Tap Conductors

[pete m.]

I am looking for the rationale behind 240.21(b) where the code states that the provisions of 240.4(b) will not be applicable.

Here is a scenario:

400 amp overcurrent device feeding 500kcmil copper conductors at 75 degrees C. A tap is made to these conductors with 4/0 aluminum at 75 degrees (the tap rules are followed with respect to conductor lenght).

It is permissible to protect the 500kcmil conductors at 400 amps (the load is less than 380 amps) utilizing 240.4(b) but the 4/0 aluminum conductors would have to terminate in an overcurrent device rated at 175 amps even though if the same 4/0 conductors were fed directly from a breaker the breaker could be rated at 200 amps (with respect to load).

Would the 500kcmil conductors also be considered a tap? I don't think they would, by definition, but why wouldn't the same logic that allows the 500kcmil conductors to be protected above their rated ampacity be allowed for the 4/0 conductors in the scenario above considering it would be permissible to protect the 4/0 at 200 amps if the 4/0 conductors were not, by definition, a tap conductor?

 

[pierre]

Re: Tap Conductors

Typically conductors are protected at their supply and the applicable requirements are followed. Tap conductors are not protected at their supply by conventional methods, so the conventional requirements do not all apply, such as 240.4(B).

 

[pete m.]

Re: Tap Conductors

Thank you for the reply Pierre.

Let me change the scenario which might make my question a little clearer.

500kcmil copper connected to a 400 amp OCPD ran into a wireway and two different 500kcmil copper conductors tapped from the feeder.

The 500 kcmil conductors that are connected to the 400 amp OCPD are considered "protected" by the 400 amp OCPD (with respect to actual load)

The 500kcmil condcutors tapped to the conductors connected to the breaker would have to terminate in an OCPD rated at no more than 350 amps.

Why is 240.4(b) permissive for the 500kcmils connected to the 400 amp OCPD but not the 500kcmils tapped to them?

 

[don_resqcapt19]

Re: Tap Conductors

Pete,

500kcmil copper connected to a 400 amp OCPD ran into a wireway and two different 500kcmil copper conductors tapped from the feeder.

Those are not tap conductors per the Article 240 definition. The tap rules would not apply.
Don

 

[infinity]

Re: Tap Conductors

Those are not tap conductors per the Article 240 definition. The tap rules would not apply.
Don

I would call them a splice.

 

[pete m.]

Re: Tap Conductors

I hate not being able to ask a question in the manner that prompts the answer I'm looking for

Thanks for your patience.

 

[charlie]

Re: Tap Conductors

Pete, Phil Simmons submitted a proposal to add that provision during the 2005 Code cycle. Panel 10 rejected the proposal during the proposal stage and reconsidered during the Comment stage. The following is from Jim Dollard' comment that was accepted:

After reviewing proposals 10-40 & 10-53 along with our panel actions and statements, my position on this issue has changed as I believe the submitter is correct. I agree with the panel statement in that the intent of both 240.21(B) and (C) is not to permit the application of 240.4(B).

However after careful review of these sections and after receiving input from installers and inspectors I believe that the clarification provided by the proposed text is necessary. The present text is not user friendly as it does not specifically point out to the user that the provisions of 240.4(B) may not be applied when using 240.21(B) or (C).

The acceptance of this text is needed to clarify the existing requirement and is editorial in nature. The result however is user friendly text, resulting in easier compliance with the present requirements.

The original Substantiation from Phil is:

This proposal is intended to clarify the issue of whether these conductors that do not have overcurrent protection where they originate are required to be not less than the rating of the device or overcurrent protection they terminate in. Since the tapped conductors or conductors on the secondary of a transformer do not have overcurrent protection where they originate, it seems logical that they should not be permitted to round up to the next standard size as provided in 240.4(B). A more logical approach seems to be that the subject conductors must have an ampacity not less than the rating of the device or overcurrent protection
they terminate in.

I trust this clears up the reason for the "new" requirement.

 

[pete m.]

Re: Tap Conductors

Thank you Charlie, and all who took the time to reply. I'm still not sure I "get it" (the substantiation) but it is as it is.
I still wonder why 240.4(b) is applicable for feeders, service, etc.. and not tap conductors. And probably always will. Perhaps I am stupid (meaning unable to learn) instead of just ignorant.

Thanks again.

Pete