110-7 Neutral Ground Test

[karl riley]

Re: 110-7 Neutral Ground Test

Dereck, I also take a voltage measurement between neutral bus and the panel at a subpanel as a quick check to see if the N/G connection is in the panel or nearby. Usually if it reads in the hundreds of millivolts it's OK, but as you say it depends on the load. Very rough indication but useful. I do love my SureTest.
Karl

 

[bennie]

Re: 110-7 Neutral Ground Test

Karl: What kind of gaussmeter do you have? I have two different ones and both will go off scale in a room with flourescent lighting.

The tie link, in a service panel, is for locating NG connections.

A dead ended circuit with L-1, L-N, and equipment ground in same raceway, a NG connection will not produce net magnetic fields.

 

[brian john]

Re: 110-7 Neutral Ground Test

dek:

If a Megger is utilized properly no damage will be done to equipment. The firm I have worked for testing every neutral in a building (26 stories) after the building was occupied. (This was supposed to be completed during construction but the contractor FORGOT). There was no damaged equipment; one needs to know the test equipment and how to properly utilize the equipment.

 

[wayne123]

Re: 110-7 Neutral Ground Test

I have found that if you have a gfi temporary feeder to the main panel in a new house that the gfi will trip if there is a N to G short anywhere in the system if you have all your N And G terminated in the panel and power to the main breaker.

 

[karl riley]

Re: 110-7 Neutral Ground Test

Bennie, when gaussmeters were coming on the market in the late 80s many had a linear response to frequency, which means they were only accurate (if that) at 60 Hz. Therefore they read too high if harmonics were present, such as from fluorescent ballasts.

I used to test every new gaussmeter that came on the market since I designed and marketed a very accurate one with a very flat frequency response (The MSI-AJK 95, now called the MSI-95).

Aside from the MSI, which is a single-axis meter with an external probe, I use the Bell 4080 triaxial for initial surveys. It has a good flat frequency response. Also The Emdex II for data recording and downloading, and Emdex Mate for simple data collecting.

A notoriously inaccurate meter is the Trifield, though on special request they can send you one with a flatter frequency response.

Tell me which ones you have. I have probably tested them (in a Helmholz coil).

And yes, if the N/G connection is contained by the circuit and limited to the EGC in an insulated cable, there will be no net current. In my experience that is unusual and the current usually gets onto other metallic paths.
Karl