Amp reading on 2400V motor

[moosewl]

We want to measure the amp load on a 2400V motor. Can we use a fluke clamp on meter that is rated for 600V? If not, how would you suggest we obtain this data?

 

[electricpete]

We often clamp onto the CT secondaries to measure current for mv motors, then multiply by CT ratio. CT leads are generally easily accessible at input to relays and ammeters. Even though it is non-intrusive, it should still be a trained person to know what he's poking around near.

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(2B)+(2B)' ?

 

[electricpete]

Sorry I jumped over the 600v part... I don't think clamp-ons have a voltage rating. But often their jaw size is a limiting factor.

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(2B)+(2B)' ?

 

[dpc]

If you are putting the clamp-on over insulated conductors, then theoretically you can use a standard clamp-on. They do have a voltage rating, I believe.

Most existing 2400 V circuits are unshielded, so I don't advise doing this unless you take precautions and wear gloves, along with PPE. As Pete mentions, you can get good results clamping on the CT secondaries and it is MUCH safer.



David Castor

http://www.cvoes.com

 

[jraef]

These days, the PPE and procedures required to even OPEN a live MV cabinet will make it less expensive to buy a proper meter and mount it to the enclosure door.

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[jraef]

I should have added:

Unless you already have it in place...

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[dpc]

Jeff: Agreed. Those 2400 V starters are scary even with the door closed.



David Castor

http://www.cvoes.com

 

[jraef]

When nobody was around once, a technician and I were troubleshooting a 4160V soft starter and energized it with the door open. We were about 15 feet away filming it with the lights off, trying to see where the crackling noise was coming from. There was an eerie spider web of plasma crawling all over the insulation on the conductors, trying to find a ground path. It looked alive. Every now and again, it would jump a sufficiently short gap and make a "snap" sound as the plasma went to ground. One spooky day that was...

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[LionelHutz]

Beyond what the others have posted, if you do decide to clamp onto an insulated conductor then I'd recommend you place the clamp with the power off and then only read it without touching while the motor is running.

 

[Zogzog]

Use the existing CT's.

 

[ScottyUK]

Agree with Zogzog: you need earthed metal between you and it. HV electricity takes no prisoners.


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If we learn from our mistakes I'm getting a great education!

 

[davidbeach]

HV electricity takes no prisoners.

That implies that it even recognizes that there might even be prisoners to be taken. Don't count on it. ;-)

 

[Skogsgurra]

A question: When did 2.4 kV step up from MV to HV?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[ScottyUK]

Skogs,

Under the new UK rules there is no longer 'medium voltage'. If it is below 1000V AC or 1500V DC it is 'low voltage' and if it is above those values it is 'high voltage'. But yes, I do miss the MV term and use it fairly frequently in conversation. I'm just trying to adapt to the new way of doing things. In my defence I plead the following:

http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=601-01-28

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If we learn from our mistakes I'm getting a great education!

 

[Skogsgurra]

The answer to my question seems to be: Year 1985 - or earlier.

That is what is said at bottom of the document.

I had no idea.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[electricpete]

I can see there would be very few situations that someone would be clamping onto a 2400vac cable. If shielded and grounded both ends, you wouldn't get a good measurement. If unshielded and energized, caution would be in order.

On the other hand, that choice/decision has very little to do with any 600vac rating of the clamp-on that I know of. Can someone explain the significance of this rating?

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(2B)+(2B)' ?

 

[jraef]

I just noticed today that ANSI/IEEE C37.42 is called "Standard Specifications for High-Voltage (> 1000V)". I never noticed that it didn't say "Medium Voltage", is that a change too or has it always said that?

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[Skogsgurra]

Pete

"If shielded and grounded both ends, you wouldn't get a good measurement."

I doubt that a motor cable ever has individual shields on each core. Are there such cables?

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[electricpete]

The particular statement you quoted would refer to 1/c shielded power cables (yes they exist, not unique to motors) and the problem trying to measure between the shield grounds. Outside the shield termination there may be other options for measurement but also other hazards.

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(2B)+(2B)' ?

 

[ScottyUK]

ePete,

The voltage rating applies to situtations where the clamp is placed around an uninsulated live conductor.


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If we learn from our mistakes I'm getting a great education!