Feeder Tap Leaves Panel Out to Disconnect. I say violation.

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Application: An industrial control panel has a 400 amp fused main disconnect. A set of #10 tap conductors leave the enclosure through a cable (not in a raceway) and go less than 10 feet to the top of a 30 amp fused disconnect which supplies power to a constant voltage transformer. There is no OCPD at the point where the taps originate (other than the 400 amp fuses in the main disco). I say that 240.21 (B) (1) (3) would require these tap feeders to be enclosed in a raceway (like conduit; not open cable or cable in a tray). If I am right, then am I also right in that if they were in a conduit that this application would satisfy 240.21?
 

Jljohnson

Senior Member
Location
Colorado
I say you are correct. In additon to the raceway violation, 240.21(b)(2)(1) says the feeder conductors must also be no less than 1/3 the ampacity of the overcurrent device (400 amps in this case) protecting them. Double-whammy.
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
240.21(B)(1) and lets the conductors size be 1/10 th the rating of the 400 A breaker. But #10 would still be too small.

240.92 might allow the #10 wire, but who has time to do all that math:)

But I agree that the conductors need protection.

Steve
 

jetlag

Senior Member
240.21(B)(1) and lets the conductors size be 1/10 th the rating of the 400 A breaker. But #10 would still be too small.

240.92 might allow the #10 wire, but who has time to do all that math:)

But I agree that the conductors need protection.

Steve

90 deg #10 wire is rated 40 amp so it is 1/10 of the 400 main

It also passes 240.92 with flying colors,,
 

jetlag

Senior Member
It is very unlikely that the terminations are rated at 90?C, so you can't use that ampacity.

So you are saying we can never use 90 deg for conductors because of the termination , that makes no sence at all , the temp rating is because of the insulation , are you saying a split bolt connector and the lugs in a disconnect box wont stand 90 deg .
 

jetlag

Senior Member
what about 240.4(d)(7) Small conductors

I never under stood why tap conductors are even allowed when they are so strict on the max breaker for conductors in all other cases. Motor laods are also allowed to go way over for the starting load,, that I can see because the start load is momentary, but tap conductors allowed to feed from a breaker 10 times their ampacity under certain conditions. I would never put one 10 times on my own property,, maybe 3 at the most because that should trip the main ok. Motor loads and tap conductors have their own set of rules.
 

kwired

Electron manager
Location
NE Nebraska
I never under stood why tap conductors are even allowed when they are so strict on the max breaker for conductors in all other cases. Motor laods are also allowed to go way over for the starting load,, that I can see because the start load is momentary, but tap conductors allowed to feed from a breaker 10 times their ampacity under certain conditions. I would never put one 10 times on my own property,, maybe 3 at the most because that should trip the main ok. Motor loads and tap conductors have their own set of rules.

Have you ever tried to put a 400 amp conductor into the lugs on a 30 amp disconnect?
 

jetlag

Senior Member
Have you ever tried to put a 400 amp conductor into the lugs on a 30 amp disconnect?

Glad you said that because it helps with the point I am trying to make , just because the wire wont go should not give you the right to reduce to # 10 in my opinion. A 1/0 could be tapped and connected to a 100 amp subpanel adjacent to the main 400 amp box and a 30 amp breaker installed . Industrial places can be very rough on a building moving pieces of steel on a hoist. If you never seen a piece of conduit pull a lose a #10 wire will virtually explode on a 400 amp breaker.
 

jumper

Senior Member
So you are saying we can never use 90 deg for conductors because of the termination , that makes no sence at all , the temp rating is because of the insulation , are you saying a split bolt connector and the lugs in a disconnect box wont stand 90 deg .

110.14(C) applies to every termination in the circuit. You might have a 90 deg conductor and split bolt, but you also need the breaker and end device/equipment terminations rated at 90 deg. Most small stuff will not be rated this high AFAIK.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
So you are saying we can never use 90 deg for conductors because of the termination , that makes no sence at all , the temp rating is because of the insulation , are you saying a split bolt connector and the lugs in a disconnect box wont stand 90 deg .
I am saying that in systems of 600 volts or less it is a very very rare case where you can use the 90?C ampacity for anything other than derating. I am not sure about the split bolt, but as far as I know there are no equipment terminations rated for 90?C ampacities until you get to some very large equipment.
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
Glad you said that because it helps with the point I am trying to make , just because the wire wont go should not give you the right to reduce to # 10 in my opinion.

I'm just glad my bosses opinion isn't like your opinion. We'd have a lot of NEC compliant taps to redo.:roll:
 

jetlag

Senior Member
110.14(C) applies to every termination in the circuit. You might have a 90 deg conductor and split bolt, but you also need the breaker and end device/equipment terminations rated at 90 deg. Most small stuff will not be rated this high AFAIK.

common breackers are marked 40 deg c I guess you will say next cant rate wire 60 deg and connect to it ,
 

jetlag

Senior Member
I am saying that in systems of 600 volts or less it is a very very rare case where you can use the 90?C ampacity for anything other than derating. I am not sure about the split bolt, but as far as I know there are no equipment terminations rated for 90?C ampacities until you get to some very large equipment.

I think you are confusing this with a circuit that is runnig on 40 amp on a 90 deg #10 , You would be correct , everthing involved would have to be 90 . Remember this is connected to a 30 amp disco and the load will never exceed 30 amp , We are talking about a fault current , The terminals wont have time to get hot the wire will blow into like a fuse link. It doesnt matter if you rate the wire 120
 
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