# motor conductor sizing



## !Tom (Dec 8, 2013)

I mostly do residential and dont run into custom circuits very often, I think i got this right but wanted to double check. I attached the name plate, sorry it uploads sideways even though the file is not.

Name plate is for 208-230, its actually on 240 residential, but its a short run so i took worst case fl current x125% Does it matter that the voltage is meant to be derived from two legs of a three phase system? Circuit lenght is less the 15 feet so i ignored vd, although the extension cord from the plug to point of use outside could be another 20 feet depending on what they buy. 

Becouse this is CEC in a residential building, 20 amp circuit circuit has to be #12, 20 amp breaker. 

But, there is also a small 120v water pump in the motor (rock saw), now im not sure if that would be part of of the fl current on the name plate or not? I just took a picture of the name plate so i might have to go back and check if the pump has its own name plate?

If my choice of #12/3 is correct then it looks like i want to go with a 14-20R receptical, and im going to want to use a 2 pole gfi breaker.

Thanks.


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## mitch65 (Mar 26, 2015)

Does the equipment have a cord on it? The other pump will not be part of the nameplate data you show. There should be an equipment nameplate somewhere on the frame of the saw with the total load


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## MechanicalDVR (Dec 29, 2007)

There has to be another nameplate as that one is just for the saw motor but that isn't a big deal.

Isn't there a cord on the saw already?


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## !Tom (Dec 8, 2013)

mitch65 said:


> Does the equipment have a cord on it? The other pump will not be part of the nameplate data you show. There should be an equipment nameplate somewhere on the frame of the saw with the total load


I think it plugs into the saw as an aux recept, i cant remember, iv been putting this off as its a free side job for my dad. Ill have to go take another look. 

So if it was, ill have to add it to the inrush current sense it all starts up at the same time eh? Probably still land under 20A but i better be sure.


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## !Tom (Dec 8, 2013)

MechanicalDVR said:


> There has to be another nameplate as that one is just for the saw motor but that isn't a big deal.
> 
> Isn't there a cord on the saw already?


The cord is only a few feet long. He needs an extension cord anyways as he takes it to jobs sometimes.


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## MechanicalDVR (Dec 29, 2007)

!Tom said:


> The cord is only a few feet long.


Not why I asked.

More often than not those saws are wired for 120v not 240v that is why I asked, what type plug is on the cord?


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## frenchelectrican (Mar 15, 2007)

Most portable rock saw are typically are wired for 120 volts in most case but there are few do run on higher voltage so please look at the cord to see what conferation it is on now ?

it should be 5-15 or 6-15 P on it now so once you see the plug conferation then you should able tell what voltage it is set up for.

If you have 6-15 or 6-20 P then it is on 240 volts.


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## !Tom (Dec 8, 2013)

MechanicalDVR said:


> Not why I asked.
> 
> More often than not those saws are wired for 120v not 240v that is why I asked, what type plug is on the cord?


I think it was actually a L14-20r plug but ill have to check. Probabky best to match that instead of the 14-20R. So yeah its deffinitly 208/240V with 120v aux. Apparently its designed to be able to run on 120V but is very underpowed. 

He has been running it off his 50 amp dryer plug, using a #14 extension cord, thus the reason im trying to get this up to code for him.


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## !Tom (Dec 8, 2013)

frenchelectrican said:


> Most portable rock saw are typically are wired for 120 volts in most case but there are few do run on higher voltage so please look at the cord to see what conferation it is on now ?
> 
> it should be 5-15 or 6-15 P on it now so once you see the plug conferation then you should able tell what voltage it is set up for.
> 
> If you have 6-15 or 6-20 P then it is on 240 volts.


Itsnone of those becouse its 3 pole 4 wir, becouse the pump is 120V


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## MechanicalDVR (Dec 29, 2007)

!Tom said:


> I think it was actually a L14-20r plug but ill have to check. Probabky best to match that instead of the 14-20R. So yeah its deffinitly 208/240V with 120v aux. Apparently its designed to be able to run on 120V but is very underpowed.
> 
> *He has been running it off his 50 amp dryer plug, using a #14 extension cord*, thus the reason im trying to get this up to code for him.


 

Wow, that could have been bad if he let the smoke out!


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## Sblk55 (Sep 8, 2017)

the name plate you posted shows that it is 1 PH it would need to be on a 30 amp to run on 115V. Bu at 240V would be barely over 13amps. most any I have been around they start the saw then start the pomp this would reduce startup surge


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## !Tom (Dec 8, 2013)

Okay im officially confused becouse I just found out it is a L6-15, only 3 prongs, yet it has 120V aux pump, and now im learning that a previouse owner may have rewired the motor. 

So maybe they rewired it for 120V, and the extension cord has been rewired to fit onto 240V reciptical. 

Im going to have to go run some continuity tests. :blink:


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## !Tom (Dec 8, 2013)

Sblk55 said:


> the name plate you posted shows that it is 1 PH it would need to be on a 30 amp to run on 115V. Bu at 240V would be barely over 13amps. most any I have been around they start the saw then start the pomp this would reduce startup surge


Yeah but becouse its on a breaker dont i need to size for 125% so the inrush current wont trip it, and that brings us up to 16.25A. Plus he may use it on a 208V at a differnt location.


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## frenchelectrican (Mar 15, 2007)

!Tom said:


> I think it was actually a L14-20r plug but ill have to check. Probabky best to match that instead of the 14-20R. So yeah its deffinitly 208/240V with 120v aux. Apparently its designed to be able to run on 120V but is very underpowed.
> 
> He has been running it off his 50 amp dryer plug, using a #14 extension cord, thus the reason im trying to get this up to code for him.


oh wow .,, 

50 amp dryer plug or 50 amp range plug ? I dont useally see many dryer that do run on 50 amp circuit.,,

but that is way out of the line what the guy done with the rocksaw.,, :blink:


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## frenchelectrican (Mar 15, 2007)

!Tom said:


> Okay im officially confused becouse I just found out it is a L6-15, only 3 prongs, yet it has 120V aux pump, and now im learning that a previouse owner may have rewired the motor.
> 
> Either the ground is not being used, or the pump is using ground as a neutral? :vs_sad:


I am not too surprised if someone did use the ground as netural that is pretty much boneheaded move on that.,,


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## !Tom (Dec 8, 2013)

frenchelectrican said:


> I am not too surprised if someone did use the ground as netural that is pretty much boneheaded move on that.,,


I edited my previouse post to guesing that it was something else, but maybe this first guess was right. Ill find out and get back to yall later.

Thanks for helping me think this through. This is all a stuff i dont deal with much.


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## !Tom (Dec 8, 2013)

frenchelectrican said:


> oh wow .,,
> 
> 50 amp dryer plug or 50 amp range plug ? I dont useally see many dryer that do run on 50 amp circuit.,,
> 
> but that is way out of the line what the guy done with the rocksaw.,, :blink:


Sorry, 30 amp is what i meant to say.


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## frenchelectrican (Mar 15, 2007)

!Tom said:


> Okay im officially confused becouse I just found out it is a L6-15, only 3 prongs, yet it has 120V aux pump, and now im learning that a previouse owner may have rewired the motor.
> 
> So maybe they rewired it for 120V, and the extension cord has been rewired to fit onto 240V reciptical.
> 
> Im going to have to go run some continuity tests. :blink:


Check it over very carefully and make sure if that owner of the rocksaw want to keep it on 240 volt side then I will suggest maybe add a transformer to downstep to 120 volt for aux pump *OR* run full 4 conductor cord and use proper 4 conductor plug. 

Either way will work the best on that set up.


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## micromind (Aug 11, 2007)

Since the motor is thermally protected, if it is connected for 230 volts, it'll protect a #14 cord. 

Further, it'd be easy to get 120 from the motor even if it's connected for 230 volts and the supply has no neutral. 

Regardless of what voltage the motor is connected for, there will always be 120 volts present on T3 & T4. 

If the motor is connected for 230 volts, the max load can be roughly 10% of the 230 volt amp rating, in this case, about 1.4 amps. 

What we're doing here is using the motor windings as an autotransformer to supply the 120 volt load.


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## micromind (Aug 11, 2007)

!Tom said:


> Sorry, 30 amp is what i meant to say.


I don't know about he CEC but according to the NEC, the largest breaker allowed for this motor operating at 230 volts would be 40 amps. 

Also, it'll run just fine on 2 legs of a 120/208 3Ø Y connected system. 

If it is operated at 208 volts, in reference to my post above, you'll have 104 volts across T3 & T4. This will operate the water pump just fine.


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## !Tom (Dec 8, 2013)

Well i went and opened the thing up to see if it had a transformer and also got a wireing diagram from a 2hp model and it looks like it actually uses the motor as a transformer? 

I just dont know what this unused brown wire is for (it had a few loose strands sticking out of the crimp). I dont see it on the wireing diagram.


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## !Tom (Dec 8, 2013)

micromind said:


> I don't know about he CEC but according to the NEC, the largest breaker allowed for this motor operating at 230 volts would be 40 amps.
> 
> Also, it'll run just fine on 2 legs of a 120/208 3Ø Y connected system.
> 
> If it is operated at 208 volts, in reference to my post above, you'll have 104 volts across T3 & T4. This will operate the water pump just fine.


Ohh so thats how it gets 120. See i just always had a hard time with motors. Its in my goal to learn more, maybe go back to school so i could get into industrial. 

And yeah there is something about max breaker size, but i actually want to install a dedicated circuit so it will probably be a 20 amp circuit, expecially sense its house wiring and i have to downgrade for that according to cec rules for ressi.

Maybe i could get it down to 15 amp, but this thing deals with some pretty tough loads when you push harder rock samples into it and i dont want any unessiary tripping.


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## frenchelectrican (Mar 15, 2007)

Yup that how you can get 120 volts for aux water pump feed by using one of the running winding connection as " autotransformer " but that will only feed other motor load ( just big enough for water pump that about it) probly couple amp the most.

some motors as you mention a brown wire some are used for thermal or tempture cut out ( that will varies a bit depending on type of motor )

I would keep that on 240 Volt 20 amp circuit that way it work the best and not change back to 120 volt that is much harder on the circuit anyway.


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## !Tom (Dec 8, 2013)

frenchelectrican said:


> Yup that how you can get 120 volts for aux water pump feed by using one of the running winding connection as " autotransformer " but that will only feed other motor load ( just big enough for water pump that about it) probly couple amp the most.
> 
> some motors as you mention a brown wire some are used for thermal or tempture cut out ( that will varies a bit depending on type of motor )
> 
> I would keep that on 240 Volt 20 amp circuit that way it work the best and not change back to 120 volt that is much harder on the circuit anyway.


yeah 120V is awfull for this application,

Thanks for that.


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## micromind (Aug 11, 2007)

The brown wire is connected to the thermal O/L and is used only when the motor is connected for 115 volts. 

The thermal will disconnect only one of the 2 run windings when it trips and since they are in parallel at 115 volts, this wire is needed to disconnect the other run winding.


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