Motor Thermal Overloads

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mstrlucky74

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Have never come across motor switches located remotely on a wall like this. They seem to be showing regular toggle type switches and not thermal overload type for the exhaust fans. As you can see in the other pic for another motor type they do show overload type. The only thing I can think of is the exhaust fan has some sort of means of disconnect internally( they don't show anything). Can they exhaust fan switches be regular toggle type as they show and not thermal overload type? Thanks.
 

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mstrlucky74 said:
Have never come across motor switches located remotely on a wall like this. They seem to be showing regular toggle type switches and not thermal overload type for the exhaust fans. As you can see in the other pic for another motor type they do show overload type. The only thing I can think of is the exhaust fan has some sort of means of disconnect internally( they don't show anything). Can they exhaust fan switches be regular toggle type as they show and not thermal overload type? Thanks.
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The motor requires a disconnecting means within sight. Overload protection can be anywhere in the circuit. Many single phase motors will often have integral overload protection, and wouldn't require any additional protection to comply with NEC. Some put thermal protection devices on drawings whether needed or not.
 
I would guess that the wall switches are to turn the units on and off, the thermal switched are providing the overload protection and a local disconnecting means at the equipment.
 
I've seen these. I don't use them. But, I have seen them in commercial buildings. As mentioned in earlier posts, tucked up near a motor for an insight disconnect/overloads.
 

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do you know where code says that Impedance protected motor is comply with code requirements and don't need external overload protection?

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Impedance protected motor is usually a shaded pole motor. Those are seldom more than 1 HP, the thermally protected ones are seldom more than maybe 1/10 hp.
 
I have seen exhaust fans that were fractional horse three phase without thermal overload protection. In that case, they could not be started automatically only manually.
 
rlundsrud said:
I have seen exhaust fans that were fractional horse three phase without thermal overload protection. In that case, they could not be started automatically only manually.
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Some three phase motors have integral thermal overload protection, but most don't.

Did you by chance mean they can't be automatically reset? I don't think NEC addresses that but isn't a good practice as a general rule to automatically reset any motor overload, that will also result in automatic starting afterward, especially for unattended equipment.
 
A Note on Shaded Pole " Stack " type motors

A Note on Shaded Pole " Stack " type motors

kwired said:
The motor requires a disconnecting means within sight. Overload protection can be anywhere in the circuit. Many single phase motors will often have integral overload protection, and wouldn't require any additional protection to comply with NEC. Some put thermal protection devices on drawings whether needed or not.
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A typical Broan bathroom exhaust fan has this type of motor:
https://en.wikipedia.org/wiki/Shaded-pole_motor

I was alerted and part of the response to a structure fire started by one of these units, no doubt in one type of locked rotor state. The tenant had left the unit on in a non rotating state for days. F 451 seems to have been reached.
This situation got hot enough to ignite the roof decking not much further above the fan that was overlaid with a metal roof.
This was in a remote area, and the firefighters were not well trained or coordinated.
The insurance adjuster seemed to have seen or heard about this matter before. I was there before things got too far out of hand, and the first thing I found was the plastic grill to the fan melted, burned and on the floor.
There was zero doubt of what caused this fire.
 
StarCat said:
A typical Broan bathroom exhaust fan has this type of motor:
https://en.wikipedia.org/wiki/Shaded-pole_motor

I was alerted and part of the response to a structure fire started by one of these units, no doubt in one type of locked rotor state. The tenant had left the unit on in a non rotating state for days. F 451 seems to have been reached.
This situation got hot enough to ignite the roof decking not much further above the fan that was overlaid with a metal roof.
This was in a remote area, and the firefighters were not well trained or coordinated.
The insurance adjuster seemed to have seen or heard about this matter before. I was there before things got too far out of hand, and the first thing I found was the plastic grill to the fan melted, burned and on the floor.
There was zero doubt of what caused this fire.
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I'll admit I don't trust some newer units much anymore. Older units didn't have all the plastic support material you may find today, those motors could get pretty hot and never melt what is supporting them, though I have seen some with so much dust/lint in them there is still some risk of fire starting .
 
LarryFine said:
I bet the dust and lint inside the fan actually ignited first.
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I agree. Shaded Pole motors are almost always designed as "impedance protected", meaning that at Locked Rotor current, the motor cannot create enough heat to cause the insulation to catch fire and before it does, a wire (fuse wire) inside is designed to fail open first. But that doesn't mean the lint / dust won't catch fire and they get past that by simply saying it is the user's responsibility to keep it clean.
 
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