Disconnecting Means for a 24V VAV Actuator

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jeremy.zinkofsky

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The VAV in question will have its coils heated and cooled by water (It does not have an electric heater). The only power it needs is for the motor that manipulates it's damper, which is 24V and is connected to the secondary of a 120V/24V XFMR. I do not know if there is an internal switch or fuse.

My question: Do I have to provide a disconnecting switch for this VAV, as is typically done. I can't find any provisions in the NEC that discuss these types of VAV's, only electric space heaters which this is not. Would this VAV be classified as AC and Refridgerating equipment (Article 440)? Or is this situation covered under Article 430.102 & Article 440.14 which states that a disconnecting means has to be readily accessible and/or visible from the equipment location. If that is so, then a seperate switch would only be needed if the VAV does not come with any type of factory installed disconnecting means. Any thoughts?
 
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Brent Koerting

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Never seen a disconnect

Never seen a disconnect

Many of my acquisition contract involves a lot of commercial HVAC with VAV systems and hydronics also (hospitals etc.) Never seen a disconnect for the low voltage!
In a sense it really never stays connected anyway (except during changes in damper) and can be disconnected from the front end computer anyway?
 
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GoldDigger

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Brent Koerting said:
Many of my acquisition contract involves a lot of commercial HVAC with VAV systems and hydronics also (hospitals etc.) Never seen a disconnect for the low voltage!
In a sense it really never stays connected anyway (except during changes in damper) and can be disconnected from the front end computer anyway?
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The small zone damper actuators that I have seen for residential use have a low power impedance protected gear motor which took the spring loaded damper to one extreme. Turning it off allowed the motor to wind backward as the damper moved to the other extreme.
 
iwire

iwire

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Spring return is very common in large commercial actuators as well and while they do return slowly they have a great deal of power and could hurt you.
 
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GoldDigger

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iwire said:
Spring return is very common in large commercial actuators as well and while they do return slowly they have a great deal of power and could hurt you.
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One of the points of my observation is that for this type of unit the motor will not just be energized during the transition from one state to another but instead stay on continuously.
I would think that those which are capable of proportional control may instead only energize the actuator motor while moving. (Similar to the linear actuator of a gate.)
 
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jeremy.zinkofsky

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iwire said:
Did you take the time to look at the exception? Clearly it applies to actuators.
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That exception discusses VAM's which is not what is used to manipulate the dampers of a VAV box. A VAM uses a motor to actuate a piston that manipulates the opening and closing of a valve. They are typically used in industrial applications. What I am talking about is like a servo that opens or closes a damper. See attached pictures.

430.102 (A) exception 3 does not apply to my situation. What I am interested in knowing is if a 24V actuator (like the one in the photo) is even considered a motor at all. I would argue that it is not and thus does not need a disconnect. Please tell me if I am wrong or if there is any building code that discusses these VAV actuators in detail.
 

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Brent Koerting

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Getting into a little more detail about VAVs

Getting into a little more detail about VAVs

I have never seen one (disconnect) and there are different types of VAVs and how the actuators work (look at what a phoenix valve actuator looks like.)
Stepping aside from codes for a second the basic system consists of the VAV, a building controller, control card, front end and is a very sensitive system. I can tell you like many systems I've been working on you could not add a disconnect in the first place, because even the wire has to be a certain size/resistance or it will fail, that is all part of a sensitive loop coming off the bldg. controller. I'm talking some pretty complicated systems with NAEs and Metasys, with control wires going to different applications, and control cards (VFDs, VAVs AHs etc.) but the control wires going to the VAV is part of a computer network such as running cat5 or fiber optic for something. That building controller wire normally will go down to a control card that is either part of or right at the VAV
This may seem like a novice question, but that wire has to originate from a building controller (computer or something) that is plugged in someplace making everything connected to it part of an appliance, being plugged in where it originates how would it fall under the codes that we are speaking of? But a step further that building controller where the 24volt wire comes out of is already protected by means of a disconnect. To me it would just be something that isolates, not disconnects if a control wire had its own disconnect.
The jobs that I've been working on has probably installed at least 300-400 VAVs in the past year alone combined.

If it was coming off a hardwired 24volt transformer with something to manually adjust the damper through that wire then you have a whole different ball of wax and code applications that are being spoken about but they just don't usually work that way for bldg. automation.
 
iwire

iwire

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Brent Koerting said:
Stepping aside from codes for a second the basic system consists of the VAV, a building controller, control card, front end and is a very sensitive system. I can tell you like many systems I've been working on you could not add a disconnect in the first place, because even the wire has to be a certain size/resistance or it will fail, that is all part of a sensitive loop coming off the bldg. controller. I'm talking some pretty complicated systems with NAEs and Metasys, with control wires going to different applications, and control cards (VFDs, VAVs AHs etc.) but the control wires going to the VAV is part of a computer network such as running cat5 or fiber optic for something. That building controller wire normally will go down to a control card that is either part of or right at the VAV
This may seem like a novice question, but that wire has to originate from a building controller (computer or something) that is plugged in someplace making everything connected to it part of an appliance, being plugged in where it originates how would it fall under the codes that we are speaking of? But a step further that building controller where the 24volt wire comes out of is already protected by means of a disconnect. To me it would just be something that isolates, not disconnects if a control wire had its own disconnect.
The jobs that I've been working on has probably installed at least 300-400 VAVs in the past year alone combined.

If it was coming off a hardwired 24volt transformer with something to manually adjust the damper through that wire then you have a whole different ball of wax and code applications that are being spoken about but they just don't usually work that way for bldg. automation.
Click to expand...

The codes apply to building automation systems and they are not too sensitive to install disconnect switches for actuators.
 
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Brent Koerting

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iwire said:
The codes apply to building automation systems and they are not too sensitive to install disconnect switches for actuators.
Click to expand...

Yes but what about the computer in itself?
I have to disagree about the one point though, if I don't have an exact amount of ohms, first the front end will not ping the device and often times cause an NAE to crash. Even the loop going to each control card has to be a full loop nothing branching off etc. or on some it will crash also. Example on one: Had too large of conductor going to a VFD, that NAE had about 9 control cards on it, crashed the NAE each time until that wire was changed out. That was on a Bacnet system with Johnson controls.
That is another interesting part that control loop is just that and is not suppose to be installed with branches. So really you have no way to isolate each VAV with a disconnect when you have 20 VAVs on a bldg. controller.
One more point I wonder about that NAE (or bldg. control) is in fact a listed appliance (small computer) so my suggestion is to look at what the manufacturer requires in the first place, like all I've worked with told exact wire that can be used with ohms and resistance.
 
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