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Old 05-28-2012, 04:30 PM   #1
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Cable sizes- a bit confused


I need two sub panels and I want to run aluminum SER. I want to feed one with 60 amps and the other with 100 amps.

The supply house calls 2-2-2-4 AL SER "100 amp cable", however the code says differently the way I am interpreting it.

What size AL SER would I need to feed a 100A and 60A subpanel in a house?

FWIW, we are now on the 2011 code, but when I went to the supply house (and he told me 2-2-2-4 would work) we were on the 2008.

Thanks!

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Old 05-28-2012, 04:39 PM   #2
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Cable sizes- a bit confused


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Originally Posted by Macro View Post
I need two sub panels and I want to run aluminum SER. I want to feed one with 60 amps and the other with 100 amps.

The supply house calls 2-2-2-4 AL SER "100 amp cable", however the code says differently the way I am interpreting it.

What size AL SER would I need to feed a 100A and 60A subpanel in a house?

FWIW, we are now on the 2011 code, but when I went to the supply house (and he told me 2-2-2-4 would work) we were on the 2008.

Thanks!
First question, do you really need 100 amps? I personally would use #2 SER and just back it with a 90 amp breaker, #4 SER for the 60 amp panel...

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Old 05-28-2012, 04:44 PM   #3
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Cable sizes- a bit confused


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First question, do you really need 100 amps? I personally would use #2 SER and just back it with a 90 amp breaker, #4 SER for the 60 amp panel...
I'm wondering about what code allows. It seems to limit the #2 AL to 90A, but why would a huge supply house that services thousands of electrician commonly call that size "100A cable"? I ask because I have seen people discussing this before on other forums and from what I remember they had reasonable explanations why 100A was allowed on #2.
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Old 05-28-2012, 04:46 PM   #4
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Cable sizes- a bit confused


The code changed and not everyone has kept up with the changes. What used to be able to be used as 100 amp cables is now 90 amp cable.
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Old 05-28-2012, 04:53 PM   #5
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Cable sizes- a bit confused


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The code changed and not everyone has kept up with the changes. What used to be able to be used as 100 amp cables is now 90 amp cable.
What year was that change, do you remember?
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Old 05-28-2012, 04:58 PM   #6
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What year was that change, do you remember?
To be honest, its only good for 75 amps... if you are on the 2008 NEC... I was offering 90 amps off the 2005 NEC which I am on in Connecticut.
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Old 05-28-2012, 04:59 PM   #7
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To be honest, its only good for 75 amps... if you are on the 2008 NEC... I was offering 90 amps off the 2005 NEC which I am on in Connecticut.
Yup, but that was changed yet again in 2011. Now it's back to the old way as long as the romex or SER isn't in contact with insulation.
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Old 05-28-2012, 05:02 PM   #8
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Cable sizes- a bit confused


The real problem started when people started using table 310.15(B)(6) for #2 SER as a feeder and not a service, it has always only been rated for 90 amps... so then the 2008 came out and enforced that you use the 60 degree column of 310.16 for type SE cables... that was the real killer.
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Old 05-28-2012, 05:02 PM   #9
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Cable sizes- a bit confused


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Yup, but that was changed yet again in 2011. Now it's back to the old way as long as the romex or SER isn't in contact with insulation.
Thanks, i was unaware of that change again... I'm lucky to still be on 2005. So 90 amps it is... The real culprit is people misusing Table 310.15 (B)(6)...

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Old 05-28-2012, 05:06 PM   #10
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The real problem started when people started using table 310.15(B)(6) for #2 SER as a feeder and not a service, it has always only been rated for 90 amps... so then the 2008 came out and enforced that you use the 60 degree column of 310.16 for type SE cables... that was the real killer.
Now THAT makes sense, I just looked into it and it seems to be the reason for the confusion. It's a shame that a 90A breaker costs more than a 100A since it's a specialty item most places.

As for the 60A sub panel, if I use #4 SER, wouldn't I be able to step up to a 70A breaker?
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Old 05-28-2012, 05:09 PM   #11
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Now THAT makes sense, I just looked into it and it seems to be the reason for the confusion. It's a shame that a 90A breaker costs more than a 100A since it's a specialty item most places.

As for the 60A sub panel, if I use #4 SER, wouldn't I be able to step up to a 70A breaker?
Sure, as long as the actual load isn't above 65 amps..

Its a shame supply houses and manufactures are not on board, because these devices should cost the same and be stocked.
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Old 05-28-2012, 05:09 PM   #12
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#4 Al SER would be limited to the 60 degree column of 55 amps.
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Old 05-28-2012, 05:13 PM   #13
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#4 Al SER would be limited to the 60 degree column of 55 amps.
Im assuming it depends on what code cycle you are on? I can use the 75 degree column..

Bummer, you are correct. scratch the above.

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Old 05-28-2012, 05:19 PM   #14
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#4 Al SER would be limited to the 60 degree column of 55 amps.
So where did the 90 amps EVER come into play then? Only the 2011 NEC, correct?

Last edited by stickboy1375; 05-28-2012 at 05:21 PM.
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Old 05-28-2012, 05:24 PM   #15
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Cable sizes- a bit confused


If the #4 was copper and using the 75 degree column it would be 85 amps. The next standard size breaker is 90 amps so you can round up.

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