NEC 240.21(b)(1) Load side taps "rating" confusion

R

ryangittens

Member
Location
usa
I have a plan reviewer stating that the conductors shall be rated not less than the rating of the equipment containing an OCPD.
For example, I have a 100A disconnect with 70 fuses and they are requiring the conductors to be rated at 100A. This doesn't seem correct but the way the code is written it can certainly be interpreted that way. Anyone else ever run into this? Is this correct?
 
2020 NEC 240.21(B)(1)(b) says "Not less than the rating of the equipment containing an overcurrent device(s) supplied by the tap conductors
or not less than the rating of the overcurrent protective device at the termination of the tap conductors." [Emphasis mine]

So you have a choice, you can make it not less than the rating of the equipment (100A) or not less than the rating of the OCPD (70A). Obviously the second choice is more advantageous.

Cheers, Wayne
 
wwhitney said:
2020 NEC 240.21(B)(1)(b) says "Not less than the rating of the equipment containing an overcurrent device(s) supplied by the tap conductors
or not less than the rating of the overcurrent protective device at the termination of the tap conductors." [Emphasis mine]

So you have a choice, you can make it not less than the rating of the equipment (100A) or not less than the rating of the OCPD (70A). Obviously the second choice is more advantageous.

Cheers, Wayne
Click to expand...
Dang, thanks! For some reason I thought the termination would be at the tap but the handbook makes it pretty clear. Thanks for the help
 
I have a new question on this thread:
When we install a solar system on an existing service, we usually make the interconnection as either a feeder tap or a backfeed breaker. When it's a feeder tap, we size the solar output conductors per 690.8 at 125% of the maximum output current, then we check the size of the tap per 240.21 on field connections (since we are installing on an existing service) and insure the tap size is also at or above the percentage of the rating of the feeder being tapped. Then referring to 705.11 for supply-side connections, this is OK. But then section 705.12(B)(1)a for load-side taps requires my tap to be sized as the sum of the 125% solar rating and the percentage assigned by the length of the tap. Question: Why the sum, and why is this the only place that requires it? Why not just the larger of the two? (This jurisdiction is using the 2020 NEC.)
 
Often, when a feeder tap is made, the conductors are sized to the 10%/10' rule in 240.21(B)(1) or or the 33%/25' rule in 240.21(B)(1). 705.12(B)(1) modifies 240.21 by requiring a larger ampacity for the tap conductors. In the case of a 10' or smaller tap you can no longer just size the tap conductors at 10% of the OCPD protecting the circuit, but instead you must add the sum of the inverter breakers to the OCPD device protecting the circuit, and then size the tap conductors at 10% of this sum.

Example: You have a 200A circuit feeding a sub panel, and this circuit is tapped to a PV system OCPD within 10'. The PV system is a 3.8 kW inverter with a 20A OCPD. The minimum size of the tap conductors is 10% of (200A + 20), or 22A. In this instance the tap conductors would need to be increased in size from #12 to #10. If this tap were made to a non-PV device, 705.12(B)(1) would not come into play, and #12 conductors would be sufficient for the tap conductors. The idea is that both the 200A OCPD in the primary circuit and the PV circuit OCPD are feeding current into a short at the tap conductors, so they need to be a little bigger to handle the additional current without melting until a breaker clears the fault. That's the way it was explained to me in a training class on the subject years ago.

Not sure why you need to look at 705.11 when making a feeder tap. That is a load-side interconnection, and 705.11 doesn't come into play.
 
PWDickerson said:
Example: You have a 200A circuit feeding a sub panel, and this circuit is tapped to a PV system OCPD within 10'. The PV system is a 3.8 kW inverter with a 20A OCPD. The minimum size of the tap conductors is 10% of (200A + 20), or 22A. In this instance the tap conductors would need to be increased in size from #12 to #10.
Click to expand...
Only if your #12 tap conductors have 60C insulation. If they have 75C or 90C insulation, then their ampacity is 25A or 30A, and so would comply with 240.21(B)(1).

Cheers, Wayne
 
wwhitney said:
2020 NEC 240.21(B)(1)(b) says "Not less than the rating of the equipment containing an overcurrent device(s) supplied by the tap conductors
or not less than the rating of the overcurrent protective device at the termination of the tap conductors." [Emphasis mine]

So you have a choice, you can make it not less than the rating of the equipment (100A) or not less than the rating of the OCPD (70A). Obviously the second choice is more advantageous.

Cheers, Wayne
Click to expand...
To follow up on this, the claim is that with a fused disconnect, the conductors do not terminate at the ocpd, therefore, the conductors must be rated for the disconnect and not the fuses. If this were a breaker disconnect it would use the breaker rating since the conductors terminate at the breaker. Reading the code, it almost seems like that's actually what they were intending.
 
ryangittens said:
To follow up on this, the claim is that with a fused disconnect, the conductors do not terminate at the ocpd, therefore, the conductors must be rated for the disconnect and not the fuses. If this were a breaker disconnect it would use the breaker rating since the conductors terminate at the breaker. Reading the code, it almost seems like that's actually what they were intending.
Click to expand...
What fuses have you ever seen that allow conductors to be directly connected to them?
What about when the breaker is in one compartment and the lugs are in a different section connected by bus bars, like some meter-mains?
 
jim dungar said:
What fuses have you ever seen that allow conductors to be directly connected to them?
What about when the breaker is in one compartment and the lugs are in a different section connected by bus bars, like some meter-mains?
Click to expand...

Good point, I don't know.

That's the AHJ's interpretation that it's some how different if it touches the fuse directly or not. For the breaker in another compartment, I'd like to hear their response for that.

This is what we're dealing with down here in FL.

Verbatim:

"I hope this will clarify the deficiency for the load side tap for the above mentioned permit. When using a manual FUSED disconnect, the fuse itself is considered the “overcurrent device” and the disconnect is the “equipment containing the overcurrent device”. The tap conductors cannot terminate to a fuse as they can to a breaker thus the differentiation between the two in the code reference. If it were based solely on the overcurrent device without regard to the termination point there would have been no reference to the “equipment containing the overcurrent device” at all. We have discussed this in depth in our monthly code advisory board meetings and the consensus has not changed. If you wish to discuss the matter further feel free to contact myself or Deputy Chief Christopher Richardson. I will include his contact information below. Thank you."
 
A corollary to the interpretation in the preceding post is that the 25' tap rule, 240.21(B)(2), may never be used with a fused disconnect. 240.21(B)(2)(2) requires that "The tap conductors terminate in a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors." But the preceding interpretation is that with a fused disconnect, tap conductors never terminate in a single set of fuses.

Pointing out this nonsensical implication may help the AHJ in question understand that they have reached the wrong conclusion. I.e. it is logically inconsistent to allow 240.21(B)(2) taps to terminate in a fused disconnect, but to require a 240.21(B)(1) tap terminating in a fused disconnect to be calculated based on the disconnect rating rather than the fuse size.

This still raises the question of why 240.21(B)(1) uses different wording than 240.21(B)(2). I'm not sure, but my understanding is that it is meant to be a broader allowance than the 240.21(B)(2) wording, not a more restrictive requirement. For example, I believe you could terminate a 240.21(B)(1) tap onto an MLO panelboard with only two circuit breakers in it, as long as the tap conductors are at least the ampacity of the panelboard rating. [The panelboard would comply with 408.36 Exception 1 if the sum of the circuit breaker ratings does not exceed the panelboard rating.] That is not something allowed under 240.21(B)(2).

Cheers, Wayne
 
ryangittens said:
mGood point, I don't know.

That's the AHJ's interpretation that it's some how different if it touches the fuse directly or not. For the breaker in another compartment, I'd like to hear their response for that.

This is what we're dealing with down here in FL.

Verbatim:

"I hope this will clarify the deficiency for the load side tap for the above mentioned permit. When using a manual FUSED disconnect, the fuse itself is considered the “overcurrent device” and the disconnect is the “equipment containing the overcurrent device”. The tap conductors cannot terminate to a fuse as they can to a breaker thus the differentiation between the two in the code reference. If it were based solely on the overcurrent device without regard to the termination point there would have been no reference to the “equipment containing the overcurrent device” at all. We have discussed this in depth in our monthly code advisory board meetings and the consensus has not changed. If you wish to discuss the matter further feel free to contact myself or Deputy Chief Christopher Richardson. I will include his contact information below. Thank you."
Click to expand...
It looks like the 'equipment' language was added in 2014. You may have to look into the CMP reasoning at that time.

IMO it was intended for equipment containing multiple over current devices.
 
wwhitney said:
I don't buy that interpretation. The entire fused disconnect is the overcurrent protective device, not just the fuse itself.

Cheers, Wayne
Click to expand...
Respectfully, I am not sure about this. My reason for questioning,

230.91 Location. The service overcurrent device shall be an
integral part of the service disconnecting means or shall be
located immediately adjacent thereto. Where fuses are used as
the service overcurrent device, the disconnecting means shall
be located ahead of the supply side of the fuses.

That said, I read and reread the first post and I don't see any reference to "tap conductors" It appears the OP was asking that give n subsequent discussion, but I wanted to clarify that he is talking about a tap conductor situation, not a standard feeder run to a fused disconnect, which I first assumed.
 
ryangittens said:
Good point, I don't know.

That's the AHJ's interpretation that it's some how different if it touches the fuse directly or not. For the breaker in another compartment, I'd like to hear their response for that.

This is what we're dealing with down here in FL.

Verbatim:

"I hope this will clarify the deficiency for the load side tap for the above mentioned permit. When using a manual FUSED disconnect, the fuse itself is considered the “overcurrent device” and the disconnect is the “equipment containing the overcurrent device”. The tap conductors cannot terminate to a fuse as they can to a breaker thus the differentiation between the two in the code reference. If it were based solely on the overcurrent device without regard to the termination point there would have been no reference to the “equipment containing the overcurrent device” at all. We have discussed this in depth in our monthly code advisory board meetings and the consensus has not changed. If you wish to discuss the matter further feel free to contact myself or Deputy Chief Christopher Richardson. I will include his contact information below. Thank you."
Click to expand...
See my reply above. The code does agree with this statement.
 
wwhitney said:
A corollary to the interpretation in the preceding post is that the 25' tap rule, 240.21(B)(2), may never be used with a fused disconnect. 240.21(B)(2)(2) requires that "The tap conductors terminate in a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors." But the preceding interpretation is that with a fused disconnect, tap conductors never terminate in a single set of fuses.

Pointing out this nonsensical implication may help the AHJ in question understand that they have reached the wrong conclusion. I.e. it is logically inconsistent to allow 240.21(B)(2) taps to terminate in a fused disconnect, but to require a 240.21(B)(1) tap terminating in a fused disconnect to be calculated based on the disconnect rating rather than the fuse size.

This still raises the question of why 240.21(B)(1) uses different wording than 240.21(B)(2). I'm not sure, but my understanding is that it is meant to be a broader allowance than the 240.21(B)(2) wording, not a more restrictive requirement. For example, I believe you could terminate a 240.21(B)(1) tap onto an MLO panelboard with only two circuit breakers in it, as long as the tap conductors are at least the ampacity of the panelboard rating. [The panelboard would comply with 408.36 Exception 1 if the sum of the circuit breaker ratings does not exceed the panelboard rating.] That is not something allowed under 240.21(B)(2).

Cheers, Wayne
Click to expand...
Very well said, Sir. I will relay this reasoning along with what @jim dungar pointed out and see how it goes. If they are not convinced then I don't believe they can be, outside of hearing it from the CMP themselves.
 
jim dungar said:
It looks like the 'equipment' language was added in 2014. You may have to look into the CMP reasoning at that time.

IMO it was intended for equipment containing multiple over current devices.
Click to expand...
Substantiation for proposal 10-32 for the 2014 code.
Substantiation: This proposal is intended to clarify the application of the
existing requirement and state the specific type of device as an overcurrent
device. This clarification is needed since a conductor fits within the definition
of “device” in Article 100. The submitter is quite confident such an application
or interpretation would not meet the intention of the Code Panel who is
responsible for this Article.
The term “equipment containing an overcurrent device(s)” could be a mainlug
panelboard, a fusible switch, a switchboard or a motor control center.
Click to expand...
 
don_resqcapt19 said:
Substantiation for proposal 10-32 for the 2014 code.
Click to expand...
That doesn't directly address the specific question from post #10 of whether terminating tap conductors on the line side lugs of a fused disconnect switch constitutes providing an "overcurrent protective device at the termination of the tap conductors."

Cheers, Wayne
 
wwhitney said:
That doesn't directly address the specific question from post #10 of whether terminating tap conductors on the line side lugs of a fused disconnect switch constitutes providing an "overcurrent protective device at the termination of the tap conductors."

Cheers, Wayne
Click to expand...
It doesn't but I was responding to this from post 12:
"It looks like the 'equipment' language was added in 2014. You may have to look into the CMP reasoning at that time."

The language needs work as I can see it being read differently for breakers, fusible disconnects. The only OCPD that you land the tap conductors on is a breaker. I don't see it as the intent but it can very easily be read as requiring the conductor match the rating of the fusible disconnect no matter what size fuse is installed.

The language in (2) for the 25' tap rule is much better than that in the 10' tap rule.
 
You must log in or register to reply here.
Top