# How can I prevent my multi-meter fuse from blowing with a brief 120VAC surge?

I wanted to test how much power a GFCI outlet uses while idle, so I hooked up my multi-meter to test the current flow. I put my test lead in the amp socket, and confirmed the current was on the order of a milli-amp, so I was safe to plug my lead into the milli-amp socket.

After doing so I measured a current of a few milli-amps. But then suddenly through testing I got a sudden current spike, and blew my 400mA fuse. I'm not sure what caused the spike... maybe tripping the GFCI, etc, but some GFCIs seem to operate this way.

Is there some way I can even this out, and absorb whatever the spike current is for that sub-second that it spikes protecting my fuse and multi-meter, but still be on the milli-amp scale? I know conceptually this is what a capacitor does, but I also know you can't simply hook a capacitor up in series and expect to get any current flow.

I'm thinking maybe there's some simple circuit, or inexpensive device I can hook up between the GFCI and my multi-meter that'll prevent the fuse from blowing, but I don't know enough about electronics to know if this is possible, or where to even begin.

EDIT: Another possibility is some sort of solid-state, fast trip 300ma circuit breaker that I put in series, before the multi-meter that'll trip before I blow the fuse? Does such a thing exist?

EDIT2: How about something like a Inrush Current Limiter? https://en.wikipedia.org/wiki/Inrush_current_limiter

On the face of it, it sounds like the solution to exactly the problem I'm having.

• how do you run something like a vacuum cleaner if the power outlet only provides few milliamps? – jsotola Sep 28 '20 at 18:42
• There are slow blow fuses which can tolerate short pulses above their ratings. I would never suggest using a higher rated fuse, say 1A, in such a role. – Brian Drummond Sep 28 '20 at 18:55
• @BrianDrummond Wouldn't this put my multi-meter in danger? Whomever designed the multi-meter put in a fast-blow fuse for a reason. Presumably to protect the electronics from damage from say even a brief, 1 amp surge. – Steve Sether Sep 28 '20 at 19:08
• "... since I have to turn off the power to the entire house." Did you not do that before you inserted the meter? Did the fridge turn on and blow your meter? I think we need a schematic of how you hooked all this up and maybe a photo too. Hit the edit link ... – Transistor Sep 28 '20 at 19:57
• @BrianDrummond could you sketch what you have in mind? I have a hard time visualizing how the protection is happening, and I think there's something I can learn here. If you have time to submit an answer that would be much appreciated. – P2000 Sep 28 '20 at 21:47

• I don't really care about measuring the surge. I'm just interested in how much power these things consume over minutes, not the first initial milli-seconds. Even some sort of cheap, sacrificial fast-blow breaker, or even I guess some cheap fast-blow fuses that cost a few cents would be OK. The fuses for the multi-meter are about a $1 or$2 a piece, which, while highway robbery is what they cost. I"m using the eevblog meter, so this isn't a cheapy from the big box store or harbor-freight. I also don't really want to buy a bunch of expensive equipment to do something relatively simple. – Steve Sether Sep 28 '20 at 20:38