Inspectors Liability

[brian john]

Went to a job site to test a newly installed service (480/277 1200 amp), GFP test, Megger and micro-ohm the Main CB. The neutral ground bond was in the wrong location, I explained to the contractor they needed to relocate the connection. The contractor installed the neutral ground bond to the load side of the neutral CT. They told me they have done numerous 480/277 over 1000 amp services and the local inspector requires them to bond the service in this way.

They wanted me to write a letter as part of my test report stating why I requested they relocate the bond connection. If indeed the inspector has been telling contractors to install the bond connection in this manner does he have any liability?

It is one thing for an inspector to wrongly require you to install anti-shorts in MC cable, then for him to require you to improperly install a bond connection that could possibility result in "nuisance" tripping or additional damage from a desensitized GFP operation.

EDITED FOR INCORRECT WORDING.....

 

[jim dungar]

The NEC requires that the ground fault SYSTEM be tested not just the ground fault RELAY. I do not believe that a neutral to ground bond on the load side of a GF sensor would pass a system test. The correct location for this bond is on the line side of the sensor. A typical GF system monitors the currents on the normal current paths only.

 

[mdshunk]

. The correct location for this bond is on the line side of the sensor.

Whaaa?

Then you have the potential for some fault current to bypass the CT, so it would seem. No?

 

[brian john]

JIM you are right my dyslexia kicked in or the 12 hours days this week edited and corrected.....

I hope this is what I meant to say.

I posted The contractor installed the neutral ground bond to the line side and should have said The contractor installed the neutral ground bond to the load side , MY APOLOGY

 

[jim dungar]

Whaaa?

Then you have the potential for some fault current to bypass the CT, so it would seem. No?

Marc,

Most GF systems do not measure the current on the ground conductor. They operate on the principle of the summation of the current in the normal circuit conductors (phases and neutral) being equal to zero. Any difference in excess of the setpoints results in a GF trip.

 

[brian john]

3-basic types of GFP protection in use today.

Ground return (not use as much as in the early days of 480/277 GFP) single CT on the neutral ground bond, sometimes used in Main tie Main switchboards.

Zero Sequence, this is usually one large window CT, in a no fault condition with a properly installed distribution system it should see Zero "0" current, under ground fault conditions it will measure the ground fault current.


Residual, comprised of 4 separate CT operates similar to the Zero Sequence.

 

[brian john]

The GFP is comprised of 3 (sometimes 4) basic components, CT or CT's GFP relay and trip coil, or flux coil or a control transformer.

We test the Control Transformer (connect voltage to verify proper operation of the GFP), pass current through the GFP CT and check for current pickup of the GFP relay at all factory presets for current, we then perform a time test of the GFP and switch operator (flux trip or trip coil) at the recommended current and delay setting. we also remove the neutral disconnect link and megger the downstream neutral to ground, if possible with the switch open we megger the line, load and across the open power contacts, lastly we measure the contact resistance of the power contacts.

If it is a new system with Residual GFP we will check all CT's. If it is a main Tie Main we will check all scenario?s of operation for correct GFP operation.

Not sure what else you would require, but pretty much I think that covers it..With exception of GFP Zone interlock systems.