- Location
- New Jersey
- Occupation
- Journeyman Electrician
A fellow electrician called me yesterday asking me about a transformer he was troubleshooting. Seems that the trans was sporadically blowing the primary CB. After opening the cover this is what he found:
-3 wire, 208 volt (Wye)primary/ 3 wire, 480 volt(Delta) secondary (Delta/Wye wired in reverse)
-XO bonded to the transformer case, burnt off completely.
Secondary voltages (approximate):
H1-H2= 490, H2-H3= 490, H1-H3= 490
H1,H2,H3 to transformer case=280 volts.
One question is why is there any voltage reading from H1, H2 or H3 to the transformer case if the Delta secondary is ungrounded? My only guess is that it had something to do with reading these voltages with a digital meter.
The other question is regarding the bonding jumper burning up on the XO. My guess is that it was carrying current back to the utility transformer XO secondary on the grounded metal raceway feeding the transformer. Any ideas?
-3 wire, 208 volt (Wye)primary/ 3 wire, 480 volt(Delta) secondary (Delta/Wye wired in reverse)
-XO bonded to the transformer case, burnt off completely.
Secondary voltages (approximate):
H1-H2= 490, H2-H3= 490, H1-H3= 490
H1,H2,H3 to transformer case=280 volts.
One question is why is there any voltage reading from H1, H2 or H3 to the transformer case if the Delta secondary is ungrounded? My only guess is that it had something to do with reading these voltages with a digital meter.
The other question is regarding the bonding jumper burning up on the XO. My guess is that it was carrying current back to the utility transformer XO secondary on the grounded metal raceway feeding the transformer. Any ideas?