I just installed a mini-split A/C system. It is 2 outdoor compressor units and 7 indoor head units. (I did 95% of the install myself, toot toot)

It was working great, but the weather had been unseasonably mild until now. (Install was done May 1, and then thru June 30, 2018, in Baltimore, MD, we had nothing but cool temps and rain)

Recently, i.e. last two days, we've been hit with a heat wave.

Also, recently, I've had three "brownout" events where the lights flickered, and power cut out in the house long enough to disrupt computers, tvs, etc. The first of these events was pretty coincidental with the start of the heat wave.

The circuit breakers did not trip. None of them, not the individual breakers or the mains.

How can I tell if my AC units are causing this or if it isn't just a general service problem from our provider?

I've tried the following:

  • Shut off all the A/C units and wait to see if the flicker happens. (this is tough though since you can't prove a negative)
  • Called my provider and asked them to check our lines. They reported no outages or brownouts in our area
  • Checked all the circuit breakers

Edit: Additional specs

My electrical service specs are

  • 200 Amp main

The breakers are

  • 1 X 50A line for the dryer
  • 1 X 40A line for the stove
  • 3 X 30A lines for the 2 A/C compressors and something else, I'm not sure what. Clothes washer maybe?
  • 29 X 15A lines for lights/outlets

That seems like a lot -- but there are still two empty slots in the panel. Although I know I shouldn't have the panel maxed out.

I'm trying to figure out how to do a load calculation to get a better idea but haven't found very good instructions on that.

Edit Spoke with neighbors in my area. There are multiple reports of lights flickering like I experienced. I'm chalking this up to the utility provider having trouble handling the spike in load this week. Also, I'm gonna buy a couple of UPSes for sensitive devices in my home.

I realize these anecdotes from my neighborhood don't prove for certain that my new A/C units are not the problem. When I am able to, and get the equipment to, perform amperage measurements, I'll take that advice and get detailed electrical information. I'd like to have that information for myself, at any rate. It seems like a good thing for any homeowner to know about their home.

  • Have you experienced these issues with the mini-split system entirely powered off? (You mention testing it, but you didn't say if it happened or not)
    – Hari
    Jul 2, 2018 at 23:53
  • when the minispilts are powered off this doesn't seem to happen. but it isn't clear; i turned them off and it happened again about a minute later, but the compressor could have still been drawin power even though the heads were off. I'm just not sure.
    – JDS
    Jul 2, 2018 at 23:56
  • Did you turn the units off at the breaker?
    – Hari
    Jul 3, 2018 at 0:18
  • no, but that's a good idea
    – JDS
    Jul 3, 2018 at 0:31
  • 1
    Is your water heater electric or gas? And that 50A breaker probably isn't the dryer breaker....also, how many of the circuits in your house feed kitchen countertop receptacles? Jul 3, 2018 at 1:16

1 Answer 1


WHY WE CAN'T ANSWER THIS QUESTION Welcome to stackexchange JDS. The problem everyone is having with your question is that you have given an excellent physical description of your problem, but almost no electrical information. To truly answer:

How can I tell if my new AC is overloading my home electric service?

We need to get the operating amperage of your AC. Then for us to try and assist in the rest of your dialog, we need to get information using and Ammeter and probably a Multimeter that gives us voltage in 1/1000 increments. Otherwise the best we can do is try to figure out if it is a utility brownout or your panel brownout.

I have attached a Panel Report and Checklist. Look at it and try fill out as much as you can so we can see what you are looking at electrical wise. Remember all of this will do no good if we cannot get at least the circuit number, what it serves, breaker size and amperes which are the first four columns from outside to inside. Also look down at the Buss Inspection area and check off what you can, and add anything that looks funny in comments.

enter image description here

I know it looks like a lot but fill out what you can and we will see what we can do.

Stay safe you will be working around live equipment.

  • thanks. this is the kind of answer i was hoping for, as indicated by "how can i tell..."
    – JDS
    Jul 3, 2018 at 17:28

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