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I have installed the 50 amp pool heater connected to the 50 amp GFCI breaker and is located outside. And I have connected to a 60 amp breaker at the panel. After a couple of seconds, when I turn on the heater, it trips my 100 amp main breaker. What would be the reason?

My 50 amp GFCI breaker is working fine. I have checked that. The total amp at the 100 amp breaker; it was around 2 amp without any appliance operating and 52 amp something with the heater on, which is less than 100 amp. Since it is the old panel, I assume there is an issue with the 100 amp breaker.

Please guide me what can I do to fix this issue.

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    Yes, can you provide a photo of the label on the inside your main panel's door please?
    – ThreePhaseEel
    Jun 25, 2021 at 11:28
  • We asked for a photo of the labeling on the inside of the breaker panel's door, not the inside of the panel itself...or is there no such label on the inside of the door?
    – ThreePhaseEel
    Jun 25, 2021 at 23:01

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What I see is you started with a 100A panel and added a 50A load to it. Now, the panel already has six 240V breakers in it. That's a little concerning, and it calls for re-doing the house's load calculation to account for the enormous new load.

That said, assuming your measurements are accurate and your 100A breaker is really tripping at 52A, that's probably a bad main breaker, as you guessed. We know from the "harpsichord look" and the style of the neutral bars that this is a very "classic" panel at least 30 years old.

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If your information is accurate; I believe you are seeing is a “non Coordinated” system.

The trip curves are different on different breakers, this happens when different series or brands are intermixed.

When I see this it is normally from a very high current that looks like a short. Your main breaker is doing its job protecting the buss.

The high current possibly a short is dropped out from the main so quickly that many clamp meters do not register it unless they have spike monitoring and can show the max value drawn.

Why are the 50a GFCI and 60amp breakers not tripping? The trip curves are different on hacr and spa panel breakers to allow motor starts and the trip curves are usually more liberal for this reason and they might be allowing more current to flow for a short time like 10, 20, 30 seconds

This would be if you really only have 2 amps being drawn on the rest of the panel that I would question with as many branch circuits as I see.

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  • Thank you for ur comments Ed, what can I do to fix this issue??
    – Yason Thaya
    Jun 25, 2021 at 17:03
  • First I would use a recording clamp meter to show the actual peak load at the main, adding a 52 amps to a 100 amp service might be a stretch I would record the values as I have a hard time believing 2 amps on a 100 amp service, from what I have measured on homes with gas and 100 amp services the load is usually around 20-30 amps. Add 20-35 amps on average for AC. This is over hundreds of homes measured some higher and some lower. Once that value is verified then check the 52 amp load and the size of the pump. remember pumps pull 3-5x on startup then take steps based on that evaluation
    – Ed Beal
    Jun 25, 2021 at 17:21

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