amperage to ground at hospital

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lmac

Member
We are setting gfi trip settings at a hospital and the general Electric tech. called me a told me he was reading 30A to ground at the main switchboard.The main switchboard is made up of two sections of outdoor switchboard. the orginal is a 4000A MLO. We added a second section with a 2500A MCB. when we open the 2500A MCB to ampe reading drops to 1.5 to 2 amps.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: amperage to ground at hospital

If the 2500 amp section feeds any panels, look for an illegal bonding screw.
Don
 

brian john

Senior Member
Location
Leesburg, VA
Re: amperage to ground at hospital

1. You may have cross connected neutrals from two separated panels.

2. Something a simple as a screw cutting into a neutral (2" switch mounting screw).

3. A 4 3 wire circuit with a 4 conductor tied into the neutral bar in the panel and grounded at the load.

4. As mentioned a neutral grounded downstream of the service in a panel or transformer.

5. Defective equipment with a neutral problem.

I have seen all of these. You can use a multi meter and a flexible CT to get close to the cause of this problem
 

catchtwentytwo

Senior Member
Re: amperage to ground at hospital

Check for any panels that have isolated grounding bars. I've seen neutrals "accidentally" terminated on them because both are "isolated" from the panel can. Another possibility is an incorrectly connected isolation transformer.
 
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