Insulation testing criteria

[txaggie84]

I hope I'm in the right forum. I am working on a mitigation plan for a house fire where lightning was the initiating cause. The lightning struck a tree 20' from the front wall directly over a water line. The copper pipe was heated to such an extent that it ignited joists where it entered the house. Fourteen branch circuits were damaged by fire and heat attack. No arcing is apparent other than small beads on a couple conductors where arcing occurred through the fire damaged insulation.

The owner wants the whole house gutted and rewired because he believes lightning has compromised his cables. I tested all the circuits in the house with a Fluke 1587 at 500V. All but two circuits tested ">550 M". The owner wants documentation stating that this is acceptable. I know about the 1 megohm/1000V "rule of thumb" but that's not quite 'official' enough. Is there a standard that covers this?

Thank you very much for your help
Gig em Ags!

Txaggie84

 

[ohmhead]

wire insulation

wire insulation

I dont have a solid solution to your question no writen instructions just some high voltage field work .

But just a thought your meg reading is ok . But when lightning hits its not 500 volts its lots of volts and amps that has heated that insulation up but if the wire has bubbles and looks like its brittle maybe badly heated this might check good on a megg reading . Now over time and under load that little bubble in that insulation might crack or become less of a insulator as its now thinner and its not bonded to that conductor so think about the years to come replace it !

High voltage will make a insulator glow it breaks down the insulation over time when lightning hits its 20 years of service in one second .Good luck take care

 

[zog]

I hope I'm in the right forum. I am working on a mitigation plan for a house fire where lightning was the initiating cause. The lightning struck a tree 20' from the front wall directly over a water line. The copper pipe was heated to such an extent that it ignited joists where it entered the house. Fourteen branch circuits were damaged by fire and heat attack. No arcing is apparent other than small beads on a couple conductors where arcing occurred through the fire damaged insulation.

The owner wants the whole house gutted and rewired because he believes lightning has compromised his cables. I tested all the circuits in the house with a Fluke 1587 at 500V. All but two circuits tested ">550 M". The owner wants documentation stating that this is acceptable. I know about the 1 megohm/1000V "rule of thumb" but that's not quite 'official' enough. Is there a standard that covers this?

Thank you very much for your help
Gig em Ags!

Txaggie84

NETA is an ANSI standard and should be all the documentation you need.

 

[txaggie84]

Zog,
Thank you very much. That is great information

TxAggie84

 

[Jake6879]

I may be incorrect so please correct me if I am wrong but unless there is another wire exposed or other conductive surface, using a megger or Hipot would not fail an exposed wire. I know with my Hipot the only way it will fail is if there is something to arc to, ie EMT, steel box, other bad insulation etc. I would expect that in a residential situation where everything would be non metallic around the wiring, that even if the insulation was compromised, it could potentially appear to pass the insulation test. Again take this with knowing that I do not use my hipot for this type of test. We test our electrical system to 1500v for 1 sec at completion but everything is metallic so if the insulation has so much as a pin hole in it, it will fail.