Timeline for At what threshold of imbalance should I consider moving breakers to attempt to balance bus loads?
Current License: CC BY-SA 4.0
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| Oct 15, 2022 at 12:58 | comment | added | supercat | @MonkeyZeus: If one were loading part of the system to nearly rated capacity for an extented period, that would run the risk that a breaker whose calibration was near the low end of the acceptable range might trip, but when using properly-functioning breakers, that's the only risk. Even if one were using a circuit slightly over rated capacity for an extended period of time, and a breaker's calibration was near the high end of the acceptable range, properly installed wiring should not get so hot as to cause a fire under any circumstances where the breaker wouldn't trip. | |
| Oct 15, 2022 at 12:55 | comment | added | supercat | @MonkeyZeus: A "100 amp service" will be able to simultaneosuly accommodate 100 amps to flow into or out of leg 1, 100 amps into or out of leg 2, and 100 amps into or out of the neutral. If one leg measures 45 amps and the other 15, then while the 45 amps is flowing into the first leg, 30 will be flowing out the neutral and 15 will be flowing out the second leg. All parts below half capacity. | |
| Oct 15, 2022 at 3:18 | comment | added | George Anderson | @MonkeyZeus Please, you are being overly dramatic here, like a few others here do as well, I won't mention names. You just said that a 100 amp service with one bus drawing 50 amps on one leg will trip the main breaker or "start a fire". The breaker/circuit would be operating at rated capacity. NO WAY would it trip out or start a fire. That's ridiculous. Most high amp draws are 240 v which would, by default, split the load evenly between both buses. Like I said above, 120v breakers as installed sequentially, will naturally, by design, pull power from each bus. | |
| Oct 15, 2022 at 3:03 | vote | accept | susie derkins | ||
| Oct 14, 2022 at 20:15 | comment | added | MonkeyZeus | @susiederkins Pretend your service is 100 amps and one leg measures 40 amps quite regularly while the other is 15. 40 is 80% of that leg's rated 50 amps. A draw of 10 amps or more will trip your main. If you add just 5 amps for an extended period like 24 hours then you risk a fire, possibly. You should transfer at least 10 amps to the other leg. | |
| Oct 14, 2022 at 19:23 | comment | added | susie derkins | Thanks, @MonkeyZeus - this makes sense. I wonder if you happen to know if there is any sort of guideline around the actual threshold of imbalance between the two buses that would indicate it being worth balancing? (I just edited my question to add this specificity to it). Or perhaps there isn't such a number...would it be acceptable for a panel to have every breaker attached to a single bus (and no breakers attached to the other bus)? As long as they don't exceed the main breaker, it won't trip...but would it otherwise cause issues? | |
| Oct 14, 2022 at 15:17 | comment | added | MonkeyZeus | @KMJ I pointed out those appliances because I really cannot think of other culprits which consistently draw a heavy load. If you have a 50-amp stove running and a 30-amp dryer in a 100-amp panel then it would be trivial to use one or two items which exceed the remaining 20 amps; regardless of bus. | |
| Oct 14, 2022 at 15:12 | comment | added | KMJ | Also the major consumers such as stoves, hot tubs, car charging, etc are all 240V so they go on both busses and end up as a balanced load regardless of where you put the breakers. You really have to go out of your way to unbalance a panel enough with 120V loads to cause a problem. | |
| Oct 14, 2022 at 14:40 | comment | added | MonkeyZeus | @susiederkins See my edit =) | |
| Oct 14, 2022 at 14:39 | history | edited | MonkeyZeus | CC BY-SA 4.0 |
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| Oct 14, 2022 at 14:36 | comment | added | MonkeyZeus | .@susiederkins Tripping the main is a symptom of an overloaded bus, yes. Assuming that all of your breakers are appropriately sized for the smallest wire on the circuit and you have no arcing issues then you are very unlikely to ever have an electrical issue. There is a lot of fault tolerance built into the electrical code with the 80% rule. I'll add to my answer how to verify that you're fine. | |
| Oct 14, 2022 at 14:22 | comment | added | susie derkins | Well, I haven't tripped the main breaker in 10-ish years of living here! Knock on wood! :) Are you saying it's not a problem as long as the main never trips? I have seen mention of possible overheating with unbalanced load. And yes, as you point out, my loads are fairly low amp (e.g. fans) or intermittent (dishwasher or washer running for an hour), but I would say that one bus does consistently have a greater load... | |
| Oct 14, 2022 at 14:03 | history | answered | MonkeyZeus | CC BY-SA 4.0 |