Troubleshooting parallel fused cutouts

[holt.liner]

I got a wire replacement project and we're upgrading a section of 13.8kv feeder, going from 336 to 477 aluminum.
During the load transfer, when paralleling fused cutouts to swap a 75kva bank, closing the new cutout causes the old one to trip open immediately.
This only happens if we don't have temporary jumpers connecting the old and new conductors at both ends of the new section.
Anyone can explain why using those temporary taps prevent the tripping?

 

[WiredUp]

It seems that the temporary jumpers play a crucial role in balancing the impedance between the old and new sections. If they're not in place,you'll get a voltage difference when you close the new cutout,which can lead to a surge of inrush current and trigger the old cutout to trip. By using the jumpers, you can equalize that difference and stop the trip from happening. This is a typical precaution during these transfers to prevent such issues. Hope Ive answered your question

 

[Pawcasso]

I got a wire replacement project and we're upgrading a section of 13.8kv feeder, going from 336 to 477 aluminum.
During the load transfer, when paralleling fused cutouts to swap a 75kva bank, closing the new cutout causes the old one to trip open immediately.
This only happens if we don't have temporary jumpers connecting the old and new conductors at both ends of the new section.
Anyone can explain why using those temporary taps prevent the tripping?

well, you don't use those temporary jumpers (taps), closing the new cutout makes the load transfer create a quick, unbridged surge. This current has nowhere else to go and can overload the old, already working cutout, making it trip instantly.
now, the jumpers, on the other hand, create a smooth, direct bypass between the old and new wires. This means the current can flow continuously, avoiding that sudden overload or imbalance at the cutouts during the switch, so the old one doesn't trip!

 

[VodkaVibe]

well, you don't use those temporary jumpers (taps), closing the new cutout makes the load transfer create a quick, unbridged surge. This current has nowhere else to go and can overload the old, already working cutout, making it trip instantly.
now, the jumpers, on the other hand, create a smooth, direct bypass between the old and new wires. This means the current can flow continuously, avoiding that sudden overload or imbalance at the cutouts during the switch, so the old one doesn't trip!

Sounds like the old fuse is just being a drama queen and can't handle the new kid on the block without proper introductions (the jumpers)! lol