Megger help

[61333]

Been some time since I use a megger, can't remember how to use the wind up toy. I need to use it for nmwu 12/2, breaker trips every two to three day with a 2 amp continuous load on a 20 amp breaker?

 

[electricalperson]

the black wire goes to ground and the red goes to the wire you want to test. make sure all loads are disconnected, including light bulbs, dimmers, gfci's and anything plugged in. start at a low voltage like 50 or 100 and continue to 1000v a reading of full scale on romex is ideal but anything over 100 megaohms is fine. megger hot to ground, neutral to ground and hot to neutral. make sure you lift all connections in the panel

 

[brian john]

I'd FOP the circuit breaker first all components involved in the panel to conductor connection.

 

[electricalperson]

I'd FOP the circuit breaker first all components involved in the panel to conductor connection.

good point

 

[K8MHZ]

The first test should be the cable only so everything on both ends should be disconnected before testing.

Do you know how to do a long term test and plot a graph? Your problem may not show up on a spot check and may need a breakdown evaluation.

Can you crank a megger for several minutes straight and maintain full power for the duration of the test? If the test needed is more than a minute long I really would suggest a battery powered tester. Especially if you don't want to interrupt the test in order to record your readings as the periodically change. In the old days, the cubs would do the cranking and the JIW's would record the information and plot the chart. Until the advent of the battery powered tester, megging was pretty much a two person endeavor.

 

[zappy]

I'd FOP the circuit breaker first all components involved in the panel to conductor connection.

What does FOP stand for?

 

[Mister Kool]

^^^^^yeah^^^^
I wanna know too ZAPPY

 

[zog]

What does FOP stand for?

Fall Of Potential

 

[brian john]

What does FOP stand for?

FOP- Fall of Potential Test, you are measuring voltage drop across a portion of the circuit with your multimeter on AC millivolts. EVERY section of any circuit has voltage drop, there is voltage drop in one inch of #12 AWG if there is load.

Readings work best if the loads are balanced. Write the readings down as you go

Measure voltage drop from the line conductor of ?A? phase to the Load conductor of ?A? phase (on the strands of the copper or aluminum) Do the same for ?B? and ?C? phase. Now narrow your test down From the ?A? Phase line conductor to the ?A? phase termination connector (lug), Then from the termination connector to the mounting bus. From mounting bus to the fuse clips, from the fuse clips to the fuse barrel, from the line of the fuse to the load of the fuse and on and on. Do the same for ?B? and ?C? phase.

For each reading you should have similar readings on the other phases, comparison test. The component or components with high readings are the source of the issue.

Tightening a bad connection only gives you a tight bad connection

 

[Cow]

Just for reference seems like the last time I FOP tested a new 2 pole 30 Siemens breaker in a residence I got around 65 milliamps with an 18 amp load(water heater).

I can't tell you what a good reading is, seems everyone keeps it a secret. I guess experience will tell you what's good and what's bad after you've done it a few times....

 

[brian john]

Just for reference seems like the last time I FOP tested a new 2 pole 30 Siemens breaker in a residence I got around 65 milliamps with an 18 amp load(water heater).

I can't tell you what a good reading is, seems everyone keeps it a secret. I guess experience will tell you what's good and what's bad after you've done it a few times....

There are no published values and readings will vary widely between device types based on load on the circuit and manufactures of the same size devices. Comparison readings are best such on a 3 pole device or between similar sized OCP's.

 

[K8MHZ]

Just for reference seems like the last time I FOP tested a new 2 pole 30 Siemens breaker in a residence I got around 65 milliamps with an 18 amp load(water heater).

I can't tell you what a good reading is, seems everyone keeps it a secret. I guess experience will tell you what's good and what's bad after you've done it a few times....

Wouldn't FOP be expressed in mV?

 

[wptski]

Wouldn't FOP be expressed in mV?

Yeah, that's a typo. I replaced one on a water heater drawing 18.3A that dropped from around 130mv to around 60mv with the new one.