Tap ampacity

[augie47]

A different thread prompted a question.
Assume a scenario where we have a 200 amp feeder and we tap that feeder with a 23 ft tap feeding a 50 amp breaker.
240.21 tap rules require that the tap conductor ampacity be 66.7 amps.
Would a #6 THWN-2 be acceptable in this situation ??
That conductor has a 90° ampacity of 75 amps and the load side device will limit the "operating" current to 50 amps.

 

[kwired]

A different thread prompted a question.
Assume a scenario where we have a 200 amp feeder and we tap that feeder with a 23 ft tap feeding a 50 amp breaker.
240.21 tap rules require that the tap conductor ampacity be 66.7 amps.
Would a #6 THWN-2 be acceptable in this situation ??
That conductor has a 90° ampacity of 75 amps and the load side device will limit the "operating" current to 50 amps.

My best guess is you are still limited to the termination temp rating, but could use 90C values for ampacity adjustments if necessary.

 

[Smart $]

My best guess is you are still limited to the termination temp rating...

I agree.

 

[iwire]

I agree.

Make it three.

 

[Carultch]

A different thread prompted a question.
Assume a scenario where we have a 200 amp feeder and we tap that feeder with a 23 ft tap feeding a 50 amp breaker.
240.21 tap rules require that the tap conductor ampacity be 66.7 amps.
Would a #6 THWN-2 be acceptable in this situation ??
That conductor has a 90° ampacity of 75 amps and the load side device will limit the "operating" current to 50 amps.

I would only consider that acceptable in the rare scenario that the termination equipment on both sides of the tap conductors are rated at 90C. Tap connectors usually are, but overcurrent devices & disconnects usually are not.


I'd say that just like with regular conductor ampacity, the whole circuit, both terminations prior to derates, and derated conductor ampacity, need to have the required ampacity.

 

[charlie b]

Would a #6 THWN-2 be acceptable in this situation ??

I think not. Under the "conditions of use" for this application, and that includes the reasonable expectation that the terminations are rated for 75C, the ampacity of that conductor is only 65 amps. You need a minimum of 66.7 amps, and you don't have it. It does not matter that the breaker rating is well below the ampacity. The tap rule merely requires that it be lower than the ampacity, and you do meet that requirement.

 

[Dennis Alwon]

A different thread prompted a question.
Assume a scenario where we have a 200 amp feeder and we tap that feeder with a 23 ft tap feeding a 50 amp breaker.
240.21 tap rules require that the tap conductor ampacity be 66.7 amps.
Would a #6 THWN-2 be acceptable in this situation ??
That conductor has a 90° ampacity of 75 amps and the load side device will limit the "operating" current to 50 amps.

As everyone else stated the #6 is not rated 75 amps since you terminations are only 75C. Let's see how many ways we can say "NO" :lol:

 

[augie47]

As everyone else stated the #6 is not rated 75 amps since you terminations are only 75C. Let's see how many ways we can say "NO" :lol:

So if I use a tap method rated at 90° and a terminal block rated at 90°, I would be good to go.

 

[infinity]

I think not. Under the "conditions of use" for this application, and that includes the reasonable expectation that the terminations are rated for 75C, the ampacity of that conductor is only 65 amps. You need a minimum of 66.7 amps, and you don't have it. It does not matter that the breaker rating is well below the ampacity. The tap rule merely requires that it be lower than the ampacity, and you do meet that requirement.

I agree with Charlie.

 

[Carultch]

So if I use a tap method rated at 90° and a terminal block rated at 90°, I would be good to go.

If the terminal block is part of a manufactured product, no. Because the product temperature rating overrides it.

Although it is questionable because you would be terminating in something other than an overcurrent device, in concept I would expect that you could terminate the #6 in to an in-line splice to a 90C rated #4, which then connects to the breaker/disconnect.


Is there any particular reason why you'd want to avoid #4 the whole way?

 

[jumper]

So if I use a tap method rated at 90° and a terminal block rated at 90°, I would be good to go.

In theory yes and then you would upsize the taps and finally terminate in an OCPD, but the tap rules may not allow this.

(2) The tap conductors terminate in a single circuit breaker
or a single set of fuses that limit the load to the ampac-
ity of the tap conductors. This device shall be permitted
to supply any number of additional overcurrent devices
on its load side.

If in said last termination to be in an OCPD it would be different.

 

[augie47]

In theory yes and then you would upsize the taps and finally terminate in an OCPD, but the tap rules may not allow this.

(2) The tap conductors terminate in a single circuit breaker
or a single set of fuses that limit the load to the ampac-
ity of the tap conductors. This device shall be permitted
to supply any number of additional overcurrent devices
on its load side.

If in said last termination to be in an OCPD it would be different.

good point....
I'm in agreement Just prepping for a class.. fortunately they ask some interesting questions so I try to look at the "what ifs"

 

[wwhitney]

So if a tap conductor is damaged at one point, it can't be repaired with a splice? The whole conductor has to be repulled so that the tap conductor terminates on the OCPD?

Just stirring the pot a little.

Cheers, Wayne

 

[augie47]

So if a tap conductor is damaged at one point, it can't be repaired with a splice? The whole conductor has to be repulled so that the tap conductor terminates on the OCPD?

Just stirring the pot a little.

Cheers, Wayne

 

[iwire]

So if a tap conductor is damaged at one point, it can't be repaired with a splice? The whole conductor has to be repulled so that the tap conductor terminates on the OCPD?

Yes, that is the reason they limit the length of tap conductors. They want to make it easy for us to change them.

 

[Smart $]

So if a tap conductor is damaged at one point, it can't be repaired with a splice? The whole conductor has to be repulled so that the tap conductor terminates on the OCPD?

Just stirring the pot a little.

Cheers, Wayne

One of the conductors to either side of a splice point must meet the definition of a tap in order for the the otherwise-dubbed splice point to be considered a termination.

 

[charlie b]

So if a tap conductor is damaged at one point, it can't be repaired with a splice? The whole conductor has to be repulled so that the tap conductor terminates on the OCPD?

That's an interesting question. I am inclined to say that it can be repaired with a splice. I view the splice as allowing the conductor to its left and the conductor to its right to become a single conductor. Put another way, a splice does not constitute a termination.

 

[petersonra]

That's an interesting question. I am inclined to say that it can be repaired with a splice. I view the splice as allowing the conductor to its left and the conductor to its right to become a single conductor. Put another way, a splice does not constitute a termination.

I agree. A splice is not the same thing as a termination.

 

[wwhitney]

I agree. A splice is not the same thing as a termination.

OK, so then augie47's suggestion of using 90C splices to transition a #6 conductor to a #4 conductor for the 75C OCPD terminals would be NEC-compliant for the example in the OP? Say you didn't have enough #4 on the truck, but have plenty of #6.

Cheers, Wayne

 

[Dennis Alwon]

OK, so then augie47's suggestion of using 90C splices to transition a #6 conductor to a #4 conductor for the 75C OCPD terminals would be NEC-compliant for the example in the OP? Say you didn't have enough #4 on the truck, but have plenty of #6.

Cheers, Wayne

The #6 would have to terminate in an overcurrent protective device. That device or terminals would be 75C