# Megger testing



## Cow (Jan 16, 2008)

Meggers are used for feeders, bc's, and everything else.

I would meg everything below the water level and nothing above.

Disconnect and isolate any line-neutral and line-line loads. I would remove all devices below the water line, it may be worth it to temporarily tie the wiring through so you can meg the whole circuit in one shot. That's up to you. 

Meg h-gr, h-h, h-n, n-gr. It's when you meg h-n and h-h, that if you've left something connected, you can burn something up by hitting it with test voltage.

It's been awhile since I've megged anything in residential, but I use a Fluke 1507. I would set it at 50v first and see what I got. If 0 megaohms, I would go through the house and make sure I didn't leave something connected.

If your reading is good I would work my way up to 250v as a final test voltage. I don't know if I'd want to take it to 500v for residential, even though Romex is rated 600v.


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## mofos be cray (Nov 14, 2016)

Up here in canada if you want to sell a mobile home that is not brand new it is required to be megged. They spec 500vdc for 1 min. I unplug everything, take gfis out, remove light bulbs, disconnect hwt and furnace, disconnect bell chime. And and thing else that is a load. I turn all the switches to on and if there is a 3 way I meg it and then change the 3 way and do it again. I dont usually remove devices but as somebody has already said, in your case all devices below the water line should be removed.


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## macmikeman (Jan 23, 2007)

This thread is begging for a Supco 500 endorsement............


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## electricguy (Mar 22, 2007)

*Electrical systems & equipment*
If equipment or wiring has been wetted, burnt or otherwise damaged:


In the case of severe flooding or damage, after repairs are made, all circuits must be tested, unless complete rewiring has been performed.
Plug-in loads (such as TVs, dryers) must be unplugged and may only be reconnected if replaced or reconditioned by a qualified repair service. Note: it is the field safety representative’s responsibility to ensure that these devices are unplugged prior to re-energization. It is the homeowner’s responsibility to ensure that the devices are repaired or replaced.
Permanently connected loads (such as heaters, ranges) must be removed and replaced or reconditioned by a qualified repair service or contractor.
Other electrical equipment (such as receptacles, fixtures) must be replaced
Electrical connections must be taken apart, cleaned and dried, and remade.
For customer service panels, if the rest of the panel has been cleaned, dried, connections redone, and has been verified through testing, only the individual breakers need to be replaced. Note that wetted molded-case circuit breakers cannot be reused and must be discarded.
If service metering has been wetted, contact the utility and indicate this on declaration the form.
Any other hazards identified must be isolated or repaired.


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## eddy current (Feb 28, 2009)

mofos be cray said:


> Up here in canada if you want to sell a mobile home that is not brand new it is required to be megged. They spec 500vdc for 1 min. I unplug everything, take gfis out, remove light bulbs, disconnect hwt and furnace, disconnect bell chime. And and thing else that is a load. I turn all the switches to on and if there is a 3 way I meg it and then change the 3 way and do it again. I dont usually remove devices but as somebody has already said, in your case all devices below the water line should be removed.


Where is that requirement from?

I’m Not sure if hitting conductors that are only rated for 300 volts with 500 volts is a good idea. 
(Canadian romex is only rated at 300 volts max)


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## em158 (Jul 7, 2016)

Neta says:

250v rated meg @500vdc >25 megohms
600v rated [email protected] > 100 megohms


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## Tonedeaf (Nov 26, 2012)

Are you in NJ???....i heard of insurance companies in NJ asking for meggering wires after water damage......if you are in NJ......the rule is if regular Romex gets wet.....the only remedy IN NJ is to replace....


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## electricbysullivan (Aug 16, 2013)

My father is an old commercial industrial specialist who loved to meg everything with a hand crank magical lunch box device as old as him.


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## mofos be cray (Nov 14, 2016)

eddy current said:


> mofos be cray said:
> 
> 
> > up here in canada if you want to sell a mobile home that is not brand new it is required to be megged. They spec 500vdc for 1 min. I unplug everything, take gfis out, remove light bulbs, disconnect hwt and furnace, disconnect bell chime. And and thing else that is a load. I turn all the switches to on and if there is a 3 way i meg it and then change the 3 way and do it again. I dont usually remove devices but as somebody has already said, in your case all devices below the water line should be removed.
> ...


70-130 in 2015 cec. I'm to lazy to go look at the # in 2018


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## electricguy (Mar 22, 2007)

eddy current said:


> Where is that requirement from?
> 
> I’m Not sure if hitting conductors that are only rated for 300 volts with 500 volts is a good idea.
> (Canadian romex is only rated at 300 volts max)



https://www.technicalsafetybc.ca/si...d_mobile_home_inspection_report_form_1143.pdf


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## varmit (Apr 19, 2009)

electricbysullivan said:


> My father is an old commercial industrial specialist who loved to meg everything with a hand crank magical lunch box device as old as him.


Yes, I have used the old hand cranked meggers many times. They were essentially a magneto. The faster the handle was turned- the higher the output voltage. They were simple, reliable and almost indestructible.


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## varmit (Apr 19, 2009)

Ryan1 said:


> We are being contracted to do repairs as necessary in a house that had been flooded. The insurance company has requested us to megger every circuit in the house. I have never performed a megger test and was under the impression those were mainly for feeders. I understand how a megger test operates, I just am unsure to what extent I have to go to complete one. Would this require me to remove all devices and equipment from my circuits to perform correctly?


Any Romex and devices that have been under water should be replaced. The water will be absorbed by the paper filler in the cable and make the cable jacket into a large straw. water can leak out on devices and connections for some time. The device and switch contacts will probably be compromised by corrosion and filth. 

For you or your company's liability, I would not want to reuse residential wiring that had been submerged. It sounds like the insurance company is trying to "cheap out" on the home owner.


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## splatz (May 23, 2015)

varmit said:


> Any Romex and devices that have been under water should be replaced.


https://www.nema.org/Standards/Secu...-Water Damaged-Electrical-Equipment-Guide.pdf


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## GatorIE (Mar 22, 2020)

splatz said:


> Link


I almost always advocate for strict adherence to this spec when water damage is involved. Even if some authority is not handing down strict requirements for which devices and materials to replace, following the NEMA recommendations is a good CYA move (and a potential upsell if you can get away with T&M).


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## paulengr (Oct 8, 2017)

eddy current said:


> Where is that requirement from?
> 
> I’m Not sure if hitting conductors that are only rated for 300 volts with 500 volts is a good idea.
> (Canadian romex is only rated at 300 volts max)



That’s the AC RMS rating, nothing to do with a DC test, but to begin with there is a huge difference between a hipot and an insulation resistance (Megger) test. IEEE 400 governs hipot tests and they have come out and stated that it destroys cable, insulation resistance is much different. It is done at lower voltages and at much lower available currents. Essentially you’re not going to be able to damage a #14 conductor with a 9 V battery that is scaled up to 500 or 1000 VDC. There just isn’t any current. You might see sparks in a test but that’s not an arc. No power there.

Finally cable us factory tested at the rated voltage times 2 plus 1000 V. So 300 V cable is factory tested at 1600 V and 600 V cable at 2200 V. The Megger test is nowhere near the actual breakdown voltage that is at least 1800-2200 V or more, As an example #14 THHN has been independently tested for VFD reasons and breaks down around 2800-3000 V. So no chance you can damage 300 V cable at only 500-1000 V.


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## GrndFault (Dec 8, 2019)

Ryan1 said:


> We are being contracted to do repairs as necessary in a house that had been flooded. The insurance company has requested us to megger every circuit in the house. I have never performed a megger test and was under the impression those were mainly for feeders. I understand how a megger test operates, I just am unsure to what extent I have to go to complete one. Would this require me to remove all devices and equipment from my circuits to perform correctly?


You do not need to remove all wiring devices but you will need to remove all lamps/loads and disconnect transformers & electronic devices such as ballasts. Switches should be placed in "On" and 3-way circuits will need to be cycled to check all wiring. 

I have not hit the 20 post requirement for adding links but is you go to biddlemeggar.com and look under Application Guides you will find "A stitch in Time" and other documents that should be of assistance.


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