# Motor overload



## Jameswest (Aug 12, 2020)

Question, I am replacing the contactor which operates a 3/4 horse power 240 V single phase motor. The motor has no thermal protection and the contactor I am replacing has no overload protection. The motor runs the hour strike in a bell tower it only runs for 2 to 3 seconds with a 1 or 2 second pause in between strikes. If I go back with a magnetic starter how do I size the overloads I think they will mostly see start up current all the time Also will a normal starter hold up to operating over 100 times A-day for the next 15 or 20 years. thanks


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## Kevin (Feb 14, 2017)

Jameswest said:


> Question, I am replacing the contactor which operates a 3/4 horse power 240 V single phase motor. The motor has no thermal protection and the contactor I am replacing has no overload protection. The motor runs the hour strike in a bell tower it only runs for 2 to 3 seconds with a 1 or 2 second pause in between strikes. If I go back with a magnetic starter how do I size the overloads I think they will mostly see start up current all the time Also will a normal starter hold up to operating over 100 times A-day for the next 15 or 20 years. thanks


Please take a few minutes to fill out your profile as per the user signup agreement.

Thank you.


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## Flyingsod (Jul 11, 2013)

if your not an electrical pro they will ask you to leave the site. just in case that happens ill give you my two cents. The issue is the number of times you start/stop not how long it runs. In facti its better to run a motor longer between stop start cycles as the both the motor and contactor produce a lot of heat on startup and longer run times allow more time to dissipate the heat. Most contactors will handle that situation just fine, unless you mean the motor stops and starts for a couple seconds between each strike, In that case noon and midnight are gonna kill things faster. If you want it to last longer pay the extra for a nema rated setup as opposed to IEC. In fact IEC stuff is only designed to start/stop 3 times an hour. Any more is beyond its design specs and you have to really upsize it to make it work.



You'll size overloads according to the full load amps (fla) as stated on the motor nameplate.

If youre not an electrical professional double check any decision you make with one.

good luck


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## telsa (May 22, 2015)

In fractional horsepower motors thermal protection is STANDARD -- and is usually 'invisible' to non-electricians. Yes, it's integral to the design.

No recent production (last seventy years) fractional horsepower motor is shipped without it.


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## Wirenuting (Sep 12, 2010)

Day light savings time.


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## Bird dog (Oct 27, 2015)

Did you ask Artemis Gordon? :wink:


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## CMP (Oct 30, 2019)

*Bell Tower Motor*



Jameswest said:


> Question, I am replacing the contactor which operates a 3/4 horse power 240 V single phase motor. The motor has no thermal protection and the contactor I am replacing has no overload protection. The motor runs the hour strike in a bell tower it only runs for 2 to 3 seconds with a 1 or 2 second pause in between strikes. If I go back with a magnetic starter how do I size the overloads I think they will mostly see start up current all the time Also will a normal starter hold up to operating over 100 times A-day for the next 15 or 20 years. thanks



The last bell I worked on sounds similar to what you have. 3/4HP 240V 1Ph. With no thermal protector in the motor either

It has a size 1 NEMA starter, and has been operating for many years.


As to sizing the overloads, that depends. You are likely correct that the motor will only run in the starting mode. It will never achieve the running speed. Further it likely runs at half voltage, wired at 230V but powered from 120V.


Typically the motor reverses direction on each stroke, and is accomplished by a reversing drum switch, and not the motor starter or contactor.


If you fill out your profile as requested, I can provide a control drawing, that has notes, and a sequence of operation.


Bell










Motor









Nameplate No TP


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## JRaef (Mar 23, 2009)

If the motor has built-in thermal protection, the mfr is required to state that on the nameplate, either with the words, or sometimes just the abbreviation "TP". If that is not there, you must assume there is no thermal protection.


That said, Article 430.33 allows for intermittent duty motors to be protected solely by the branch OCPD, i.e the breaker or fuse feeding power to it, so long as that device is sized per the rules in Table 430.52. We don't know how your situation is wired, you will have to determine that on your own.


A typical NEMA contactor is going to be good for 1 million electrical operations. At 156 operations per day (12 factorial x 2), that's 6410 days or about 17-1/2 years.


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## micromind (Aug 11, 2007)

telsa said:


> In fractional horsepower motors thermal protection is STANDARD -- and is usually 'invisible' to non-electricians. Yes, it's integral to the design.
> 
> No recent production (last seventy years) fractional horsepower motor is shipped without it.


Looking in my Leeson motor catalog, 1/3 HP, 4 pole (1725 RPM) ODP (Open Drip Proof) there are 3 motors listed that have auto reset O/Ls, 2 are manual reset and 2 have none. 

The other FHP sizes are similar.

Often, I'll install a single phase motor with no O/L and use something like a Square D 2510 or an Allen Bradley 600 manual motor starter (with a heater element) to control it. These are just a bit larger than a standard light switch and can be purchased with an enclosure or mounted in a box that's large enough to accomodate them. 

Sometimes using a motor with an built-in auto reset O/L is not exactly the safest thing to do; if power is still applied when it cools, it'll start with no warning. 

Sometimes using one with a manual reset is not practical because it's located in an area that's not easy to get to. 

Even if its automatically controlled, there's usually someplace to mount a manual reset starter switch.


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## Jameswest (Aug 12, 2020)

Thanks for all the imfo, I'm having a hard time figuring out where to fill out my credentials on the page


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## CMP (Oct 30, 2019)

To edit your profile, in the upper right corner of the page, click on your User Name.
When you get to your user page, in the upper left of the menu bar, click User CP (control panel). Then click Edit Your Details and fill it in.


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## splatz (May 23, 2015)

I think these are still a thing. I had one installed ahead of my oil burner, it was ancient. When it failed I called Beckett to figure out WTF. The techs I spoke to had no idea what it was, people use HP rated toggle switches. 



https://www.se.com/us/en/product-range/7474-fractional-horsepower-starters/


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## Bird dog (Oct 27, 2015)

splatz said:


> I think these are still a thing. I had one installed ahead of my oil burner, it was ancient. When it failed I called Beckett to figure out WTF. The techs I spoke to had no idea what it was, people use HP rated toggle switches.
> 
> 
> 
> https://www.se.com/us/en/product-range/7474-fractional-horsepower-starters/


Used them on schools with FHPs. IIRC never on residential.


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## 460 Delta (May 9, 2018)

splatz said:


> I think these are still a thing. I had one installed ahead of my oil burner, it was ancient. When it failed I called Beckett to figure out WTF. The techs I spoke to had no idea what it was, people use HP rated toggle switches.
> 
> 
> 
> https://www.se.com/us/en/product-range/7474-fractional-horsepower-starters/


Yeah I've used them on machine tools before, I used Furnas/Siemens. They make them with or without overload protection.


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## micromind (Aug 11, 2007)

splatz said:


> I think these are still a thing. I had one installed ahead of my oil burner, it was ancient. When it failed I called Beckett to figure out WTF. The techs I spoke to had no idea what it was, people use HP rated toggle switches.
> 
> 
> 
> https://www.se.com/us/en/product-range/7474-fractional-horsepower-starters/


These are the 2510s that I use. They come in 1 or 2 pole, with or without a heater type O/L and 3 pole with no O/L. 

I use the 3 pole versions as disconnecting means for 3Ø motors up to 5HP at 208-240 and 10HP at 480. You can get a locking provision that attaches to the front of any of them.


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