Ground testing

[Richard L. Bennett]

Paul and Bob

Thanks for the help - I hope some one can help out a little -

rlb

[Pierre Belarge]

Iam new to this forum ,but I have been in the electrical industry for many years.

This thread is really a moot topic.

There is no real reason known for the 25 ohms to ground for a ground rod. Grounding in a service of any kind does not help in the opening of a circuit breaker or fuse.

One of groundings purposes is for lightning or some other transient event that may cause significant damage to the building through the electrical system.

For homes, grounding protection for transients and lightning does not improve significantly with much lower resistance (ohms). Lightning is not like the current we make and use, it behaves differently, of which I will not go into detail here. There are some areas such as central Florida which will benefit from more grounding (reflected in the more restrictive local codes), but generally this is not so.


Testing of grounding systems for dwelling units is generally a waste of the consumer's money. I can see other services you can offer that would benefit them more... more bang for the buck.

Learning how to use this equipment well takes training and experience over time. A good visual inspection of the grounding system is generally sufficient. Look for loose connections, look for corrosion or broken conductors. Look to see if there is a connection period.

Also remember that certain testing and other inspections of the electrical systems may legally require you to use the proper PPE.

[Paul W. Abernathy]

Very relevant if a HI wants to know about it and what the NEC mandates for it...not every HI will attempt to test it or wish to deal with it.

The information here is to explain the many issues that HI's get asked about and run into....not to train them to test the 25 or less ohms.......in the end the HI makes that choice regardless but I think we as a whole agree it is not something the HI should deal with.

[Greg Fretwell]

I have worked on some pretty big projects and the only time I know of them testing ground electrode resistance was toll booths and radio tower equipment shelters. Both are significant lightning targets. They get Ufers, ground rings with radials and long rods (40' is not uncommon).
Inspectors usually just insure there is an accepted ground electrode like a Ufer or two rods. If you are in a place that never uses plastic (strong plumber union state) the water pipe is an excellent electrode by itself. The NEC requires the suplimental electrode because it is a "national" code and plastic is pretty popular in a lot of places.

[Jay Moge]

Originally Posted by pabernathy

Very relevant if a HI wants to know about it and what the NEC mandates for it...not every HI will attempt to test it or wish to deal with it.

The information here is to explain the many issues that HI's get asked about and run into....not to train them to test the 25 or less ohms.......in the end the HI makes that choice regardless but I think we as a whole agree it is not something the HI should deal with.

I'm with you on this thought Paul. knowlage is powerfull, and when a client asks me "what should the ohms reading be on the ground for my house?" well now i have the answer, i'll test it and proove to my client that i am knowlagable above and beyond my intended scope. not to seem "overqualified" but it helps boost the confidence of my client with my service. people are more comfortable with someone whose knowlage is greater than it needs to be for that task. if i asked a carpenter how to build a house, he'd know how, but ask a strucural engineer, and he'll know how and why. as a HI, i feel we need to know and learn as much about every aspect of a house in order to have the knowlage needed to do a good job. if we don't know it, and it's wrong, the client will never know and it won't look good on us.

[Pierre Belarge]

Yes you tell them it is required to be 25 ohms... then you do this testing... they will procede to ask you why is it required to be 25 ohms? What will be your answer... there is no answer as to the origin of why 25 ohms was chosen. It is not known and most who understand enough about grounding are not able to figure this out, as the figure of 25 ohms makes no sense at all.

Testing for grounding is really in the realm of Cell towers and the like as they need very low ohm values. So all kinds of earth studies and ground resistance measurements are taken yearly or more often to make sure the resistance is stable.

If you really want to prove to your customer how knowledgeable you are, tell them that the resistance to ground is not relavent, just that there is a path to ground for the potential lightning or utility transients.

I have a ground rod tester - there is approximately an 8% difference in testing than the 3 point testing. I have been testing rods for a couple of years and in the northeast here, I average around 120 - 200 ohms for single rods and 70 - 110 for two rods. Far from 25 ohms, but still effective for the lightning and transient events.

[Bob Badger]

Originally Posted by Pierre Belarge

I have been testing rods for a couple of years and in the northeast here, I average around 120 - 200 ohms for single rods and 70 - 110 for two rods. Far from 25 ohms, but still effective for the lightning and transient events.

And at 120 to 200 ohms still comply with the NEC as long as the grounding electrode system does not consist of just one single ground rod.

A single uffer at 120 ohms meets code.

Just a little background on Pierre he has been an successful EC, an electrical inspector and he is an instructor.

He is also a contributing editor to electrical handbooks,

Trust him when he talks about grounding he is both a knowledgeable man and one that is consumed with electrical safety.

He has shut down a concert over bad cords, he is not one to blow of safety.

Bob

[Paul W. Abernathy]

Pierre,


The idea here was to explain the 25 OHMs or less requirment as listed in the NEC YET to meet the code (2) rods are being demanded in most areas regardless and (2) rods will meet the NEC requirement simply based on the acceptacle by the NEC as it is written.

[Richard L. Bennett]

All good information

I sort of looks like we are pulling the layers off an onion

Does anyone ever measure current to ground or is this just a Telecom thing?

Me thinks I better be 0

I did some internet checking and the use of DC to check a ground is ok but one must be sure that there is not galvanic (hope I spelled that right) action

At one time it was the norm on a 3-4 point test before the test equipment of today was developed

rlb

[Bob Badger]

Originally Posted by rbennett

Does anyone ever measure current to ground or is this just a Telecom thing?

Me thinks I better be 0

In a typical house (or any US building) they will very likely be current on the grounding electrode conductor.

This is because of the distribution system in the US having countless bonds to the earth form the neutral.

The GEC in the building ands up carrying some of the neutral current.

In a neighborhood that has all metal water distribution piping the current can equal the current on the service neutral.

Bob

[Richard L. Bennett]

Neutral current should have a # with it

Do HI's ever measure current on anything?

Do HI's ever measure temp diff on HVAC units?

Do HI's ever measure water pressure and flow rate?

Do Hi's ever measure gas and CO and CO2 etc.

What do and should we measue ??

rlb

[Brian E. Kelly]

Originally Posted by rbennett

Neutral current should have a # with it

Do HI's ever measure current on anything?

Do HI's ever measure temp diff on HVAC units?

Do HI's ever measure water pressure and flow rate?

Do Hi's ever measure gas and CO and CO2 etc.

What do and should we measue ??

rlb

Measure what ever you have the expertise and equipment to measure. Make sure you charge enough for your measurements, and that your insurance company is aware of what you are doing.

[Richard L. Bennett]

10-4

rlb