Taps from Transformer Secondary

[richwaskowitz]

I would really appreciate it if someone could verify the following is Code compliant with 240.21(B), and that there is no other pertinent section I could be violating.

I provided a sketch. I hope it is visible.

1. The taps are less than 10 feet
2. Taps are in raceways
3. Taps are 10 AWG (30 A )
4. Taps terminate in 30 A fused disconnects with 30 A fuses
5. The ampacity of each tap (30 A) is not less than 10% of the 150 A primary protection (15 A)
6. The 93 kVA transformer primary protection is set at 150 A (FLA x 133%)
7. This is in an industrial setting
8. The total of the four circuits does not exceed 125% of the FLA of the secondary of the transformer (112 FLA x 1.25 = 140 A)

 

[richwaskowitz]

Did I just read in 240.4 (F) that I cannot do what I depicted because those conductors would not be considered protected by the primary device???? Does this stop me right here?

 

[david luchini]

Did I just read in 240.4 (F) that I cannot do what I depicted because those conductors would not be considered protected by the primary device???? Does this stop me right here?

What you are showing is acceptable per 240.21(C).

 

[richwaskowitz]

Doesn't 240.4 (C)(1) (the last sentence) say the same thing as 240.4 (F) in that in my case where the secondary is 3 phase delta-wye, the conductors cannot be considered protected? I still think that it is saying I cannot do because of the wye secondary.

 

[david luchini]

8. The total of the four circuits does not exceed 125% of the FLA of the secondary of the transformer (112 FLA x 1.25 = 140 A)

Nothing would prevent the four circuits from exceeding 125% of the FLA of the secondary of the transformer.

 

[david luchini]

Doesn't 240.4 (C)(1) (the last sentence) say the same thing as 240.4 (F) in that in my case where the secondary is 3 phase delta-wye, the conductors cannot be considered protected? I still think that it is saying I cannot do because of the wye secondary.

They are protected by the 30A fuses, not by the primary OCPD.

 

[richwaskowitz]

I say the transformer is protected from overload by the 4 30 A circuits. 4 x 30 = 120 = less than 125% of FLA of 112 A.

What I am nit-picking over is 240.4. Is that rule absolute or does 240.21 (C) (2) OR (3) trump 240.4? Now I think I CAN do it like said earlier.

 

[david luchini]

I say the transformer is protected from overload by the 4 30 A circuits. 4 x 30 = 120 = less than 125% of FLA of 112 A.

It is...I'm saying it doesn't need to be. You could have 10 30A fused disconnect switches on the secondary, if you wanted.

What I am nit-picking over is 240.4. Is that rule absolute or does 240.21 (C) (2) OR (3) trump 240.4? Now I think I CAN do it like said earlier.

240.4 says that that multiphase transformer conductors shall not be protected by the primary OCPD. That's fine. 240.21 says the protection of the secondary conductors doesn't need to be at the point the conductors receive their supply. In this case, you have 4 sets of fuses on the secondary protecting your 4 sets of secondary conductors.

In other words, you are NOT protecting the secondary conductors with the primary OCPD, so you are in compliance with 240.4.

 

[richwaskowitz]

Oh. I know I should have stayed in law school. I get tied up in the language and sometimes I end up talking myself into something that it really doesn't say. Unless someone else chimes in and says something to the contrary (not that I don't accept your help here) I will go ahead and implement this scheme.

Thanks again.