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Old 07-24-2017, 03:04 PM   #1
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Code for SER in Attic Space


I am running a 125Amp sub-panel off of my 200amp main panel with 1/0-1/0-1/0 Aluminum SER Cable w/ 2AWG Ground. 1st question is will that wire meet code for the correct size and second is this sub-panel is in a slab poured addition and I would like to to run it in the attic to get to the main panel. Can I run it exposed or does it have to be protected with PVC? I think in the walls it just has to be 1.25 inches away from the edge but i could be wrong with that. Is this more of a question i would need to call my local inspector for?
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Old 07-24-2017, 03:21 PM   #2
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Re: Code for SER in Attic Space


Exposed in the attic is fine. Derating would be required if the cable is buried in insulation.
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Old 07-26-2017, 01:04 AM   #3
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Re: Code for SER in Attic Space


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1st question is will that wire meet code for the correct size
No, 1/0 aluminum is only rated at best for 120 amps and thus is too small. It used to be suitable for 125 amp feeders in residential uses but no longer. Somehow it magically became unsafe for feeders such as this but safe for carrying the same load in a different setting. Grrr.

What size you need depends on what version of the NEC your area is using and whether or not this cable runs through insulation in the attic.

If you are running through insulation AND using the 2011 or 2014 NEC, the cable is derated as brric pointed out. You're stuck using the 60C ampacity column in the table. You will need 3/0 aluminum.

If you're not running through insulation, or running through insulation and using the 2017 NEC, only 2/0 is needed.

You may also need larger cable after derating for ambient temperature. What's the highest temperature the attic sustains in hot weather?

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Can I run it exposed or does it have to be protected with PVC?
Are you running the cable on top of the joists or drilling to go through them? If on top, you may need to protect the cable. Does this attic have a permanently mounted ladder or stairs? If so, you'll need protection for the cable's entire run up there. Wood guard strips at least as high as the cable are fine. If no ladder or stairs, protection is only needed within 6' of the opening.

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I think in the walls it just has to be 1.25 inches away from the edge but i could be wrong with that.
You are correct. It can make installing cable interesting when using larger diameter cables in 2x4 framed walls.
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Old 07-26-2017, 06:56 AM   #4
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Re: Code for SER in Attic Space


Chances are he can not put a 125 amp breaker in his main panel anyway.
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Old 07-26-2017, 09:30 AM   #5
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Chances are he can not put a 125 amp breaker in his main panel anyway.
+1
Use a 100 amp breaker in the main even if the sub and sub panel breaker are 125 amps.
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Old 08-16-2017, 12:02 PM   #6
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Re: Code for SER in Attic Space


I do have a 125amp breaker installed in my main breaker.
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Old 08-16-2017, 12:18 PM   #7
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Re: Code for SER in Attic Space


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I do have a 125amp breaker installed in my main breaker.
Is your main panel rated to use a 125 amp breaker. Likely exceeds the stab rating of the panel. Change to 100 amp to meet the rating of the SER cable.

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Old 08-16-2017, 01:12 PM   #8
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Re: Code for SER in Attic Space


K will do. Thank.
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