100 amp Sub 80ft from main panel.

Old 09-09-17, 04:03 PM
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100 amp Sub 80ft from main panel.

Hey all, long time lurker.
I am currently installing a 100 amp sub panel in our basement as we are turning it into a living space and need more power. Main panel is in the garage on main level about 80ft away.
It will need to go through a concrete wall and go under the crawl space to get to the downstairs sub.
My thought is this, use 3-3-3-5 ser copper or possibly 4-4-4-6 ser copper. Im not oposed to AL but have a few tight bends that would be a pain, also the sub pannel is rather small and is already in the wall currently (Simons E0816ML1125F with a ground bar added and neutral not bonded)

My thought process is as follows
100amp breaker in the main panel (with tie down kit?)
Ser cable out bottom of recessed main panel and into conduit to run along the wall until out of the garage concrete wall and into the crawl space. I would need to cut the pvc outer coat of ser cable to run the cables in the conduit up until out of concrete where I would just run the ser cable pvc jacket and all on the crawl space to the sub.

(House has x2 200 amp panels)
Lastly it might be a little cheaper to even run 4 thhn copper wires, but that would require conduit for the whole run, which isn't a terrible idea since it will be in a crawl space.

Let me know your thoughts and what you think may be better in my situation.
Old 09-10-17, 04:34 AM
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The sheath from the SER should not be removed .
Old 09-10-17, 06:09 AM
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Hold down kit for the circuit breaker in the service (main) panel is not required. IF you "back feed" a circuit breaker in the sub-panel then that CB requires a hold down. Main circuit breaker in sub panel is not required if sub is in the same building as the service panel.

I cannot advice on the use of SER cable. Conduit with THHN/THWN is always my preferred choice.

Generally speaking, cable (an assembly of more than one conductor) is limited to the Ampacity shown in the 60 degree C. column which for #4 would mean 70 amperes. Even using individual conductors in conduit #4 is limited to 85 amperes or rounded up to the standard CB size, 90 amperes. For a full 100 ampere feeder you would need to run #3 copper individual conductors plus a #8 copper equipment grounding conductor. IF your sub-panel loads are primarily 240 volts then you could downsize the neutral conductor to handle the maximum unbalanced (120 volt) loads.
Old 09-10-17, 07:17 AM
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3-3-3-5 Cu SER is good for 100A as long as it's not buried within insulation. For SER not buried in insulation you can use 75*C rating (NEC 338.10(B)(4)). If using conduit as a protective sleeve do not remove jacket to place in conduit, use conduit large enough for the SER to pass through easily.

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