Meggering Existing Wiring

[FaradayFF]

Hey Guys,
When Meggering the existing wiring low voltage wiring, are you looking to be read above a specific ohmic value to conclude that the insulation is OK? Can a megger test further compromise the existing wiring?
Thanks,
EE

 

[tom baker]

By low voltage do you mean conductors with 600 v insulation?
HVAC techs that work on 24v consider 120 to be high voltage….

 

[don_resqcapt19]

One testing manual has the following voltage recommendations for insulation testing.

Normal circuit voltage	Test voltage	Minimum resistance
Between 0 V to 50 V AC	250 V DC	0.5 MΩ
Between 50 V to 500 V AC	500 V DC	1 MΩ
Between 500 V to 1000 V AC	1000 V DC	1 MΩ

 

[GoldDigger]

Once you have isolated the wiring from all equipment, the greatest risk I see of increasing existing damage to wiring would be if the damage is already severe enough to fail the megger test and required replacement.

 

[ptonsparky]

Use that chart with some caution. Testing, you have conductors that show 300 meg but one at 2 meg. Somethings fishy.

 

[tom baker]

"Stitch in Time - Manual of insulation testing for the practical man ", by Biddle is an excellent reference

A STITCH IN TIME " A Stitch in Time... " The Complete Guide to Electrical Insulation Testing

A STITCH IN TIME " A Stitch in Time... " The Complete Guide to Electrical Insulation Testing

www.academia.edu