post-lightning service call - Electrician Talk - Professional Electrical Contractors Forum

WMA · 10-05-2009, 04:12 PM

A customer called to say that a lightning strike knocked out several branch circuits, but not the main breaker. The satellite modem, plugged in at the panel, was fried, along with the control panel of the gas stove.
She was able to reset all of the breakers.
The next day, a lighting circuit tripped when she turned on the porch light. This is when she called me.
I found no short in the lighting circuit, and was able to reset the breaker. In the panel, I found a few loose terminations at both breakers and the neutral/ground bars. I also found that the grounding electrode conductor was undersized, #6 for a 200amp service, and that it terminated at the meter socket, not in the panel. There is no grounding/bonding of the satellite dish.
The house is built on ledge, on a mountaintop. The trench for the underground service had to be blasted; I suspect the ground rod(s) got buried in the trench.

My question is, what other troubleshooting, if any, should I do, given these circumstances? The grounding obviously needs to be addressed. But is there anything I should do to test the house wiring for more subtle damage?

Thanks in advance

MDShunk · 10-05-2009, 04:44 PM

Quote:

Originally Posted by WMA

...But is there anything I should do to test the house wiring for more subtle damage?

Yes. You really need to do a megger check of all the branch circuits, from the panel.

wingz · 10-05-2009, 05:36 PM

Quote:

Originally Posted by WMA

I also found that the grounding electrode conductor was undersized, #6 for a 200amp service, and that it terminated at the meter socket, not in the panel.
The house is built on ledge, on a mountaintop. The trench for the underground service had to be blasted; I suspect the ground rod(s) got buried in the trench.

#6 to ground rods is correct.

mcclary's electrical · 10-05-2009, 05:43 PM

Quote:

Originally Posted by WMA

A customer called to say that a lightning strike knocked out several branch circuits, but not the main breaker. The satellite modem, plugged in at the panel, was fried, along with the control panel of the gas stove.
She was able to reset all of the breakers.
The next day, a lighting circuit tripped when she turned on the porch light. This is when she called me.
I found no short in the lighting circuit, and was able to reset the breaker. In the panel, I found a few loose terminations at both breakers and the neutral/ground bars. I also found that the grounding electrode conductor was undersized, #6 for a 200amp service, and that it terminated at the meter socket, not in the panel. There is no grounding/bonding of the satellite dish.
The house is built on ledge, on a mountaintop. The trench for the underground service had to be blasted; I suspect the ground rod(s) got buried in the trench.

My question is, what other troubleshooting, if any, should I do, given these circumstances? The grounding obviously needs to be addressed. But is there anything I should do to test the house wiring for more subtle damage?

Thanks in advance

200 amp panel #6 to rods is correct. Unless it's going to a water pipe, then you would need #4. If there is no water pipe GEC, I quite often, just put a #4 on the rods anyway. (i know I don't have to) I would recommend megging all branch circuits.

480sparky · 10-05-2009, 06:02 PM

It's a landslide. I vote for meggering too.

WMA · 10-05-2009, 11:15 PM

Thanks. I'm a bit embarrassed to admit that in 28 years, I've not laid eyes on a megger. An old post on the Mike Holt forum suggests that our moderator is the intergalactic authority on them.
Is the Extech autoranging digital #380260 still the megger of choice for sub-480v testing?
So, you disconnect each cable at the panel. Do you leave the rest of the circuit intact? Remove light bulbs and connected appliances?
And what is the normal range of readings for a house-full of romex?

480sparky · 10-05-2009, 11:37 PM

Quote:

Originally Posted by WMA

Thanks. I'm a bit embarrassed to admit that in 28 years, I've not laid eyes on a megger. An old post on the Mike Holt forum suggests that our moderator is the intergalactic authority on them.
Is the Extech autoranging digital #380260 still the megger of choice for sub-480v testing?
So, you disconnect each cable at the panel. Do you leave the rest of the circuit intact? Remove light bulbs and connected appliances?
And what is the normal range of readings for a house-full of romex?

You also need to by-pass any electronic devices, such as GFCIs, dimmers, furnace & AC (electronics!), surge-portection receptacles (yes, they are available). Start off with a lower voltage (say, 100V) for a first test. If you missed something, you'll find it here instead of burning something up.

WMA · 10-06-2009, 09:12 AM

So a meter with a low test voltage of 250, like this Extech I'm looking at, is not appropriate for this application?

mcclary's electrical · 10-06-2009, 10:07 AM

Quote:

Originally Posted by WMA

So a meter with a low test voltage of 250, like this Extech I'm looking at, is not appropriate for this application?

Like 480 said, always start with your lowest setting. It doesn't HAVE to be 100. Standard meg for 600 volt wire is 1000 volts. So if your settings start at 250, that's fine.

JohnJ0906 · 10-06-2009, 07:58 PM

Quote:

Originally Posted by mcclary's electrical

Like 480 said, always start with your lowest setting. It doesn't HAVE to be 100. Standard meg for 600 volt wire is 1000 volts. So if your settings start at 250, that's fine.

Start with a low voltage setting, to make sure that you removed everything, such as dimmers, GFCIs, etc.

Mine has 200 Ohm (continuity) and 200Kohm settings, at battery voltage. I use the 200K first, before applying a real voltage. (250, 500, 1000 VDC)

WMA · 10-06-2009, 11:45 PM

Quote:

Originally Posted by JohnJ0906

Start with a low voltage setting, to make sure that you removed everything, such as dimmers, GFCIs, etc.

Mine has 200 Ohm (continuity) and 200Kohm settings, at battery voltage. I use the 200K first, before applying a real voltage. (250, 500, 1000 VDC)

So, what's an acceptable reading at, say, 1000 VDC?

RIVETER · 10-07-2009, 12:37 AM

I believe that using a megger is a good thing to do. You will be testing the integrity of the insulation of your conductors to ground, and to each other. I would also look for a better way to ground the system (not thru rock}. A person has to remember that their own electrical system is, for all practical purposes, independent from the ground,{Dirt, Rock, Sand) or what have you that the building is on. Once you have "EARTH GROUNDED" your system it should be as safe as it can be. There is a great difference between Grounding and Bonding.
The reasons, and I think there are only "TWO", for system grounding; that is to protect your system from lightning strikes and from possible PRIMARY TO SECONDARY, SHORT CIRCUITS at your service transformer; Or at least I cannot think of another reason.
Once you have properly grounded your electrical system (BONDING IS KING)

RIVETER