Fused disco

[GerryB]

On a supply side connection are the conductors sized to the service rated disco,in this case 60 amp disco and 100 amp pamel, or to the fuses installed in the disco, in this case 35 amp.

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[luckylerado]

If I understand you correctly, you have a 100 amp panel feeding a 60 amp rated disconnect with 35 amp fuses to the load?

Size the wire for the OCP which cannot exceed 60 amp feeding the line side of the disconnect and 35 amp wire to the load.

 

[petersonra]

the conductors are always sized minimally at least to the load.

usually, you are required to size the conductors so they are protected by the OCPD, although the tap rules allow for some dispensation.

 

[GerryB]

I was looking at 230.79(D), which says the disconnecting means shall not have a rating less than 60 amps, and then 230.42(B), which says the minimum ampacity...shall not be less than the rating of the service disconnect, thus #6 for 60 amps. But the one line calls for #8 because of the 35 amp fuses. I was thinking #8 to the load is ok but #6 line side. Am I wrong?

 

[petersonra]

I was looking at 230.79(D), which says the disconnecting means shall not have a rating less than 60 amps, and then 230.42(B), which says the minimum ampacity...shall not be less than the rating of the service disconnect, thus #6 for 60 amps. But the one line calls for #8 because of the 35 amp fuses. I was thinking #8 to the load is ok but #6 line side. Am I wrong?

article 230 only applies to the service equipment.

downstream of the service disconnect it is no longer service conductors.

 

[Zee]

I think OP may be asking about conductors on the line side of his disco. The tap conductors.
Or maybe he means both the conductors on the line side and on the load side and thinks they follow the same rules.
Unclear.
All he says is, "the conductors" ?????

Which conductors.... upstream or downstream from disco?

 

[GerryB]

I think OP may be asking about conductors on the line side of his disco. The tap conductors.
Or maybe he means both the conductors on the line side and on the load side and thinks they follow the same rules.
Unclear.
All he says is, "the conductors" ?????

Which conductors.... upstream or downstream from disco?

line side, upstream, thought #6 would be the minimum.
100 MB panel, tap the #3 conductors before the main, Ilsco bugs, feed the 60 amp service rated disconnect. Disco will be fused at 35 amp.

 

[kwired]

"The ampacity of service-entrance conductors shall not be less than either 230.42(A)(1), (A)(2), or (A)(3)"

This is how 230.42 starts out.

(A) (1) says The sum of the noncontinuous loads plus 125 percent of continuous loads.

What load is being supplied can factor into this.

For installations of a single load (like a pumping station) I have for years always supplied lesser conductor then the overcurrent device rating. Take a 480 volt 100 HP motor for example. I have always supplied those with 2/0 coppper (which is what the motor needs) and 175 amp fuses in a 200 amp fuse holder. 75 HP pumps uses same 200 amp fuse holder but 150 amp fuses and 1AWG copper conductor. This practice complies with what is mentioned in (A)(1).

 

[jaggedben]

Everyone, this the PV forum. I think it can be assumed we're talking about interpreting 705.12(A).

GerryB, I think it's a grey area. I've run across quite a few people who think the supply side conductors have to be #6 for 60A based on 230.79(D). But alternatively one could argue that the PV disconnect fits under 230.79(A) or (B) (if it's just a single inverter, two microinverter circuits). Or one could argue that it is not a service disconnecting means and isn't bound by any of those requirements.

With that said, with the specs you stated I'd probably just install #6 and avoid controversy.

For what it's worth, I had one AHJ insist that the conductors on the line side had to be sized the same as the other service entrance conductors feeding the main panel. i.e. it was a 100 amp service so they had to be #4, even though I was installing a 30A PV system. It wasn't worth fighting that one.

 

[ggunn]

For what it's worth, I had one AHJ insist that the conductors on the line side had to be sized the same as the other service entrance conductors feeding the main panel. i.e. it was a 100 amp service so they had to be #4, even though I was installing a 30A PV system. It wasn't worth fighting that one.

Agreed. I choose my battles carefully.