Megger vs GFPE

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George Stolz

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Windsor, CO NEC: 2017
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Service Manager
Is there a problem with leaving conductors connected to the load side of a GFPE breaker in the off position, and meggering them? Could it damage the breaker?
 

big john

Senior Member
Location
Portland, ME
Is this a large frame power circuit breaker? Gnerally no, there's no risk from megging those.

Some insulated case breakers with fancy trip units have voltage taps to the bus. There's often a way to defeat those for testing, read the manual.

If this is a small molded case breaker, I would be very careful about megging it, though.
 

ActionDave

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Durango, CO, 10 h 20 min from the winged horses.
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https://www.dropbox.com/s/1rkwz3117qnu2le/2015-10-23 16.16.04.jpg?dl=0

https://www.dropbox.com/s/nh465bn48dpxo37/2015-10-23 16.16.12.jpg?dl=0

This is the breaker is question. An aside question: is it legal to supply a 400A rated switch from this breaker?
First link is dead. Second link shows a sticker that says PASSED and an 800 number, call that if you have any questions I suppose. To the right is a sticker that says 600A.

I think your good. Any more info needed, use that 800 number.
 

Cloud

Member
Location
PH/VN
Amperes indicates how much load can the switch provide. It doesn't mean that all of the 600 A from the main will flow through it. Depends on what equipment is connected. Is it a fuse disconnect?
 

George Stolz

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Location
Windsor, CO NEC: 2017
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Service Manager
It's a 600A frame with a 600A rating plug supplying a 400A rotary switch ahead of a VFD for a large motor (200 HP 480V ?). Currently the 600A trips without any indication as to why at the load side of the rotary switch (data logging on site shows no abhorrent behavior before the 600A trips.)

I suspect the outdoor feeder (overhead in RMC on a rack) has an intermittent ground fault that only presented itself during a 48-hour period of sustained rain. Other symptoms include a fair amount of slag remnants on the rotary switch denoting an arc, possibly due to water getting into the enclosure with the rotary switch and the VFD.

Before I order a new switch I want to be sure that the feeder is good, but am concerned that I might damage the GFPE in the breaker supplying the circuit. I would just as soon not have to suit up and remove the conductors from the breaker to test them.
 

Cloud

Member
Location
PH/VN
In my case, if in doubt about the GFI, I'll just isolate the cables to test downstream. But yeah, I think for the breaker this size, it is safe to test it directly as sir big John said.
 

George Stolz

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Location
Windsor, CO NEC: 2017
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Service Manager
That trip unit is a "Microversatrip Plus" There are no voltage connections, only CTs. I've tested tons of those at 1kV, you'll be fine.

Suppose I tested them and witnessed a peculiar cadence to the reading at 250VDC - instead of infinite resistance steady, it blipped to infinite in a steady one second rhythm. The rest of the time it hovered at a lower value that I don't recall - somewhere over midrange for 250 VDC. All three phases displayed the odd rhythm. What would that tell you?
 

big john

Senior Member
Location
Portland, ME
Our analog meggers will flutter when the battery is low, I would eliminate test error first.

Second, if you're testing the circuit and not just the main, I would assume there was still something connected to ground causing that reading. If the flutter is hapoening like clockwork then something with an electronic circuit is causing it: Look for power metering
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
Our analog meggers will flutter when the battery is low, I would eliminate test error first.

Second, if you're testing the circuit and not just the main, I would assume there was still something connected to ground causing that reading. If the flutter is hapoening like clockwork then something with an electronic circuit is causing it: Look for power metering

A flutter to zero or a flutter to infinity?
 

big john

Senior Member
Location
Portland, ME
A flutter to zero or a flutter to infinity?
They usually just swing somewhere in the neighborhood of what the actual reading is.

If you're seeing full-scale deflection, I think something in the circuit is causing it. Simple check: Meg a separate circuit. If it holds steady, you know its not a megger problem.
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
By "power metering" I assume you're speaking of CTs clamped around the conductors, no direct connection right? They must have that, because the landlord is supplying this one motor from their MDP, and sending the tenants a bill.

I'll proceed with the hot work permit, get into the MDP and get rid of the CTs and test again. I bet the problem is just water infiltration at the outdoor enclosure and the conductors are fine.

Thanks John. :cool:
 

big john

Senior Member
Location
Portland, ME
By "power metering" I assume you're speaking of CTs clamped around the conductors, no direct connection right?
Your CTs are fullt insulated for the bus voltage, they should not cause a problem.

I am thinking that there are actual voltage taps somewhere, like to a digital EMON submeter. Also look for surge protectors or PF correction equipment.
 
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