NEC Experts: Single Conduit Between Main and Transfer Switch?

300sniper

300sniper

Gun Plumber
Joined
May 20, 2020
Member Number
695
Messages
483
Loc
Greenwood, CA
I have a 320a/400a meter main, with two 200a main breakers feeding two 200a sub panels, one for the garage, and one for the main part of the house. I am about to add a 24kw generator and ATS. I only want to back up the house panel.

My question is, can I run a single conduit from the main to the transfer switch, run conductors from my main breaker to the ATS, then back through the same conduit to the main panel, then back to my house sub panel? I am confused with that would require upsizing the conductors due to to 3+ in the conduit (5), or if de-rating even applies in this situation.
 
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1oddtech said:
Do you have a photo of your setup?
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Posted above. I need to mount the ATS to the left of the meter section due to there not being enough space on the right. If I had space on the right, it would be simple to nipple between the two sections.
 
Fullsize80cherokee said:
yea that sucks your gutter is in the way on the right, your feeders would’ve been long enough to go to the ats and everything
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Yeah. I’ve have almost enough 3/0 on hand to do what I want. It’s going to to be lame to buy all 4/0 at today’s prices if I have to upsize.
 
Fullsize80cherokee said:
I don’t see a reason to upsize. 3/0 is more than enough for 200amp residential feeder. I don’t see why they couldn’t go in the same conduit.
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I think they can go in the same conduit, but when you have 4-6 conductors in a conduit, you need to downrate the conductors to 80%. 3/0 THHN would only be rated at 180a, rather than 225a. That’s IF in this situation the same conductors making a loop is considered in the conductor count.
 
300sniper said:
I think they can go in the same conduit, but when you have 4-6 conductors in a conduit, you need to downrate the conductors to 80%. 3/0 THHN would only be rated at 180a, rather than 225a. That’s IF in this situation the same conductors making a loop is considered in the conductor count.
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what are the wires in the main panel now? The original installer ran all the feeders in one conduit.
 
Chevy_man said:
De-rating and pipe fill doesn't apply to nipples.

Do it, the worst you can get is a correction notice if it's inspected.
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But also out any money spent on copper. It’s going to be inspected, so I want to do it right the first time.
 
Then ask your inspector that will be inspecting it if it is ok or not? I bet he will know if he will pass it or not better than any random on the internet. Usually getting into a pissing match with the inspector does not end favourably.
 
I'd say your best bet would be to mount the transfer switch below the customer side of the meter base. Going to the right of it would require going around it to get to the other side since you can't go thru below the meter base.
 
You better hope to god one of those push-in ko fillers don’t rattle out and land on the busses under it. :shocked:
They’re supposed to be installed from the OUTSIDE of the can.
 
300sniper said:
Posted above. I need to mount the ATS to the left of the meter section due to there not being enough space on the right. If I had space on the right, it would be simple to nipple between the two sections.
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Check the clearance requirements with the utility first. If it was me I’d mount the ats inside the building.
 
I would mount the transfer switch to the left of your meter with the tops flush with each other. Mount a NEMA 3R gutter above that spans both and then just nipple straight up. Simple and looks good and you don’t have to **** around with derating.
 
Animalmother said:
I would mount the transfer switch to the left of your meter with the tops flush with each other. Mount a NEMA 3R gutter above that spans both and then just nipple straight up. Simple and looks good and you don’t have to **** around with derating.
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That was my original thought, and I’ve been looking for a 6x6x42 3R gutter because my OCD won’t let me use a 36” that doesn’t extend over the whole thing…
 
300sniper said:
That was my original thought, and I’ve been looking for a 6x6x42 3R gutter because my OCD won’t let me use a 36” that doesn’t extend over the whole thing…
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No doubt that would drive me insane. Speaking of that the trough that’s too short under your panels drives me insane. :laughing:
 
300sniper said:
That was my original thought, and I’ve been looking for a 6x6x42 3R gutter because my OCD won’t let me use a 36” that doesn’t extend over the whole thing…
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Use a 48" and move it over another 6"? Cut a 48" one down to 42"
Doesn't seem that anyone makes a 42" 3R gutter.

Aaron Z
 
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