Disconnect for Roof Top Exhaust Fan

[Sean.Day72]

I've seen some debate on here.

Replacing a bunch of roof top exhaust fan that are about 20 years old. None have existing disconnects on the roof within line of site of the fan.
Some GE combo disconnect Motor Starters in the mechanical room below some I couldn't not locate a disconnect/motor starter. It looks like they are fed directly from a breaker?

I guess the first question, from Article 430 it appears these are required within line of site UNLESS there is a disconnect that can be locked in the open position. I believe we meet this exception.

If we are to add a local disconnect what is the best way to go about doing this. The exhaust fan are mounted on top of a roof curb with the conduit coming up right in through the bottom. We would have to cut a hole through fan shroud, length of flex, weatherproof hub, and mount the disconnect to the side of the fan. I don't really want to field modify a fan to install a disconnect..Thinking of use a smaller Nema 3R rotary type motor disconnect. Most are 2 HP motors.

 

[augie47]

The disconnect must be within sight unless you meet one of the exceptions in 430.102(B)..... not likely unless this is industrial....
Depending on how your fans are made, the switch is often adjacent to the motor under the top.

 

[Sean.Day72]

This is a school HVAC reno project.
What if the disconnect is located in the plenum above the ceiling tile just below the exhaust fan?
If you add a disconnect switch underneath the fan shroud, you won't see it until you remove it. Is there a code issue with that?

 

[brantmacga]

This is a school HVAC reno project.
What if the disconnect is located in the plenum above the ceiling tile just below the exhaust fan?
If you add a disconnect switch underneath the fan shroud, you won't see it until you remove it. Is there a code issue with that?

You would have to remove the top to access the motor for service, which would then expose the switch. Usually it's a speed control switch as well for balance adjustments.

 

[Sean.Day72]

Ok thank you, These are controlled through the BAS for start/stop and interlocked with their respective Air Handler. They do have the dial type speed controller for test and balance adjustments.

The maintenance guy actually just told me they are just snap toggle switches.

 

[kwired]

Ok thank you, These are controlled through the BAS for start/stop and interlocked with their respective Air Handler. They do have the dial type speed controller for test and balance adjustments.

The maintenance guy actually just told me they are just snap toggle switches.

Snap switch located under the weather cap is what I see nearly all the time.

 

[jap]

You would have to remove the top to access the motor for service, which would then expose the switch. Usually it's a speed control switch as well for balance adjustments.

To me this defeats the whole purpose of the disconnect.

The disconnect should be off and or locked out prior to the removal of the shroud.

All it takes is one time of one firing up on you while your in process of removing the shroud on a rooftop exhaust fan it will remind you just exactly what the reasoning is behind disconnect rule.

JAP>

 

[hbiss]

Snap switch located under the weather cap is what I see nearly all the time.

That's what I see too.

To me this defeats the whole purpose of the disconnect.

The disconnect should be off and or locked out prior to the removal of the shroud.

All it takes is one time of one firing up on you while your in process of removing the shroud on a rooftop exhaust fan it will remind you just exactly what the reasoning is behind disconnect rule.

Typical mushroom fan, the cover or shroud is easily removable to expose the motor and belt. No problem doing it with the fan in operation.

-Hal

 

[tom baker]

To the OP, it’s possible your installation was done before the code change to require a disconnect within sight of the motor(with exceptions as pointed out)

 

[brantmacga]

To me this defeats the whole purpose of the disconnect.

The disconnect should be off and or locked out prior to the removal of the shroud.

All it takes is one time of one firing up on you while your in process of removing the shroud on a rooftop exhaust fan it will remind you just exactly what the reasoning is behind disconnect rule.

JAP>

I know there are many iterations of the roof-top exhaust fan, but all thousand-plus of them I've ever seen, when you take the top shroud off, you only see a vertically mounted motor and the switch. There is yet another layer of steel between your hands and the fan blades. You have to remove the entire assembly from the curb to access the shaft-mounted fan.

edit to add.... I'm talking about the small EF's you'd see over a restroom or just general room exhaust. For belt-driven cooking exhaust fans, we have a disconnect switch on the outside of the housing.

 

[jap]

That's what I see too.



Typical mushroom fan, the cover or shroud is easily removable to expose the motor and belt. No problem doing it with the fan in operation.

-Hal

Generally if you're having to remove the hood the dang thing isn't operating anyway.

JAP>

 

[jap]

I know there are many iterations of the roof-top exhaust fan, but all thousand-plus of them I've ever seen, when you take the top shroud off, you only see a vertically mounted motor and the switch. There is yet another layer of steel between your hands and the fan blades. You have to remove the entire assembly from the curb to access the shaft-mounted fan.

Dang,,, you must do a lot of roof work. I've only seen 900 or so.

JAP>

 

[brantmacga]

Dang,,, you must do a lot of roof work. I've only seen 900 or so.

JAP>

Yes. Restaurant work.

 

[augie47]

It seems somewhat of a Catch22.
I agree with japs concern that the switch being under the shroud does not make it readily accessible to ALL but it is accessible to anyone required to work on the unit and considering how many are factory supplied that way it must be widely accepted.

 

[jap]

Yes. Restaurant work.

I'm with ya.

I have to bring up the safety thing every now so others wont think I'm a complete rebel.

JAP>

 

[kwired]

I know there are many iterations of the roof-top exhaust fan, but all thousand-plus of them I've ever seen, when you take the top shroud off, you only see a vertically mounted motor and the switch. There is yet another layer of steel between your hands and the fan blades. You have to remove the entire assembly from the curb to access the shaft-mounted fan.

edit to add.... I'm talking about the small EF's you'd see over a restroom or just general room exhaust. For belt-driven cooking exhaust fans, we have a disconnect switch on the outside of the housing.

I seen lots of belt driven ones with the switch under the top shroud as well. Switch is used when changing belt more often than any other activity on those.

 

[hbiss]

I have also seen, where the power comes up through the roof next to the fan curb, a switch installed in a Bell box that's mounted to the curb. Sealtite in and sealtite out and through the vent opening to the motor.

-Hal

 

[brantmacga]

I seen lots of belt driven ones with the switch under the top shroud as well. Switch is used when changing belt more often than any other activity on those.

I know the type you're talking about, I've only seen it a handful of times though on older buildings. The EF's we use on kitchen hoods are belt driven, but a little different from the mushroom top, and they are hinged to open for cleaning the duct. They have a cord routed out the side for an external disconnect.

 

[Sean.Day72]

Well I got the OK the snap switch under the hood is cool for our small >2HP exhaust fans. Actually, most modeles come pre-installed with a snap switch from Greenheck.

One last wrinkle..a select few Exhaust Fan are getting Brand new VFD with controls from the Building Automation System to help with active test and balance. Fancy new stuff. Any specifical considerations to be made when disconnecting a motor which is powered from a VFD.

 

[jap]

I'm a huge fan of factory installed disconnects.

JAP>