mstrlucky74
Senior Member
- Location
- NJ
Calculate Feeder Size
- Thread starter mstrlucky74
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Fulthrotl
~Autocorrect is My Worst Enema.~
- Occupation
- E
publicgood
Senior Member
- Location
- WI, USA
For your estimating purposes, matching the feeder to the 80A breaker is sufficient. CU or AL and specific wiring methods according to whatever specifications you received.
I don't quite understand why you will feed a 100A panel with an 80A breaker! Am I missing something here?
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
To allow use of smaller wire if the calculated load on the panel is well below 80A?
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I'm thinking about the breaker, not the wires.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
And I am saying that if you did not use the smaller breaker you could not use smaller wires. (without invoking tap rules)
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- Location
- New Jersey
- Occupation
- Journeyman Electrician
Most commercial style panels are 100 amp minimum so as Digger stated if your calculated load is only 80 amps (or less) then your feeder only needs to be 80 amps. We've installed 100 amp panels with 60 amp feeders.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Given they are immediately adjacent to each other the two or three dollars difference in Copper cost isn't going to make any real difference. I would not even worry about it and make it one hundred amp circuit and be done with it. You never know what you might want to hook up there later. Some decisions are not worth spending more than about 20 seconds making.
However if you insist on going through the exercise you need to know what the calculated load is. The problem is you've already selected an 80 amp circuit breaker. I don't recall if 80 amps is a so-called standard size breaker rating or not but if it is you might have a little leeway in the ampacity of the conductors but for such a short distance it's just not worth the time to to even look at it especially since you already selected the 80 amp circuit breaker
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Standard size listed in 240.6
If you are observant enough, you would see the calculated load (from the load schedule) is above 80 amps. Why choose a breaker with lower rating?:happysad:
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I cannot read his attachment so show me.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Max per phase in load schedule appears to be about 5.6kVA plus the unevaluated existing load on some circuits. Doesn't look like more than 80A to me unless you add the three phase numbers.
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IDK how you do things but granting you have 5.6kVA per phase, you should arrive at a line current of 80.89A! We don't choose 80A breaker for that.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
The panel schedule lists line to neutral loads.
5600 divided by 120 equals 47.
How do you do it?
P.S. All breakers are single pole, therefore all loads are line to neutral.
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mstrlucky74
Senior Member
- Location
- NJ
Thanks guys!!!
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