Inverter AC-side Wire Sizes and OCPD

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DetroitEE

Senior Member
Location
Detroit, MI
I'm working on designing a system which involves a Solectria inverter. The Max. Continuous Output Current listed on the cut sheet for 480V is 100A. I multiply that by 125% as required by article 690 for OCPD and wire size, and there's my rating, 125A fuse in the AC disconnect, #1 wires.

Then I looked at the installation manual; the manufacturer states that the AC disconnect should be connected to a 150A circuit for this model, and the integral fused disconnect needs 150A fuses. Would it be a violation of 110.3(B) to install 125A OCPD and #1 as I originally calculated, since this is technically not following the manufacturers installation instructions? I will most likely revise our drawings to accommodate this just to be sure, I'm just curious if it would've been a violation.

They also state that 90 degree conductors are required...is this common for inverters?
 
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DetroitEE

Senior Member
Location
Detroit, MI
I'm working on designing a system which involves a Solectria inverter. The Max. Continuous Output Current listed on the cut sheet for 480V is 100A. I multiply that by 125% as required by article 690 for OCPD and wire size, and there's my rating, 125A fuse in the AC disconnect, #1 wires.

Then I looked at the installation manual; the manufacturer states that the AC disconnect should be connected to a 150A circuit for this model, and the integral fused disconnect needs 150A fuses. Would it be a violation of 110.3(B) to install 125A OCPD and #1 as I originally calculated, since this is technically not following the manufacturers installation instructions? I will most likely revise our drawings to accommodate this just to be sure, I'm just curious if it would've been a violation.

They also state that 90 degree conductors are required...is this common for inverters?

Anyone?
 

BillK-AZ

Senior Member
Location
Mesa Arizona
The most likely reason is that the 100A on the specification sheet is at the nominal 480 volts and the inverter will operate at the same power even if the utility voltage is lower. The specification sheet shows the voltage can be -12%/+10% so the current can vary inversely and be 12% above nominal. This moves the fuse selection to 150A.

The smaller Solectrias I just bought have disconnects with 75?C terminals (common for disconnects), so 90?C wire is needed to get useful ampacity at higher temperatures.
 

tallgirl

Senior Member
Location
Great White North
Occupation
Controls Systems firmware engineer
As an aside, inverters do actually run hot, so you will need to make sure your temperature deratings are done properly.

The amount of heat, in watts, is the DC input times (1 - efficiency) -- if an inverter is 90% efficient and has 10KW input, you get 9KW of AC power and 1KW of heat. Make sure you get rid of that heat, or it will come back to bite you.
 
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