Multimeter shock hazard question

Thread Starter

ebeowulf17

Joined Aug 12, 2014
2,945
I don't intend to deliberately do this, but...

Hypothetically, let's say I've got my DMM in voltage measurement mode with the probes plugged into the appropriate sockets. Now, if one probe is connected to line voltage, and the other probe isn't touching anything, does the second probe present a possible shock hazard? If I touched the floating probe with one hand and my other hand was grounded, could I get shocked?

I would've thought the answer was no. I'd assumed that there was enough impedance to make the loose probe harmless.

The reason I ask is because l was talking with a co-worker about the new-ish Fluke T6 series of electrical testers, and he directed me to the following video:


The video includes a lot of cursing and name calling because he's frustrated with how poorly the unit works, but the intriguing part starts around 5:30 into the video.

The T6 line includes non-contact voltage measurement which requires a ground, and one grounding option is through the hand of the user. In the video, he lays out a scenario where the user could could be exposed to line voltage through the inputs of the meter. I'm not surprised he can get a scary looking voltage reading for the video, but I'd have thought it was a "ghost" voltage through massively high impedance, and that you could touch it without being harmed.

It's hard for me to imagine that Fluke made a product with the risks implied in the video, and my understanding of meters would've told me this should be harmless, but I'm just not sure. What do you think?
 

BR-549

Joined Sep 22, 2013
4,938
The floating probe shouldn't harm you if you're on the voltage function. Current function should be close to a dead short......it will bite.
 

crutschow

Joined Mar 14, 2008
23,532
The meter impedance should be at least a megohm and so the current from from the unconnected probe should be less than a mA.
That may bite a little, but shouldn't harm you as it typically takes several tens of mA of current through the chest to kill.
 

MisterBill2

Joined Jan 23, 2018
4,055
The floating probe shouldn't harm you if you're on the voltage function. Current function should be close to a dead short......it will bite.
If it happens that somebody made a very dumb error and plugged the probes into the current jacks then there would be just a few ohms between the probes and the shock hazard would be very real. But if the operator is paying attention and understands how to use the meter correctly, then, in the voltage mode with the probes connected to the voltage input, the resistance would be at least 10 megohms, and so the current would be very small. I (current)= volts/ ohms. Thus for a thousand volts and 10 megohms, I=1000/10,000,000 which solves to be 0.1 milliamp. So that would not be a shock hazard.
One place I worked at somebody grabbed a meter off a bench and put the probes across 480 volts, fused at 100 amps. The meter leads were connected to read current. The fool destroyed the meter and burned his hands and startled the whole shop. All because the fool was to lazy to check where the leads were connected on the meter he grabbed without asking if he could use it.
 

MrChips

Joined Oct 2, 2009
19,421
Rule #3 - Always set the range switch to the highest voltage range when finished with using the meter (assuming that there is no OFF position on the range switch).
 

MisterBill2

Joined Jan 23, 2018
4,055
Always unplug the leads after measuring current because some people never check where they are connected. See my previous post as to why that is important.
 
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