Megger Test

[cars0508]

Hello

I am hoping you can answer this question. We had a fire in our condo building. The wires outside were damaged. The Management is now saying we need a Megger test done. We had one done and it failed. Then they realized they did not unplug all appliances including dishwashers. So they did another test and it passed. But the electrician would not sign off saying it passed. Is this true that it could have failed the first time because everything wasn't unplugged?

 

[Dennis Alwon]

How did they do a megger test without unplugging everything. I would think it would have damaged the equipment, appliances etc in the house

 

[cars0508]

I am not sure why they did it without unplugging everything. They better not have damaged my dishwasher which was still plugged in. So do you think since everything is now unplugged that it will pass? Are you familiar with Megger testings? Thanks!

 

[charlie b]

Yes, we are all familiar with that test. If everything is disconnected from the power source, then the megger test will tell you whether the fire damaged the wires' insulation enough to allow current to leak from the metal portion of the wire, past the insulation, to the conduits and boxes through which the wires pass. If the insulation had been weakened in this manner by the fire, it could result in arcing and perhaps another fire. That is why the megger test is conducted - to check the wires (that you can't visually inspect because they are inside walls) for damage.

You run the test by applying a high voltage (much higher than the 120 volts that runs the DW) and measure the resulting current. If nothing is connected at the time, the current will only be whatever can sneak its way through the insulation. That is always very small, when the wires are in good condition. But if something is connected, they will measure lots of current immediately. When they see that, they should immediately stop the test. And yes, they would call that a failed test. Even if the DW was plugged in, so long as it was not running at the time of the test (i.e., its on/off switch was in the off position), its motor and heater would not be impacted by the test. Whether the electronic controls could have been damaged, I cannot say. I would definitely tell them to check the equipment.

 

[roger]

I would suggest a second company be brought in to do a another test. To do an insulation test a voltage has to be put into wiring, this can be different levels, 250, 500, 1000 for example. It depends on the level and the equipment connected whether it may have been damaged. If the second test was good I don't understand why the EC won't stand behind it.

Roger

 

[hillbilly1]

I would suggest a second company be brought in to do a another test. To do an insulation test a voltage has to be put into wiring, this can be different levels, 250, 500, 1000 for example. It depends on the level and the equipment connected whether it may have been damaged. If the second test was good I don't understand why the EC won't stand behind it.

Roger

I agree, not to throw dispersions at the original company that tested it, but they clearly did not know how to properly perform the test.

 

[cars0508]

Yes, we are all familiar with that test. If everything is disconnected from the power source, then the megger test will tell you whether the fire damaged the wires' insulation enough to allow current to leak from the metal portion of the wire, past the insulation, to the conduits and boxes through which the wires pass. If the insulation had been weakened in this manner by the fire, it could result in arcing and perhaps another fire. That is why the megger test is conducted - to check the wires (that you can't visually inspect because they are inside walls) for damage.

You run the test by applying a high voltage (much higher than the 120 volts that runs the DW) and measure the resulting current. If nothing is connected at the time, the current will only be whatever can sneak its way through the insulation. That is always very small, when the wires are in good condition. But if something is connected, they will measure lots of current immediately. When they see that, they should immediately stop the test. And yes, they would call that a failed test. Even if the DW was plugged in, so long as it was not running at the time of the test (i.e., its on/off switch was in the off position), its motor and heater would not be impacted by the test. Whether the electronic controls could have been damaged, I cannot say. I would definitely tell them to check the equipment.

Thank you so much!1

 

[ramsy]

..You run the test by applying a high voltage (much higher than the 120 volts that runs the DW) and measure the resulting current..

Are you sure that won't destroy the GFCI, required for DW, or elsewhere in SABC's?

 

[roger]

Are you sure that won't destroy the GFCI, required for DW, or elsewhere in SABC's?

I would think the EC would remove all questionable items, don't you when you megger a dwelling?

Roger

 

[cars0508]

I would suggest a second company be brought in to do a another test. To do an insulation test a voltage has to be put into wiring, this can be different levels, 250, 500, 1000 for example. It depends on the level and the equipment connected whether it may have been damaged. If the second test was good I don't understand why the EC won't stand behind it.

Roger

For some reason it did pass and the company would not sign off on it because they didn't want to held liable if the building caught on fire again. So what I don't understand is why they did it in the first place if they weren't going to sign off. I am just hoping to god that since it failed the first time, then they turned off all dishwashers

Yes, we are all familiar with that test. If everything is disconnected from the power source, then the megger test will tell you whether the fire damaged the wires' insulation enough to allow current to leak from the metal portion of the wire, past the insulation, to the conduits and boxes through which the wires pass. If the insulation had been weakened in this manner by the fire, it could result in arcing and perhaps another fire. That is why the megger test is conducted - to check the wires (that you can't visually inspect because they are inside walls) for damage.

You run the test by applying a high voltage (much higher than the 120 volts that runs the DW) and measure the resulting current. If nothing is connected at the time, the current will only be whatever can sneak its way through the insulation. That is always very small, when the wires are in good condition. But if something is connected, they will measure lots of current immediately. When they see that, they should immediately stop the test. And yes, they would call that a failed test. Even if the DW was plugged in, so long as it was not running at the time of the test (i.e., its on/off switch was in the off position), its motor and heater would not be impacted by the test. Whether the electronic controls could have been damaged, I cannot say. I would definitely tell them to check the equipment.

So are you saying that ALL appliances have to be unplugged for an accurate reading? Correct?

 

[ramsy]

I would think the EC would remove all questionable items, don't you when you megger a dwelling?

Roger

Remember when service occurs while occupied, someone is always watching you. The person paying is usually breathing down your neck.

Unless devices are being replaced, its not likely anyone will pay for tearing things apart, especially when they want to use the kitchen in a few hours.

Its also unnecessary.

 

[roger]

Remember when service occurs while occupied, someone is always watching you. The person paying is usually breathing down your neck.

Unless devices are being replaced, its not likely anyone will pay for tearing things apart, especially when they want to use the kitchen in a few hours.

Its also unnecessary.

So you don't think the electronics in certain items will be damaged when doing an insulation test? What was the reason for your question in post "8 about?

Roger

 

[roger]

For some reason it did pass and the company would not sign off on it because they didn't want to held liable if the building caught on fire again. So what I don't understand is why they did it in the first place if they weren't going to sign off. I am just hoping to god that since it failed the first time, then they turned off all dishwashers


So are you saying that ALL appliances have to be unplugged for an accurate reading? Correct?

Yes, the test is for the premise wiring conductors, all external devices that have a connection between the hot and neutral (any minute amount of current flow) should be removed or isolated for an accurate result

Roger

 

[hillbilly1]

Hello

I am hoping you can answer this question. We had a fire in our condo building. The wires outside were damaged. The Management is now saying we need a Megger test done. We had one done and it failed. Then they realized they did not unplug all appliances including dishwashers. So they did another test and it passed. But the electrician would not sign off saying it passed. Is this true that it could have failed the first time because everything wasn't unplugged?

When you say the wires outside were possibly damaged, was this the service wires? A/C unit wires? If the inside wiring was not affected by the fire, it should have been isolated from the wiring outside being tested.

 

[ramsy]

So you don't think the electronics in certain items will be damaged when doing an insulation test? What was the reason for your question in post "8 about?

Roger

Not sure if destroying kitchen GFCI's with a Megger test is worse than ruining Mom's dinner plans.

Pretty sure doing both would not go well.

 

[tortuga]

We disconnect all equipment before doing a megger test, GFCI's, lighting fixtures, all appliances, dimmers, range hood, ceiling fans, bath fans .. Everything in the house is unplugged/disconnected to the NEC 'outlet'. Toggle switches are all switched on and left in. Then each circuit is done one at a time with neutrals unlanded one at a time then re-landed.

The new meggers we use probably wont destroy electronics as they output 1000V for 1 min but the megger is powered by like 9 AA batterys so the energy level is in miliamps, and if anything electronic is plugged in it goes to zero really fast.
We also go thru the house with a 'Ideal Sure test' and do voltage drop tests which are much more revealing. When you have 80% voltage drop on a receptacle outlet the megger reading wont detect that, but the sure test will.
The test is part of an 'evaluation' and also includes labeling the panel and a load analysis.
Insurance carriers usually want a detailed report with photos, permit history, and a floor plan, if your doing a re-cert after a fire.
We have done them for many carriers. They typically insist on a panel change no matter what, which they often cover.
Cheers

 

[cars0508]

We disconnect all equipment before doing a megger test, GFCI's, lighting fixtures, all appliances, dimmers, range hood, ceiling fans, bath fans .. Everything in the house is unplugged/disconnected to the NEC 'outlet'. Toggle switches are all switched on and left in. Then each circuit is done one at a time with neutrals unlanded one at a time then re-landed.

The new meggers we use probably wont destroy electronics as they output 1000V for 1 min but the megger is powered by like 9 AA batterys so the energy level is in miliamps, and if anything electronic is plugged in it goes to zero really fast.
We also go thru the house with a 'Ideal Sure test' and do voltage drop tests which are much more revealing. When you have 80% voltage drop on a receptacle outlet the megger reading wont detect that, but the sure test will.
The test is part of an 'evaluation' and also includes labeling the panel and a load analysis.
Insurance carriers usually want a detailed report with photos, permit history, and a floor plan, if your doing a re-cert after a fire.
We have done them for many carriers. They typically insist on a panel change no matter what, which they often cover.
Cheers

Thank you so much! So far we passed as far as the wires inside the walls are ok. But they did find and issue in my panel. And when the first test was done they did NOT disconnect my dishwasher which concerns me.