feeder tap rules

[KHall]

I just started renovations on an existing building. The main service switch is a 400A, 3P disconnect switch fused at 400A. Off the load side of the switch there are two sets of 2/0 THHN copper per phase. One set of 2/0 runs about 15 feet thru a wireway and terminates in a 200A main circuit breaker protecting a lighting panel. The second set of 2/0 run about 10 feet into the wireway where they are each tapped with (2) #4 THHN copper conductors. Then the two sets of #4 terminate in a 100A,3P disconnect switch which is fused at 100A. This second set, with the 2/0 being tapped by the #4 just doesn't seem right to me. I have read art. 240.21(B) and I can't quite determine if or what it specifically violates. Any help would be appreciated!

 

[raider1]

The second set of 2/0 run about 10 feet into the wireway where they are each tapped with (2) #4 THHN copper conductors.

You are not permitted to "Tap a Tap".

240.21 states "Conductors supplied under the provisions of 240.21(A) through (H) shall not supply another conductor except through an overcurrent protective device meeting the requirements of 240.4"

So what you have is a violation of 240.21.

Chris

 

[hurk27]

I just started renovations on an existing building. The main service switch is a 400A, 3P disconnect switch fused at 400A. Off the load side of the switch there are two sets of 2/0 THHN copper per phase. One set of 2/0 runs about 15 feet thru a wireway and terminates in a 200A main circuit breaker protecting a lighting panel. The second set of 2/0 run about 10 feet into the wireway where they are each tapped with (2) #4 THHN copper conductors. Then the two sets of #4 terminate in a 100A,3P disconnect switch which is fused at 100A. This second set, with the 2/0 being tapped by the #4 just doesn't seem right to me. I have read art. 240.21(B) and I can't quite determine if or what it specifically violates. Any help would be appreciated!

The 2/0 and #4 is in violation of 310.15(B)(6) also If this is a dwelling this allowance is if the conductors supply the whole load of the house, if not a dwelling then it can't even be used.

 

[raider1]

The 2/0 and #4 is in violation of 310.15(B)(6) also If this is a dwelling this allowance is if the conductors supply the whole load of the house, if not a dwelling then it can't even be used.

Good point, I wasn't looking at the ampacities of the 2/0 and the #4 just the fact that tapping a tap conductor is a violation of 240.21.

Chris

 

[KHall]

more information

more information

Sorry I did not include this ... the building is a commercial project and the system voltage is 120/208, 3 phase. Two follow up questions:

1- We actually had this run by the local Inspections Dept as well. They had no problem, reasoning that the 2/0 were "parallel" service conductors and not a feeder. Is that possible?

2- Regarding just the ampacity issue, would not the 2/0 THHN copper (rated for 195A, terminating in a 200A main breaker) and the #4 (rated for 95A, terminating in a disconnect switch fused at 100A) be protected at the next higher standard overcurrent rating?

Thanks so much for your insight!

 

[kwired]

Sorry I did not include this ... the building is a commercial project and the system voltage is 120/208, 3 phase. Two follow up questions:

1- We actually had this run by the local Inspections Dept as well. They had no problem, reasoning that the 2/0 were "parallel" service conductors and not a feeder. Is that possible?

2- Regarding just the ampacity issue, would not the 2/0 THHN copper (rated for 195A, terminating in a 200A main breaker) and the #4 (rated for 95A, terminating in a disconnect switch fused at 100A) be protected at the next higher standard overcurrent rating?

Thanks so much for your insight!

Ampacity of 75 degree 4 AWG copper is 85 amps - next size up standard overcurrent device is 90 amps.

Ampacity of 75 degree 2/0 AWG copper is 175 amps - this is a standard size overcurrent device.

95 and 195 amps is from the 90 degree column. You can use 90 degree ampacities for derating insulation for high ambient temperature or number of conductors in raceways but still have to have a minimum size based on terminal temperature which will be 75 degrees. The 100 amp equipment could even be 60 degree terminals depending on how old it is.

Your inspection department needs some training on services, feeders, and parallel conductors.

 

[david luchini]

Sorry I did not include this ... the building is a commercial project and the system voltage is 120/208, 3 phase. Two follow up questions:

1- We actually had this run by the local Inspections Dept as well. They had no problem, reasoning that the 2/0 were "parallel" service conductors and not a feeder. Is that possible?

No, this is not possible. Service Conductors are the conductors from the service point to the service disconnecting means. The two sets of 2/0 you describe are after the service disconnecting means. The are feeders, not service conductors.

2- Regarding just the ampacity issue, would not the 2/0 THHN copper (rated for 195A, terminating in a 200A main breaker) and the #4 (rated for 95A, terminating in a disconnect switch fused at 100A) be protected at the next higher standard overcurrent rating?

2/0 has an ampacity of 175 and #4 has an amapcity of 85. If they were proper tap conductors per 240.21(B), they would need to have an ampacity "not less than the rating of the OCPD at the termination of the tap conductors." So, no, the next higher standard overcurrent rating cannot be applied to tap conductors.

 

[qcroanoke]

I agree with Kwired and David. Especially the part about the inspection department.

 

[petersonra]

I just started renovations on an existing building. The main service switch is a 400A, 3P disconnect switch fused at 400A. Off the load side of the switch there are two sets of 2/0 THHN copper per phase. One set of 2/0 runs about 15 feet thru a wireway and terminates in a 200A main circuit breaker protecting a lighting panel. The second set of 2/0 run about 10 feet into the wireway where they are each tapped with (2) #4 THHN copper conductors. Then the two sets of #4 terminate in a 100A,3P disconnect switch which is fused at 100A. This second set, with the 2/0 being tapped by the #4 just doesn't seem right to me. I have read art. 240.21(B) and I can't quite determine if or what it specifically violates. Any help would be appreciated!

The 2 sets of #4 is a violation. 1/0 is the smallest size you can run in parallel.