See breaker busting spikes?

We are having a problem with one of our AC compressors tripping and wearing out breakers. About every 3-4 months the breaker trips and is basically sensitive after that (e.g., I think its worn down) until it’s replaced.

Looking at the graph (below) in IoTaWatt all looks good w/ a max draw of about 2.6kW at startup and then settling to about 1.9kW running. I’m wondering if there’s a much larger but shorter timespan spike happening that’s causing the breakers to wear out.

Is there a way for IoTaWatt to see and log that? Any other thoughts?


What amperage is the breaker rated for? I have to AC compressors (upstairs + downstairs units) connected through a single breaker for ~28 years without any failure. However, as you can see, I do not see any major in-rush current spike like you’re seeing. I wonder if your AC compressor unit has a failing capacitor, or something similar?

Thanks. Yep, it could definitely be a start capacitor. We have two compressors with each on it’s own 2-pole 40a breaker.

I’m not sure the spikes I’m seeing would be enough to damage a breaker though.

Do you have a 2-stage? So the higher jumps are when it’s in 2nd stage? Or is that the second compressor kicking in?

BTW, my full day chart doesn’t show the starting spikes. They only show when I get down to about a 3 hr time period.

That plot is showing time-weighted average of about 30 samples taken over a 15 second period. You can zoom in closer and get the average of about 10 cycles over 5 seconds, but that’s as much resolution as possible with IoTaWatt.

Just to throw in my two-cents, piston compressors usually have a compression release that releases the cylinder pressure when it stops. It’s normal for it to stop on the compression stroke as that’s where the resistance is. If the pressure release isn’t working, it will try to start against a large load and draw a lot of current. With the compression released, it starts easily. Mine makes a hiss when it stops as it releases the pressure. Could be something as simple as a defective or intermittent release valve.


Single stage compressors, so yes the higher usage plateaus are when both compressors are running simultaneously.

Here is a much shorter time range. Still looks much less ‘spikey’ than yours, FWIW. :wink:

And here is what 5s data looks like. :wink:

Yep. Here’s a startup for mine:

This is kind of interesting though I don’t fully understand pf and Varh.