Outdoor feeder tap rule for backup loads

BackCountry

BackCountry

Electrician
Location
Southern California
Occupation
Licensed Electrician and General Contractor
I want to make sure I have the outdoor feeder tap rule down correctly:

I’ve got an existing 400a panel with 60a, 100a and 200a OCPD’s feeding a house and a well. The 400a panel is outdoor on a panel board. The 200a and 100a panels are inside of a residence, with conduit coming up out of the slab directly into the panels, all of which have a main breaker. The 60a well panel is outdoors and has a main breaker also.

We are installing a BESS and PV with a transfer switch rated at 200a — if I’m reading this right, I believe I can simply intercept the existing 200a feeder, direct that to our transfer switch, and then the load side of the transfer switch can be Polaris tapped to all three loads (60, 100 and 200a) and no backup loads panel would be required.

Let me know if I’m reading that right. The outdoor tap rule requiring that the main breaker be as close as possible to the entrance is the only question, the conduit goes right into each panel stubbed out of the slab. And they’d all be downstream of the 200a OCPD, with only the 100a and 60a conductors being undersized.
 
Fred B

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
Tap rules aside you have a 400A system that is splitting off to 360A of potential demand, NP there but you are suggesting for your BESS giving all three only 200A max? Have you done a loads calculation to determine all loads can be operated on 200A?

Also the ATS at 200A not adequate to feed through potential 360A of load. Your 200A breaker at the ATS would be constantly tripping even under "normal" "service supply" condition. You would need at least a 400A transfer switch, then tap rules can be considered.
Either way seems you at best would require significant load shedding of some sort if BESS is only 200A.

Review 240.21(B)(4) your taps must meet ALL of the conditions.
AFA use of "Polaris" connectors, must be rated to the max amperage.
 
BackCountry

BackCountry

Electrician
Location
Southern California
Occupation
Licensed Electrician and General Contractor
Fred B said:
Tap rules aside you have a 400A system that is splitting off to 360A of potential demand, NP there but you are suggesting for your BESS giving all three only 200A max? Have you done a loads calculation to determine all loads can be operated on 200A?

Also the ATS at 200A not adequate to feed through potential 360A of load. Your 200A breaker at the ATS would be constantly tripping even under "normal" "service supply" condition. You would need at least a 400A transfer switch, then tap rules can be considered.
Either way seems you at best would require significant load shedding of some sort if BESS is only 200A.

Review 240.21(B)(4) your taps must meet ALL of the conditions.
AFA use of "Polaris" connectors, must be rated to the max amperage.
Click to expand...

Yes, I’ve calculated the loads and also observed max loading with a multi meter. The 400a panel is only fed by a 25kva tx on the utility side — this a large residence that was over built with multiple panels. I have yet to see it pull more than 80a, so I’m not worried about loading or nuisance tripping. Most of the loading is from a pool panel that will be excluded from backup.

As it sits now, the 400a panel has 560a of breakers with the 6 breaker rule (it doesn’t have a main disconnect). I would be moving 360a (3 breakers) over to a 200a ATS with BESS, PV and generator. I was just hoping to avoid having to put in a backup loads panel. Polaris 250’s are rated in excess of 200a, no concern there.

Existing feeder conductors for the 200a panel are 2/0 CU. The 100a panel is 1/0, and the 60a panel is #4, so conductor wise everything looks good for the OCPD’s at the terminating panel.
 
W

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
BackCountry said:
Existing feeder conductors for the 200a panel are 2/0 CU. The 100a panel is 1/0, and the 60a panel is #4, so conductor wise everything looks good for the OCPD’s at the terminating panel.
Click to expand...
2/0 Cu has a 75C ampacity of 175A. So you can only protect it at 200A if the 200A feeder is supplying the entire load of the dwelling unit as per 310.12. But you said the 100A panel is also in the residence, so is the 200A feeder supplying the entire load of the dwelling unit?

Cheers, Wayne
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
wwhitney said:
2/0 Cu has a 75C ampacity of 175A. So you can only protect it at 200A if the 200A feeder is supplying the entire load of the dwelling unit as per 310.12. But you said the 100A panel is also in the residence, so is the 200A feeder supplying the entire load of the dwelling unit?
Click to expand...
Sounds like the answer is no since there is a 400 amp panel feeding three different loads.
 
J

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
To answer your original question...
Yes, I think you understand the outside tap rule and from your description the general concept is compliant as far as the tap rules.

In addition to what Wayne raised, the 'next size up' rule cannot be used for tap conductors. So you probably need to downsize the panel main breakers, I think even if 310.12 applies to them.
 
BackCountry

BackCountry

Electrician
Location
Southern California
Occupation
Licensed Electrician and General Contractor
wwhitney said:
2/0 Cu has a 75C ampacity of 175A. So you can only protect it at 200A if the 200A feeder is supplying the entire load of the dwelling unit as per 310.12. But you said the 100A panel is also in the residence, so is the 200A feeder supplying the entire load of the dwelling unit?

Cheers, Wayne
Click to expand...

There are two separate panels in the residence, thank you for pointing that out. The 2/0 is existing and incorrect. I will change out the main breaker in that panel to 175A.
 
BackCountry

BackCountry

Electrician
Location
Southern California
Occupation
Licensed Electrician and General Contractor
jaggedben said:
To answer your original question...
Yes, I think you understand the outside tap rule and from your description the general concept is compliant as far as the tap rules.

In addition to what Wayne raised, the 'next size up' rule cannot be used for tap conductors. So you probably need to downsize the panel main breakers.
Click to expand...

Got it. I’ll go through each panel and the table, without rounding up, and replace each main breaker as needed to comply with the 75 degree amp rating of the existing feeder conductors.
 
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