120v single phase Soft Start?

[Jeff423]

My job site table saw pops the circuit breaker if I plug it in directly, but works fine (in the same outlet) if I run it through about 100' of 14 ga. extension cord. I guess because the cord limits the current.
In my old job we used a lot of "soft start" starters on larger 3 ph. motors and was wondering if something like that was available for 120v single phase motors? I did a search and got conflicting opinions.

 

[arjay]

I've had several routers with soft start so I'd assume they are available.Im guessing you're using 15 amp circuits? or overloaded 20 amps? That's hard on that motor using that cord

 

[Jeff423]

Thanks, I'd forgotten about routers. My router does have a soft start but it's also a variable speed motor.
I think I have a bad 15A breaker. When I plug it into an outlet on a different 15A breaker it does fine.
I agree 15A and 100' of 14 ga. extension cord is not optimal.

 

[arjay]

Don't recall the numbers offhand,but those little saws pull a lot of voltage at startup.If that breakers tripped a number of times,it's probably shot [emoji1]
I would definitely replace it.

 

[rick1085]

Let us know what the nameplate info is on the motor. I might be able to help more.
Most strongly suggest that you not use the 100ft cord as that will only lower the voltage. Thereby, increasing the amperage. Changing the breaker might be a quick fix. Your description of the the cord usage is just the opposite of what should be happening with the breaker.

 

[erics]

I assume that when you mention change the breaker that you do so with the same amperage certainly not higher. The line loss in a 100' 14ga extension is the exact cause of your starting issue. A full startup draw of 12-15 amps would be best plugged directly into the outlet. If a 100' cord is required then try to get a 10ga one.

 

[BC38]

I assume that when you mention change the breaker that you do so with the same amperage certainly not higher. The line loss in a 100' 14ga extension is the exact cause of your starting issue. A full startup draw of 12-15 amps would be best plugged directly into the outlet. If a 100' cord is required then try to get a 10ga one.

I think you're misunderstanding.
As I'm understanding it, with the saw plugged straight into the outlet - WITHOUT the 100' cord - the breaker trips when the saw is starting up.

With the saw plugged into the cord and the cord plugged into the outlet it DOESN'T trip the breaker - because the resistance of the cord is acting as a restriction and limiting the inrush current the motor draws at startup. Basically the resistance of the cord is acting as a soft start by limiting the startup current.

Using the cord may or may not hurt the saw. If it is limiting the current and/or dropping the voltage below what the motor requires, you may damage the motor by running it in an undervoltage/undercurrent condition. If you have that kind of problem you'll know - because the cord will get very warm - even HOT - if you run the saw for any length of time. If you can run the saw continuously for 10 minutes and the cord doesn't start to get really warm, then you're probably not hurting the saw. What is the gauge of the cord pigtail that came on the saw? I's probably not more than 14 gauge - same as your extension cord.

You definitely need to replace that breaker with one of the same rating. The fact that the saw doesn't trip other 15 amp breakers is the telltale symptom. You have a breaker that is weak - probably from being repeatedly tripped and reset. Replace it and you should be good to go.

Just don't upsize the breaker - because it is sized to protect the wiring for the circuit. A larger breaker would allow more current than the wiring can handle - possibly leading to an electrical fire.

What you can do is see if you can get a slow-trip breaker that will fit your electrical panel. This type would still be rated for 15 amps continuous current, but will be rated to handle a higher current spike without tripping. Another name for this type is a "slow-blow" breaker...

 

[rick1085]

BC38, please give adtional info on "slow blow" breaker. I've supplied tens if not hundreds of thousands of thermo magnetic circuit breakers over the last 40+ years and haven't heard that term associated with a single pole 15a breaker. Only for fuses. Now with an electronic trip industrial breaker, there would possibly be instantaneous or even short time adjustment. Fairly certain OP doesn't have that option. Also, you are correct in that OP can only replace with a 15a.

If OP has access to a clamp on meter, that would diagnose most of the problem.

One more thing. An extention cord will not limit current, only voltage. Current (amprage) will always go up, not down.

Just realized BC 38 must be referring to a high magnetic breaker. Good thinking that might just work.

 

[BC38]

BC38, please give adtional info on "slow blow" breaker. I've supplied tens if not hundreds of thousands of thermo magnetic circuit breakers over the last 40+ years and haven't heard that term associated with a single pole 15a breaker. Only for fuses. Now with an electronic trip industrial breaker, there would possibly be instantaneous or even short time adjustment. Fairly certain OP doesn't have that option. Also, you are correct in that OP can only replace with a 15a.

If OP has access to a clamp on meter, that would diagnose most of the problem.

One more thing. An extention cord will not limit current, only voltage. Current (amperage) will always go up, not down.

Just realized BC 38 must be referring to a high magnetic breaker. Good thinking that might just work.

Yeah I may be mis-applying industrial terms in a non-industrial residential situation, but regardless of how you describe them I am pretty certain you can get breakers with a longer delay, even for residential panels, and that is what I'm referring to.

In this case it is definitely the startup (a.k.a. inrush) CURRENT that is tripping the breaker. Since current is a function of voltage/resistance whether the cord is causing a voltage drop or restricting the current rise is really kind of a matter of perspective, isn't it? Breakers don't trip due to voltage changes, they trip due to excess current.

Either way, the cord is what is dampening the effect of the inrush current and keeping it from exceeding the breaker's ability to handle the load and causing it to trip. Feel free to correct me if I have any of that wrong...

 

[brigeton]

I had the same issue with my air compressor. It's a 3 hp. I was able to change the motor leads and hook it up to run on 240v instead of 120v then installed a 240v plug. You can even hear the difference in the way it starts now. Check the motor wiring diagram & see if it can be wired for 240v. If not you could even buy a 240v motor for it.

 

[Ga Johnny]

Now that switchgear and circuit breaker class is over,

the soft start he's thinking about is probably some sort of capacitor arrangement or set up, I don't recall ever having seen one for a 120v load though

 

[Andrew2105]

Perhaps the motor could use some maintenance..bearings, rewind or?

 

[Hillbilly77]

I think I have a bad 15A breaker. When I plug it into an outlet on a different 15A breaker it does fine.

I think you have your solution.

For less than $10 and about five minutes of your time you can swap out the defective breaker.

 

[BC38]

Now that switchgear and circuit breaker class is over,

the soft start he's thinking about is probably some sort of capacitor arrangement or set up, I don't recall ever having seen one for a 120v load though

Actually the router soft start is a rheostat, and they sell them on eBay. Here's a completed auction for one...
Universal Variable Voltage Router Fan Speed Control Controller 120V AC 15 Amps | eBay

 

[Rastoff]

I think I have a bad 15A breaker. When I plug it into an outlet on a different 15A breaker it does fine.

You've discovered your own problem. Believe it or not, circuit breakers go bad over time.

But you might have two problems. An unloaded 15A table saw motor should not pull 15 amps on startup. In fact, it should draw less than 5 amps.

So, I think you have a weak breaker on one hand AND a tired saw motor on the other.

Actually the router soft start is a rheostat, and they sell them on eBay. Here's a completed auction for one...

No, the rheostat is used for the variable speed and a capacitor circuit is used for a "soft" start. Neither is a single component circuit and both use resistors and capacitors to make the circuit work properly.

Here is one example:

 

[jcelect]

Simple Math!

P=IxE P(wattage) fixed value by the requirements of the motor, I(amperage) , E(voltage) determined by the supply system. On a 100ft, 14ga, multi stranded extension cord the voltage will drop(drastically) so the value of I will increase!
Any capacitor start/induction run AC motor(most common on small appliances) the inrush current at start is 8-10 times the normal FLA (Full Load Amps)and the inrush current drops off as the motor comes up to speed. 1/2hp motor FLA = 9.8amps, 3/4hp motor FLA = 13.8, and 1hp motor FLA = 16.0 Do the math!!!!!!!!!!!!!!!!!!!

 

[Jeff423]

Thanks for all the replies. The saw is brand new and is 15FLA. I think the replies by jcelect and BC38 explain the issue.
To summarize the condition: When the saw is plugged into outlet A, controlled by 15A breaker A, the breaker trips every time the saw is started. When the saw is plugged in to 100' of 14ga. extension cord which is plugged in to outlet A it starts fine. When the saw is plugged directly in to outlet B controlled by 15A breaker B it starts fine. Therefore I believe, as explained by BC38 and jcelect, that breaker A is faulty and the 100' of extension cord is limiting the inrush current and keeps it from tripping. I'm going to replace breaker A. I would rather plug it in directly and not use the extension cord.
I was an Aviation Electronics Technician in the Navy and can barely change a light bulb or breaker now. I'm very impressed by the level of expertise on this forum.

Thanks,

Jeff

 

[arjay]

It's also possible that there's some other appliance on that circuit drawing current,especially if it's an older home that's had some do it yourself electric work in the past.You wouldn't believe some I've seen over the years [emoji57]

 

[Steve912]

Thanks for all the replies. The saw is brand new and is 15FLA. I think the replies by jcelect and BC38 explain the issue.
To summarize the condition: When the saw is plugged into outlet A, controlled by 15A breaker A, the breaker trips every time the saw is started. When the saw is plugged in to 100' of 14ga. extension cord which is plugged in to outlet A it starts fine. When the saw is plugged directly in to outlet B controlled by 15A breaker B it starts fine. Therefore I believe, as explained by BC38 and jcelect, that breaker A is faulty and the 100' of extension cord is limiting the inrush current and keeps it from tripping. I'm going to replace breaker A. I would rather plug it in directly and not use the extension cord.
I was an Aviation Electronics Technician in the Navy and can barely change a light bulb or breaker now. I'm very impressed by the level of expertise on this forum.

Thanks,

Jeff

"And Bob's yer uncle!"

Sounds like you got it. My thought was faulty start capacitor, if motor has one.