i'm convinced!

[Charlie Bob]

After reading several posts over here and research, i've decided to invest on a Megohmeter.
-Budget: $200-$300
-Residential & commercial field
-What brands and models you all recommend?
-Should i save a little more money or that's just enough for now?
I appreciate all the tips you all, they should help make up my mind.

 

[macmikeman]

With your budget, and since it will be your first megger purchase, the Supco 500 is worth looking into. I have one and I have a Biddle that cost a couple of grand. The Supco cost me about $170 brand new. The Supco is better when you need to show a customer that they have a problem and they do not know an ohm from a wagon wheel. It reads out in "bad" "caution" and "good" ranges, although the "good" stamp is kinda hard to read as it blends into the background of the label. But it has red, yellow and green led's so its kinda easy to show the customers a bad wiring run.

Side note: Although the Supco says it puts out a 500 volt output, I have measured it with a Fluke meter and it is actually closer to 400 volts dc. The Biddle outputs 500dc and 1,000 dc just like it says on the dial. But it costs more for that baby.

 

[George Stolz]

I finally broke down and bought a Fluke 1507, haven't had a chance to really use it yet, but seems easy to use and I've never heard a cross word about it. I paid $421 for mine through my supplier.

 

[hillbilly1]

I bought a used one from a rental company, they had the recent calibration done, and I get it recalibrated at least once a year, Biddle brand, hand crank or plug in. Works great for what I use it for.

 

[zog]

With your budget, and since it will be your first megger purchase, the Supco 500 is worth looking into. I have one and I have a Biddle that cost a couple of grand. The Supco cost me about $170 brand new. The Supco is better when you need to show a customer that they have a problem and they do not know an ohm from a wagon wheel. It reads out in "bad" "caution" and "good" ranges, although the "good" stamp is kinda hard to read as it blends into the background of the label. But it has red, yellow and green led's so its kinda easy to show the customers a bad wiring run.

Side note: Although the Supco says it puts out a 500 volt output, I have measured it with a Fluke meter and it is actually closer to 400 volts dc. The Biddle outputs 500dc and 1,000 dc just like it says on the dial. But it costs more for that baby.

So what makes you think any reading you are getting from this thing is accurate? Ever had it calibrated?

 

[zog]

I bought a used one from a rental company, they had the recent calibration done, and I get it recalibrated at least once a year, Biddle brand, hand crank or plug in. Works great for what I use it for.

This is the best bet for a small budget, get a decent, calibrated, megger froma rental company. Protech is a good start.

 

[macmikeman]

So what makes you think any reading you are getting from this thing is accurate? Ever had it calibrated?

The major use for this particular unit is to check motor windings for go/no go. It is of no use for long term repeated insulation resistance testing to predict winding life , and the price tag reflects that. Will it find flaws in nm cable insulation such as pinched cable? You bet. As I said, it is also very good for demonstration purposes to the electrically uneducated masses, which when performed properly, will help to increase the income so as to afford the more expensive megger testing equipment.

 

[khixxx]

The major use for this particular unit is to check motor windings for go/no go. It is of no use for long term repeated insulation resistance testing to predict winding life , and the price tag reflects that. Will it find flaws in nm cable insulation such as pinched cable? You bet. As I said, it is also very good for demonstration purposes to the electrically uneducated masses, which when performed properly, will help to increase the income so as to afford the more expensive megger testing equipment.

Never mind I reread the post.

 

[zog]

The major use for this particular unit is to check motor windings for go/no go. It is of no use for long term repeated insulation resistance testing to predict winding life , and the price tag reflects that. Will it find flaws in nm cable insulation such as pinched cable? You bet. As I said, it is also very good for demonstration purposes to the electrically uneducated masses, which when performed properly, will help to increase the income so as to afford the more expensive megger testing equipment.

So I am guessing, no, it has never been cakibrated.

 

[macmikeman]

So I am guessing, no, it has never been cakibrated.

Yep your right, now why would I spend 500 to get a 170 dollar unit cakibrated in the first place? I posted in my first response I have an expensive biddle also, it is very accurate I have checked it with a variable resistor on multiple occasions.

 

[wptski]

The major use for this particular unit is to check motor windings for go/no go. It is of no use for long term repeated insulation resistance testing to predict winding life , and the price tag reflects that. Will it find flaws in nm cable insulation such as pinched cable? You bet. As I said, it is also very good for demonstration purposes to the electrically uneducated masses, which when performed properly, will help to increase the income so as to afford the more expensive megger testing equipment.

It will find flaws in NM cable like a "pinched" cable! You'll have to explain that one, please?

 

[macmikeman]

It will find flaws in NM cable like a "pinched" cable! You'll have to explain that one, please?

Not like some sort of circuit tracer, won't track the exact spot, that you have to find yourself. Sometimes damaged insulation does not result in a direct contact short circuit between conductors, but given enough current or a further breakdown in the insulation an arking fault is possible. The use of a continuity tester or ohm meter on a pinched cable may read out perfectly fine, yet using the Supco 500 you will get a strong caution reading or a bad cable reading in many of the cases I have seen. I don't make a practice of megging all romex jobs by any means, but there are a few house builders I have worked around where I meg all work before and after drywall out of experience with their ability to damage my work in all sorts of head scratching ways.

 

[wptski]

Not like some sort of circuit tracer, won't track the exact spot, that you have to find yourself. Sometimes damaged insulation does not result in a direct contact short circuit between conductors, but given enough current or a further breakdown in the insulation an arking fault is possible. The use of a continuity tester or ohm meter on a pinched cable may read out perfectly fine, yet using the Supco 500 you will get a strong caution reading or a bad cable reading in many of the cases I have seen. I don't make a practice of megging all romex jobs by any means, but there are a few house builders I have worked around where I meg all work before and after drywall out of experience with their ability to damage my work in all sorts of head scratching ways.

So your not refering to a simple pinched cable? Your talking about damaged cable? We've been through this before. Even at 1000V, it's not going to jump a gap like a cut or nick in the insulation. You need at least 5KV for that.

 

[mivey]

So your not refering to a simple pinched cable? Your talking about damaged cable? We've been through this before. Even at 1000V, it's not going to jump a gap like a cut or nick in the insulation. You need at least 5KV for that.

So in a home, if a 1000V megger is out, and a TDR is out, how would you check the wiring (post-drywall, post lightning)?

 

[wptski]

So in a home, if a 1000V megger is out, and a TDR is out, how would you check the wiring (post-drywall, post lightning)?

Checking for what? You won't detect a nicked wire that's for sure with 1000V. What's the difference between a nicked wire and the stripped end or even cut end? It was stated in that other thread that if you used a high enough voltage to find a nicked wire, the wire ends had to be capped with insulators to prevent arcing.

Try an experiment with some NM-B by nicking one wire and see how close you'd have to get the other wire used to get it to arc across.

 

[zog]

Yep your right, now why would I spend 500 to get a 170 dollar unit cakibrated in the first place?

Thats what I was wondering, so whats the point of even buying one if you have no idea of its accuracy?

I posted in my first response I have an expensive biddle also, it is very accurate I have checked it with a variable resistor on multiple occasions.

That is not a calibration, better than doing nothing, but not a calibration. Not sure where you get $500 for a calibration, we get all our equipment tested for a couple grand and the guy is here all week. Megger costs us about $20 to have calibrated I would guess.

 

[mivey]

Checking for what? You won't detect a nicked wire that's for sure with 1000V. What's the difference between a nicked wire and the stripped end or even cut end? It was stated in that other thread that if you used a high enough voltage to find a nicked wire, the wire ends had to be capped with insulators to prevent arcing.

Try an experiment with some NM-B by nicking one wire and see how close you'd have to get the other wire used to get it to arc across.

The voltage required to jump an air gap is not in question.

I was just curious as to what procedure you use to check for damaged wiring after drywall installation or a lightning strike.

 

[mivey]

Thats what I was wondering, so whats the point of even buying one if you have no idea of its accuracy?

I would think saying you have no idea might be an extreme. Repeated use on different circuits may indicate a problem, much like you might be able to detect if your meter went wacko between calibration tests.

He might not get data precision but he might only be looking for a general pass/fail result.

 

[wptski]

The voltage required to jump an air gap is not in question.

I was just curious as to what procedure you use to check for damaged wiring after drywall installation or a lightning strike.

Since I'm not a electrician, neither situation has confronted me yet. What procedure do you use?

I have meggered exsisting branch circuits by first making sure all loads are disconnected. Sarting at 50V first and if that reads very low, double check for loads again and/or maybe a GFCI.

 

[mivey]

...What procedure do you use?...

For drywall, burred wires in my boxes. Circuits are meggered later, but not just for the drywallers.

For lightning: Open all boxes for a visual. Visually check what you can in attic and under house. Look for smoke trails. If there is a big blow-out, might get more aggressive and remove some boxes to look inside wall. Megger.