What is the best and safest way to measure for current on a fan shaft or motor shaft?

Ralph,

I just soldered a VOM lead to a small brass brush and touch the brush to the shaft while it is running and meausre the voltage between ground and the shaft. I have been told that 0.3 volts can cause bearing damage. The motor that I checked had up to 7 volts AC and had been loosing bearing about every 3 months. Make sure to apply the brush in an area void of a keyway or key.

John J

Thanks John for the rapid reply. Sounds good.

Ralph,
I mounted a DC brush to a phenolic stick with the lead coming off to a spring loaded clamp. Once you checked the voltage, move the clamp to ground and put a current clamp around it to measure the shaft current.
This will only work for low frequency current. If your problem is VFD related, you will need a Rogowski Coil to measure the high frequency current.
As far as voltage is concerned, many papers have been written and most drives technicians are taught to pay close attention to the voltage. I prefer to jump to the obvious, namely the current. That is what causes EDM.
My experience is that current (low and high frequency) should be limited to 500 mA.

I have seen people using welding cable with removed insulation plaved on top of exposed part of the shaft.

new to me. is there any portable equipment that has similar function offered in the market?

if no, how necessary is to have this excercise in the plant?

You can find a lot of info on this subject onhttp://www.sohreturbo.com/

I have a CSI shaft current accessory. I don't think they sell it anymore. Hint: the contact wand is made from a spiral brush used for gun barrel cleaning. You hunters and terrorists know what I mean.

Walt

Walt, Mine came chambered for a 22 cal but I prefer the .44 Magnum

This message has been edited. Last edited by: Danny Harvey,

aint familiar to that. im thinking of improvising parang in to trim the brush.

Question for Ron,

You mentioned that a Rogowski Coil should be used for high freq VFD applications. I don't know anything about these coils.

What freq ranges are you talking about. Most VFD's only get up to about 15Khz that I'm aware of.