We were recently asked to install a 75 KVA, 480v primary/ 120/208v secondary transformer to match other similar installations already installed at this R&D center. The primary was protected with a 90 amp, 480 volt breaker, and the secondary conductors which were 3/0 THHN, went to a 200 amp main breaker on a panel. However, previous to feeding this 200 amp breaker, a tap was made to another 200 amp main breaker and panel. All secondary wiring is 3/0, and the distances from the transformer to the first panel is 40' and an additional 25' to the second. Is this secondary protection Code compliant?
Transformer secondary protection
- Thread starter rifi
- Start date
- Status
- Location
- Logan, Utah
Transformer secondary conductors must be protected against overcurrent in accordance with one of the methods specified in 240.21(C).
240.21 does not permit transformer secondary conductors to be tapped before they terminate at an overcurrent protective device.
Chris
240.21 does not permit transformer secondary conductors to be tapped before they terminate at an overcurrent protective device.
Chris
- Location
- Illinois
- Occupation
- retired electrician
If both taps originate at the transformer it is compliant with the rules in the NEC. If the second tap is connected at a point other than the transformer, it is a violation as Chris said.
I'a af afraid, I'm a bit confused by the original post and I think that might be reflected in the answers. I am not clear as to the originating point of the two
so-called "taps" , but as stated above, if both orginate at the transformer and both meet the 240.21(C) rules, you would be compliant. I believe a 40 ft "secondary conductor would not comply unless it were outside.
so-called "taps" , but as stated above, if both orginate at the transformer and both meet the 240.21(C) rules, you would be compliant. I believe a 40 ft "secondary conductor would not comply unless it were outside.
- Location
- Logan, Utah
What i envisioned when I read the OP was a 40' set of transformer secondary conductors to the first panel where they tapped off the conductors to feed a second panel 25' away from the first panel.
If that is the arrangement then there are 2 violations 1st the 40' length of secondary conductors does not corispond to any of the rules in 240.21(C) for interior transformer secondaries, and second the tap on the secondary conductors.
Chris
If that is the arrangement then there are 2 violations 1st the 40' length of secondary conductors does not corispond to any of the rules in 240.21(C) for interior transformer secondaries, and second the tap on the secondary conductors.
Chris
- Status