What do these current readings mean?

I was demonstrating my clamp on ammeter to a friend the other day and got some readings I couldn’t explain. The load was a 4000 watt 240V heater with a small fan motor. I measured the current at 17.6 amps and was explaining to my friend how the other lead would also measure the same. You probably know where this is going, sure enough, the other lead measures 18 amps. At my friend’s suggestion, I put the clamp on the ground lead and it showed .3 amps.

The heater is relatively new and works okay so I’m not terribly concerned but it did leave me wondering what was going on.

The fan motor is 120v and is drawing .3 amps.

In a perfect world the conductor would be perfectly centered in the jaws.
If you do not live in a perfect world there could be up to a 1.5% error shown.

Look at page 6 of this link as an example- http://assets.fluke.com/manuals/31_33___umeng0100.pdf


EDIT- Looking back and seeing you have the "additional" .3 showing on ground I fully agree with tdkkart. There is a 120V load returing on ground.
Just like an "old" 3-wire dryer or oven circuit does. As compared to the "new" 4-wire oven and dryer circuits.

Would a manufacturer intentionally use ground as a conductor? Everything I've read here on GJ says that's a bad thing.

LG63 said:

Would a manufacturer intentionally use ground as a conductor? Everything I've read here on GJ says that's a bad thing.

Click to expand...

It was done completely intentionally for many years, and caused no real issues until the government went looking for reasons to stick their nose into things yet again.

tdkkart said:

It was done completely intentionally for many years, and caused no real issues until the government went looking for reasons to stick their nose into things yet again.

Click to expand...

Well, kinda.
Just like my example of an "old" 3-wire dryer and oven circuit. Anything 120V returned on ground. Like the light bulb and some timers.

A few code cycles ago the NFPA determinded that this was not a good thing. Hence why there are now 4 wires running to dryers and ovens.
The 120V loads return on the neutral like there supposed to. That allows the ground to be carrying nothing, so there is less impedance to help clear a fault faster if it happens.
While there may have never been any real issues, it is (and always has been in my opinion) a less than a proper way to have a safe electrical install.

EDIT- These currents returning on ground can add up if there are many of them on a subpanel which has the grounds and neutrals seperated.
Not very likely though.

Those readings are all within the accuracy of the meter. The .3 is just float of the meter or stray mag field from the conductors. You have no 120V circuit in that and it sure isn't returning on the ground.

"Less impedance" has nothing whatsoever to do with grounds and fault clearing.

Mark is correct on this one

tdkkart said:

It was done completely intentionally for many years, and caused no real issues until the government went looking for reasons to stick their nose into things yet again.

Click to expand...

malibu101 said:

Well, kinda.
Just like my example of an "old" 3-wire dryer and oven circuit. Anything 120V returned on ground. Like the light bulb and some timers.

A few code cycles ago the NFPA determinded that this was not a good thing. Hence why there are now 4 wires running to dryers and ovens.
The 120V loads return on the neutral like there supposed to. That allows the ground to be carrying nothing, so there is less impedance to help clear a fault faster if it happens.
While there may have never been any real issues, it is (and always has been in my opinion) a less than a proper way to have a safe electrical install.

EDIT- These currents returning on ground can add up if there are many of them on a subpanel which has the grounds and neutrals seperated.
Not very likely though.

Click to expand...

Sorry guys, NOT AT ALL true. Some of what I read on message boards really scares me.

The return current was NEVER allowed to be carried by the equipment ground. NEVER EVER.
Older dryer circuits used two hots and a NEUTRAL. The equipment ground was omitted. The NEUTRAL served as both the grounded and grounding conductors (neutral and ground).
It was required to either be part of an SEU cable assembly or be white insulated if part of another cable assembly or in conduit. A bare ground was NEVER used for this purpose.
From what I hear, it was not "the govt sticking it's nose into things" (sorry Mr. conspiracy), it was the govt trying to save copper during WWII as far as I know.

I don't know how this myth ever got started, but it is a shame that it is still being perpetuated to this day.

Current on ANY grounding conductor or grounding electrode conductor is NOT a good thing. And the manufacturer of this heater is certainly NOT allowing even .3A of current to flow on it.