240.21 existing

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mparkstexas

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I am working on a job with a 225kVA transformer 277/480 primary, 120/208 3 phase secondary. There are 2 sets of 4#500, 1/0G in 4"C going to an existing 800 MCB panel, "DPL2" which is 10' away from the transformer.

I am putting a 225A panel and tapping off this panel, "DPL2", and putting on new equipment for the restraunt remodel.

I got a comment from the city that the secondary feeder from the transformer is "violating the TAP fules. Please upsize or reduce OCP in DPL2." I was looking at 240.3.B and 240.21.C for reference.

Any ideas on how I can respond. Or what would be the best design to correct the issue?

Thanks,
 
CHeck my math
your 225kVA has a sec FLA of 625A an your paralleled 500kCmil would yield a capacity of 760A.

These Sec TAp conductors per 240.21 (C) (2) re limited to a conductor length of 10 feet (not distance between enclosures)
240.21(C) States in part "

The provisions of 240.4(B) shall not be permitted for transformer secondary conductors.

You need a 700A OCPD or larger conductors.

What Code are your working under and does your jurisdiction require you to bring current installation to the newest Code???
 
Which code cycle are you on?

See 240.21(B)

240.21(c)(2)(2) vs 240.21(c)(3) Conductors exceed 10", not the length of the raceway.

And the FPN

Edit to add - Answers based on 08 NEC
 
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The wording "The provisions of 240.4(B) shall not be permitted for transformer secondary conductors." was added in the 2005 Code.
The original installation may have been completed prior to that Code being adopted in your area.
You might approach the AHJ with the possibility that you not disturb the existing installation and feed your 225 amp panel directly from the transformer (provided the primary complies with the 125% protection rule)
 
I don't see a delta-wye listed in 240.4(F). Think that kills the 125% rule. It's pretty limited application.
 
Rockyd said:
I don't see a delta-wye listed in 240.4(F). Think that kills the 125% rule. It's pretty limited application.
Click to expand...

450.3(B) the table protection of trans 600V or less
this one qualifies for pri ocp@125% eliminating additional protection of the secondary.
 
I don't believe it does per 08 NEC 240.21.(c)

We are talking about the feeder, not the transformer.
 
augie47 said:
The wording "The provisions of 240.4(B) shall not be permitted for transformer secondary conductors." was added in the 2005 Code.
The original installation may have been completed prior to that Code being adopted in your area.
You might approach the AHJ with the possibility that you not disturb the existing installation and feed your 225 amp panel directly from the transformer (provided the primary complies with the 125% protection rule)
Click to expand...

I'm pretty sure Augie was refering to the portection requirments for a trans per 450.(3)(B).

The conductors are protected per 240.21(C) (as you mention). (2) (etc).

actually the more I look at the op the pri ocp is critical per part (4) where as these conductors appear to leave the enclosure they are fed from and terminate in a panel .
 
augie47 said:
The wording "The provisions of 240.4(B) shall not be permitted for transformer secondary conductors." was added in the 2005 Code.
The original installation may have been completed prior to that Code being adopted in your area.
You might approach the AHJ with the possibility that you not disturb the existing installation and feed your 225 amp panel directly from the transformer (provided the primary complies with the 125% protection rule)
Click to expand...
Gus,
Yes those words were added for the 2005 code, but that was not a code change. The previous code required the same thing, but many were not following the code rules because they did not really read the words. To make it 100% clear new language was added for the 2005 code.

The wording in the 2002 and earlier codes required that the conductors have an ampacity that is not less than the device that the conductors are terminated at. The rule in 240.4(B) does not change the maximum permitted ampacity of the conductor...it only changes the maximum permitted OCPD for that conductor. A transformer tap consisting of parallel 500 kcmil terminated on an 800 amp breaker was not permitted by the rules in the codes previous to 2005.
 
Thanks Don, I knew the right verbage would be here sooner, or later. :)
 
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