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Old 10-09-2012, 04:49 PM   #1
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How to Connect 1/0 Aluminum to 70A Breaker?


How do you connect a 1/0 aluminum feeder cable to a Homeline - HOM270 breaker? The SPEC sheet for the HOM270 shows this breaker is designed for #8-2 AWG... so is there an adapter available that allows a 1/0 to connect to this breaker?

In case you're wondering... the reason I'm connecting a 1/0 to a 70 amp breaker is to compensate for the voltage drop which occurs on a 250 ft. feeder (between the service panel at the house) to the outbuilding sub-panel.

CMA = K x I x L x 2/7.2 = 21.2 x 70 x 250 x 2 / 7.2 = 103,056 CMA... and a 1/0 is 105,600... so this is the proper cable to get 70 amps to a sub-panel 250 feet away. I considered using copper, but due to budgeting issues, aluminum was the only realistic choice at this time.

Thanks for your help!

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Old 10-09-2012, 05:44 PM   #2
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How to Connect 1/0 Aluminum to 70A Breaker?


Easy answer is that you don't connect it to that breaker.

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Old 10-09-2012, 05:55 PM   #3
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How to Connect 1/0 Aluminum to 70A Breaker?


You connect a smaller conductor to the breaker, and then use appropriate connectors (like split bolts) to transition to the larger conductor. You can do the transition inside the panel, so you only need a foot or so of smaller wire.
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Old 10-09-2012, 07:42 PM   #4
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How to Connect 1/0 Aluminum to 70A Breaker?


Think I may have figured out the problem... I was using 7.2 in my calculation because an electrician told me this is the number he always uses when calculating CMA. But upon reading an article online I see that Max Voltage Drop is dependent on the circuit voltage (which in my case is 240v) and the max allowable voltage drop (Ed) is 5%... which equals 12v for a 240v feeder circuit. Therefore by code I am allowed to use a 100A breaker on a 1/0 feeder circuit which is 250 feet in length.

CMA = K x I x L x 2 / Max Ed
21.2 x 100 x 250 x 2 / 12 = 88,333 CMA = 1/0

The problem (having to use a 70A breaker) is eliminated because a 100A breaker will accept wire from #4 to 2/0... and I have a 1/0 cable!

That is... unless I'm supposed to be taking 5% of 120v (6v) which changes everything.

So this Max Ed is truly the key.

Does anyone know if I'm supposed to take 5% of 120v or 5% of 240v?

Thanks for your feedback!
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Old 10-09-2012, 07:46 PM   #5
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How to Connect 1/0 Aluminum to 70A Breaker?


There is no code in the NEC limiting voltage drop to less than any percent.
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Old 10-09-2012, 10:11 PM   #6
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How to Connect 1/0 Aluminum to 70A Breaker?


Quote:
Originally Posted by infoseek View Post
Think I may have figured out the problem... I was using 7.2 in my calculation because an electrician told me this is the number he always uses when calculating CMA. But upon reading an article online I see that Max Voltage Drop is dependent on the circuit voltage (which in my case is 240v) and the max allowable voltage drop (Ed) is 5%... which equals 12v for a 240v feeder circuit. Therefore by code I am allowed to use a 100A breaker on a 1/0 feeder circuit which is 250 feet in length.

CMA = K x I x L x 2 / Max Ed
21.2 x 100 x 250 x 2 / 12 = 88,333 CMA = 1/0

The problem (having to use a 70A breaker) is eliminated because a 100A breaker will accept wire from #4 to 2/0... and I have a 1/0 cable!

That is... unless I'm supposed to be taking 5% of 120v (6v) which changes everything.

So this Max Ed is truly the key.

Does anyone know if I'm supposed to take 5% of 120v or 5% of 240v?

Thanks for your feedback!
I admire your interest in learning the calculations ... it is beneficial to know how it is done .. BTW you use 240 volts not 120. Also there is much to know to provide a code compliant installation ... it is more than just running the correct size wire.

In the future try this ......

http://www.electrician2.com/calculat...alculator.html


Last edited by Stubbie; 10-09-2012 at 10:14 PM.
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