Meggering Lighting Circuit with LED type lights ?

[Davebones]

Occasionally we would have a breaker trip that feeds our parking lot lights . This happens just once in a great while , usually during a bad storm . We would megger the circuit to ground to verify we didn't have a dead short to ground before resetting the breaker . We have had a couple of the lights changed to LED types to see how we like them before doing the whole parking lot . I know some things like VFD's and electronic equipment you have to be careful about meggering the circuit while they are tied in . My question is it safe to megger the lighting circuit with LED type light fixtures on it ?

 

[iwire]

I would not.

 

[GoldDigger]

As long as the selected megger output voltage is no higher than the peak voltage of the normal AC source you could probably get away with it.
Meggering at higher voltages risks destruction of the LED driver circuits, if not the LEDs themselves.

 

[Fulthrotl]

As long as the selected megger output voltage is no higher than the peak voltage of the normal AC source you could probably get away with it.
Meggering at higher voltages risks destruction of the LED driver circuits, if not the LEDs themselves.

i'm not thinking its a risk, i'm thinking it's a certainty.

 

[Electric-Light]

You don't fill up a tire to 300 psi to check for leaks expecting it to not blow up in your face. Common sense goes a long way.

My guess is you have something that rubs up for a split second at a nicked, over stripped or a strand poking out at a splice somewhere as the poles sway around in the wind and meggering won't catch that at a reasonable voltage. If it started after the LED experiment, the most logical places to check for black marks around any wiring disturbed when those few LED lights were installed.

 

[big john]

These can be a pain to find. You could try splitting and megging at less than peak voltage, but if you have an intermittent air gap, that might not show anything.

Depending on how much time you want to invest in this you can either fit each fixture with inline fuse holders or split the circuit and fuse it in a pole base to divide-and-conquer.

Just have to be careful to try and get a fuse size that will blow before your breaker pickup.

 

[Electric-Light]

I am changing my response slightly. Stick with your multimeter or a megger that has a test range at 100v or below. Surge protector element, or MOVs shunt out excess voltage. since LED ballasts are vulnerable to surge damage, it's likely they use MOVs. It could cause a false reading or wear them out if you apply more voltage than they normally see in normal use. Staying well below the rated voltage is preferable both to avoid damage to LED ballast as well as well as avoiding false reading

This ballast from a disposable integral ballast LED lamp has an MOV that clamps at 270v and it's only rated for use at DC 225v or less. The fixture ballast can contain MOVs that protects against common mode surge too. 120-277v ballasts should handle 250v range fine, but 120v only fixtures may not. Same advise for anything that use line side electronics such as VFDs and electronic ballasts.