I have a small workshop room in my apartment which shares a breaker with an adjacent room. By small I mean closet sized; I work mostly on small models so the most "heavy duty" tool I'm using is a small shop vac or a hotdog-style air compressor.

That said, I'd like to avoid tripping the breaker on accident (this hasn't happened yet, but someone is about to be living in the room which shares this breaker, so I'm trying to be prepared to be a little more courteous) and I'm wondering how hard it would be to just install an ammeter in a handy box so I can see how much current I'm using. If I use one of those analog panel mount ones, is it safe to wire it in series with the two workshop outlets and mount it in a blank handy box on the wall?

Something like this (only 0-20A instead of 50):

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Obviously there's inherent danger working with electricity, but if I am careful I see no reason this shouldn't work, and it should make it easy for me to avoid tripping the breaker and cutting the power from my roommate's room.

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    Would you be open to having an indirect system, where there's a current transformer/current sensor around the line, and then the meter is connected to read the sensor output, with an appropriate scale/legend of course? – ThreePhaseEel Feb 11 '19 at 4:49
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    Do you own the house or is it a rental? Do you positively hate Kill-a-Watts? – Harper - Reinstate Monica Feb 11 '19 at 5:43
  • Yes -- do you own this place or rent it? – ThreePhaseEel Feb 13 '19 at 1:50

Building a small panel with a panel mounted meter would be doable but it can be more work than meets they eye, you have to cut the cover for the meter, and you need a lot of room inside - the terminal studs on the back of the meter are usually pretty long and uninsulated.

An alternative would be to use a good heavy duty plug strip with a 12A breaker in the strip. This way with any luck the breaker on the power strip would trip before the breaker in the panel. You could use a Kill-a-watt with the power strip to get an idea what kind of load your tools demand.

If someone in the other room plugs in a space heater or hair dryer when you're already drawing a few amps, there's not much you can do from your end to avoid tripping the breaker.

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