8Amp corded mower trips 15Amp rated circuit breaker

theguyz wrote: ↑ Also your extension cord could be causing problems if too long or and to high of gauge. Also if ground pins are missing.

Zamboni wrote: ↑ Yep, bet he's using a 16 or even 18 gauge long extension cord. Blades need sharpening, long grass, crap extension cord = circuit breaker tripping.

Jon Lai wrote: ↑ Assuming the mower was designed and functioning properly, though, the motor should just stall instead of pulling more than 8A (what it was rated for)

robsaw wrote: ↑ Sure wouldn't rely on this thread for electrical knowledge.

Long cord with resistance that REDUCES voltage AND current will not trip the breaker at 8A load. Amps at both ends of the cord are the same - a matter of physics.

There will NOT be a resistive limiter to make an 8A rated electric motor that would otherwise be 15A rated.

Many electric motors can and will draw more than their rated current if the motor RPM is slowed by heavy load.

Is there another load on this circuit that isn't identified? Old/worn breaker is possible. Or the mower motor has some sort of fault in the winding drawing extra current.

Zamboni wrote: ↑ Its not drawing more than 8amps....its not getting the 8amps because of voltage drop IF he is using 16 gauge extension cord. I don't think 16 gauge extension quite carries 8amps even at short length, so when the motor is taxed it trips the breaker. Probably runs hot also if its a 50' cord.

robsaw wrote: ↑ Sure wouldn't rely on this thread for electrical knowledge.

Long cord with resistance that REDUCES voltage AND current will not trip the breaker at 8A load. Amps at both ends of the cord are the same - a matter of physics.

There will NOT be a resistive limiter to make an 8A rated electric motor that would otherwise be 15A rated.

Many electric motors can and will draw more than their rated current if the motor RPM is slowed by heavy load.

Is there another load on this circuit that isn't identified? Old/worn breaker is possible. Or the mower motor has some sort of fault in the winding drawing extra current.

ChicoQuente wrote: ↑ The long cord won't REDUCE voltage AND current. It will create a voltage drop which will result in increased current as the motor will pull more current to compensate for the lower voltage in attempting to maintain it's rated RPM. I agree that on an 8A load it probably won't trip the breaker alone but it could if combined with any other issue.

But until OP returns with more information we'll never know what the problem is.

craftsman wrote: ↑ What you are seeing is actually expected.

Electric motors have two current ratings (more if you want to look at current graphs and different situations but that's another discussion) - free current and stall current. Free current is the standard number people see when the motor is running freely (ie no extra resistance and running at the rated RPM). Stall current is just what it sounds like... when the motor is under heavy load and is stalling. The motor uses more power to try to move when stalled or stalling than when the motor is free running.

In your case, the 8A rating is probably based on free current - ie the lawnmower consumes 8A of current when the motor is running freely at the operational RPM. When your lawnmower hits a rough/thick patch of grass, the motor loses speed and starts to stall which will increase the current draw. If the rough/thick patch is small, the higher current draw is short as the motor recovers quickly. However, if the rough/thick patch is larger, the higher current draw is much longer as the motor's speed can't recover causing a prolonged higher current draw that may trip the breaker.

Elfwood wrote: ↑ Thanks. Yes that fits my observation of when the mower trips the breaker. So if I purchase a 12A mower, will it trip even more frequently (on rough/thick patches) since it's closer to the breaker's limit of 15A? Or is the 12A mower more powerful and able to push through the rough/thick patches on free current (without stalling)?

Elfwood wrote: ↑ Thanks. Yes that fits my observation of when the mower trips the breaker. So if I purchase a 12A mower, will it trip even more frequently (on rough/thick patches) since it's closer to the breaker's limit of 15A? Or is the 12A mower more powerful and able to push through the rough/thick patches on free current (without stalling)?

jzmtl wrote: ↑ Should trip less or none.
The technical explanation is what limits the current through motor isn't the resistance of the windings (that's a dead short and will allow close to 100 amps), but back EMF created by rotor when it's spinning. If it slows down too much it loses that limit and getting closer and closer to short circuit, so more and more current is going through till it either burns or in your case trips the breaker. A 12A motor will have more torque while running and not slow down as much to lose that limit.

Elfwood wrote: ↑ Thanks. Yes that fits my observation of when the mower trips the breaker. So if I purchase a 12A mower, will it trip even more frequently (on rough/thick patches) since it's closer to the breaker's limit of 15A? Or is the 12A mower more powerful and able to push through the rough/thick patches on free current (without stalling)?

engineered wrote: ↑ It could still trip if you let the mower bog down. With your current mower, you could try sharpening the blade and going slower over the tough patches. When you get your new mower, make sure the blade is sharp and avoid letting it bog down. Either slow down, or do more overlap (ie, run mower on 50% of last pass).
Our EV charges for 16+ hours at 12A on a 15A circuit with no issues, just to put your mind at ease. Of course, I can't run my 12A mower on the same circuit at the same time.