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I am trying to measure the current in a high voltage DC circuit (over 10 kV) and have an idea I think will work, but I want to make sure before I break equipment or create a dangerous situation due to a misunderstanding.

My plan is to use a multimeter to measure the current (in milli-amps) over a 10 ohm resistor placed in series with the load (the resistance of the load is not known) and between the load and ground. As I am using a normal multimeter with a maximum voltage rating of 600 VDC, I want to make sure that this maximum voltage refers to the potential difference between the two points that I'm measuring and not to the actual voltages involved and that I can accurately measure the current. Additionally, I want to make sure that (even if that is true and the multimeter can measure the current in this way) this method will not make the multimeter charged and dangerous to touch.

If what I'm suggesting will not work, is there a different way to measure current that I am not considering?

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    \$\begingroup\$ Think about this: if the multimeter does not have ANY connection to earth/ground, how can is "see" that voltage? Also: it worries me in ways that you cannot imagine that you're working on something with 10 kV DC yet you have to ask this question. Perhaps you should educate yourself more before working with high voltages? \$\endgroup\$
    – Bimpelrekkie
    Commented Sep 19, 2021 at 18:30
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    \$\begingroup\$ The ratings on the multimeter are for voltages between its connections, that doesn't mean you can safely measure any voltage, do you think it would be safe to use it to measure 10 V (much less than what the meter can handle) at a device that is at 1 MV (Mega Volt) above earth/ground while you're standing on earth, holding that multimeter? Across what will that 1 MV be? Hint: you will not survive this. \$\endgroup\$
    – Bimpelrekkie
    Commented Sep 19, 2021 at 18:34
  • \$\begingroup\$ Thank you for your quick replies! Your response matches my understanding of what would happen (including the danger of the multimeter itself becoming dangerously charged). Is there a different technique for current measurement that would not entail such risk, besides having the measurement device placed far away from the display (as I plan to do anyway)? \$\endgroup\$
    – Alix
    Commented Sep 19, 2021 at 18:40
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    \$\begingroup\$ What you are trying to do is outside the scope of the meter's intended use. Can you measure the current on the ground side? This is much safer. If you use the meter to measure current on the high side, you need to isolate the meter sufficiently so you don't get an arc from inside the meter to surrounding objects, including you (i.e., don't touch the meter). \$\endgroup\$
    – qrk
    Commented Sep 19, 2021 at 18:42
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    \$\begingroup\$ Find or hire someone who is qualified and competent to work with high voltages. It's not worth risking your life if you don't know exactly how to do it. \$\endgroup\$
    – John D
    Commented Sep 19, 2021 at 18:44

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For battery powered and handheld multimeters, the voltage to ground doesn't matter because they are floating devices.

I have seen such multimeters used in exactly the scenario you mention: to measure small currents in a HV rack with the instrumentation sitting at 10 kV.

The main difficulties are: a) how to power the instruments and b) how to operate them.

If you use local battery power and only interact by watching the multimeter, there is no problem.

However, do note, that whenever there is a short circuit in your HV load (which can very easily happen due to arcs) the full HV can drop momentarily across your series resistor and thus across your multimeter.

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