Lightning Strike...

[1793]

I have had a call to check out the electrical system of a single family dwelling that more than likely was hit by lightning. Customer said that most all electronics were blown.

Customer called the Power Co. and they felt it was safe to stay in the house. I would like to get some input as to where to mostly focus my attention to see what if any damage was done to the electrical system.

As always your input and insight is greatly appreciated.

Norb

[ November 07, 2005, 07:03 PM: Message edited by: 1793 ]

 

[bphgravity]

Re: Lightning Strike...

The biggest issue with lightning is conductor insulation damage. Check all ungrounded grounded conductors for insulation resistance. Make visual inspections of the service, lighting and applaince panels, and various outlets throughout the home. If there is any accessible space about the cables like in an attic space, check to see if there is any visual signs of damage on the surface like melting, scortching, or other altering deformaties.

Finally, sell your customer a whole house TVSS.

 

[hurk27]

Re: Lightning Strike...

Norb I hate to say this but your heading into possible future legal problems when getting into lightning damage. While most of the time lightning will only damage the electronics, with a direct strike, It can do some wiring damage in areas not easily accessible without the right equipment. Many times in the case of NM, lightning will blow off the insulation down in walls right where the NM crosses water lines or other grounding sources, even reading it with a meager will not show it, But later on these uninsulated wires get moved by a rodent or anything and come into contact with wood you could have pyrocarbonization of the wood around these bare conductors and eventually could lead to a fire. This is where you have to have the right equipment to be able to view down these walls to look for the damage. These scope can be costly, I would opt out and at most help the home owner to find a company who specializes in this type of work. Of course it's always up to the owner if they want to take a chance and turn the power back on, but if you give the go ahead then its your butt if something goes wrong.

 

[Physis 2]

Re: Lightning Strike...

Wayne, you're all but saying that the walls should be taken down to inspect the wiring. What tools exist to verify the insulation integrity otherwise?

Edit: Error B.

[ November 07, 2005, 11:36 PM: Message edited by: Physis 2 ]

 

[bphgravity]

Re: Lightning Strike...

I doubt the structure was directly hit by lightning. There would be other evidence such as damage to the structure itself. It was most likely a nearby strike or a surge on the incomming service form a strike on the distribution system.

The electronic components were damaged due to their lack of tolerance for transient spikes, whereas the impedance of the supplying conductors are not as great and therefore less likely to be effected.

 

[1793]

Re: Lightning Strike...

I don't think the house itself was hit. According the to HO, a tree close to the overhead lines was hit.

Can lightning strikes close to supply lines cause damage to electronic equipment and not necessarily affect the house wiring system?

Norb

 

[bphgravity]

Re: Lightning Strike...

Sure. Lightning is only a problem when it encounters resistance. Resistance creates heat, heat burns things up. A mild to moderate surge on the power system is capable of being contained within that system if the duration and intensity is not that great, however a high resistance component such as DVD player may react adversely to that surge current.