I have a transformer that sets next to a 3500 amp switchboard. We feed the transformer from a breaker in the switchboard. Planning on using the tap rule of 25' we dip down under the slab to across the room to a main breaker panel that was supposed to be bottom fed but came in top fed which now makes our tap a few feet too long. Because we are going under the slab which is usually considered outside the building is there any exception that would allow this. I don't think there is but thought I would ask just in case I'm missing something.
Transformer Tap
- Thread starter ramIII
- Start date
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I see no provision which would all you to combine the two tap rules. What size tap? It might be easier to just use an OCPD adjacent to the transformer.
The tap is 600 amp. It's all set up with floor poured with panel cans mounted which were shipped ahead. This electrical room has zero extra space. We had to rework the whole layout to make everything fit. It would not fit as laid out by the EE of record. The panel has a 600 amp main with a 400 amp sub feed breaker on the top side. I just spoke to the local SQ D rep and he said we could swap the breakers from one end to the other which will make us code compliant. All the covers should still work. It's only a couple of feet but from experience this inspector will grant no leeway.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
If the inspector is a stickler with the ruler it's best to figure out a solution before you have to do it twice. If moving the CB allows you to stay within the 25' of tap conductors you're good.
We are going to move the CB and make it code compliant. Don't have time to order another bottom fed interior. Looks like it's our mistake as we missed changing to bottom fed on the approved submittals sent back to SQ D. 80 panels on this project. Some top fed some bottom fed. Now if we could not have changed the breaker I might have begged for a couple feet from the inspector but would have done so before pulling the cable. Would have asked since most of the tap is outside(under the building) could you give a little. Luckily we can make it work without asking to ask.
- Location
- Illinois
- Occupation
- retired electrician
I would count the underground as being outside, but with the outside transformer conductor rule in 240.21(C)(4), only the load end can be inside, so it only works for transformers that are installed outside.