit? What section? To what size?

Specifically: 11.4 kw inverter @ 240 VAC = 47.5 A @ 125% = 59 Amps ===> 6 AWG wires.

Last time i checked Code requires a neutral on inverter output circuits, so can i use smaller than #6?

Can the EGC be #10 or #8?
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Does the Code permit me to downsize the neutral on an inverter output circuit? What section? To what size?

Specifically: 11.4 kw inverter @ 240 VAC = 47.5 A @ 125% = 59 Amps ===> 6 AWG wires.

Last time i checked Code requires a neutral on inverter output circuits, so can i use smaller than #6?

Can the EGC be #10 or #8?

If the neutral is only used for voltage reference then it can be sized down but it can be no smaller than the EGC. Size the EGC using Table 250.122. BTW, the code does not necessarily call for a neutral on an inverter output. Some inverters don't have a neutral connection at all.
 

Smart $

Esteemed Member
Location
Ohio
If the neutral is only used for voltage reference then it can be sized down but it can be no smaller than the EGC. Size the EGC using Table 250.122. BTW, the code does not necessarily call for a neutral on an inverter output. Some inverters don't have a neutral connection at all.
Keep in mind if it is a combo EGC/GEC it'll have to be sized per 250.66
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Does the Code permit me to downsize the neutral on an inverter output circuit? What section? To what size?

705.95(B). Allows it to be sized "equal to or larger than the equipment grounding conductor." And only in the situation ggunn mentioned.

Generally it's no help for circuit conductors 10awg and under. Among other things, if you upsize your conductors for voltage drop you are required to upsize the EGC as well, so you don't generally win if you're always using 10awg on outputs 30A and under.

Specifically: 11.4 kw inverter @ 240 VAC = 47.5 A @ 125% = 59 Amps ===> 6 AWG wires.

In my opinion the neutral could be 10awg if it's only for sensing.

Last time i checked Code requires a neutral on inverter output circuits, so can i use smaller than #6?

Code does not require a neutral, but most inverters require it to function.

Funny, I never actually take advantage of this section. I think I figure that as long as the run is short the cost of extra copper is not worth the time lost if my crew gets confused or if I have to argue with an inspector. At 6awg vs 10awg that might start to change, especially if it's a longer run.
 
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Zee

Senior Member
Location
CA
thanks guys,
I will go with a number 10 egc and match that size in the neutral.

Inv. Is transformer less and ungrounded so I'll forgo a GEC.
Ggunn, thanks for the original reply.
jaggedben,
I agree usually it is not worth fussing with downsizing on 20 or 30 amp inv.s.
Here however I don't want to wrestle too much 6 awg !
smart $, I appreciate the reminder on EGC vs GEC sizing.
 
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