Is this a compliant service?

[farmantenna]

dwelling unit. 2020 code 240.21?
400 amp service rated ATS with single breaker outside the house. Two individual 4/0 AL SER feeders going from back of ATS to two individual flush mounted 200 amp MB panels 30' inside the house. The SER has 2/0 AL ground wire.
Appears to be non compliant tap. There's a 200 amp feeder on a 400 amp circuit breaker. I think it will be safe because the ground is large enough for the fault current and the feeder and panel load will be limited to 200 amps. This type of installation has been passed by two different inspectors.

I ask for your opinions.

 

[infinity]

Two individual 4/0 AL SER feeders going from back of ATS to two individual flush mounted 200 amp MB panels 30' inside the house. The SER has 2/0 AL ground wire.

What size EGC do you think is required? The #4/0 tap conductors are too small for 200 amps and the length of 30' inside the house is too long. So the answer to the title of this thread is no.

 

[ptonsparky]

The service may be fine. The taps aren't.
Taps would need to be outside 240.21(5).
FWIU, 310.12(B) would not allow a reduction in required feeder size even if outside.

 

[Greentagger]

4/0 AL is good for 180 A. Long as calculated load is less than 180A , you are allowed to go up to next standard size breaker? Maybe I missed something? Maybe part panel load will be limited to 200A?

 

[augie47]

4/0 AL is good for 180 A. Long as calculated load is less than 180A , you are allowed to go up to next standard size breaker? Maybe I missed something? Maybe part panel load will be limited to 200A?

I think you are missing 240.21(B) "The provisions of 240.4(B) shall not be permitted for tap conductors."

 

[ptonsparky]

OP. Did the 3rd inspector reject it? If so what violations were quoted?

 

[Greentagger]

Yep, missed the tapped portion. Didn’t realize terminated under 400A circuit breaker.

 

[kwired]

I think you are missing 240.21(B) "The provisions of 240.4(B) shall not be permitted for tap conductors."

I agree that by wording these should at least be 250 aluminum conductors.

I also see this as a little overkill, after all one could supply exactly same loads if the 4/0 conductors in question were service conductors.

One other thing not mentioned yet is the length of tap is over 25 feet, if a portion of that (at least 5 feet) were outdoors I'd still be ok with the length though.

 

[jaggedben]

I think you are missing 240.21(B) "The provisions of 240.4(B) shall not be permitted for tap conductors."

For sure one of the dumber rules in the book, but it's there.

 

[infinity]

One other thing not mentioned yet is the length of tap is over 25 feet, if a portion of that (at least 5 feet) were outdoors I'd still be ok with the length though.

These 30' tap conductors cannot be run with 25' within the structure. They must terminate nearest their point of entry just like service conductors. That means that almost the entire length would need to be outside.

240.21(B)(5) Outside Taps of Unlimited Length.
Where the conductors are located outside of a building or structure, except at the point of load termination, and comply with all of the following conditions:
(1) The tap conductors are protected from physical damage in an approved manner.
(2) The tap conductors terminate at a single circuit breaker or a single set of fuses that limits the load to the ampacity of the tap conductors. This single overcurrent device shall be permitted to supply any number
of additional overcurrent devices on its load side.
(3) The overcurrent device for the tap conductors is an integral part of a disconnecting means or shall be located immediately adjacent thereto.
(4)The disconnecting means for the tap conductors is instal⁠led at a readily accessible location complying with one of the following:
a. Outside of a building or structure
b. Inside, nearest the point of entrance of the tap conductors
c. Where installed in accordance with 230.6, nearest the point of entrance of the tap conductors

 

[Little Bill]

I agree that by wording these should at least be 250 aluminum conductors.

I also see this as a little overkill, after all one could supply exactly same loads if the 4/0 conductors in question were service conductors.

One other thing not mentioned yet is the length of tap is over 25 feet, if a portion of that (at least 5 feet) were outdoors I'd still be ok with the length though.

You apparently skipped right over post #2

 

[wwhitney]

So if the 4/0 Al feeders were in fact in parallel, terminating in a splice box inside, with sufficiently short 200A taps to the 200A MB panels, then the install would be compliant, I believe. As then the 83% rule applies to the 400A residential feeder, and 83% * 400A < 2 * 180A.

Cheers, Wayne

 

[infinity]

As then the 83% rule applies to the 400A residential feeder, and 83% * 400A < 2 * 180A.

Also with the next size up rule 360 amp parallel feeder conductors could be used with a 400 amp OCPD.

 

[kwired]

Also with the next size up rule 360 amp parallel feeder conductors could be used with a 400 amp OCPD.

One could parallel them, especially if the two panels being supplied are in close proximity to one another. Still need to (per code wording) increase to 250 aluminum for the tap to each panel though.

 

[infinity]

One could parallel them, especially if the two panels being supplied are in close proximity to one another. Still need to (per code wording) increase to 250 aluminum for the tap to each panel though.

That's correct due to the tap rules.

 

[farmantenna]

OP. Did the 3rd inspector reject it? If so what violations were quoted?

This setup has been done SEVERAL times in one town and in once in another town and the installing electrician had no idea of the violations because the inspectors haven't said a tying.

 

[farmantenna]

Someone explain to me how I can arrive at these homes, multi-million dollar homes, to help my coworker and see this installation ,even though I'm not even there to work on or around the service, and realize its not compliant and not one inspector has said anything and they are there to specifically inspect the service?

 

[GoldDigger]

Yep, missed the tapped portion. Didn’t realize terminated under 400A circuit breaker.

If they were still service conductors (no upstream OCPD) there would be no tap rule applicable and the setup could be permitted (except for multiple service restriction.) It is somewhat paradoxical that adding an upstream OCPD makes the conductor non-compliant.

 

[kwired]

Someone explain to me how I can arrive at these homes, multi-million dollar homes, to help my coworker and see this installation ,even though I'm not even there to work on or around the service, and realize its not compliant and not one inspector has said anything and they are there to specifically inspect the service?

Inspectors are human and make mistakes. If they ever figure out they are letting this go when it shouldn't be that way they likely recognize it when they encounter it again. May be too late to do anything with things they have already approved though.

I wouldn't be too concerned about what may be too late to do anything with though, different scenarios already been brought up here where same conductors supplying same load are NEC compliant, and for average dwelling loading, they probably aren't even loaded to anywhere close to their ampacity anyway unless you have a feeder that has almost entirely HVAC and other long time loads like pool pumps, well, etc. connected to it.