Transformer Secondary Taps

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stevenje

Senior Member
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Yachats Oregon
1) 150KVA 480/208V transformer with a primary fused disconnect next to it.
2) Three 200A 208/120V fused disconnects fed from transformer within 10 feet.
3) The three disconnects need to have individual line side feeder conductors from the transformer.
4) You can not have the three disconnects tap off a set of secondary conductors from the transformer (in a gutter).
Does this sound correct?
Thank you.
 
My interpretation of the wording in 240.21 is that a single set of secondary conductors can serve only one load, or you can serve multiple loads but each load must have its own set from the transformer. So yes I agree you cant have one set then split it up further.

Regarding your #2, take note of note #2 in table 450.3(B). That would only be compliant if secondary protection is not required.
 
electrofelon said:
...Regarding your #2, take note of note #2 in table 450.3(B). That would only be compliant if secondary protection is not required.
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I believe that the three 200 amp OCPDs are compliant with Note 2 to Table 450.3(B). The secondary FLA is 416 and a 125% of that is 520 amps. Note 1 permits me to use a single 600 amp OCPD. Three 200 amp devices does not exceed 600 amps, so they are permitted.
 
Conductors requiring OCPD from a transformer secondary per 240.21(C), cannot terminate in anything other than a single OCPD. The conductors need to go directly from their source, to the OCPD, without any opportunity for current to branch elsewhere. You can route multiple secondary conductor circuits of the same transformer in the same wireway, but branching multiple taps from a common secondary conductor wouldn't be permitted.

Once on the load side of the first OCPD, you can feed as many loads as desired. Provided you protect the branch circuits as the NEC requires in general.
 
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