Tap of one set of parallel conductors

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beanland

beanland

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I had a client raise a question for which I am not sure where to look in the NEC to determine whether it is permissible. This is a tap of service conductors ahead of main disconnect for a PV system (230.82(6)). There are three sets of conductors in parallel. The client asked if they could tap just one of the three, using piercing taps. The piercing taps are adequate and rated for the PV load. But, it seems wrong to tap one of a parallel set of conductors. Does anyone have an NEC citation indicating this is acceptable or unacceptable.

I have asked them if they can land the PV at the service conductor terminals rather than tap cable itself and am waiting to hear the reply. It may also be feasible to add a breaker to the main panel for the PV. But, an alternate solution is not what I am seeking, I am seeking an NEC citation relating to the original request.

Thanks.
 
It may take a little "reading between the line" but I would say 310.10(H) addressing parallel conductors being terminated in the same manner would be the applicable section.
 
beanland said:
I had a client raise a question for which I am not sure where to look in the NEC to determine whether it is permissible. This is a tap of service conductors ahead of main disconnect for a PV system (230.82(6)). There are three sets of conductors in parallel. The client asked if they could tap just one of the three, using piercing taps. The piercing taps are adequate and rated for the PV load. But, it seems wrong to tap one of a parallel set of conductors. Does anyone have an NEC citation indicating this is acceptable or unacceptable.

I have asked them if they can land the PV at the service conductor terminals rather than tap cable itself and am waiting to hear the reply. It may also be feasible to add a breaker to the main panel for the PV. But, an alternate solution is not what I am seeking, I am seeking an NEC citation relating to the original request.

Thanks.
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The code does not directly address this issue, and it has been the subject of some debate in here. Some AHJ's will allow it, others will not.
 
ggunn said:
The code does not directly address this issue, and it has been the subject of some debate in here. Some AHJ's will allow it, others will not.
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I agree.

Not when it comes to service conductors that is.

JAP>
 
Found it:

forums.mikeholt.com/showthread.php?t=170330

Brief summary: you can overload the conductors that you tap when the PV is outputting. If this were a load then the argument would be more of a legalistic question about the code, but with PV you are basically defeating the protection of the upstream overcurrent protection device.

You should be able to use multi-terminal Polaris blocks to tap all conductors in the same spot, if you have to do it that way.
 
Complex to say the least

Complex to say the least

Thank you for the comments and, especially, the link to the prior discussion. Since a parallel set of conductors are connected together at both ends, injecting current on one will change the current flow in both. The other thing that will happen is that the resistance of the more heavily loaded conductor, if any, will increase as it heats up due to current flow which forces the current onto the cooler wire; there is a negative feedback scheme in play.

I am going to side on a strict interpretation of the code: that cables must be terminated in the same manner. Adding a tap to one changes the nature of the termination of one of the parallel conductors.

Another issue is that a piercing tap does change the cross section of the conductor at the location of the tap; this could be construed as an additional violation of the paralleling rules.
 
ActionDave said:
The tap is adding some extra conductor at the one spot and not to the entire length, no?

I'm just thinking out loud but that seems right.
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How does that change the termination of the conductor?


JAP>
 
Is this what you are talking about doing ,just with different size conductors, Tapping say a 500 MCM with 250 MCM
 

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What your talking about by definition of parallel conductors is tapping a single conductor. If you can tap Half of a single conductor than you can tap 1/4 of a single conductor as i illustrated in the drawing

And if you can tap a 1/4 than you can tap 1/8 at what % does it stop
 
david said:
What your talking about by definition of parallel conductors is tapping a single conductor. If you can tap Half of a single conductor than you can tap 1/4 of a single conductor as i illustrated in the drawing

And if you can tap a 1/4 than you can tap 1/8 at what % does it stop
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I dunno. When the ampacity of the tapped portion of the conductor gets to be less than 125% of the inverter output current, maybe?
 
Well, my answer representing an authority here, would be we install the conductors based on the ampacities assigned in chapter three, to assign a different ampacity to a conductor would take engineering supervision.

The NEC gives permission to tap a conductor (single conductor).

If you are going to split a conductor, as in this conversation an just tap 1/3 of the conductor you are going to need engineering supervision, if you want to pay and electrical engineer to design the circuit than I would except the engineers findings
 
I don't see how tapping 1 conductor of a group of parallel conductors is in any way compliant with the intent, spirit or letter of the code. As david noted, conductors in parallel are considered 1 conductor in the eyes of the code. The whole idea of tapping just 1 of the group violates everything in 310.10(H)(2) is trying to achieve of equal current division.
 
texie said:
I don't see how tapping 1 conductor of a group of parallel conductors is in any way compliant with the intent, spirit or letter of the code. As david noted, conductors in parallel are considered 1 conductor in the eyes of the code. The whole idea of tapping just 1 of the group violates everything in 310.10(H)(2) is trying to achieve of equal current division.
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I agree.

I believe an IPC should be considered a termination given the intent of the code requirements.
 
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