Ampgard contatcorss

[rovineye]

I use several Cutler-Hammer AMPGARD vacuum-break starters (7200 volt/400A) in a 2 high cubicle. What I find disturbing is the ground scheme. When the contactor is opened and load disconnected, the contatcor is then shut to short the load side and ground. But the ground bar only grounds to the enclosure structure, not solidly to a ground bus. The path for this ground is thru sheetmetal screws and the like, most of which have paint under the heads. Continuity from the ground bar to my actual ground has been as high as 30 ohms. Normally I look for 0.1 ohms or less.
The resolution has been proposed to clean off the paint and get good continuity. I am going ahead with a ground lead directly from that ground bar to my ground bus (once I figure out where to connect it), to get a good solid ground when the load is grounded thru the contactor.

This is shipboard ungrounded system, and I have a good ground connection from hull to ground bus.

Anyone else use these contactors and noticed the same configuation?

 

[ScottyUK]

Your solution sounds much more reasonable than grounding through the panel steelwork. Is this a C-H panel or a third party type using their equipment? Either way it sounds like a horrible design. What does the manufacturer / panel builder say?


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If we learn from our mistakes I'm getting a great education!

 

[rovineye]

Scotty,
This is standard Cutler Hammer panel. That is what really surprises me. The response is that the ground path is sufficient as it is not carrying a fault, only potential grounding of the load circuit. But hey, that is from a salesman. On our next installation, later this year, I am gong to reject the installation which should force them into a formal answer.

 

[jraef]

It's true that the grounding of the output side is not intended to be the circuit ground conductor path. The purpose is mainly just to provide a path to ground to bleed off any residual cable capacitance. It doesn't need much.


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[ScottyUK]

Even if it isn't part of a fault-rated current path it sounds like it has been built down to a price instead of up to a standard. What happened to building things properly?


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If we learn from our mistakes I'm getting a great education!