Reducing 750 Aluminum

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hillbilly1 said:
Polaris taps to smaller copper. If this is a non-CT meter base, then it’s probably 400 amp or less, so is the engineer requesting 750 for voltage drop? If so, the wire size can be reduced substantially using the Polaris taps, or the compression lugs as Augie47 suggested.
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Isnt 750 Aluminum only good for 385 AMPs at 75 degree terminals?
 
There is a reason a 320A Meterbase only accepts up to 600 wire.
How far is the Meterbase from the pole? If your running 750 for VD then put in 600CU to the pole, then double your 750 AL on the load side of the meter.

FWIW, I don’t think the 320 can has the allowed space for bending 750 in the top lugs either.
I know I wouldn’t want to terminate that crap in a can that small with any bends at all.
 
According to B.310.15(B)(2)(7) 750MCM AL is 425A for RHO 90 and LF 100 .

Assuming that You need to match the ampacity once you are out of the duct bank.

500MCM AL will get you 426.8A at 104 deg F as long as you can get the free air rating for say at least last 10 ft of the run. (350 MCM CU would provide 444.4A )

If the actual load is less (which seem to be likely) you can get away with less.

There is a free software “Conductor Ampacity Calculator“ at https://www.mc-group.ca/software_downloads.htm that can help you find the right configuration of wires taking in to account ambient temperature. Although I would start with RFI about the calculated load – maybe the guy who pays for all of this could get you some answers.
 
Arester said:
According to B.310.15(B)(2)(7) 750MCM AL is 425A for RHO 90 and LF 100 .

Assuming that You need to match the ampacity once you are out of the duct bank.

500MCM AL will get you 426.8A at 104 deg F as long as you can get the free air rating for say at least last 10 ft of the run. (350 MCM CU would provide 444.4A )

If the actual load is less (which seem to be likely) you can get away with less.

There is a free software “Conductor Ampacity Calculator“ at https://www.mc-group.ca/software_downloads.htm that can help you find the right configuration of wires taking in to account ambient temperature. Although I would start with RFI about the calculated load – maybe the guy who pays for all of this could get you some answers.
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None of that makes much sense to me. I see you are from Canada, I don't know much about Canadian code or methods, but in the states you would use table 310.15(B)(16) for the vast majority of applications and would need to use the 75 degree column. Using the 90 degree column is possible if on each end you transition to conductors with the 75 degree ampacity for your terminations.
 
electrofelon said:
None of that makes much sense to me. I see you are from Canada, I don't know much about Canadian code or methods, but in the states you would use table 310.15(B)(16) for the vast majority of applications and would need to use the 75 degree column. Using the 90 degree column is possible if on each end you transition to conductors with the 75 degree ampacity for your terminations.
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I just wanted to show that once you get out of the ground and can use free air rating – the wire size can be reduced with simple splice. All the data I provided is for 75 degree ampacity - just the ambient is different (20 deg C) - underground and 40 deg C above ground. (Using 310.15(B)(16) with temp correction factor)
 
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