Wire Size Using Tap Rule

[SteveO28]

Here is the scenario. We are feeding a temp service from a piece of switchgear 340' from the drawn utility pole using a 300amp breaker. We are bringing (3) 500kcmil AL feeders to a 24x24 j box with ilsco distribution blocks. Then tapping the 500's to the two fused disconnects. My coworker is telling me that we need to continue the 500's on the load side of the distribution block to the line side of the two disconnects to carry the full ampacity of the feeders. Then we can change the wire size after the fuse. I read the tap rule differently. As we are less than 10' and carrying more than the 1/10 of the ampacity of the feeder, then we can step the wire down right at the tap to 4/0 for the 200amp, and #1 or #2 for the 100amp. Looking for more opinions on the topic.

 

[infinity]

There are no taps in your illustration therefore the taps rules do not apply. There should not be a ground in the 4".

 

[LarryFine]

You are correct; tap conductors need only be sized to their OCPDs.

 

[SteveO28]

There are no taps in your illustration therefore the taps rules do not apply. There should not be a ground in the 4".

There are taps as described by the ILSCO distribution block. 500 in, (1) 4/0 and #2 out with appropriate sized grounds. There is a ground in the 4". 1/0 as described in the top right corner.

 

[SteveO28]

There are no taps in your illustration therefore the taps rules do not apply. There should not be a ground in the 4".

Why should there not be a ground? this is coming from a piece of switchgear, not a new service.

 

[Seven-Delta-FortyOne]

There are no taps in your illustration therefore the taps rules do not apply. There should not be a ground in the 4".

Well if I’m reading this correctly, he wants to tap out of the J-box.

In that case, yes you are correct, your taps are permitted, except your wire sizes are wonky.

If you’re running cu to the 200A, you only need 3/0. If Al you need 250

Likewise on the 100A, if Al it’s not “1 or 2”, it will need to be #1 al or #3 cu

 

[winnie]

There are no taps in your illustration therefore the taps rules do not apply. There should not be a ground in the 4".

As I read the description, there is a 300A service disconnect at the pole, and a 340 foot long feeder that splits at a distribution block. The wires between the distribution block and the fused disconnects would be taps.

However if the OP could somehow make the 300A device not the service disconnect, eg. if 230.85 applies, then perhaps all the wires being discussed are service entrance conductors....

 

[Seven-Delta-FortyOne]

Why should there not be a ground? this is coming from a piece of switchgear, not a new service.

So you have a 300A OCPD somewhere ahead of this, which is the service disconnect?

 

[SteveO28]

As I read the description, there is a 300A service disconnect at the pole, and a 340 foot long feeder that splits at a distribution block. The wires between the distribution block and the fused disconnects would be taps.

However if the OP could somehow make the 300A device not the service disconnect, eg. if 230.85 applies, then perhaps all the wires being discussed are service entrance conductors....

There is a 300amp breaker in the switchgear 340 from the 24x24 jbox

 

[SteveO28]

So you have a 300A OCPD somewhere ahead of this, which is the service disconnect?

Correct. A 300amp breaker in a piece of switchgear 340' from the pole/ temp service

 

[petersonra]

This appears to be all outside so the tap rules are seriously relaxed.

 

[infinity]

There is a 300amp breaker in the switchgear 340 from the 24x24 jbox

Disregard my initial response. When I saw the pole I thought that these were service conductors and they're actually a feeder.

 

[SteveO28]

Well if I’m reading this correctly, he wants to tap out of the J-box.

In that case, yes you are correct, your taps are permitted, except your wire sizes are wonky.

If you’re running cu to the 200A, you only need 3/0. If Al you need 250

Likewise on the 100A, if Al it’s not “1 or 2”, it will need to be #1 al or #3 cu

Thank you for the response. We are running AL XHHW from the blocks to the line side of the disconnect, so I believe the 4/0 and #2 would work. I did leave that piece out

 

[jim dungar]

If these are service conductors, the rules from 240 do not apply. Service conductors need to follow the rules in 230.

 

[SteveO28]

Disregard my initial response. When I saw the pole I thought that these were service conductors and they're actually a feeder.

No worries. Thank you for the response. I think describing this as a temp service is throwing people off. In reality it is strictly a feed to two disconnects that will be utilized for a temp service.

 

[SteveO28]

If these are service conductors, the rules from 240 do not apply. Service conductors need to follow the rules in 230.

Not service conductors. Strictly a 300amp feed from switchgear to two fused disconnects.

 

[jim dungar]

Not service conductors. Strictly a 300amp feed from switchgear to two fused disconnects.

Okay.
In your first post you said you had a temp service.

 

[infinity]

No worries. Thank you for the response. I think describing this as a temp service is throwing people off. In reality it is strictly a feed to two disconnects that will be utilized for a temp service.

That's exactly it. I read temp service and pole and missed the part about it being a feeder.

 

[SteveO28]

Okay.
In your first post you said you had a temp service.

Yea I should have left the temp service wording out. I think it is confusing people. I really should have said I'm running a 300amp feed to a distribution block in a jbox then to two fused disconnects. Was looking to confirm I can size the wires based on the fuses in the disconnects and not 300 amp the feeder size (500kcmil) as my coworker insisted.

 

[Seven-Delta-FortyOne]

Thank you for the response. We are running AL XHHW from the blocks to the line side of the disconnect, so I believe the 4/0 and #2 would work. I did leave that piece out

How are you getting 4/0 al and #2 al for 200A and 100A feeders?