10' Tap rule

[infinity]

I have an installation where I need to apply the 10' tap rule. The device fed by the tap conductors is rated at 100 amps (no OCPD), the device has a calculated load of less then 100 amps, the feeder conductors are protected at 400 amps and the tap conductors are rated for 100 amps. Is this code compliant? I say it complies with 240.21 but I've gotten some other opinions regarding the omission of and OCPD where the tap conductors terminate. Specifically 240.21(B)(1)(a) and (b).

240.21 Location in Circuit.
Overcurrent protection shall be provided in each ungrounded circuit conductor and shall be located at the point where the conductors receive their supply except as specified in 240.21(A) through (H). Conductors supplied under the provisions of 240.21(A) through (H) shall not supply another conductor except through an overcurrent protective device meeting the requirements of 240.4.
(A) Branch-Circuit Conductors. Branch-circuit tap conductors meeting the requirements specified in 210.19 shall be permitted to have overcurrent protection as specified in 210.20.
(B) Feeder Taps. Conductors shall be permitted to be tapped, without overcurrent protection at the tap, to a feeder as specified in 240.21(B)(1) through (B)(5). The provisions of 240.4(B) shall not be permitted for tap conductors.
(1) Taps Not over 3 m (10 ft) Long. Where the length of the tap conductors does not exceed 3 m (10 ft) and the tap conductors comply with all of the following:
(1) The ampacity of the tap conductors is
a. Not less than the combined calculated loads on the circuits supplied by the tap conductors, and
b. Not less than the rating of the device supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors.
(2) The tap conductors do not extend beyond the switchboard, panelboard, disconnecting means, or control devices they supply.
(3) Except at the point of connection to the feeder, the tap conductors are enclosed in a raceway, which shall extend from the tap to the enclosure of an enclosed switchboard, panelboard, or control devices, or to the back of an open switchboard.
(4) For field installations where the tap conductors leave the enclosure or vault in which the tap is made, the rating of the overcurrent device on the line side of the tap conductors shall not exceed 10 times the ampacity of the tap conductor.
FPN: For overcurrent protection requirements for panelboards, see 408.36.
(2) Taps Not over 7.5 m (25 ft) Long. Where the length of the tap conductors does not exceed 7.5 m (25 ft) and the tap conductors comply with all the following:
(1) The ampacity of the tap conductors is not less than one-third of the rating of the overcurrent device protecting the feeder conductors.
(2) 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. This device shall be permitted to supply any number of additional overcurrent devices on its load side.
(3) The tap conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.

 

[kbsparky]

I have an installation where I need to apply the 10' tap rule. The device fed by the tap conductors is rated at 100 amps (no OCPD).....

From your quote:

....(2) 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. This device shall be permitted to supply any number of additional overcurrent devices on its load side....

Hmmm .... that only applies to the 25 foot taps ....

I see your dilemma upon further re-reading of the section of the Code ...

 

[augie47]

What is the "device" at termination ?

 

[infinity]

From your quote:

....(2) 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. This device shall be permitted to supply any number of additional overcurrent devices on its load side....

Hmmm .... that only applies to the 25 foot taps ....

I see your dilemma upon further re-reading of the section of the Code ...

That's where I was going with this. The requirement for an OCPD in the 25' rule but not in the 10' rule.

What is the "device" at termination ?

This is for a 100 amp rated dimming panel tapped from a 400 amp feeder.

 

[augie47]

If it's associated with Art 520 (Theaters, Audience Areas of Motion Picture and Television Studios, Performance Areas, and Similar Locations), it appears 520.25 would require a OCP & Disconnect.
Beyond that my next step would be the UL classification and see if that equipmemt requires OCP.

 

[infinity]

If it's associated with Art 520 (Theaters, Audience Areas of Motion Picture and Television Studios, Performance Areas, and Similar Locations), it appears 520.25 would require a OCP & Disconnect.
Beyond that my next step would be the UL classification and see if that equipmemt requires OCP.

Not sure that 520.25 would apply to this installation since each individual dimmer has it's own OCPD. The dimming panel has no OCPD except for the 400 amp device ahead of the feeder conductors. This dimming panel only has 100 amp tap conductors.

 

[augie47]

with each dimmer having it's own OCP and the device is rated at 100 amps, it seems you have met the criteria of 240.21(B)(1)

 

[IslandSparky]

You might have satisfied the tap rule, but are you adequately protecting the dimmer panel? Likewise, how are you ensuring the dimmer panel loads will not exceed 100A?

I think you need a breaker.

 

[infinity]

You might have satisfied the tap rule, but are you adequately protecting the dimmer panel? Likewise, how are you ensuring the dimmer panel loads will not exceed 100A?

I think you need a breaker.

Well I thought so too until I re-read the 10' tap rule. IMO the installation complies as is without an OCPD at the end of the tap conductors.

 

[wireguy8169]

Can you put an OCPD

Can you put an OCPD

Just wonder if the install will not allow for an ocpd, if it does and it doesnt break the bank maybe add it....might make you feel better..

 

[IslandSparky]

Well I thought so too until I re-read the 10' tap rule. IMO the installation complies as is without an OCPD at the end of the tap conductors.

What is limiting load? Do you think you could tap a 400A feeder with a 100a feeder terminating in a 100A panelboard? The fact that the panelboard has branch circuit breakers doesn't limit the power unless the sum of the breakers is less than 100a.

Nothing prevents you from replacing a 20A breaker with a 80A breaker.

If you were talking about a 70kW heater, no problem... but you are effectively talking about another tap in-line.

 

[infinity]

What is limiting load? Do you think you could tap a 400A feeder with a 100a feeder terminating in a 100A panelboard? The fact that the panelboard has branch circuit breakers doesn't limit the power unless the sum of the breakers is less than 100a.

Nothing prevents you from replacing a 20A breaker with a 80A breaker.

If you were talking about a 70kW heater, no problem... but you are effectively talking about another tap in-line.

The device is rated for 100 amps. The calculated load is less than 100 amps. This complies with the 10' tap rule. Personally I don't like it but the engineer is saying that it's compliant and I see no wording in this section to say otherwise. Just wondering why the 25' rule requires an OCPD and the 10' rule does not.

240.21 Location in Circuit.
Overcurrent protection shall be provided in each ungrounded circuit conductor and shall be located at the point where the conductors receive their supply except as specified in 240.21(A) through (H). Conductors supplied under the provisions of 240.21(A) through (H) shall not supply another conductor except through an overcurrent protective device meeting the requirements of 240.4.
(A) Branch-Circuit Conductors. Branch-circuit tap conductors meeting the requirements specified in 210.19 shall be permitted to have overcurrent protection as specified in 210.20.
(B) Feeder Taps. Conductors shall be permitted to be tapped, without overcurrent protection at the tap, to a feeder as specified in 240.21(B)(1) through (B)(5). The provisions of 240.4(B) shall not be permitted for tap conductors.
(1) Taps Not over 3 m (10 ft) Long. Where the length of the tap conductors does not exceed 3 m (10 ft) and the tap conductors comply with all of the following:
(1) The ampacity of the tap conductors is
a. Not less than the combined calculated loads on the circuits supplied by the tap conductors, and
b. Not less than the rating of the device supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors.
(2) The tap conductors do not extend beyond the switchboard, panelboard, disconnecting means, or control devices they supply.
(3) Except at the point of connection to the feeder, the tap conductors are enclosed in a raceway, which shall extend from the tap to the enclosure of an enclosed switchboard, panelboard, or control devices, or to the back of an open switchboard.
(4) For field installations where the tap conductors leave the enclosure or vault in which the tap is made, the rating of the overcurrent device on the line side of the tap conductors shall not exceed 10 times the ampacity of the tap conductor.
FPN: For overcurrent protection requirements for panelboards, see 408.36.

 

[glene77is]

Inifinity,

quote
Just wondering why the 25' rule requires an OCPD and the 10' rule does not.
end quote

Is there some practical industrial issue here ?

 

[iwire]

Rob, as you know 240 addresses OCP of conductors so IMO as far as that goes you are all set.

But IMO you still have to protect the equipment.

Do the instructions indicate the use of a 400 amp feeder?

 

[elohr46]

The requirement for an OCPD in the 25' rule but not in the 10' rule.

A load calc is needed to use the 10' tap rule.

I agree with you that this install is code compliant as is provided the load calc is accurate.

 

[RB1]

Dimmers are listed in the product category NMTR in accordance with UL508. 409.21(B) requires a single overcurrent device sized per 409.21(C). I think this is going to be a problem with the proposed install.

 

[infinity]

Rob, as you know 240 addresses OCP of conductors so IMO as far as that goes you are all set.

But IMO you still have to protect the equipment.

Do the instructions indicate the use of a 400 amp feeder?

The dimming panel is rated for 100 amps according to the nameplate. 240.21 tells me that I can connect a device to the tap conductors if such a device is rated not less than that of the tap conductors and that the calculated load of the device is less than that of the tap conductors. Not sure what the instructions may or may not say at this point. It is a good thing to check out. I'll see if I can acquire some further information on this panel.

 

[iwire]

The dimming panel is rated for 100 amps according to the nameplate. 240.21 tells me that I can connect a device to the tap conductors if such a device is rated not less than that of the tap conductors and that the calculated load of the device is less than that of the tap conductors. Not sure what the instructions may or may not say at this point. It is a good thing to check out. I'll see if I can acquire some further information on this panel.

Rob in my opinion the only thing that 240.21 can apply to is the conductors. It can not modify the protection requirements of the dimmer.

240.21(B) Feeder Taps. Conductors shall be permitted to be tapped,......

Tap Conductors. As used in this article, a tap conductor is
defined as 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 elsewhere in 240.4.

 

[iwire]

240.21 tells me that I can connect a device to the tap conductors if such a device is rated not less than that of the tap conductors

Maybe that is the problem, I think you are saying it backward.

The conductors must be rated at least as much as the device.

Not less than the rating of the device supplied by the tap conductors

It is saying that the tap conductors supplying the 100 amp dimmer must be rated at least 100 amps. The 100 amp dimmer should not be capable of overloading 100 amp conductors.

 

[infinity]

Maybe that is the problem, I think you are saying it backward.

The conductors must be rated at least as much as the device.



It is saying that the tap conductors supplying the 100 amp dimmer must be rated at least 100 amps. The 100 amp dimmer should not be capable of overloading 100 amp conductors.

You're correct, I had it reversed.

Rob in my opinion the only thing that 240.21 can apply to is the conductors. It can not modify the protection requirements of the dimmer.

OK so how do we apply the 10' tap rule with no OCPD at the device?