Checking amps on 2400 volt motors

[hockeyoligist2]

The boss wants us to check the amps on some 2400 volt motors tomorrow. My Fluke amp meter is rated for 600V. He is saying we can check the amps at the "peckerhead" with this meter. Clamp on with the motor off, start it, look at the amps from a distance and shut the motor off before removing it. I'm not comfortable with this at all.

 

[Pierre C Belarge]

Let me calmly state NO WAY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[Jhaney]

call in sick tomorrow!!!!

 

[480sparky]

call in sick tomorrow!!!!

"Hey, boss (cough, cough!), I'm not gonna (hack!) make it in today. I plan on (sneeze, sniffle.....) living through the day."

 

[wireguru]

wow. i would call the police and report an attempted murder.

 

[Jhaney]

call in sick tomorrow!!!!

while out sick work on your resume and maybe apply for a new job....might be healthier:grin:

 

[billsnuff]

does your equipment measure up................

http://www-group.slac.stanford.edu/essg/pdf/ABCs_of_Multimeter_Safety.pdf

and we ain't got to PPE or HRC or EI...... NFPA 70E

I agree with the rest...........STAY HOME

 

[Cold Fusion]

It is fairly common to use 600V CTs on shielded wire - provided the shields are not stripped back and are terminated.

But I still wouldn't with a hand-held 600V clamp-on. Motor connection boxes are too tight. The risk is low, but the consequences of a FUBAB are very high.

Before I did measurements with covers open, I'd first look at the motor starter cabinet. The overloads may well be running off of CTs, or current sensors. If so, get the schematic, and see where to tap into this circuit.

If not that, then I'd look at using a split, flexible CT in the motor starter cabinet - on the leads to the motor. Get one rated for the intended use. I won't say what rating is required, I can't see your installation.

Plenty of vendors make good equipment just for these jobs. Get the right equipment.

(FUBAB = Fouled up beyond all belief)

cf

 

[zog]

Actually from a safety aspect that will work fine, you can shut the motor down, hook up your meter, turn the motor on and you will read 0 Amps. A clamp on meter won't work on that cable if it is sheilded, which it probally is.

There is a better way to do it but you will need to provide more info about the system, no meters in this system?

 

[zog]

posted at the same time Cf

 

[Cold Fusion]

posted at the same time Cf

I guessed that:smile:

(cut) A clamp on meter won't work on that cable if it is sheilded,(cut)

Are you sure?

Most I have seen have the shield (still around the conductor) run up through the CT, then shield separated from the conductor and the braid termination run back through the CT and grounded on the incoming side of the CT.

Wouldn't work on a Rogowski sensor, but should work on a CT. I don't know about a Hall effect, I haven't used any yet - nor gone through the physics.

I don't do the installation or MV terminations. Just hook up the LV side, and use them. If I'm missing something here, let me know, I'll go through the installations again - till I understand the physics.

cf

 

[hockeyoligist2]

Actually from a safety aspect that will work fine, you can shut the motor down, hook up your meter, turn the motor on and you will read 0 Amps. A clamp on meter won't work on that cable if it is sheilded, which it probally is.

There is a better way to do it but you will need to provide more info about the system, no meters in this system?

Yes, they have meters at the VFD's. But another boss, higher up, thinks they are not correct. He doesn't even know AC from DC........ if you know what I mean! He is doing some kind of "study" and wants to know if the actual amps are the same.

 

[hockeyoligist2]

call in sick tomorrow!!!!

Already did. I went to see the Doc. after my first post, I have an infection in a very old skin graft. He said go home, no boots, gave me a shot and antibiotics. No work the rest of the week and maybe longer. It was bad news, but it might save my life!

Could the meter blow? I'm worried about my coworkers now!

 

[zog]

Most I have seen have the shield (still around the conductor) run up through the CT, then shield separated from the conductor and the braid termination run back through the CT and grounded on the incoming side of the CT.

Right but he wont be able to run the ground sheild back through the clamp on meter, this is how a CT is installed but not an option for this test.

I do need to correct my last post, it wont read zero, but the reading will not be accurate.

 

[zog]

Could the meter blow? I'm worried about my coworkers now!

If they get too close to the terminations, yes it could, that meter wont like 2400V across it.

 

[zog]

Yes, they have meters at the VFD's. But another boss, higher up, thinks they are not correct. He doesn't even know AC from DC........ if you know what I mean! He is doing some kind of "study" and wants to know if the actual amps are the same.

Use the clamp on meter at the same place the CT's are installed at the VFD. Same deal, shut it down, install, then start back up.

 

[hockeyoligist2]

Use the clamp on meter at the same place the CT's are installed at the VFD. Same deal, shut it down, install, then start back up.

We discussed that and the big boss is saying the CT's may be the wrong size. He wants a "true " reading...... We have a company that we use for our high voltage stuff, they could do the tests, but the big boss doesn't want to spend the money.

 

[480sparky]

We discussed that and the big boss is saying the CT's may be the wrong size. He wants a "true " reading...... We have a company that we use for our high voltage stuff, they could do the tests, but the big boss doesn't want to spend the money.

So you're the sacrificial lamb?

 

[hockeyoligist2]

So you're the sacrificial lamb?

I was, but I'm home sick, so, my coworkers are now. I called one of them and read him the posts I have received on this. He asked me to copy and e-mail it to him. He said he would print it out and give it to the boss in the morning. Of course I'll have to leave out some of my comments!

 

[Cold Fusion]

We discussed that and the big boss is saying the CT's may be the wrong size. (cut).

This is where I usually shut it down, safe it out, and read the numbers on the CT - see exactly what the ratio is.

One time ,when there was a lot of skepticsm, I stripped off the outer insulation on a trouble light cord, cut the white, wrapped 10 turns around the CT, (still installed on the main conductor), wirenutted the white back together, pluged the cord into a 120V receptacle. Read the CT output and compared it to a direct reading on the lamp cord. Total cost was about an hour and $25 for a new trouble light. However, it took about 1.5 days to convince the management the physics was good.

My test results? As I recall I used a 100W bulb, and the CT was marked 100:5. We saw about .4A on the CT output - amazed everybody

cf