CT shorting using terminal blocks 4

I have always used the shorting screws in the shorting terminal block and never had any problems.

It probably depends on the maintenance staff. If no one will ever remove a screw then option 1 should work just fine. On the other hand, if you live and work in the real world, I'd go with the jumpers (at the terminal block) and leave out the screws so that gear in service has no shorting screws in place.

I once visited a plywood mill that was having some problems with arcing ground faults on the primary distribution not tripping the main breaker. Upon inspection of the main breaker wiring, we found shorting jumpers on the backside of the terminal blocks for the bushing CT secondary wiring. It had come that way from the factory about 30 years ago. The relay had been religiously bench-tested every 3 years, but no one ever bothered with a primary injection test.

But back to actual subject - For a truly unused CT, I'd take a belt and suspenders approach - use wire jumpers and the shorting screws.

Oops, I mis-read your question. For an unused CT I would do both, screws and a jumper, and make sure it is documented, so 10 yrs from now, when someone wants to use the CT it is known where it is shorted.

As a CT manufacturer, I always vote for the shorting screws, as on most designs, the shorting bar is also grounded.

Shorting with jumpers works fine. Shorting on a grounded shorting bar is better.

To me, shorting bars/screws are very reliable and the risks of a relay not performing due to only pulling one shorting method outways the very minimal gains of having 2 shorting methods.

Just my $0.02 worth.

Thanks for the info.

We have been doing the belt and suspenders approach for shorting, but were looking at if we need a grounding jumper in addition to the grounding provided by the shorting screws.

David and Scott- it is interesting you both only want one method used, but it is the opposite one. I'll have to dig in some more and see if we have a consistent past practice here.

Do you use terminal block drawings that show the shorting screw locations?