# Megger new home circuits



## JabElecPlumbHeat (Oct 21, 2018)

We wire new RTM homes that ship out to North Dakota, and the 3rd party inspection agency (we are a Canadian company) has a small list of test we need to do. One of them is to megger test the circuits. It reads "Enter the voltage and length of time at which the electrical system dielectric strength was conducted. This will normally be 1080V/1 Sec." That seems a little much to me, and at what point should we do this? Rough in, but then you're tieing in all your receptacle joints (extra time) or during finishing, but then you have to make sure that led lights, appliances, GFCI's, etc aren't in yet.

I may have answered my own question lol.... during finishing, install the receptacles, megger test, then carry on with the work...

Has anyone else been required to do this? 

Thanks!


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## macmikeman (Jan 23, 2007)

Only when working on housing associated with the Pearl Harbor Naval Base. 
I guess base engineers don't trust afci circuit breakers well enough to do the job they are designed for.


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## HackWork (Oct 2, 2009)

I wouldn't megger at any voltage above the insulation's rating.


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## splatz (May 23, 2015)

JabElecPlumbHeat said:


> I may have answered my own question lol.... during finishing, install the receptacles, megger test, then carry on with the work...


I think that's reasonable - install as much as possible that won't need to be disconnected for the test, perform test, then finish. 

I would figure on 500V for a megger test on a 240V system using the rule of thumb, twice the system voltage. (There isn't a 480V setting.) For 600V insulation, it shouldn't be a problem to test at 1080V, except that the Fluke 587doesn't have 1080V, would 1000V be OK? :biggrin: 

I'm wondering where they got 1080V and searched it, how about this... 



> The U.S. Department of Housing and Urban Development, Manufactured Housing and Standards
> Division issued a memorandum in June of 2000 to All Primary Inspection Agencies and All State
> Administrative Agencies regarding dielectric strength testing of modular and manufactured
> homes as specified in standard # 24 CRF 3280.810(a).
> ...


So it's a L-G and N-G test ... must be performed without the main bond in place... but you can do it at the very end.


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## splatz (May 23, 2015)

HackWork said:


> I wouldn't megger at any voltage above the insulation's rating.


You also wouldn't megger at any voltage below the insulation's rating.


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## HackWork (Oct 2, 2009)

splatz said:


> You also wouldn't megger at any voltage below the insulation's rating.


Sure I would. Over the years I have meggered quite a bit in schools, hospitals, data centers, etc. when they were paying our company to do so as part of the job specs.

I just wouldn't waste the time doing it in resi new construction if I wasn't being paid for it.


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## HackWork (Oct 2, 2009)

splatz said:


> For 600V insulation, it shouldn't be a problem to test at 1080V


What makes you say that?


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## sbrn33 (Mar 15, 2007)

I would just make up a few values and call it good. Megging in resi is just stupid.


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## splatz (May 23, 2015)

HackWork said:


> What makes you say that?


Just what I have gathered is typically done, keep in mind the megger makes a lot of volts but not a lot of amps, as seen in many apprentice hazing hijinks. 

The attachment below is a clip from the Biddle book, "A Stitch in Time"


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## HackWork (Oct 2, 2009)

AFAIK, you don't need much current to blow a hole in the insulation. 

What would you do if you blew the insulation in an unknown spot?

As for what OP's question, it doesn't seem to make much sense to megger at the Finish. What if you found an issue with the cable? You would have to tear the walls down to find it. You should megger at the Rough.


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## splatz (May 23, 2015)

HackWork said:


> As for what OP's question, it doesn't seem to make much sense to megger at the Finish. What if you found an issue with the cable? You would have to tear the walls down to find it. You should megger at the Rough.


For acceptance testing by the buyer, he doesn't really care if it was OK at the midpoint of the manufacturing process, he wants the finished product tested. 

Now it would make sense to do your own midway test at rough in before drywall goes on. (For a subcontractor, it would also help show that the wiring was OK before the drywallers got into it.)


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## Cow (Jan 16, 2008)

HackWork said:


> I wouldn't megger at any voltage above the insulation's rating.



It's standard procedure like Splatz mentioned to do twice the system voltage/insulation rating.


We regularly meg 480v motor circuits and motors at 1000vdc without issue. 



If requested, I would have no problem megging Romex rated 600v at 1000vdc provided I can start the testing off at lower voltages first to verify no devices are still connected.


For the regular resi service call though, we will typically meg Romex/UF at 250/500vdc as standard practice when needed.


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## HackWork (Oct 2, 2009)

I never knew that, I thought you had to stay within the insulations rating.


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## splatz (May 23, 2015)

ARTICLE 550 — MOBILE HOMES said:


> *550.17 Testing.*
> (A) Dielectric Strength Test. The wiring of each mobile
> home shall be subjected to a 1-minute, 900-volt, dielectric
> strength test (with all switches closed) between live parts
> ...


....


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## eddy current (Feb 28, 2009)

Canadian Romex (NMSC or NMD90) is only rated for 300 volts. OP said he’s with a Canadian company. What is the insulation rating of the wire used?


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## electricguy (Mar 22, 2007)

sbrn33 said:


> I would just make up a few values and call it good. Megging in resi is just stupid.



And then the guy looses his CSA manufactured home certification, he has a set of standards to adhere to, good plan NOT


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## JabElecPlumbHeat (Oct 21, 2018)

Wow thanks for all the replies guys! Yes we’re a Canadian company, but we use NMB (USA, 600v) wire, not NMD (Canadian, 300v) since the homes end up in the USA. I know on industrial sites we’ve always meggered at one voltage setting above the wire rating, when testing cables and motors, and never had issues. I’m most worried about electronics in gfi’s, drivers, etc malfunctioning after. Now I’m wondering about the AFCI/GFCI breakers, since megging from the line side of the panel came up. 

Has anyone seen devices fail after megging, that would be the main question here...


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## JabElecPlumbHeat (Oct 21, 2018)

So it's a L-G and N-G test ... must be performed without the main bond in place... but you can do it at the very end.[/QUOTE]


That's how we don't have to worry about ruining appliances... perfect! Thanks!


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## JabElecPlumbHeat (Oct 21, 2018)

splatz said:


> I think that's reasonable - install as much as possible that won't need to be disconnected for the test, perform test, then finish.
> 
> I would figure on 500V for a megger test on a 240V system using the rule of thumb, twice the system voltage. (There isn't a 480V setting.) For 600V insulation, it shouldn't be a problem to test at 1080V, except that the Fluke 587doesn't have 1080V, would 1000V be OK? :biggrin:
> 
> ...





JabElecPlumbHeat said:


> So it's a L-G and N-G test ... must be performed without the main bond in place... but you can do it at the very end.



That's how we don't have to worry about ruining appliances... perfect! Thanks![/QUOTE]

I'm thanking Splatz, but I don't know how, too new at posting lol. I tried quoting above, didn't work, oh well, I'll figure it out!


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## electricguy (Mar 22, 2007)

electricguy said:


> And then the guy looses his CSA manufactured home certification, he has a set of standards to adhere to, good plan NOT



Here is the CEC spec


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## brian john (Mar 11, 2007)

NETA Standards

From Table 
100.1

Equipment in Volts Minimum Test Voltage, DC
Recommended Minimum
EQUIPMENT VOLTAGE 250 TEST VOLTAGE 500. 

MINIMUM ACCEPTABLE 
RESISTANCE IN MEGOHMS 25

EQUIPMENT VOLTAGE 600 TEST VOLTAGE 1,000. 

MINIMUM ACCEPTABLE 
RESISTANCE IN MEGOHMS 100


I know of no 1000 VDC and below "Meggers" that have variable voltage other than fixed settings of 50, 100, 250, 500 and 1000 VDC.

In the USA as NM is 600 VAC rated it is acceptable to test at 1000 VDC.

We were just hired to test some homes owned by a foreign government we had to perform the following test.


Insulation Resistance Test (Megger) all branch circuits at 500 VDC
Impedance test at main service.
Fault current test at main service
Functional test of all AFCI and RCD(GFCI) circuit breakers
Impedance Test at each outlet
Fault current Test at each outlet
Voltage drop Test at each outlet
RCD (GFCI)Test at each outlet to include pickup current and timed test at 1X and 5X
Polarity Test at each outlet
Continuity Test (ohmic) of the EGC at each outlet


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## MechanicalDVR (Dec 29, 2007)

JabElecPlumbHeat said:


> We wire new RTM homes that ship out to North Dakota, and the 3rd party inspection agency (we are a Canadian company) has a small list of test we need to do. One of them is to megger test the circuits. It reads "Enter the voltage and length of time at which the electrical system dielectric strength was conducted. This will normally be 1080V/1 Sec." That seems a little much to me, and at what point should we do this? Rough in, but then you're tieing in all your receptacle joints (extra time) or during finishing, but then you have to make sure that led lights, appliances, GFCI's, etc aren't in yet.
> 
> I may have answered my own question lol.... during finishing, install the receptacles, megger test, then carry on with the work...
> 
> ...



This is a common requirement on all the government/military contracts I've been on and many MRI jobs as well.


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## tmessner (Apr 1, 2013)

HackWork said:


> AFAIK, you don't need much current to blow a hole in the insulation.
> 
> What would you do if you blew the insulation in an unknown spot?
> 
> As for what OP's question, it doesn't seem to make much sense to megger at the Finish. What if you found an issue with the cable? You would have to tear the walls down to find it. You should megger at the Rough.


If you test at the rough you do not catch the drywall screw in the wire. don't ask how I know that. We changed more afci breakers on randomly tripping circuit before it finally stayed tripped and we could isolate and locate the problem. after the house was finished and occupied. I am sure the owner thought we were incompetent klutzes.


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## MechanicalDVR (Dec 29, 2007)

tmessner said:


> If you test at the rough you do not catch the drywall screw in the wire. don't ask how I know that. *We changed more afci breakers on randomly tripping circuit before it finally stayed tripped and we could isolate and locate the problem*. after the house was finished and occupied. I am sure the owner thought we were incompetent klutzes.


Hence the reason for megging new circuits before energizing.


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## nrp3 (Jan 24, 2009)

brian john said:


> NETA Standards
> 
> From Table
> 100.1
> ...


What type or types of testers are you going to use and how are you going to do these tests? These sound like UK? requirements. I've seen the multifunction testers they offer for that market, never seen one in person though. I imagine you could probably get the Fluke ones here by finding the right vendor.


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## brian john (Mar 11, 2007)

nrp3 said:


> What type or types of testers are you going to use and how are you going to do these tests? These sound like UK? requirements. I've seen the multifunction testers they offer for that market, never seen one in person though. I imagine you could probably get the Fluke ones here by finding the right vendor.



I cannot find a link to the exact model right now. Had to order the tester from a UK website.

Kyoritsu 

https://www.kew-ltd.co.jp/en/products/007/

I also have several meters that perform different functions to comply with the test specs. 

Really losing money on this as I spent hours and hours researching the test for a job that never came to be last year that was for a complete high rise owned by a European firm. Had I landed that job, well sometimes you spend money to make none.


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## Nukie Poo (Sep 3, 2012)

tmessner said:


> If you test at the rough you do not catch the drywall screw in the wire. don't ask how I know that. We changed more afci breakers on randomly tripping circuit before it finally stayed tripped and we could isolate and locate the problem. after the house was finished and occupied. I am sure the owner thought we were incompetent klutzes.




We megger right after drywall but before spackling if possible . The idea, as previously mentioned, it to catch the errant drywall screw but Before they finish spackling, painting or wallpaper hanging so repairs aren’t so traumatic. If any paneling, wainscoting, etc. comes later, we have a baseline clear condition and any subsequent tripping can almost directly be attributable to the carpenters and you can prove it if you log everything. CYA


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