Ground fault detection and monitoring

I would opt for permanent monitoring. In order to get them to pay attention set up timers that will force a shut down when timed out. It works for use here... 4 hours to fix the problem or else.

One installation I worked with had used 3 CT's (VT's? my electrical hat is sitting crookity) to light bulbs, say 480v-120v. When the bulb was out, you had a loss of phase. Really low tech. It's easy to connect the 120V, or whatever voltage you need to a PLC for monitoring.

The problem here is the contactors.
When using offline, you should close all contactors without having the main breaker on.
Now you can see a fault in any motor.
it means all contactors must be on, and this means you will have to redesign your system to have a separate power system for the control.
example when you switch on a light the fault can be on, but away when switched off.
when i am doing groundfault tests every piece of equipment must be switched on. especially the firepump (i work a lot on commercial ships.)

You make no mention of what ambient conditions exist around this equipment. I think that is most important to know. Humidity temperature variation, dust, etc etc. You also make no mention of equipment size or value.

From shipboard experience our two main problem sources were water oriented - either condensation or saltwater intrusion into equipment - especially DC.

I think at the minimum I would do meggar check on motors a week before startup. That may allow enough time to dry out a motor or do other repair work.

I do not see the justification for ground detector when equipment is deenergized. Meggar will work just fine.

Dan Bentler

leitmotif said:

You make no mention of what ambient conditions exist around this equipment. I think that is most important to know. Humidity temperature variation, dust, etc etc. You also make no mention of equipment size or value.

From shipboard experience our two main problem sources were water oriented - either condensation or saltwater intrusion into equipment - especially DC.

I think at the minimum I would do meggar check on motors a week before startup. That may allow enough time to dry out a motor or do other repair work.

I do not see the justification for ground detector when equipment is deenergized. Meggar will work just fine.

Dan Bentler

Click to expand...

I had all this typed out then read what Dan said ... I concur...:

If you have a megger, you should do a megohm test of all the motor circuits before you close the main circuit after being offline. I would think you will find your ground faults quickly that way and be able to isolate them to a particular motor circuit in most cases.

If you have contactors that all drop out, you can do a quick meg test of the motors from the bottom (disconnected output side) of the contactors. This will prove the whole motor circuit except for the contactor itself. If you expect or wish to test the contactor too, then yes you need remote power and a separate isolator (probably interlocked) and would have to disconnect wires from any VFDs or softstarters before you run the insulation test..

I don't like to touch any local motor disconnects during the test as opening and closing them (in the wet food environment especially) can mask symptoms or temporarily hide a fault. If I find a fault, then I look to split it among the cables and devices downstream but always try to test the whole circuit from the last protection device onward at first. During PM most of the time, it will test good, and you move on to the next motor.