# Vfd Current And Voltage Measurements

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### #1 ej45

ej45

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Posted 30 October 2008 - 01:13 AM

I normally use the drive panel meters for voltage and current readings, but everyone keeps asking me at work where to measure voltage and measurement with a VOM. I would check line voltage at the input but can you measure current? The line side current always seems different than the drive meter. If I measure a 480VAC drive at line input at 50 amps with a clamp current meter, it always seems to read higher at the drive for example 58 amps.

### #2 martin

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Posted 03 November 2008 - 08:14 AM

Hi,
Some power is used for the fans and other electronic circuitry within the drive; not all for the output side alone.
Regards
Martin

### #3 AB2005

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Posted 03 November 2008 - 05:02 PM

QUOTE (martin @ Nov 3 2008, 02:14 PM) <{POST_SNAPBACK}>
Hi,
Some power is used for the fans and other electronic circuitry within the drive; not all for the output side alone.
Regards
Martin

For me, clamp-on meter can not measure correctly the input/output current of VFD because of high frequency output switching. Analog AMP meter can. When you checked the current, what was the output cuurent displayed on drive LCD etc..? 50A and 58A is too big diffrence.

"Don't assume any thing, always check/ask and clear yourself".

### #4 kens

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Posted 05 November 2008 - 09:00 AM

QUOTE (ej45 @ Oct 30 2008, 02:13 PM) <{POST_SNAPBACK}>
I normally use the drive panel meters for voltage and current readings, but everyone keeps asking me at work where to measure voltage and measurement with a VOM. I would check line voltage at the input but can you measure current? The line side current always seems different than the drive meter. If I measure a 480VAC drive at line input at 50 amps with a clamp current meter, it always seems to read higher at the drive for example 58 amps.

Remember that the drive will be modifying the output wave form and voltage also. You should not expect to see the same current on the drive output as the input. If you wan to see the motor current then I would rely on the drive display, if any.
An expert is one who knows more and more about less and less until he knows absolutely everything about nothing

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