motor overloads

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I have a kitchen exhaust fan in a commercial kitchen. Currently it is turned on and off via breaker. I would like to add switch and or motor starter before fan to keep staff out of panel. Just need some clarification on overloads.
1. 1 1/2 hp motor 120 v has thermal overloads built in
2. it will be continuous duty, running the whole time kitchen in operation.

I thought I could use just a general duty 20a switch to control since the motor has overloads built in. But I stumbled on the continuous duty aspect. I will check nec when I get home but was just hoping for some extra info as well.
thanks
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
I have a kitchen exhaust fan in a commercial kitchen. Currently it is turned on and off via breaker. I would like to add switch and or motor starter before fan to keep staff out of panel. Just need some clarification on overloads.
1. 1 1/2 hp motor 120 v has thermal overloads built in
2. it will be continuous duty, running the whole time kitchen in operation.

I thought I could use just a general duty 20a switch to control since the motor has overloads built in. But I stumbled on the continuous duty aspect. I will check nec when I get home but was just hoping for some extra info as well.
thanks

As far as I know you would need to use a 30 amp switch which is rated for 2 HP since a 20 amp switch is only rated for a 1HP motot.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
If your motor has built-in thermal protection, that's all you need for OL protection. I'm not sure why you think "continuous" has anything to do with this.

But yes, the switch needs a 1-1/2HP rating and a 20A switch does not have that, so when you buy one capable of 1-1/2HP, you will find it is a 30A rated switch. that doesn't automatically mean however that any 30A rated switch has a HP rating, you need to start WITH that criteria.
 
If your motor has built-in thermal protection, that's all you need for OL protection. I'm not sure why you think "continuous" has anything to do with this.

But yes, the switch needs a 1-1/2HP rating and a 20A switch does not have that, so when you buy one capable of 1-1/2HP, you will find it is a 30A rated switch. that doesn't automatically mean however that any 30A rated switch has a HP rating, you need to start WITH that criteria.

I had read a few previous threads where continuous duty was mentioned.i thought I read that even though it has overloads, the fact that motor was continuous duty changed the install. Which led me to ask the forum.
Thanks for the answer
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
I had read a few previous threads where continuous duty was mentioned.i thought I read that even though it has overloads, the fact that motor was continuous duty changed the install. Which led me to ask the forum.
Thanks for the answer
I think continuous or not can change the conductor sizing, but not whether or not an OL relay is needed. OL protection is always needed, but built into the motor is one of the acceptable options.
 

rlundsrud

Senior Member
Location
chicago, il, USA
While I have reservations about ever saying Jraef is mistaken, OL protection isn't required on fractional horse motors if manually started. I am certain you are referring to the OP, in which case they are required. For the record I'm just stating this as a clarification, however deep down I'm sure it's so I can throw my two cents in even if the pot minimum is a dollar.
 

kwired

Electron manager
Location
NE Nebraska
While I have reservations about ever saying Jraef is mistaken, OL protection isn't required on fractional horse motors if manually started. I am certain you are referring to the OP, in which case they are required. For the record I'm just stating this as a clarification, however deep down I'm sure it's so I can throw my two cents in even if the pot minimum is a dollar.
You need to dig a little deeper on that one. See 430.32(D). A permanently installed motor still needs to follow same protection rules as automatically started motors.

Though you may be able to get by without overload protection on certain non permanently installed applications, I think it is still a good idea in many instances, especially if it is something that operates unattended, as that motor will attempt to deliver any power it is capable of delivering even if it overheats in the process.
 

rlundsrud

Senior Member
Location
chicago, il, USA
You need to dig a little deeper on that one. See 430.32(D). A permanently installed motor still needs to follow same protection rules as automatically started motors.

Though you may be able to get by without overload protection on certain non permanently installed applications, I think it is still a good idea in many instances, especially if it is something that operates unattended, as that motor will attempt to deliver any power it is capable of delivering even if it overheats in the process.


I knew I would regret saying that, it is under non permanently installed. Thanks for the clarification.
 

kwired

Electron manager
Location
NE Nebraska
I knew I would regret saying that, it is under non permanently installed. Thanks for the clarification.
Code or not, I don't know why you wouldn't want to have motor overload protection, motors will try to deliver the load demanded and if that is more then they are rated for they will overheat. Only exception maybe some intermittent duty application where you are there supervising the thing when it runs, like maybe a winch or hoist, or some power tools. Anything that runs unattended needs overload protection regardless of what code may say IMO.
 
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