Megger test live MDSB

[82angelfan]

Working on a hospital, doing a shutdown to install a new Siemens VL style with HG frame 150 amp breaker and cable in the main gear. The breaker has an added ground fault module installed that will have a CT on the ground. 3ph 4W.

Because of the phase of the job we cannot Megger the cables yet. Is it safe to Megger the phases at a later date and what could happen if we Megger the neutral and ground. The gear is only 15 years old.

I hate to schedule a second shut down as this is a reginal trauma center and we are working on an ER expansion.

 

[busman]

If you mean Megger the Neutral and Ground while operating, you will have a short circuit and the Megger will never reach test voltage. Did I miss something?

Mark

 

[82angelfan]

If you mean Megger the Neutral and Ground while operating, you will have a short circuit and the Megger will never reach test voltage. Did I miss something?

Mark

No, you didn't. The gear we are in is not the service entrance. I am assuming the neutral is not bonded. I was more concerned about damaging electronics in the breakers and surge protection. I believe my GF was planing on skipping megger between ground and neutral for that very reason. I also found an engineering forum that mentions testing in use 480 equipment at 500vdc instead of 1000vdc. Any experience with that?

 

[ATSman]

From what I remember from my field testing days, for the GF system to work properly, the neutral should only be grounded at one point: at the service entrance (or closest to the supply transformer.) Of course the neutral bus to grounding electrode link must be removed to get a proper reading. On a 480V system we used a 1000VCD megger. You can double check that voltage with the NETA Acceptance Testing specs. All testing needs to be done with the equipment de-energized, as busman stated. Yes you can megger the phase cables at a later shutdown date.

 

[82angelfan]

From what I remember from my field testing days, for the GF system to work properly, the neutral should only be grounded at one point: at the service entrance (or closest to the supply transformer.) Of course the neutral bus to grounding electrode link must be removed to get a proper reading. On a 480V system we used a 1000VCD megger. You can double check that voltage with the NETA Acceptance Testing specs. All testing needs to be done with the equipment de-energized, as busman stated. Yes you can megger the phase cables at a later shutdown date.

I was trying to avoid a later shut down. As it happens, we may be postponing all shut downs until work is complete. We were simply trying to piggy back off of a complete utility shutdown and install all the cable and breakers into the gear and then megger at a different time.

 

[ATSman]

I am confused, in post #3 you state the gear you are installing the breaker is downstream of the service entrance gear so why would a utility outage be required?

 

[82angelfan]

I am confused, in post #3 you state the gear you are installing the breaker is downstream of the service entrance gear so why would a utility outage be required?

A utility outage is not required. There will be a utility outage soon for So Cal Edison to replace transformers and a capacitor cabinet. We were trying to utilize this outage to tie in cable and install a breaker. We need to do this three times. Once for each system. We are working in a regional trauma center that handles emergencies from a large area. Every shut down requires careful planning.