i have a job I’m probably going to start in the coming weeks for (3) temp chillers. The job is for a major university. They have given us the go ahead to tap their university owned utility transformers which supply a building. They are going let us tap three transformers. As there is several different feeds that could be switched over in the gear room. Each chiller has a max over current protection of 1000 A. my plan was to tap the secondary side which is 480 V and run rigid out of a box to a 1200 amp disconnect and then fuse the conductors down to 1000 amp and then run to boxes for the temporary chillers. I’m just having a hard time understanding that tap rules and I’m getting kind of confused because I’ve never done something like this on a utility transformer. Does anyone have any insight on this? I greatly appreciate the help. I understand my run is not gonna be more than 25 foot. Should be somewhere around 15 foot before I hit the disconnect. I know I need to be 1/3 of the overcurrent device. But is there anything else I should take into consideration?
Outside tap question
- Thread starter Cursitti
- Start date
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
I think you might mean customer owned MV transformers with LV secondaries.
Are these outdoor transformers?
If these are customer transfomers your secondary conductors need to be tapped per the requirements in 240.21(C). Remember distances are for the 'one way' conductor length not the physical distance.
@jim dungar yes they are outdoor mv transformers with 480v secondary. So would i take the primary to secondary ratio and multiply by 1/3? For my feeders to the disconnect?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Master Nater
Senior Member
- Location
- Midwest
- Occupation
- Electrical Magician
do you know what the difference between a "feeder tap" and a "service conductor" is?
the utility.
the utility.
I understand which is feeder and which is service. I’ve just never delt with outside stuff off a customer owned transformer. Their engineer is laying this in my lap. I just wanted to ask opinions. I tend to second guess myself.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
You could also use the rule for unlimited tap length for outdoor installs.
@jim dungar that’s what i was thinking as well but I’ve never ran into this situation and just wanted to make sure i was heading into the right direction.