Amperage on 200 amp 100 amp service, 75°/90°

H

Hofebrand

Member
Location
Montana
Occupation
Electrician
Good morning, since I'm new to the forum this might have already been a topic. When sizing conductors for a 200 amp service, and a 100 amp service, why is it "common" to use 4/0 Aluminum for 200 amps and #2 for 100 amps in the 90° column when it states clearly on every termination point in the panel box we should size wire in the 75°column? 4/0 Aluminum is rated for 180 amps in the 75° column and #2 is rated for 90 amps in the 75° column. Is this because the calculated load will never exceed the amperage? What if its for agriculture purposes as well (non dwelling)? Can someone please simplify this. Thank you much

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infinity said:
For some dwellings service conductors can be sized at 83% of the service disconnect rating so they're not being sized at 90° C. Also you can use T310.12.
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Ok i understand now, so it has nothing to do with the 90° column, it's OCP amperage size x the percentage allowable. This is obviously only for feeders. What about the non feeders in the panel, that land on the breakers? Let's say i have a #4 Aluminum

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Hofebrand said:
Is this because the calculated load will never exceed the amperage?
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Basically, yes. The calculated loads should not exceed 180 and 90 amps, respectively.

Hofebrand said:
What if its for agriculture purposes as well (non dwelling)?
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Those should be fully sized and not with load diversity allowances.
 
Hofebrand said:
Ok i understand now, so it has nothing to do with the 90° column, it's OCP amperage size x the percentage allowable. This is obviously only for feeders. What about the non feeders in the panel, that land on the breakers? Let's say i have a #4 Aluminum
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For service conductors or feeders that are carrying the entire load of the dwelling you can use the 83% rule. For everything else (feeders or branch circuits) the standard 75° C ampacity from T310.16 would apply.
 
darekelec said:
If I go from Polaris multi tap to street wires can I use 90 deg column?
Meaning both connections are rated 90 deg.
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What does 'street wires' mean? Utility owned service drop or lateral? If they are not covered by the NEC then you don't need to worry about what column to use. But also the utility is likely supposed to provide those splices.

As for NEC covered wires on customer side of the splice...
So far as I've seen all Polaris are rated 90C so theoretically yes, you can use the 90C column when considering such splices. However your conductor size will probably be determined by the terminals at the other end of the conductor, i.e. you still have to use the 75C column. If you are actually trying to use the 90C column to size conductors I would double check the temp rating of the Polaris or other brand connectors.
 
Hofebrand said:
Ok i understand now, so it has nothing to do with the 90° column, it's OCP amperage size x the percentage allowable. This is obviously only for feeders. What about the non feeders in the panel, that land on the breakers? Let's say i have a #4 Aluminum

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also note 240.4(B), the "next size up" rule (Larry mentioned post #4 but I wanted to provide the code reference). That applies to both feeders and branch circuits.
 
darekelec said:
Polaris multi taps are 90 deg connections so I’m good.
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As Jaggedben stated, all Polaris lugs are 90° rated, but won't you eventually terminate in a panel? All panels that i have used require all wires to be terminated in the 75° column. (Square D, Eaton panels)

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Hofebrand said:
Good morning, since I'm new to the forum this might have already been a topic. When sizing conductors for a 200 amp service, and a 100 amp service, why is it "common" to use 4/0 Aluminum for 200 amps and #2 for 100 amps in the 90° column when it states clearly on every termination point in the panel box we should size wire in the 75°column? 4/0 Aluminum is rated for 180 amps in the 75° column and #2 is rated for 90 amps in the 75° column. Is this because the calculated load will never exceed the amperage? What if its for agriculture purposes as well (non dwelling)? Can someone please simplify this. Thank you much

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Click to expand...
Our local utility provider for years had a blue book that supplied the minimum size of service conductors. #2 Aluminum SEU cable was always good for 100 amp services & 4/0 Aluminum for 200 amp services. Maybe a year ago read that some where the make you use a larger size when running SER cable from service panel to any sub panels. Now with more & more EV chargers being installed in houses and some locations banning natural gas in new houses wonder if that 83% rule will have to be looked at & possibly increased.
 
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