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Lightning damage investigation. #13121 08/25/02 11:08 AM
Joined: Mar 2001
Posts: 2,056
Redsy Offline OP
How little or how much assessing to a residential wiring system should be conducted after a hit?
I did one yesterday and found..

Fried TV, Computer, Microwave.
No ground rod.
Water meter not jumpered.

I installed a rod and jumpered the meter.
It had been a couple weeks since the hit and she said that everything else was operating OK.
I explained the megger test but informed her that if everything was not disconnected, the test would provide questionable results. Also, if everything was disconnected, and unsatisfactory, or marginal readings were observed it could be extremely difficult and costly to locate the problem.
She is going to think about it .

Anyone else have any ideas?

Work Gear for Electricians and the Trades
Re: Lightning damage investigation. #13122 08/25/02 12:10 PM
Joined: Apr 2001
Posts: 507
golf junkie Offline
Sounds like you did fine Redsy. Here in the rural midwest these are frequent.

Did one a few weeks ago. A rural house, the lightening entered the residence through the CB radio mast, came down the antenna lead to a shelf in the kitchen where the radio equipment was located. It was a 12vdc radio powered by a 120vac/12vdc converter, both the radio and power supply were reduced to a burned lump of electronics.

The lightening entered the house power system through the plug strip that the power supply was using. Followed that circuit back to the main service entrance and then went to ground through the water well, destroying the well controller and submersible well motor in the process.

Total damage was;
All devices on the kitchen circuit replaced.
Kitchen and Well ckt. breakers replace.
Well controller and motor.

Somehow, none of the kitchen appliances were my surprise.

Also they were very lucky not to have a major fire in the kitchen. There was a small fire that burned itself out quickly damaging only the wallpaper.


Note: the service was properly grounded with a water pipe bond and ground rod, yet the lightening chose to follow the electrical ckt. to ground through the pump motor.

Re: Lightning damage investigation. #13123 08/25/02 02:01 PM
Joined: May 2001
Posts: 717
George Corron Offline
Was the antenna mast grounded? I often find that is the 'welcome mat' for such things.

Redsy, without going into details, I can just about write your exact scenario (matter of fact it is written up for class) and after installing proper ground rod and jumpering water meter, guy has not had any problems since.

Re: Lightning damage investigation. #13124 08/25/02 11:56 PM
Joined: Apr 2002
Posts: 2,527
Bjarney Offline
gj— Interesting comments about the submersible-pump damage. Of course, different regions have different practices, but do you know if the damaged pump was in a plastic or metal casing? Do you know if that’s understood to make any difference?

Re: Lightning damage investigation. #13125 08/27/02 04:44 AM
Joined: Aug 2002
Posts: 36
TE Offline
I would do by best to physically inspect the wiring of the circuits the fried items were on.It may be a difficult thing to accomplish, but I have seen insulation badly melted on type NM inside of wall cavities after a strike.

Re: Lightning damage investigation. #13126 08/27/02 07:33 AM
Joined: Oct 2000
Posts: 5,389
sparky Offline
would not a good meggin' do?

Re: Lightning damage investigation. #13127 08/27/02 11:27 AM
Joined: Mar 2001
Posts: 2,056
Redsy Offline OP

Iam considering megging.
I'm not sure she wants to pay the cost for what may result in more questions or more work. And still be inconclusive.

Well, here goes...

What about installing an AFCI on the circuit that had the damaged appliances.
If the insulation has been compromised, the resulting arc-fault shoul be a parallel type.

Re: Lightning damage investigation. #13128 08/27/02 12:25 PM
Joined: Oct 2000
Posts: 5,389
sparky Offline
sounds easier than x-ray vision, i get headaches from eyestrain...... [Linked Image]

Re: Lightning damage investigation. #13129 08/27/02 03:33 PM
Joined: Oct 2001
Posts: 597
ElectricAL Offline
Square D, in Data Bulletin 0760DB0201R06/02 titled: "The Truth About AFCIs", states:
Is equipment available for testing after wiring is installed so that contractors can demonstrate that their work has been competently completed?

...we are not aware of special equipment available for such testing. If wiring is installed competently, there should be no reason for any testing that is not done for a circuit without an AFCI. However, there are two possible practices that can be used to test the installation, if a test is desired:

[*]Probably the best test is to install an AFCI, at least temporarily, in the circuit. For this test to be efeective, the circuit must be complete, since it must be energized as in service with 120 volts. First, use the test button to verify that the AFCI is functioning properly. Then leave the AFCI in the energized circuit for some period of time. If it does not trip, that is an indication that the circuit is acceptable.

[*](describes using a Megger - Al)


Al Hildenbrand
Re: Lightning damage investigation. #13130 08/27/02 07:03 PM
Joined: Apr 2001
Posts: 507
golf junkie Offline
Bj- Don't know about the submersible pump casing.

Using a AFCI to "test" a circuit sounds flakey to me. I would trust a megger to find any insulation faults......I don't think that an AFCI can do that.


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