Fire and Damage

[mkgrady]

At this customers house a 7,800 volt overhead line dropped on to the CATV and Telephone lines out at the street. Both lines run to the house in an underground conduit. The conduit had flames shooting out the house end of the conduit and it set the shingles on fire. The home owner noticed something was wrong when their CATV receptacles around the house started sparking and smoking. Luckily he was smart enough to extinguise the fire outside.

It appears that any CATV coax and any telephone wire that was connected may need to be replaced. It won't be easy because his basement has a finished plaster ceiling. I assume his ceiling will look like swiss cheese by the time the cables are re-run.

Five or six circuit breakers tripped on the 200 amp main panel. My question is about the extent of the testing required on the all the power wiring in the house. Should all circuits be meggered? Should only the ones that tripped be meggered? Any suggestions on what needs to be done? I may be meeting with the insurance adjuster and GC later today.

 

[Fulthrotl]

At this customers house a 7,800 volt overhead line dropped on to the CATV and Telephone lines out at the street. Both lines run to the house in an underground conduit. The conduit had flames shooting out the house end of the conduit and it set the shingles on fire. The home owner noticed something was wrong when their CATV receptacles around the house started sparking and smoking. Luckily he was smart enough to extinguise the fire outside.

It appears that any CATV coax and any telephone wire that was connected may need to be replaced. It won't be easy because his basement has a finished plaster ceiling. I assume his ceiling will look like swiss cheese by the time the cables are re-run.

Five or six circuit breakers tripped on the 200 amp main panel. My question is about the extent of the testing required on the all the power wiring in the house. Should all circuits be meggered? Should only the ones that tripped be meggered? Any suggestions on what needs to be done? I may be meeting with the insurance adjuster and GC later today.

i'd disconnect everything that will be smoked by a megger, and megger the whole house. make sure to check the service ground as well... both ufer and cold water..
i'd also be looking at replacing all the circuit breakers. it's not very much money, and after a hit like that, you really don't know if they are serviceable.

 

[nakulak]

it is possible that there is wiring damage in the house that you will not be able to find by megging it; so whatever the insurance company is willing to pay is going to be the determining factor in what gets replaced. Any warranty you provide will be a liability. Try not to stick your neck on the chopping block.

 

[brian john]

You either trust your knowledge and test equipment or hire a firm that can and does.

 

[mkgrady]

The insurance company sent an electrical consultant. He did not believe the power wiring need to be meggerred. I told him he can take responsability for that decision and I will not. Now he believes meggerraring is a good idea.

Contrary to what I have learned in the past he suggested leaving all light bulbs in place except for flourescent bulbs. He claims leaving the bulbs in place allows the meggar to test the neutral. I'm concerned the voltage could damage the bulbs. My plan was to remove all bulbs and test the neutral seperately. What I am not sure of is whether or not I can test a flourescent ballast or should they be disconnected like all appliances and cord connected things.

My plan is to jump out all dimmers, gfi receptacles, remove all bulb, close all switches, unplug everything and run the tests. I'm just not sure about flourescent fixtures. Any other suggestions are appreciated.

 

[John120/240]

If in doubt I would disconnect everything. The insurance company is already on the hook

for a sizeable bill. How many flourscent fixtures are there ?

 

[mkgrady]

If in doubt I would disconnect everything. The insurance company is already on the hook

for a sizeable bill. How many flourscent fixtures are there ?

There are only a few in clothes closets. I'm trying to make sense of his contention that all bulbs should stay in place during the meggar testing except for flourescent, and his contention that if incandescent bulbs are left in place it will also test the neutral at the same time. Even if that is true, since the neutral would have to be disconnected at the panel I don't know what he thinks is being saved.

 

[Fulthrotl]

There are only a few in clothes closets.
I'm trying to make sense of his contention that all bulbs should stay in
place during the meggar testing except for flourescent, and his contention
that if incandescent bulbs are left in place it will also test the neutral at
the same time. Even if that is true, since the neutral would have to be
disconnected at the panel I don't know what he thinks is being saved.

well, first... he thought meggering was unnecessary.

now, he thinks meggering in series with a resistor is
a valid test.

he's an idiot. if you can make sense of his reasoning,
that worries me about you.....

putting 1,000 volts on a device designed for 120 volts
will not go well. tell him you can test his theory on HIS
home entertainment center.

if he is neither a licensed electrician, nor a registered
professional engineer, then his input is not worth
considering, especially if it makes no sense.

here's my spin on it..... if it were my deal to do, i'd
pull the gfci breakers, afci breakers, and gfci receptacles.
on the receptacles, tie the hots together to test downstream,
same with the neutrals. unscrew the lightbulbs. unplug the
disconnect on fluorescent fixtures. turn all the light switches on.
remove dimmers, and tie the hot and switch leg together.

i'd unplug everything in the house. don't forget garbage
disposal, bathroom fans, etc. i know you won't.. just sayin'...

if you are using a lower powered megger like a fluke combo
unit, open all the circuit breakers, and megger both sides of
the panel, at 1,000 volts. with a fluke, you should see into
gigaohms.

then, do one circuit at a time, at 1,000 volts. as you charge up
the megger the longer runs will take more time to soak than the
shorter ones.

after they are all done, you should have readings above a gigohm
most likely, and your applied voltage should be above 1kv.

if the voltage hunts around, and the megohms won't climb steadily,
you have a problem on that circuit.

assuming they are all good on the hot legs, lift the neutral break link,
and check the neutrals from the neutral bus to ground. in theory,
they should not be grounded out in the wiring. if they are shorted to
ground, lift them one at a time and see which ones are shorted.

megger the other ones to ground. they should read like the hots.

when you find the grounded neutral problems, and fix that, and all
wires hold 1KV, you are good to go.

i'd replace, as a matter of safe procedure, every single breaker, including
the main.

 

[mkgrady]

Thanks Ful. That was very informative and appreciated.