Megger testing of residential circuits

[Don Hester]

Okay, general question here. Have anyone hear of a HI Megger testing residential circuits as part of their home inspection?

I have not personally ever used a megger but from what I understand that type of test would be very time consuming or am I missing something.

Please enlighten me.

[Roland Miller]

All mobile homes are required by NEC to be "Dielectric Strength Tested" (Megger) with luminaries and appliances installed.. And have a continuity and operational test with polarity checks.

[Don Hester]

Robert,

I understand the principle of it I just have never heard of anyone one doing it. From my understanding also it would require you to remove the conductors to test as you can damage equipment and GFCI/AFCI.

From what I know (which is rudimentary) of the testing protocol this would be a time consuming procedure.

I am hoping one of the Sparkys in here will chime in.

[Roland Miller]

Robert,
I am hoping one of the Sparkys in here will chime in.


They did!

1.) Make sure that the breaker box is disconnected from line power and ground.
*Performing the test with line power connected can cause a shock hazard or
damage the Hipot tester.
2.) Remove the Jumper between the Neutral and Ground busses located within
the breaker box.
3.) Using a splitter kit, attach one HV lead to the neutral bus and the other HV
lead to one of the input line busses. *You must use a jumper (heavy gauge
wire) to connect both the input line busses together. Now the neutral and
both line input busses are be connected to the HV output of the Hipot tester.

29246
4.) The Return of the Hipot tester should then be connected to the ground bus of
the breaker box.
5.) In order to simplify the testing process, make sure that only 1 circuit breaker
is closed during the test.
6.) Once a test has been performed make sure the tester is OFF. Move on to the
next area by closing each circuit breaker and performing a Hipot test
sequentially until all areas have been tested.

[Don Hester]

They did!

1.) Make sure that the breaker box is disconnected from line power and ground.
*Performing the test with line power connected can cause a shock hazard or
damage the Hipot tester.
2.) Remove the Jumper between the Neutral and Ground busses located within
the breaker box.
3.) Using a splitter kit, attach one HV lead to the neutral bus and the other HV
lead to one of the input line busses. *You must use a jumper (heavy gauge
wire) to connect both the input line busses together. Now the neutral and
both line input busses are be connected to the HV output of the Hipot tester.

29246
4.) The Return of the Hipot tester should then be connected to the ground bus of
the breaker box.
5.) In order to simplify the testing process, make sure that only 1 circuit breaker
is closed during the test.
6.) Once a test has been performed make sure the tester is OFF. Move on to the
next area by closing each circuit breaker and performing a Hipot test
sequentially until all areas have been tested.


Rolland, Sorry.

Thank you for the reply. You confirmed what I assumed. I am wondering when performing this test how much time it would take to test a standard 200 amp panel circuits.

Just trying to get a feel for how long and intensive this is.

- - - Updated - - -


Time consuming and costly. Some of the things that would need to be disconnected before testing would include appliances, GFCI receptacles, AFCI/GFCI circuit breakers, lamps in fixtures, HVAC equipment, transformers, lighted wall switches, dimmers, thermostatically controlled fans, ETC.

As you can see from this list, which is not all inclusive, this type of testing in a dwelling is not really practical unless there was some hard evidence that some of the wiring may be damaged.


Rolland, I replied before I saw this comment. This is what I was thinking but wanted to make sure because as I stated I have never seen anyone do it and only have a little knowledge from what I have read on the testing protocol. I want to have some confirmation of what I was reading and not missing something because of my lack of real world understanding.

[Roland Miller]

Rolland, Sorry.

Thank you for the reply. You confirmed what I assumed. I am wondering when performing this test how much time it would take to test a standard 200 amp panel circuits.

Just trying to get a feel for how long and intensive this is.

- - - Updated - - -




Rolland, I replied before I saw this comment. This is what I was thinking but wanted to make sure because as I stated I have never seen anyone do it and only have a little knowledge from what I have read on the testing protocol. I want to have some confirmation of what I was reading and not missing something because of my lack of real world understanding.

It is time consuming. Roberts list is not correct but it would be a safe one to follow. I just had a home inspection for a house I am selling and it lasted 3 hours with 2 other special inspectors involved. This would be one to have a reputable electrical contractor do if you are not comfortable doing it. It is a specialized electrical test. I wouldn't offer it unless there was evidence of fire, lightning strike, flooding or other damage that could degrade the electrical system ( or if requested by someone)..

- - - Updated - - -

OBTW--I would estimate it taking 2-3 hours in addition to the other things you may be inspection..

[Roland Miller]

Which part of the list is incorrect? Can any of those item withstand a 1000 volt test?


I didn't mention a voltage. 250 volts is available for an insulation test. It is quit common to only use 2 times the operating voltage to test with. And there are several time quantities that can be used and useful. Mobile homes are mandated by the NEC as to Voltage used--1 minute 900 volts and 1080 volts for 1 second with switches closed and luminaries or appliances installed..

[Roland Miller]

So using the voltage/time parameters you've mentioned, can any of the items in post #6 survive those tests?


It's your list. You need to provide supporting evidence of each item. Otherwise it is just your opinion..

PS--I helped already with the GFCI.

[Roland Miller]

Its just your opinion. Maybe you should check with some of your cronies. I know the answer and have already posted that the NEC requires it in mobile homes.

[Roland Miller]

Maybe you should read the entire NEC section.
I did. It just says a listed lumanaire or appliance is not required to be part of the test. It doesn't say it couldn't be. You should re-read it and impress us some more..

Why don't you tell us what we are trying to accomplish with a megger test? I don't believe you understand the circuit connection and the desired outcome.

[Roland Miller]

29247

[Roland Miller]

See Roland, we're just having a friendly conversation where we all, including myself, can learn something but as usual you take the low road with your comments. I have done megger testing in the past but it was many years ago and I can't remember if it was AC or DC. Given the information that you've provided I'll assume that it was DC.

So do feel confident that there is no possibility that something may be damaged by the 900 volt/1 minute test that you've mentioned?


I don't know the answer to your question and was hoping you would provide additional information..I don't feel like you are receptive to learning from me and I don't feel capable of teaching you anything. That being said, I would also guess we are a lot more alike then we would care to admit...Since this is going down a bunny trail at this point I will bow out...

[Roland Miller]

I have made some inquiries since I didn't initially know the answer to Robert's question. I am now confident that ALL devices, appliances and all luminaries will remain connected and not be damaged by a megger insulation test if done as outlined by me above.

[Ted Menelly]

Megger testing? Home inspection? The sellers home, not your buyers? Could and should never happen as part of a home inspection.

As a stand alone inspection by a licensed and insured electrical contractor? Sure.

[Roland Miller]

Okay, general question here. Have anyone hear of a HI Megger testing residential circuits as part of their home inspection?

I have not personally ever used a megger but from what I understand that type of test would be very time consuming or am I missing something.

Please enlighten me.

I see you went to another forum and got advice that contained wrong information. Be careful what you believe..