Feeder Disconnect/Tap Rules

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J2H

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Wisconsin
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Broadcast Engineer/Licensed Electrician
For an upcoming transmitter install, I discovered that the 200 amp fused disconnect with 125 A fuses, I intend to use is tapped from a 4 wire 3/0 feeder with #2 wire . There is also a #3 tap from the 3/0 feeder supplying a 100 amp single phase panel fed from phases A and C (high leg delta service). The supply for the 3/0 feeder is tapped directly from an outdoor ATS with 400 amp overcurrent protection and runs about 35 feet through a crawlspace and then a ceiling to the location of the junction box containing the taps to the panel and disconnect.

The neutral and EGC for the 100 amp panel are tied to the 3/0 feeder.

In my mind the 3/0 feeder is a violation of the 240.21 tap rules since it is both greater than 25 feet and supplies other taps. In addition, the neutral and EGC connection is a 250.24(5) violation.
Would the following be a compliant solution:

1) Install a 200 amp fused disconnect within 25 feet of the supply to the 3/0 feeder.
2) Subject to a load calc reduce the 100 amp panel breaker to 70 amps.
3) Break the EGC/neutral connection in the junction box and pull a #4 EGC(EMT is 2 in so it would not be overfilled) or use the EMT as the EGC.
4) Supply the 125 amp OPCD/Disconnect for the transmitter with #1 since the allowances of 240.4(B) are not permitted for tap conductors.
 
Conductors are copper or aluminum? I assume in (4) you mean #1 copper, but then (2) would not be necessary unless the #3 conductors are aluminum.

Otherwise what you say sounds correct to me.
 
J2H said:
For an upcoming transmitter install, I discovered that the 200 amp fused disconnect with 125 A fuses, I intend to use is tapped from a 4 wire 3/0 feeder with #2 wire . There is also a #3 tap from the 3/0 feeder supplying a 100 amp single phase panel fed from phases A and C (high leg delta service). The supply for the 3/0 feeder is tapped directly from an outdoor ATS with 400 amp overcurrent protection and runs about 35 feet through a crawlspace and then a ceiling to the location of the junction box containing the taps to the panel and disconnect.

The neutral and EGC for the 100 amp panel are tied to the 3/0 feeder.

In my mind the 3/0 feeder is a violation of the 240.21 tap rules since it is both greater than 25 feet and supplies other taps. In addition, the neutral and EGC connection is a 250.24(5) violation.
Would the following be a compliant solution:

1) Install a 200 amp fused disconnect within 25 feet of the supply to the 3/0 feeder.
2) Subject to a load calc reduce the 100 amp panel breaker to 70 amps.
3) Break the EGC/neutral connection in the junction box and pull a #4 EGC(EMT is 2 in so it would not be overfilled) or use the EMT as the EGC.
4) Supply the 125 amp OPCD/Disconnect for the transmitter with #1 since the allowances of 240.4(B) are not permitted for tap conductors.
Click to expand...
I agree, is both greater than 25 foot tap (and not an outdoor tap) and also it can not supply additional taps.
 
jaggedben said:
Conductors are copper or aluminum? I assume in (4) you mean #1 copper, but then (2) would not be necessary unless the #3 conductors are aluminum.

Otherwise what you say sounds correct to me.
Click to expand...
All conductors are copper. I questioned whether it was compliant to have the potential for 225 Amps of load on a feeder with an ampacity of 200 amps. It appears that is compliant as long the feeder is sized correctly for the connected load.
 
Are there other loads served from the ATS? Or could the 400A breaker in the ATS simply be downgraded to 200A to make everything compliant?
 
jaggedben said:
Are there other loads served from the ATS? Or could the 400A breaker in the ATS simply be downgraded to 200A to make everything compliant?
Click to expand...
That's not a bad idea and might be possible. There are other loads; they are the current "main" transmitter, fed as an outdoor feeder tap from the ATS, and some panels fed off a 200 amp disconnect but those are currently very lightly loaded, since the site was once a combined studio and transmitter facility but the studio has been moved.

It would be unlikely, for both transmitters to be operating at the same time(only reason would be to run one into a test load while the other was on the air). I don't have the specs on the HVAC load or the additional panels right now, but can get them the next time I am at this site. I think the HVAC load along with the other loads(mostly continuous) will result a calculated load greater than 200 amps.

In an ideal world everything from the load side of the 400 amp breaker in the ATS should probably be reworked with either a 500 or 600 kcmil feeder to a rectangular wire way tapped to the appropriate disconnects or a 400 amp distribution panel installed, but that is outside of the scope of work of this project, but should be noted to the client(I'm the license holder for the company, but do not always have the final say).
 
jaggedben said:
Conductors are copper or aluminum? I assume in (4) you mean #1 copper, but then (2) would not be necessary unless the #3 conductors are aluminum.

Otherwise what you say sounds correct to me.
Click to expand...
Just revisiting this, regarding (2). Conductors are indeed copper. I was suggesting to reduce the size of the panel breaker to keep the sum of the OCPDs supplying the tap conductors less than 200 amps.
But unless I am missing something, there is no code requirement to do this. If I understand correctly as long as feeder can carry the 125% of the continuous load and 100% of the non-continuous load and is properly protected, the tap conductors are appropriately sized for the load and protected at their ampacity, the install is compliant.

The same is true for the panel bus-it needs to be protected at no greater than its rated ampacity, so the 100 amp breaker can stay as you said.
 
That is correct.

Also note that properly sized overcurrent devices are essentially always rated higher than the actual load, sometimes by a little, sometimes by a lot. So as you sum them together you will most often at some point get a sum that's higher than the required feeder ampacity.
 
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jaggedben said:
That is correct.

Also note that properly sized overcurrent devices are essentially always rated higher than the actual load, sometimes by a little, sometimes by a lot. So as you sum them together you will most often at some point get a sum that's higher than the required feeder ampacity.
Click to expand...
Thank you for the information. I know that's very common with the typical panel, I just wanted make sure that this acceptable for a feeder as well.
 
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