Fractional HP Motor Overcurrent question

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cptviggi

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We have fractional hp exhaust fans on the job. Best I can tell, they have no built in thermal protection. I plan on using the breaker as short circuit protection and buying manual motor starters with properly sized heaters to satisfy a disconnecting means within site from and overcurrent protection. I believe this to be right.
One of the guys working for me is adamant that I am over doing it citing the fact that MMS's are never installed in residential bath exhaust or even furnace blower motors etc. and that a motor rated switch at the unit is all that is required.
He has me second guessing my self now.
What is the proper way to protect a fractional hp motor for an exhaust fan that draws 3-4 amps at 100v? Thanks
 
cptviggi said:
We have fractional hp exhaust fans on the job. Best I can tell, they have no built in thermal protection. I plan on using the breaker as short circuit protection and buying manual motor starters with properly sized heaters to satisfy a disconnecting means within site from and overcurrent protection. I believe this to be right.
One of the guys working for me is adamant that I am over doing it citing the fact that MMS's are never installed in residential bath exhaust or even furnace blower motors etc. and that a motor rated switch at the unit is all that is required.
He has me second guessing my self now.
What is the proper way to protect a fractional hp motor for an exhaust fan that draws 3-4 amps at 100v? Thanks
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Take a look at NEC 430.32(D): Motor and Branch Overload Protection - Continuous-Duty Motors - One Horsepower or Less, Nonautomatically Started

Also: 430.33: Motor and Branch Overload Protection - Intermittent and Similar Duty

Also see 430.42 Motors on General-Purpose Branch Circuits

According to 430.42, if the motor is on a general-purpose branch circuit, and 1HP or less, you must follow 430.32(D).

If not-on a general-purpose branch circuit, you then must determine if it is Intermittent or Continuous duty. I am inclined to think a bathroom exhaust fan is intermittent, but this section of 430.33 is perplexing: "Any motor application shall be considered to be for continuous duty unless the nature of the apparatus it drives is such that the motor CANNOT operate continuously with load under any condition of use." If this is just a normal fan, I would be inclined to say if someone leaves the switch on, the exhaust fan CAN operate continuously. And then I would go back to 430.32(D).

430.32(D) takes us to 430.32(B) which allows one of the following overload protections:
1) Separate Overload Device
2) Thermal Protector
3) Integral with Motor
4) Impedance-Protected
 
cptviggi said:
We have fractional hp exhaust fans on the job. Best I can tell, they have no built in thermal protection. ...
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What makes you believe the fan motor have no thermal protction? Also, what do the EF manual/installation instructions say?

Perhaps more details on the job, exhaust fans/motors will help.
 
you mentioned bathroom exhaust fans and furnace blowers. If that is what you have bath exhaust fans are usually impedance protected, furnace blowers are generally thermally protected or protection is provided in the furnace and all you need to do is follow the nameplate. Should the nameplate specify a particular fuse size then you would need to comply with that, but you just don't see that on newer furnaces, or even ones made in the past 20 years or so.
 
Clarification

Clarification

This is a larger commercial renovation $2mil+,and the exhaust fans are for movement in the crawl spaces underneath the building where there is no full basement( dirt subfloor etc).They are controlled by the TC sub, not sure the parameters. The residential fans and blower motors were his example of why we don't needs MMS's with OC protection.
My motors are in a ductwork housing where the nameplate is buried and inaccessible/ no stickers anywhere I can read. The common practice in our locale is for the the sheet metal to be fabbed offsite thus no instructions came with it. The tin knocker foreman doesn't even understand the questions I am asking of him! lol (prefabricated electrical assemblies have just hit our location and have really shaken things up, but anyway)....
I understand new furnaces and bath EF have protection, but the older ones did not.
I'll take a look at those code sections.... Thanks
 
cptviggi said:
....
My motors are in a ductwork housing where the nameplate is buried and inaccessible/ no stickers anywhere I can read. The common practice in our locale is for the the sheet metal to be fabbed offsite thus no instructions came with it. The tin knocker foreman doesn't even understand the questions I am asking of him! lol (prefabricated electrical assemblies have just hit our location and have really shaken things up, but anyway)...
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This size project usually has engineered electrical plans. See if you can get the make and model, if not off the fan, from the tin knocker, GC or whoever spec'd or ordered them. There is at the very least a cut sheet somewhere for that size project (ask GC).
 
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Good call

Good call

I never thought to check their submittals. The prints aren't very good and it's a DOD job where the fine print says something like we're responsible for making it right even if the prints are wrong at no extra charge. We haven't had 1 change order accepted with a request for price change approved. I was thinking of writing an RFI but the Engineer sits on them for so long, we'd be done by the time we got an answer!
 
cptviggi said:
I never thought to check their submittals. The prints aren't very good and it's a DOD job where the fine print says something like we're responsible for making it right even if the prints are wrong at no extra charge. We haven't had 1 change order accepted with a request for price change approved. I was thinking of writing an RFI but the Engineer sits on them for so long, we'd be done by the time we got an answer!
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I understand.

Please elaborate as best you can on the following from your previous post...
cptviggi said:
They are controlled by the TC sub, not sure the parameters.
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Tc sub

Tc sub

The fans are to be controlled by the temperature controls sub contractor. They are going to put a relay inline with the feed and control it with a Johnson controls system. Not sure how it will be programmed and what the control point is ie temp senser, humidistat, timer etc. Best I can tell, the fans are only there to exchange the air so it doesn't become stagnant or pose a confined space issue. Left my code book at work and can't find my old one. Will have to wait until Monday to look up those articles.
 
cptviggi said:
The fans are to be controlled by the temperature controls sub contractor. They are going to put a relay inline with the feed and control it with a Johnson controls system. ...
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With what information you've provided, here's my assessment...

Ground fault and short circuit protection is covered under 430.53.

A 20A general purpose branch circuit will supply power for multiple exhaust fans (i.e. their motors) [430.32(B), 430.42(A), 430.53(A)(1)&(2), 430.53(D)].

Exhaust fans* will be automatically started [430.32(B)] with a controller*.

This assessment is based on two assumptions: Where overload protection is required, fractional horsepower motors used for commercial projects typically have 1) built-in thermal overload protection, or 2) where the preceding is not true, overload protection is provided as an integral part of the controller. Both the exhaust fans and controller are * furnished by others.

PS: Don't forget about the local disconnect for each motor. A motor-rated snap switch will suffice.
 
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OL protection needed unless thermal protection in motor.

OL protection needed unless thermal protection in motor.

I read the code as follows. 430.32 (B) states that OL protection is needed unless there is either thermal protection, protective device integral with the motor or the windings are impedance protected.
The fans are automatically started by a thermostat via the Johnson controls system so 430-32(D) is out.
430-32(D) does not apply to my situation but would apply to a residential bath exhaust fan- non-automatically started and within site from the controller ( fan timer). the resi fans may also be internally protected, IDK about that.
Newer furnaces don't need OL's because they are integrally protected. If the blower motor itself is not, the high limit would cut out if the blower motor stopped working.
I don't see 430-22 as applying to this situation as an intermittent motor that could not operate continuously under any circumstances. I think this applies to motors as specified in the table, where there is a fixed stoppage such as an elevator reaching the top or bottom of it's travel or a valve completely opening etc.
The right course of action is to determine if the fans on my job have internal protection. If they do not, I need to provide it. My coworker is right in his examples but they do not apply to my situation... at least that is how I see it.
 
Regarding "Overload protection is provided as an integral part of the controller" When the TC contractor puts a relay inline with the fan feed, his control wiring is independent from the motor feed. The motor could burn up and as long as there was a call from the thermostat, the relay would be closed offering no protection from the controlling device.
 
cptviggi said:
Regarding "Overload protection is provided as an integral part of the controller" When the TC contractor puts a relay inline with the fan feed, his control wiring is independent from the motor feed. The motor could burn up and as long as there was a call from the thermostat, the relay would be closed offering no protection from the controlling device.
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Exactly. Controller is furnished by others.

Apparently you're not picking up what I'm laying down. I giving you an out. Its on the "others" to supply the proper equipment.
 
cptviggi said:
Gotcha....
Not sure if I can win that fight, but it's worth a conversation with the PM.
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Don't forget first and foremost that it's usually the motor that has built-in overload protection. so you have two tiers of "provided by others" before you should supply any overload protection equipment for these motors.

FWIW, I've never run across a thermal overload relay for a fractional hp motor in all my years...
 
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