Primary Injection Test for Ground Fault Protection 230.95

[ron]

Is it typical in your installations where ground fault protection is required per 230.95, that the performance requirement found in 230.95(C) is done with primary injection testing or with some other less "all encompassing" method?
I believe that primary injection testing is the "only" real way, but I'm discussing the issue and am looking for other similar or dis-similar opinions.

 

[zog]

Is it typical in your installations where ground fault protection is required per 230.95, that the performance requirement found in 230.95(C) is done with primary injection testing or with some other less "all encompassing" method?
I believe that primary injection testing is the "only" real way, but I'm discussing the issue and am looking for other similar or dis-similar opinions.

There isnt really another option, you can "Fool" the CT by using multiple wraps from your test lead but that is about it. Remmember you are not just testing the relay you are testing the CT and all woring to ensure it was properly installed. A self test only tests the relay, nothing else.

 

[rcwilson]

Primary InjectionTesting of Ground Fault Units

Primary InjectionTesting of Ground Fault Units

Othr test methods cannot find problems like:
Reversed neutral CT connections on 4-wire systems,
Neutral grounded downstream,
Improper interlocks on Main-Tie-Main switchgear with two sources,
Correct connection of neutral CT to correct breaker in switchgear,
Matching neutral and main CT ratings, (1200A N CT on 2000 A breaker)
Incorrect routing of cables through zero-sequence CT's.

These are typical of the problems I used to find in services and switchgear when checking ground fault protection on 480 V gear.


When I was in the testing business, we found problems with about 30% of the ground fault installations.

 

[brian john]

Reversed neutral CT connections on 4-wire systems,

Zero sequence and this is not relevant, residual and it is an issue.

Neutral grounded downstream,

HOW?

Improper interlocks on Main-Tie-Main switchgear with two sources,[/quotes]

Interlocks? or proper wiring of contacts and GFP wiring?

Incorrect routing of cables through zero-sequence CT's.

HOW?

 

[jim dungar]

Is it typical in your installations where ground fault protection is required per 230.95, that the performance requirement found in 230.95(C) is done with primary injection testing or with some other less "all encompassing" method?
I believe that primary injection testing is the "only" real way, but I'm discussing the issue and am looking for other similar or dis-similar opinions.

The NEC article requires testing of the ground fault SYSTEM not of the individual components. The ground fault system includes the: GF relay, GF sensor(s), OCPD trip mechanism, and the neutral-ground bonding. Secondary injection only tests the OCPD trip and the GF relay. Some GF sensors contain a test winding, which functions the same as a primary injection testing, but most circuit breakers use an external neutral sensor without a self test winding.

 

[ron]

While I agree with the statements made, I'm being told that I'm being too hardheaded and that most AHJ's accept secondary injection testing or by simply pushing the test button on the GFP relay (if there was one).

 

[brian john]

NO you are not hard headed you are being what some folks PROFESSIONAL.

 

[mayanees]

... Primary vs. Secondary Injection testing

... Primary vs. Secondary Injection testing

I think good practice is to use Primary injection testing as the initial acceptance test, then on periodic maintenance testing - check CT continuity and employ secondary injection.
JM

 

[zog]

I think good practice is to use Primary injection testing as the initial acceptance test, then on periodic maintenance testing - check CT continuity and employ secondary injection.
JM

I would say that is very reasonable

 

[rcwilson]

Brian - you have done a lot of testing. My wording was not precise.


{QUOTE=brian john]Zero sequence and this is not relevant, residual and it is an issue. [/quotes]

Correct - reversed neutral CT wiring only creates issues on 4-wire residual systems where the three phase and neutral CT signals must all add to zero. Usually reversed wiring leads to false trips.

Neutral grounded downstream.

HOW?

Primary Injection by itself cannot find a grounded neutral. But part of a good GF test is to lift the neutral-ground bonding jumper and verify the neutral is floating. Of course this must be done de-energized. A bonding screw left in place on a downstream panel is the usual culprit. Some instruments will incorrectly read 277V ballasts as neutral-ground shorts.

Improper interlocks on Main-Tie-Main switchgear with two sources,[/quotes]

Interlocks? or proper wiring of contacts and GFP wiring?

When there are two sources, auxiliary contacts and/or interconnection of CT wiring for the Mains and Ties is needed to prevent a ground fault looking like a large single phase load on one transformer and to prevent false trips.

Incorrect routing of cables through zero-sequence CT's.

HOW?

- I've seen neutral conductor routed backwards through the CT. Another installation did not have any condutors through the CT. Both tested fine with the front pushbutton.