Feeder tap violation 240.21?

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Dale001289

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Construction wants to tap a 2AWG (115A) feeder with #4AWG (85A) for temp power to two separate 50A loads. The upstream CB that supplies both loads is rated 100A, therefore it seems the #4AWG would be unprotected. Both loads are considered continuous duty. They’re arguing it’s just temp power for a couple months so it doesn’t really matter.


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The feeder is 100 amps due the size of the OCPD. If using #4 AWG conductors then a tap rule applies. You could simply use #3 AWG (100 amps) and avoid the tap rule altogether. Although this is temporary the same rules apply as if it were permanent. You would still need to determine if the equipment is permitted to be protected by the 100 amp OCPD.
 
Review of tap rules in 240.21 would help in determining appropriate installation of these taps.

Assumption of conditions not given (10ft tap) (conductors all THHW) (Each load provided separate tap).
240.21(B)(1)(4) allows a min conductor size on as little as 10% of tapped conductor rating = as little as a #14
240.21(B)(1)(1)(a) and (b) conductor size not less than overcurrent device at the point of termination of the tap conductor = as little as a #8

2140.21)B)(1)(1)(a) Not less than the combined calculated loads on the circuits supplied by the tap conductors. If both loads are supplied by a single tap then the #4 would not be allowed. You are now back to 310.16 min conductor size for 100A
 
Fred B said:
Review of tap rules in 240.21 would help in determining appropriate installation of these taps.

Assumption of conditions not given (10ft tap) (conductors all THHW) (Each load provided separate tap).
240.21(B)(1)(4) allows a min conductor size on as little as 10% of tapped conductor rating = as little as a #14
240.21(B)(1)(1)(a) and (b) conductor size not less than overcurrent device at the point of termination of the tap conductor = as little as a #8

2140.21)B)(1)(1)(a) Not less than the combined calculated loads on the circuits supplied by the tap conductors. If both loads are supplied by a single tap then the #4 would not be allowed. You are now back to 310.16 min conductor size for
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infinity said:
The feeder is 100 amps due the size of the OCPD. If using #4 AWG conductors then a tap rule applies. You could simply use #3 AWG (100 amps) and avoid the tap rule altogether. Although this is temporary the same rules apply as if it were permanent. You would still need to determine if the equipment is permitted to be protected by the 100 amp OCPD.
Click to expand...

Infinity, What if the loads were intermittent, non-continuous duty. Would this make a difference?


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240.21(B)(1) The ampacity of the tap conductors is as follows:
(1)(a). Not less than the combined calculated loads on the circuits supplied by the tap conductors
 
Dale001289 said:
Both loads are rated 50FLA. They’re for industrial space heaters so I’d say they’re probably continuous. But what if they were intermittent?


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240.21(B)(1)(1)(a)
Nothing in tap rules to allow for continuous vs non-continuous. Tap conductors are not given any diversity allowance.
 
Fred B said:
240.21(B)(1)(1)(a)
Nothing in tap rules to allow for continuous vs non-continuous. Tap conductors are not given any diversity allowance.
Click to expand...

I was looking at 220.82(C)(4) & (5), but I don’t think it applies since they’re not separately controlled


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Is this a dwelling unit? 220.82 only applies to dwelling units, and for service load calculations, and not related to tap conductors. Information you provided indicated not a dwelling unit.

Are you trying to justify the smaller conductors, already installed?
Are you providing just one set of conductors for both loads?
Additional info related to heating loads:

220.51 Fixed Electric Space Heating.
Fixed electric space-heating loads shall be calculated at 100 percent of the total connected load. However, in no case shall a feeder or service load current rating be less than the rating of the largest branch circuit supplied.
Exception: Where reduced loading of the conductors results from units operating on duty-cycle, intermittently, or from all units not operating at the same time, the authority having jurisdiction may grant permission for feeder and service conductors to have an ampacity less than 100 percent, provided the conductors have an ampacity for the load so determined.

AHJ may allow for undersized conductors with justification. Seems some arbitrary criteria involved. Would think it would require some equipment that would prevent simultaneous operation.

Also:
670.4 Supply Conductors and Overcurrent Protection.
(A) Size.
The size of the supply conductor shall be such as to have an ampacity not less than 125 percent of the full-load current rating of all resistance heating loads plus 125 percent of the full-load current rating of the highest rated motor plus the sum of the full-load current ratings of all other connected motors and apparatus, based on their duty cycle, that may be in operation at the same time.
Informational Note No. 1: See Table 310.16 through Table 310.20 for ampacity of conductors rated 2000 volts and below.
Informational Note No. 2: See 430.22(E) and 430.26 for duty cycle requirements.

No indicator as to type of industrial heat being provided.
 
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