Tap Conductors 2023 NEC 705.12(A)(3) and 240.21(B)(2)

JimmysLimeade

JimmysLimeade

EE Student & PV Design
Location
Utah
Occupation
PV Design
I am trying to figure out what part of a PV interconnection this applies to. I can't find a super clear definition of what is considered a tap conductor. Take this diagram for example:
1743445399999.png
Is the tap conductor at point 1, 2, or 3?
 
JimmysLimeade said:
I am trying to figure out what part of a PV interconnection this applies to. I can't find a super clear definition of what is considered a tap conductor. Take this diagram for example:
View attachment 2576477
Is the tap conductor at point 1, 2, or 3?
Click to expand...
Tap conductor is #1.
2 and 3 are the feeder

Your system would not be compliant, though. The most PV current that you can push through the tap is 32A on a 40A OCPD.
 
Let's say your wire segments (1), (2), and (3) have ampacities of 100A, 200A, and 200A respectively. Then:

Wire segment (2) can receive 80A from the PV from one end, and 200A from the utility from the other end. In both cases, with an ampacity of 200A, it is protected at its point of supply at no more than its ampacity. It is not a tap conductor.

Wire segment (1) can also receive 80A from the PV from one end, and 200A from the utility from the other end. As its ampacity is only 100A, then it is a tap conductor with respect to the utility source. So it needs to comply with 2023 NEC 705.12(A)(3).

Wire segment (3) can receive 80A from the PV and 200A from the utility, all at one end. So it is a tap conductor, although we don't need to look at 240.21(B) for it, as it is covered by 705.12(A)(2).

Cheers, Wayne
 
ggunn said:
Your system would not be compliant, though. The most PV current that you can push through the tap is 32A
Click to expand...
Should have clarified, this is just for ease of understanding on my end :) not meant to actually use
ggunn said:
Tap conductor is #1.
2 and 3 are the feeder
Click to expand...
wwhitney said:
Let's say your wire segments (1), (2), and (3) have ampacities of 100A, 200A, and 200A respectively. Then:

Wire segment (2) can receive 80A from the PV from one end, and 200A from the utility from the other end. In both cases, with an ampacity of 200A, it is protected at its point of supply at no more than its ampacity. It is not a tap conductor.

Wire segment (1) can also receive 80A from the PV from one end, and 200A from the utility from the other end. As its ampacity is only 100A, then it is a tap conductor with respect to the utility source. So it needs to comply with 2023 NEC 705.12(A)(3).

Wire segment (3) can receive 80A from the PV and 200A from the utility, all at one end. So it is a tap conductor, although we don't need to look at 240.21(B) for it, as it is covered by 705.12(A)(2).
Click to expand...
This is super helpful, thank you!
 
wwhitney said:
Let's say your wire segments (1), (2), and (3) have ampacities of 100A, 200A, and 200A respectively. Then:

Wire segment (2) can receive 80A from the PV from one end, and 200A from the utility from the other end. In both cases, with an ampacity of 200A, it is protected at its point of supply at no more than its ampacity. It is not a tap conductor.

Wire segment (1) can also receive 80A from the PV from one end, and 200A from the utility from the other end. As its ampacity is only 100A, then it is a tap conductor with respect to the utility source. So it needs to comply with 2023 NEC 705.12(A)(3).

Wire segment (3) can receive 80A from the PV and 200A from the utility, all at one end. So it is a tap conductor, although we don't need to look at 240.21(B) for it, as it is covered by 705.12(A)(2).

Cheers, Wayne
Click to expand...
He still has a problem with 705.12(B) in the main panel.
 
ggunn said:
Tap conductor is #1.
...
Click to expand...
Assuming it has an ampacity of less than 200A, yes.

The definition of a tap conductor is in 240.2. It's "a conductor, other than a service conductor, that has overcurrent protection ahead of its point of supply that exceeds the value permitted for similar conductors that are protected as described in 240.4."
 
ggunn said:
He still has a problem with 705.12(B) in the main panel.
Click to expand...
Most likely, although it would be OK if the main panel busbars have only two connections, the 200A main breaker and the feed-thru lugs. Meaning all other circuits have been relocated to the subpanel.

[In fact a third connection would be OK under 705.12(B)(6).]

Cheers, Wayne
 
Tap conductor. Short-ckt and grd-flt protection are provided by the OCPD upstream. Overload protection is provided by the OCPD downstream. IF you look at 240.21, it states that the three types of overcurrent are provided at the source. 240.21(A) allows everything below it to be different. 240.21(B) is for taps.
 
jaggedben said:
The definition of a tap conductor is in 240.2. It's "a conductor, other than a service conductor, that has overcurrent protection ahead of its point of supply that exceeds the value permitted for similar conductors that are protected as described in 240.4."
Click to expand...
Although that definition is rooted in the paradigm that conductors have only one point of supply. Implicit in my answer is that the way to adapt that definition to multiple sources of supply is (a) add the OCPD ratings together when multiple sources of supply are combined at one end of the conductor and (b) treat the two ends separately when there is at least one source of supply at each end.

Cheers, Wayne
 
wwhitney said:
Although that definition is rooted in the paradigm that conductors have only one point of supply. Implicit in my answer is that the way to adapt that definition to multiple sources of supply is (a) add the OCPD ratings together when multiple sources of supply are combined at one end of the conductor and (b) treat the two ends separately when there is at least one source of supply at each end.

Cheers, Wayne
Click to expand...
I've certainly had the thought that 705 should just say something along the lines of what you say here, but it doesn't quite do that. So with respect to whether there is a clear definition of a tap conductor in the NEC, I think there is a clear definition in 240 when there's one source of supply, and not such a clear definition in cases covered by 705.

FWIW I've been prepared to argue to an AHJ that the maximum distance from my load-side PV tap point to the overcurrent device on the load side of the feeder (i.e. new main breaker in existing subpanel) should be subject to 240.21(B) at the most restrictive, but I never actually had to argue the point.
 
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