Question on OCPD

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ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
View attachment HBL.pdf

See attached pdf. Here is a very simplified drawing of a PV system we are building. My contention is that the exception to 690.9(F) says that the 300A fuses on the service side is all the OCPD necessary for the AC side of this system. All the wiring is sized to withstand well over the 300A at 240V and the 36A at 2000V available from the service. The inspector is balking. What say you?
 
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electrofelon said:
I'll take a stab at it. Are you questioning whether the one transformer can be used that way without primary protection?
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The one on the left, yes. It is protected by the 300A fuse, which limits the current from the service to 36A at 2000V.
 
ggunn said:
The one on the left, yes. It is protected by the 300A fuse, which limits the current from the service to 36A at 2000V.
Click to expand...

I posed this question last year sometime. It is an interesting quandary. The language doesn't specifically say that we can protect that transformer through the other transformer, but does it have to? logically it is protected. Perhaps showing him the language regarding conductors protected by the primary ocpd would sway him.

Btw, i assume you are using low cost 2kv pv wire for the 2k run. It's a cool trick, that is what i did at my house for my service because I am 2000 feet from the nearest line. Except, I didn't want to pay for custom transformers so I am running it at 2400v. The run is 2 12 guage 2kv pv wires.
 
electrofelon said:
I posed this question last year sometime. It is an interesting quandary. The language doesn't specifically say that we can protect that transformer through the other transformer, but does it have to? logically it is protected. Perhaps showing him the language regarding conductors protected by the primary ocpd would sway him.
Click to expand...
Where is that language?
 
electrofelon said:
I posed this question last year sometime. It is an interesting quandary. The language doesn't specifically say that we can protect that transformer through the other transformer, but does it have to? logically it is protected. Perhaps showing him the language regarding conductors protected by the primary ocpd would sway him.
Click to expand...
Yeah, I think that's the ticket. If the 2000V conductors are protected, how could the transformer that they feed not be protected?

electrofelon said:
Btw, i assume you are using low cost 2kv pv wire for the 2k run.
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Yes, that's exactly it. 1000' of #6, which is overkill but a whole lot cheaper than running the whole way at 240V. Voltage drop was killing us.
 
electrofelon said:
......or it might backfire and he could conclude, " see it specifically gives us permission for protecting conductors but it doesn't for protecting transformers so therefore you cant."
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I don't think that will happen. This inspector has his issues but he is ultimately rational.
 
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