Meg Ohm Wires

[brian john]

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.

I have meggers that have 10 VDC and 100 VDC settings

Meggers with 50-100-250-500-1000 VDC settings

Meggers with 250-500-1000-2500-5000 VDC

 

[Controls Guy]

Meggar Results - Dry Wires

Meggar Results - Dry Wires

I came into the forum looking for a second opinion on some underground meggar results and saw your post.

With the service disconnect open and all branch circuit breakers closed, you can megger from L1 bus to L2 bus and look for very high resistance, followed by L1 to neutral and L1 to ground, then repeat with L2 to neutral and L2 to ground. The assumption here is that all branch circuits are intact and properly wired.

At a glance, the megger will try to find a path of current through all branch circuits from L1 or L2 simultaneously. If megger readings are low, opening one breaker at a time until the bad reading goes away will identify a faulty branch.

Make sure nothing is plugged into any outlets and you unscrew light bulbs. The megger can damage loads and bulbs rated at 120 or 240.


My Fluke megger has a 250, 500 and 1000 volt test feature. I use the 1000 volt setting on my Fluke megger with the following philosophy:

Wires rated at 600 volts have to exceed their rating and a known dry, effectively insulated conductor will pass. Test a brand new roll of wire to see what I am referring to. My Fluke reveals infinite ohms (>4000 MegOhms) or 4 billion ohms on brand new, dry wire on a roll.

The test current from a megger is so low, you won't damage the wire insulation with momentary tests.

Safety Tip: never use a megger in environments where gas vapors are present or other flammables. This includes concealed areas where you suspect wires and flammables and fuel tanks/piping to be in close proximity. I have an aviation background, and there are many horror stories of folks blowing up aircraft with meggers.

Meggers are expensive overhead if not needed on a regular basis. Might want to consider calling some of your larger, local electrical suppliers to see if they have rental units.

 

[johngary]

Thanks for your help

Thanks for your help

The stitch in time reference was all I needed thank you for you guidance in helping me to become more informed.

John Gary