Service Drop Calc

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ccschoch

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Location
CA
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Electrician
I'm working on a duplex with 2 100a panels fed by a shared 1/0 AL service drop. I've been talking to the utility about a new service drop so I can upgrade one of those to 200a to accomodate an addition. I've got the load calcs done on the existing and the addition.

Long story short, the utility told me they're cool with 1/0 AL feeding up to 245 amps. I can't figure out where they got that from - even with 83% reduction at 90 degrees it's no where close to 245a. Am I missing something?
 
They know what they have and what it can do, they do not follow NEC guidelines. Many times if you look at the size of their transformers they are much smaller than what you'd expect.

Roger
 
For sure. It's just a way wider gap than I was expecting. Definitely good news on my end.

Sidenote, they never asked for load calcs on the 200a panel. I'm guessing they looked at peak usage of the existing and aren't worried - but I'm not sure I'm coming below even 245a total for both panels on the 1/0 (there's still appliances/hvac up in the air), so obviously I'm somewhat concerned. But I'm probly overthinking things?
 
ccschoch said:
I'm working on a duplex with 2 100a panels fed by a shared 1/0 AL service drop. I've been talking to the utility about a new service drop so I can upgrade one of those to 200a to accomodate an addition. I've got the load calcs done on the existing and the addition.

Long story short, the utility told me they're cool with 1/0 AL feeding up to 245 amps. I can't figure out where they got that from - even with 83% reduction at 90 degrees it's no where close to 245a. Am I missing something?
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Take a look at table 310.15(B)(19)-(2017) or 310.19-(2020) Ampacities of Single-Insulated Conductors in Free Air... a 1/0 Aluminum is rated for 263A.
 
Rock86 said:
Take a look at table 310.15(B)(19)-(2017) or 310.19-(2020) Ampacities of Single-Insulated Conductors in Free Air... a 1/0 Aluminum is rated for 263A.
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Yup! Totally spaced on that, appreciated. Spent 13 hours shoveling gravel to prep for rebar yesterday, don't think my brain was firing on all cylinders haha.
 
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