Electrical Circuits Question: I have a 200A main panel which is fully utilized. I recently put in an in ground swimming pool and a finished basement - so I put in a main lug 20 circuit 100A panel downstream to service my pool and basement.
I have a 200A main panel which is fully utilized. I recently put in an in ground swimming pool and a finished basement - so I put in a main lug 20 circuit 100A panel downstream to service my pool and basement.
Everything went all right until recently my 200A main breaker occasionally trips . This happened tonight when both central air units were on, (one -4 ton unit one 2 ton unit) my pool pump 15A and my washing machine.
I went to the main panel and measured 19A off one leg and 45 off the other. I may try load balancing and move the 4 ton unit to the leg drawing 19A - but I can't understand why this would trip a 200A main?
Hi Mike - Great Electrical Repair Question! Mike - keep in mind that the starting amps of any motor is quite high. This is commonly called Lock Rotor Amps LRA and will be found on the A/C Unit Label Information. If both A/C units start at the same time and there is a moderate load in the home you may trip your main breaker. So how can you solve this? One option is to have a Time Delay Relay installed on one of the A/C units as to prevent both units from starting at the same time. The relay can be installed on the thermostat control voltage side of the circuit. You mentioned that you may try to balance the load of the A/C units, however they are most likely 240 Volts and should themselves be balanced. You can balance the panel loads by repositioning the higher 120 Volt loads onto the low reading buss. Let me know how it works out.
Thanks for your quick response on this holiday weekend - you are correct both AC units are running on 240V and by default are load balanced - its been a long week. The LRA on the 4 ton unit is 105 and the LRA on the 2 ton unit is 55. The 4 ton units's compressor outside shows a min fuse rating of 29A and a max of 50A - I was surprised to see that the 30A breaker that the 4 ton unit is on has never tripped. I thought I may have needed a new 200A main or maybe the terminals on it were loose. I guess if both units fire at the same time and my pool pump, well and other appliances are on at the same time I will have a potential problem. As for the time delay relay what manufacturer/rating would you recommend? I will also look at moving some of the higher 120V circuits, but the time delay relay sounds like a real fix.
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