VOM Question

Well the only way that you'll really know for sure, is if you get an answer from the manufacturer. I doubt that their service desk will tell you why. They will just properly repeat that it works fine in the stated currents.

I suspect that their instrument goes into a non-linear response at the higher currents. Now if you had a complete circuit diagram with all of the parts labeled and some time to kill you could do a reverse analysis to look for which part goes non-linear at about 300mA.

GA Redfred and smartly stated

VOM's are used on small conductors. Maybe the MFG does not want you to burn the conductor up.

Which manufacturer makes that suggestion--the VOM or the cable manufacturer?

Rhkramer:

VOM manufacturer. You know it is something like the stadard protection for human is 30mA RCD. But why 30mA?

I don't understand a few things:

• aside: what is RCD?
• Is the VOM manufacturer suggesting that you test cables by running an (external) test current through the cable, and then knowing or measuring that test current, measure the voltage drop and calculate the resistance from that?
• Normally, I'd just use an ohm (O of VOM) scale, and, in that case, the current flow is controlled by the VOM design. Of course, that won't give me a great deal of precision, so I might need to use the first method to get an accurate resistance measurement.

If it is the first method, I don't know why the VOM manufacture would specify the current to be 30 mA other than for safety reasons, but maybe someone else knows something. I'd be tempted to contact the VOM manufacturer.

Well, RCD means Residual Current Device if I got it right. I saw the 30mA on the case of this device and that is.

Well, to tell the truth. Beside the Ohm scale, we also have current scale specify for each of ohm value. I got that from an VOM meter. And well, back to my original question, I got it from a training question of electrical safety. I am sorry for that.

30mA, yes, it states on the RCD which we are using to protect human from being shocked.

In here, it is not so easy to contact manufacturer for such a question but I think we are insiders of in electrical world, we must know to the very last limit of things.

Hope to hear from you and the everybody else.