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#175136 - 02/23/08 06:16 AM Rooftop Equipment
highground Offline
Member

Registered: 11/14/04
Posts: 50
Loc: Chama, NM
Hello,

I have a rooftop vent fan (3HP 480V) that the customer wants to control with a frequency drive. The panel is within sight (in the shop below). Is a disco required on the roof and prior to the drive to provide lockout capability, or does one on the roof suffice?

Also, do you guys provide additional motor protection in addition to the drive? (assuming it provides overcurrent protection)

Thanks in advance,

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#175138 - 02/23/08 07:23 AM Re: Rooftop Equipment [Re: highground]
BPHgravity Offline
Member

Registered: 04/08/03
Posts: 141
Loc: Port Charlotte, Florida
I don't exactly follow your installation description. However, Part IX of Article 430 identifies all your requirements for providing disconnecting means.

You will need to determine where and how you are obtaining both overload and ground-fault / short-circuit protection of the motor. It is possible this is all being doen by the VFD.
_________________________
Bryan P. Holland, ECO.
Secretary - IAEI Florida Chapter

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#175140 - 02/23/08 07:28 AM Re: Rooftop Equipment [Re: highground]
sparkyinak Offline
Member

Registered: 07/08/07
Posts: 1286
Loc: Alaska
You still need a disconnect on the roof if the motor i accessible on the roof and you can use a VFD down in the control room. You also want to check that the rooftop unit will not be affected by the VFD control like built in alarm or control circuits since the VFD is altering the power.
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#175145 - 02/23/08 08:22 AM Re: Rooftop Equipment [Re: sparkyinak]
Yoopersup Offline
Member

Registered: 03/04/03
Posts: 826
Loc: Michigan
2005 N.E.C. 430.102 B States: Must be within sight of the MOTOR Unless meets Exceptions 430.102 (B) Exception (a)or(b).
Thats the way I read it anyway.

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#175157 - 02/23/08 09:44 AM Re: Rooftop Equipment [Re: Yoopersup]
sparkyinak Offline
Member

Registered: 07/08/07
Posts: 1286
Loc: Alaska
If the motor can be serviced from the roof, the disconnect downstairs will not be in site.
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#175159 - 02/23/08 11:23 AM Re: Rooftop Equipment [Re: sparkyinak]
Yoopersup Offline
Member

Registered: 03/04/03
Posts: 826
Loc: Michigan
I agree that why I noted must be within sign . Kinda hard to see thru the roof!
BUT what if they had a skylight?
:))

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#177478 - 05/04/08 07:18 AM Re: Rooftop Equipment [Re: Yoopersup]
mikethebull Offline
Member

Registered: 03/18/07
Posts: 101
Loc: Rhode Island
I also agree although it is in 440.14. Also was a service receptacle within 25 feet or on the roof with the equipment this is 210.63.

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#177481 - 05/04/08 09:11 AM Re: Rooftop Equipment [Re: highground]
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5300
Loc: Blue Collar Country
From a practical standpoint, such a motor need two different types of protection; overcurrent as well as overload.
Overcurrent protection is what you get from fuses and breakers. Overload protection is what you get from the heaters in the starter. It's quite possible for a VFD to provide this secondary protection.

As for the disconnect ... I wish folks would forget the fine print of the code, and look at the application from a servicing standpoint. Do you want to shut it off before you work on it - or not? If so, doesn't it make sense to have some disconnecting means at the site of the motor? Why make / expect the guy to run up and down ladders multiple times, hope his LOTO is adequate, worry about automatic controls, etc?

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#177484 - 05/04/08 01:25 PM Re: Rooftop Equipment [Re: renosteinke]
NORCAL Offline
Member

Registered: 09/25/02
Posts: 805
 Originally Posted By: renosteinke


As for the disconnect ... I wish folks would forget the fine print of the code, and look at the application from a servicing standpoint. Do you want to shut it off before you work on it - or not? If so, doesn't it make sense to have some disconnecting means at the site of the motor? Why make / expect the guy to run up and down ladders multiple times, hope his LOTO is adequate, worry about automatic controls, etc?


Thank you a little common sense is always in order.

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#177533 - 05/06/08 04:12 AM Re: Rooftop Equipment [Re: NORCAL]
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
Mike,
 Quote:
I also agree although it is in 440.14.

Article 440 does not apply to vent fans.
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