NETA Level III
Something to keep an eye out for if you come across EATON Magnum DS switchgear. The main circuit breaker shorting block is located in close proximity to grounded cubicle hardware, which can cause a short to develop in the CT secondary wiring circuit.
Long story short, this issue was discovered when attempting to megger the CT secondary wiring during acceptance testing. After lifting the known single ground, continuity tests revealed a short remaining somewhere in the circuit.
This was obviously unexpected as there should only be a single ground. It took about 15 minutes to narrow the problem down to the shorting block, which was was lifted from where it was mounted and tested fine.
Once put back in place, the short returned. At first it was thought that the block insulation was defective, but after a close visual inspection it was noticed that the shorting pins were making slight contact with an adjacent mounting screw.
Short.
No Short.
As a temporary fix, electrical tape was put over the screw to give some insulation. It was recommended that the contractor swap the position of the two blocks.
Photos were taken once everything was back together, ground was lifted during the test.
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