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Old 06-08-2016, 10:39 PM   #1
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Default Is a Disconnect required ahead of the VFD?

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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Old 06-08-2016, 10:42 PM   #2
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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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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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Old 06-08-2016, 10:48 PM   #3
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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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Old 06-08-2016, 11:01 PM   #4
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Have you seen 430.102(b)


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Old 06-08-2016, 11:02 PM   #5
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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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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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Old 06-08-2016, 11:33 PM   #6
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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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Old 06-09-2016, 08:27 AM   #7
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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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Old 06-09-2016, 08:32 AM   #8
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I'm imagining something like this and I'm thinking no other disconnect required



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Old 06-09-2016, 08:40 AM   #9
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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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Old 06-09-2016, 08:46 AM   #10
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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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Old 06-09-2016, 08:57 AM   #11
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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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Old 06-09-2016, 09:19 AM   #12
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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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Old 08-02-2016, 04:01 PM   #13
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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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Old 09-07-2016, 10:42 AM   #14
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Quote:
Originally Posted by Hdinj View Post
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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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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Old 09-07-2016, 10:50 AM   #15
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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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Old 09-07-2016, 11:08 AM   #16
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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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