# Is a Disconnect required ahead of the VFD?



## Hdinj

I have seen several 480v Air Handlers in a commercial ceiling that a VFD but no Disconnect ahead of the VFD. The VFD has an on/off switch but it was explained to me that a disconnect switch is not required because the On/off switch in the VFD kills the power to the whole unit and VFD itself. They are fed by a dedicated 480v circuit. 

Is this correct or do I need a disconnect switch?


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## MechanicalDVR

Hdinj said:


> I have seen several 480v Air Handlers in a commercial ceiling that a VFD but no Disconnect ahead of the VFD. The VFD has an on/off switch but it was explained to me that a disconnect switch is not required because the On/off switch in the VFD kills the power to the whole unit and VFD itself. They are fed by a dedicated 480v circuit.
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> Is this correct or do I need a disconnect switch?
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> Sent from my iPhone using Tapatalk


In years of HVAC control work in NJ I have never seen an air handler without a disconnect with in site.


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## Hdinj

I agree that is why I thought it was strange when I was told the VFD is the disconnect. Is case that the on/off switch in the VFD would be acceptable as the disconnect?


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## ponyboy

Have you seen 430.102(b)


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## MechanicalDVR

Hdinj said:


> I agree that is why I thought it was strange when I was told the VFD is the disconnect. Is case that the on/off switch in the VFD would be acceptable as the disconnect?
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> 
> Sent from my iPhone using Tapatalk


I doubt it, or you would see it often. That could save some serious dollars on s many multi unit projects.


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## Hdinj

Any opinion on the following code?

430.128 Disconnecting Means. 
The disconnecting means shall be permitted to be in the incoming line to the conversion equipment and shall have a rating not less than 115 percent of the rated input current of the conversion unit. 


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## Wirenuting

A control "switch" is not considered a "means of disconnect".

While your working on that fan, can I open the door to that freq drive and using a screwdriver, push the bypass contactor in?

Remember, there are bigger idiots out there then just me.


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## ponyboy

I'm imagining something like this and I'm thinking no other disconnect required 










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## MechanicalDVR

Biscuits said:


> I'm imagining something like this and I'm thinking no other disconnect required
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Can that actually be locked out? Most airhandlers have more than just a blower motor load nowadays.


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## Wirenuting

MechanicalDVR said:


> Can that actually be locked out? Most airhandlers have more than just a blower motor load nowadays.


I haven't seen that brand yet. But they all have a handle that can be locked. 

Now the trick is to get the cover off to work on the drive. LoL

All the air handlers here have a drive for each motor. Supply side and return air side. Exhausts are separate. It's easier to automate the buildings temperature control.


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## ponyboy

What I'm used to with rtus is a the drives all being inside the unit and an integrated disconnect on the outside of the unit that shuts everything down. I've installed lots of drives like the one I posted for chiller packages that have multiple water exchangers 


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## backstay

MechanicalDVR said:


> Can that actually be locked out? Most airhandlers have more than just a blower motor load nowadays.


The Code only says disconnect, but the ones I've seen, there is a piece that pulls out of the handle to install a lock in the off position.


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## oliquir

the one in the picture is a real disconnect (cuts power to the vfd) and not an on/off control switch


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## frenchelectrican

Hdinj said:


> I have seen several 480v Air Handlers in a commercial ceiling that a VFD but no Disconnect ahead of the VFD. The VFD has an on/off switch but it was explained to me that a disconnect switch is not required because the On/off switch in the VFD kills the power to the whole unit and VFD itself. They are fed by a dedicated 480v circuit.
> 
> Is this correct or do I need a disconnect switch?
> 
> 
> Sent from my iPhone using Tapatalk


I know I may bring up a old topic but again let me remind you guys if you going to put a disconnect switch between the VFD and the motor .,,

You going need a aux switch concats to send a signal to the main VFD to keep from enerigzed the load side.,, 

and check the VFD manufacter instruction about useing aux concats to islolated the connection.


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## MechanicalDVR

I'd think that an RTU or similar piece of equipment that contains 1, 2, 3, or more VFDs would have a common disconnect for the whole unit and not have any need for a disco just for a single VFD inside. I've spent serious time inside huge air handlers that have control vestibules and can't recall any with individual discos for a single VFD.


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## frenchelectrican

MechanicalDVR said:


> I'd think that an RTU or similar piece of equipment that contains 1, 2, 3, or more VFDs would have a common disconnect for the whole unit and not have any need for a disco just for a single VFD inside. I've spent serious time inside huge air handlers that have control vestibules and can't recall any with individual discos for a single VFD.



Ya it is simuiair to my area too in my country.,, and it super rare to see individual disconnections devices like that .,,


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