Hey everyone,
Im a newer contractor Journeyman Lineman and im looking for some feedback on some things ive witnessed but am trying to reason, which is when paralleling in fused cutouts, closing one causes the other to drop open. The common scenario is replacing a section of a feeder of 3 phase primary conductor, then swaping load from old to new. for example lets say the feeder is 13.8kv/ 7970 multi grounded wye, radial feed, wire replacement mid-feeder. The wire pull will consist of replacing exsisting 336 aluminum primary conductor to 477 aluminum conductor. the existing conductor to be replaced will be out-rigged on the pole to make room for the new conductor. once the new conductor is installed, it is dead-ended to the pole where we install permanent taps from the source side from existing conductor to the new, energizing the new wire, and temporary taps are made from the out-rigged (old) wire to the new wire to keep the out-rigged wire energized since this wire still carries the load. At the other end of the new wire install, again permanent taps are also made from new to existing and if temporary taps from old to new are not installed at this end as well, we can experience the issue. The issue is when swapping load from old to new. for example, lets say we start at the source side of the new wire and the first load to swap is a 3 phase 75kva transformer bank 120/208 grounded wye with each transformer behind a 10 amp fused cutout. to avoid an outage we would install fused 10 amp cutouts in parallel with the exsisting ones on the old wire to the new wire. when closing in each of the new cutouts the old one would open within a second or so. any ideas? installing temp taps from old to new at both ends of the wire negates this issue, but i guess im just having trouble understanding why. thanks!
Im a newer contractor Journeyman Lineman and im looking for some feedback on some things ive witnessed but am trying to reason, which is when paralleling in fused cutouts, closing one causes the other to drop open. The common scenario is replacing a section of a feeder of 3 phase primary conductor, then swaping load from old to new. for example lets say the feeder is 13.8kv/ 7970 multi grounded wye, radial feed, wire replacement mid-feeder. The wire pull will consist of replacing exsisting 336 aluminum primary conductor to 477 aluminum conductor. the existing conductor to be replaced will be out-rigged on the pole to make room for the new conductor. once the new conductor is installed, it is dead-ended to the pole where we install permanent taps from the source side from existing conductor to the new, energizing the new wire, and temporary taps are made from the out-rigged (old) wire to the new wire to keep the out-rigged wire energized since this wire still carries the load. At the other end of the new wire install, again permanent taps are also made from new to existing and if temporary taps from old to new are not installed at this end as well, we can experience the issue. The issue is when swapping load from old to new. for example, lets say we start at the source side of the new wire and the first load to swap is a 3 phase 75kva transformer bank 120/208 grounded wye with each transformer behind a 10 amp fused cutout. to avoid an outage we would install fused 10 amp cutouts in parallel with the exsisting ones on the old wire to the new wire. when closing in each of the new cutouts the old one would open within a second or so. any ideas? installing temp taps from old to new at both ends of the wire negates this issue, but i guess im just having trouble understanding why. thanks!