Kohler 14 RESA generator - 70A breaker keeps tripping

GeoffO
GeoffO Registered Users Posts: 6 ✭✭
I'm off-grid in southern OR at 3200' and this time of year I depend on the generator to keep our batteries alive quite often due to the short days and occasional snow. We've been here about 6.5 yrs and all is well until in the last few weeks, the generator's 70A fuse has tripped a few times without explanation. I have an Outback inverter which reports generator stats when running and I've noticed it seems to trip when the generator's input is slightly over 10kw for a few minutes, which at 240v is still under 45A per my math. So I'm wondering if the generator's circuit breaker is faulty or if it really is intended to trip at that load level? In the past I never bother checking this load level, but we ran 2 mini-splits and 2 oil space heaters when it was running just to warm the house up while the batteries were being charged and the generator never complained, never had a tripped circuit breaker. Thoughts?

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Can you give us a little more information about your system/loads?

    Are you loads "true" 240 VAC, or 120 VAC loads (or 120?240) spread over L1/L2/Neutral?

    Have you "rewired" any of your larger "120 VAC" loads (unbalanced)?

    What is the AC input (genset) / breaker max input current programmed into the inverter? Depending on the "brand" of AC inverter,... either program the inverter for breaker rating (i.e., 70 amps)--And the inverter will automatically derate to 80% of 70 Amps (at least some vendors do the "auto derate") or program 70*0.80=~56 amps.

    Obviously, if all your (major) loads are 240 VAC, then 10,000W/240VAC=42 amps... But if these were (worst case) all 120 VAC loads between L1 and Neutral, then 10,000W/120VAC=83 amps...

    There can be other issues... "Poor Power Factor" (such as large induction motors) can make the current drawn be higher than "simple" math would indicate:
    • 10,000 Watts * 1/240 VAC = 42 Amps (simple math)
    • 10,000 Watts * 1/0.60 Power Factor * 1/240 VAC = 69 Amps (complex math due to phase angles between voltage/current due to loads such as induction motors)
    In general for US standard breakers and fuses, they should not trip below 80% of rated current, and should trip >100% of rated current (can take minutes to hours depending on current/breaker design). Running between 80-100% is "iffy" (for short term surging loads like mother starting--Should not be a big issue).

    Another issue is that breakers sometimes fail/wear out. I would not expect this to happen for newish breakers... But older breakers, or sometimes other issues (vibration from engine, loose/corroded wiring on breaker terminals causing localize overheating, etc.) can cause breakers to "trip early"....

    In general, it would not be a bad idea to purchase a Current Clamp DMM (digital multi-meter) and measure the current on L1/L2/N and make sure everything is as expected.

    There are AC only current clamp meters (very common) and AC+DC current clamp meters... For AC systems, AC only meter is fine. However, for our AC / DC power systems, an AC+DC current clamp meter is very nice to have around... A couple example of AC+DC clamp meters:

    https://www.amazon.com/UNI-T-Digital-Handheld-Resistance-Capacitance/dp/B0188WD1NE (inexpensive meter)
    https://www.amazon.com/Auto-Ranging-Resistance-Klein-Tools-CL800/dp/B019CY4FB4 (mid-priced meter)

    There can be other "complex" AC interaction issues (using AC transformers, 3 phase systems, large induction motors, etc.) that can cause "circulating currents" (currents that are induced by "some component" that does not go anywhere useful--Like current between genset/inverter/transformers/neutrals/safety grounds). I don't think that is happening here... But a current clamp meter can sometimes expose those issues too.

    Also, there are circuit breakers with Aux Trip Coils--For example used an an "emergency stop" button (trips main breaker for emergenchy power off). Just need to "understand" your components your system(s) have and what possibly can go wrong.

    I would go with an AC+DC current clamp DMM first (i.e., check that L1 and L2 current are being shared correctly--Vs running mostly 120 VAC loads on L1 and Neutral).

    Anyway, my first guesses...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • GeoffO
    GeoffO Registered Users Posts: 6 ✭✭
    Bill - thanks VERY much for your extensive comments! Where to start...

    I'll buy one of the current clamp meters you've mentioned, a friend also suggested that path. I'm not an electrician, nor was I around when the system was installed so I'll have to figure out where the lines are to measure, but I can work that out.

    It's a "normal" residential wiring system with typical loads as far as I know. Some are 240AC, like the 2 mini-splits, water pump etc. but most are 120 VAC. We use propane for water heater, cloths dryer and range so those big on-grid loads are not electric.

    Haven't "re-wired" any of our 120 VAC loads.

    My Outback Radian inverter is programmed for maximum 50A input current.

    The thing that makes me think it's the breaker is that the generator has worked fine with no tripping over the prior 6 years, and as I think I mentioned originally, we even loaded it heavily with 2 mini-splits, 2 oil-based space heaters when running as we were somewhat desperate to get the house warmed up when the generator was running, and it never tripped. Now when the batteries are low and the generator comes on, I can't use any of these items and if the Outback Mate3 display shows over 10kw input, I can expect the breaker to trip soon thereafter. Though it doesn't when I'm in the 7kw range. When the batteries are partially charged and/or the sun is out, and if I turn on the generator, the input wattage is way less, such as in the 3kw or less range and there's no circuit breaker tripping.

    If something has changed with my inverter so that it's drawing much larger loads (at low battery levels), that could explain a larger load when the generator is running, but I never looked at the Mate3 display when the generator was running so don't know if there's been a change there. But even if it has changed, the totals showing when the generator breaker trips still seem well below the 80% breaker level you've mentioned. 

    My understanding is that circuit breakers are usually one of the last components to fail, but from what's been said here, does that seem the most likely scenario, or can't say? Also, I don't know if breakers fail this way - work up to a lower amperage than before, i.e. just trip earlier than they should.

    Thanks again for your insights on the issue.

    -Geoff
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Current Clamp Meters are pretty easy and very safe to use... Just separate one wire at a time and "clamp" around it. AC meters do not need to "zero". DC meters need to "zero" for best accuracy (DC Meters will "drift" from zero over time).

    Circuit breakers (and fuses) are designed to be "unreliable". They are designed to open if too much current flows. And they can fail.

    With your breaker(s), just clamp the AC meter around one wire that leaves the breaker and see what the current flow is... If the current flow is >80% of the breaker's rating, you are in the range where the breaker "could trip"... For short term current surges, generally they will not, but it is certainly possible.

    The easy answer would be to simply replace the breaker with a new one... They generally are not too expensive and it may fix your issue. Using a clamp meter lets you see if there are other issues before you spend the money on a new breaker.

    There are different types of circuit breakers--Thermal, magnetic, etc... Each can have its own issues. And there are counterfeit circuit breakers out there too (this is a UK based YouTube poster so terms are a bit different than US):

    https://www.youtube.com/watch?v=2TJEzdqtXlQ

    Not saying that is an issue you have--But be careful where you purchase your replacement.

    There are also GFI (ground fault interrupter) and Arc Fault breakers too... Becoming more common as a requirement for home wiring (protect against electrocution "ground fault" and arcing wires "arc fault")... Don't know what kind of breaker you have (plain, GFI, AF)--But there are other types that can be tripping for reasons other than "simple" overload current. GFI and AF breakers are known to trip due to leakage current (AC power to water puddle) or Arc Fault tripping when plugging in a brushed "universal" motor (like a vacuum cleaner).

    Example of a failed GFI (in UK, called a residual current breaker):

    https://www.youtube.com/watch?v=K3lBJMpPaOU

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • GeoffO
    GeoffO Registered Users Posts: 6 ✭✭
    Thanks again Bill. I finally reached a Kohler tech from a local authorized service rep and he confirmed what you and I have been discussing - seems it could be the circuit breaker. I've ordered the Kohler part number for that breaker so I expect it should be the right one. Will let you know after it's installed if that solves the problem.

    -Geoff
  • GeoffO
    GeoffO Registered Users Posts: 6 ✭✭
    Got the part in a few days ago, installed it and problem went away. In the last day before I changed it out, the breaker was only lasting 2 minutes before it tripped, and at load levels that just a week earlier were no problem. Great to have the problem solved. Thanks again for your comments.

    -Geoff
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Very happy to hear that your new breaker is working!

    Most of the time, the "easy" answer is the correct answer (failing breaker in this case).

    Take care,
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset