Meg Ohm Wires

[johngary]

I need some help in using a Meg Ohm meter to test wires.

The inspectors want me to meg ohm wires that have been covered before inspection to verify that there are no nails or screws that has damaged the wire integrity.

I understand the principle of the meg ohm meter -- I just need some help on how to hook it up so that I can get a reading that the inspector will accept.

Help -- awaiting your valued answeres

Thanks John Gary

 

[zog]

I need some help in using a Meg Ohm meter to test wires.

The inspectors want me to meg ohm wires that have been covered before inspection to verify that there are no nails or screws that has damaged the wire integrity.

I understand the principle of the meg ohm meter -- I just need some help on how to hook it up so that I can get a reading that the inspector will accept.

Help -- awaiting your valued answeres

Thanks John Gary

Either provide real details or call a real testing company.

 

[480sparky]

What authority does the inspector have do require megging?

 

[George Stolz]

What authority does the inspector have do require megging?

Given the option of meggering and removing all the drywall, I think everyone involved would prefer meggering. JMO

 

[480sparky]

Given the option of meggering and removing all the drywall, I think everyone involved would prefer meggering. JMO

I agree. But how many AHJs require it?

 

[George Stolz]

I agree. But how many AHJs require it?

It's not unheard of. Does it matter?

I just need some help on how to hook it up so that I can get a reading that the inspector will accept.

I think you should probably discuss the testing method that the inspector will accept with the inspector in question, no?

Left to my own devices, I would ensure that you have removed all temp lighting and receptacles from the branch circuit wiring, and then connect the megger to the EGC at at the main panel supplying the circuits. Pigtail and cap the conductors at each splicing point. Test each home-run ungrounded and grounded conductor to panel EGC and document the results.

Make sure you make the customer aware of their mistake, and that your time meggering the circuits is billable to them at a premium rate due to the use of special equipment.

 

[zog]

So we are all assuming this is a residential job?

 

[quinn77]

Ive seen screws and nails pierce NM cables without faults. very rare but ive seen it with my own eyes...prob wouldnt hurt to meg conductors to prove continuityof each conductor...just a thought.

 

[cadpoint]

....
The inspectors want me to meg ohm wires that have been covered before inspection to verify that there are no nails or screws that has damaged the wire integrity.

I understand the principle of the meg ohm meter -- I just need some help on how to hook it up so that I can get a reading that the inspector will accept.

Look up "A Stitch in Time" with a your favorite search engine.

...
Ive seen screws and nails pierce NM cables without faults. very rare but ive seen it with my own eyes...prob wouldnt hurt to meg conductors to prove continuityof each conductor...just a thought.

MO
I guess they won't let you energize the electrical panel, if they would a AFCI
will do about the same, all those NM circuit with those nails will trip and also show you some possible wire problems.

Don't get me wrong it's odd that a meg session is required, but the same amount of work might follow, it might well be a duplication of work, also.

 

[480sparky]

Look up "A Stitch in Time" with a your favorite search engine. .........

Stitch in Time.

 

[brian john]

I agree. But how many AHJs require it?

Around here it is an option BUT it must be by an approved testing company.

 

[Dave6]

At the risk of stating the obvious...I don't recall ever using a megger that worked on less than 1kv, (usually 5kv or 10kv). Ass-u-me-ing that this wire is rated at 600v...it is something to think about.

Putting "a stitch in time" in the tool box. thanks.

 

[ptonsparky]

The megger I use has several test votage ranges of 50 to 1000 volts.

I have also seen nails driven through romex with "no damage". I guess that is what we are looking for with the megger...no damage.

AFCIs that aren't junk to begin with would be good insurance after megging. Even then, after they nuisance trip once, you will never know for sure.

 

[ohmhead]

Well i agree a AFCI is what it is i would not trust it .

A megger is going to detect a problem before a AFCI will thats just my way of thinking and as far a the voltage of the wire to megger voltage testing a 600 volt wire at 1000 volts its not going to blow it out 600 volt ac wiring is rated at 600 volts but its actually a rating given for used or applied voltage of insulation and it can handle more voltage than what is stamped on the conductors thats the safe voltage which at tested current & load on conductor can run at that voltage .

You megg test between wires and if the insulation is weak at 1000 volts it will bleed thur that uncut insulation to ground or other conductor or tiny pin hole but a AFCI needs a cut or connection thur a air gap in the insulation to actually spark the gap so a megg test is better because of the higher voltage applied .

Meaning you need to have a spark gap connection before a AFCI works correctly which is not going to fined a minor cut in insulation and if its not the thing doesnt detect a cut or nick or future issue that will get worse. So fix it now or wait 1 year with AFCI when its to late But a megger will detect a problem before you have one .


Megg it

 

[boboelectric]

I agree. But how many AHJs require it?

Just the real ones that will let you off without a rough-in inspection.Other inspectors could say you didn't have an ok to board it up. Do it.

 

[johngary]

Never Assume

Never Assume

Additional information to the request
1 it is a residential job
2 the owner finished the job without getting inspection
3 that mens the walls are covered with sheet rock
4 the person who stated the it would be cheaper to meg ohm the wires than to remove the sheet rock -- got the point of the question.
5 the authority of the inspector in this case is that they will accept a meg ohm of the wire as an acceptable means to prove the integrity of the wires. Remember the owner violated the code and the inspector is siting the job due to cover without inspection.
6 my simple question is if you have used a meg ohm meter before and if so how did you connected it to the wires to prove the insulation integrity of the wires.
7 this is often required when a house has been in a flood condition and before the inspector will let the owner re-energize the electrical system they require that the wires be meg ohmed.
So I am looking for advice -- not curt answer by someone who has been there and done that -- please advice only from qualified persons.
Thanks -- john gary

 

[ohmhead]

Additional information to the request
1 it is a residential job
2 the owner finished the job without getting inspection
3 that mens the walls are covered with sheet rock
4 the person who stated the it would be cheaper to meg ohm the wires than to remove the sheet rock -- got the point of the question.
5 the authority of the inspector in this case is that they will accept a meg ohm of the wire as an acceptable means to prove the integrity of the wires. Remember the owner violated the code and the inspector is siting the job due to cover without inspection.
6 my simple question is if you have used a meg ohm meter before and if so how did you connected it to the wires to prove the insulation integrity of the wires.
7 this is often required when a house has been in a flood condition and before the inspector will let the owner re-energize the electrical system they require that the wires be meg ohmed.
So I am looking for advice -- not curt answer by someone who has been there and done that -- please advice only from qualified persons.
Thanks -- john gary

Well if you want a qualified person then hire one .

If you ask a question online ill give you a honest answer.

If you need to test its not a difficult process its using voltage from insulation to insulation or ground one wire to the other you dont need a heart surgen to come out for a megg test .

Your tester reads megg ohms on you digital lcd screen if you getting above 1 megg on romex your fine if you getting hundreds of meggs your fine go to the web pages suggested there great for you if you dont have the know how . thers more to testing you should read that first then ask more questions . ill give you a answer .

 

[ptonsparky]

I had some time so I took my Fluke 1507 to the basement. It has 50v 100v, 250v, 500v, and 1000v settings. Black lead to #4 going to CCE. About 8' away is a mini screwed to 2x4 with 1/2 rock between it & the 2x. That is where the red lead was attached. Meter showed > or maxed readings on all voltages under 1000v. The 1kv shows 1873 mega ohm.

Moved red lead to 3/4" strap screwed to underside of floor joist about 8' away. Over scale again until 1kv which then gave me a 2.4G reading.

A spare 10/2g that I have running to the garage tests out at >11 G.

My thoughts are that if you test at less than 1KV it is a waste of time.

Now off to my first service call. It is -18, with no wind. Lucky me.

Normally I would have been happy with at 2.4G reading.

 

[ggonza]

You have two options:
1-You could megger the whole house in one go (although it might be a more hassle than what it's worth). If so, like someone else said remove all devices and equipment and wirenut all your apples and bananas together. (you need to establish electrical continuity throughout the house on each leg and ground wires.) Turn off the MAIN breaker so as not to read continiuty through the POCO transformer. Remove MAIN bond jumper, to determine the egc and grounded conductor do not have any objectional "bonding" elsewhere.
Your tester should have two wires, one of them could be looked at as the "hot" conductor. The other one as a " return". Your average home has four wires. start by attaching each wire to different legs of your system, turn the megger on. If your reading pins out at maximum( the one I've used goes to >4000 M Ohms). then there is no "shorts" between the two conductors. If it goes down to 0 or any where in that low range, then you've got current flow between two conductors that aren't supposed to. To test all the wires repeat these steps betweeen every combination of conductors. It should be six different tests in all. A-B, A-N, A-G, B-N, B-G, N-G.

 

[ggonza]

sorry wasn't done yet. Make sure to replace the MAIN bond jumper. If you have to much trouble with that, you could just megger the wires between boxes to simplify it. althogh it could take alot of time.