Tap Rule

[jumpinjohnny]

Good afternoon to all. I need to make sure I understand the tap rule in Article 240.21 (B) (2). I have electric heat at 100 A. At this I point I am told I have Approximately 50A on the compressor. I am running #4 THHN to my heater and I want to tap with #8 THHN to the compressor,according to this article is this allowed. This is commercial application.

 

[augie47]

??

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I think your question needs some help

.... I have electric heat at 100 A. At this I point I am told I have Approximately 50A on the compressor. I am running #4 THHN to my heater.... .

If you have 100 A of electric heat the #4 is too small to begin with

Approximately 50A on the compressor. ....... want to tap with #8 THHN to the compressor,.

#8 would not be adequate for a 50 amp compressor

 

[Cavie]

Why would #8 not be adiquate for a 50a compressor???????

 

[augie47]

#8

#8

I am assuming (dangerous, I know) we are discussing a 50 amp compressor load and not a compressor marked with 50 amp MCA. Again, to me, we need more information. If it is a 50 amp MCA condition,as in Art 440, obviously #8 would be adequate. If it is a 50 amp comprerssor motor as in Art 430, obviously not. Let me re-state my original post..the #8 MIGHT NOT be adequate.

 

[jumpinjohnny]

I think your question needs some help




If you have 100 A of electric heat the #4 is too small to begin with




#8 would not be adequate for a 50 amp compressor

You are correct I actually have 83 amps so according 310.16 #4 will cover the heat and #8 will cover A/C according to 75 and 90 degree column.

 

[jumpinjohnny]

I am assuming (dangerous, I know) we are discussing a 50 amp compressor load and not a compressor marked with 50 amp MCA. Again, to me, we need more information. If it is a 50 amp MCA condition,as in Art 440, obviously #8 would be adequate. If it is a 50 amp comprerssor motor as in Art 430, obviously not. Let me re-state my original post..the #8 MIGHT NOT be adequate.

? MCA...It is an air conditioner maxfuse 50 Amp hence the tap off of the heater ckt noncoincident load.

 

[augie47]

Tap

Tap

o.k., I'll try again with the new info.( still a bit limited for me to picture--but thats me)
my opinion:
1st lets discuss the 83 amp heat load..actual load ? If so, 424.3 would require the branch circuit to be 103 amp rating. If you have taken that into consideration, and 83 is the calculated load, then the #4 would be adequate, however, a 90 amp breaker would be the maximum you could use.

You say airconditioner, and noconcident load (not a heatpump evidently) then the compressor could be "tapped" from the #4 feeder, assuming you provide the 50 amp max fuse as you stated.

To answer your original question, as I see it. If you have a #4 feeding a calculated heat load (not actual) of 83 amps, protected by the correct breaker (90 amps) and you have a compressor (nocoincident) with a 50 amp max fuse, you could tap the #4, provide 50 amp fuse protection and feed the compressor and obey the lengh rule on the #8 tap.

 

[e57]

Hmmm.... Back to the original question. Are these all "branch circuits" or feeders to panels that serve the branch? IMO you can not have taps on other than pretty specific items on the 'branch' portion. Where it would differ greatly if it were from a feeder.

See code and commentary in italics:

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 (G). No conductor supplied under the provisions of 240.21(A) through (G) shall supply another conductor under those provisions, 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 located as specified in that section.
-----------------------------------------------------------------

210.19(4) Other Loads. Branch-circuit conductors that supply loads other than those specified in 210.2 and other than cooking appliances as covered in 210.19(A)(3) shall have an ampacity sufficient for the loads served and shall not be smaller than 14 AWG.
Exception No. 1: Tap conductors shall have an ampacity sufficient for the load served. In addition, they shall have an ampacity of not less than 15 for circuits rated less than 40 amperes and not less than 20 for circuits rated at 40 or 50 amperes and only where these tap conductors supply any of the following loads:
(a) Individual lampholders or luminaires (fixtures) with taps extending not longer than 450 mm (18 in.) beyond any portion of the lampholder or luminaire (fixture).
(b) A fixture having tap conductors as provided in 410.67.
(c) Individual outlets, other than receptacle outlets, with taps not over 450 mm (18 in.) long.
(d) Infrared lamp industrial heating appliances.
(e) Nonheating leads of deicing and snow-melting cables and mats.
Tap conductors are generally required to have the same ampacity as the branch-circuit overcurrent device. Exception No. 1 lists specific applications in subparts (a) through (e) where the tap conductors are permitted with reduced ampacities. These tap conductors are required to have an ampacity of 15 amperes or more (14 AWG copper conductors) for circuits rated less than 40 amperes. The tap conductors must have an ampacity of 20 amperes or more (12 AWG copper conductors) for circuits rated 40 or 50 amperes.

Not sure if the installation would comply with 430.28 either???

But if these are feeder taps under 240.21(B)(2), I think you got it...

 

[haskindm]

Be careful in figuring the ampacity of conductors. Refer to 110.14(C) - unless you know that all terminations are rated for 75 or 90 degree conductors, you must use the 60 degree column of 310.16. 90 degree terminations are extremely rare. The 75 degree rating for #8 is 50-amps, so if your compressor draws 50-amps, 440.32 tells you to increase this by 125%, thus the number 8 would not be adequate. If the minumum circuit ampacity (MCA) is 50-amps AND all terminations are rated 75 degrees it would be OK.