Local Start/Stop for VFD driven Motor

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Electriman

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Dear Friends,

Based on NEC we have to have a disconnect switch for motors and starters in visible distance. Since the starters are usually inside MCC room and motors are in the field, we place a local H-O-A near the motors. My question is for those motors that is driven by VFD, do we need to place a local H-O-A near the motor since the VFDs are in MCC room? My VFDs have start/stop push buttons on the panel, but I don't think it meets NEC since it is not in visible distance of the motor. Any Idea?
 
A HOA does not qualify as a disconnecting means even if it is within sight of the motor, or controller for that matter. You must disconnect the controller, ie line side conductors and or the conductors at the motor. Try 430.128 for you VFD.

Start at 430.101 for more detail. 2014 NEC
 
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As mentioned you need a local disconnect by the motor. You can use a set of aux contacts with the disconnect to disable your drive when
the local is switched off.
 
ptonsparky said:
A HOA does not qualify as a disconnecting means even if it is within sight of the motor, or controller for that matter. You must disconnect the controller, ie line side conductors and or the conductors at the motor. Try 430.128 for you VFD.

Start at 430.101 for more detail. 2014 NEC
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But that is normal practice. The HOA will interrupt the main line contactor. You don't see any disconnect means near the motor excapt an HOA that is control circuit of the main contactor or starter.
 
Aleman said:
As mentioned you need a local disconnect by the motor. You can use a set of aux contacts with the disconnect to disable your drive when
the local is switched off.
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That is what I think so. I will use an HOW and wire it to VFD main disconnect so whenever some body wants to turn it off he can do locally. I am not sure if the control system is also acceptable since my motors can turn on and off using DCS and I can send a signal from HOA to turn the motor on and off.
 
Electriman said:
That is what I think so. I will use an HOW and wire it to VFD main disconnect so whenever some body wants to turn it off he can do locally. I am not sure if the control system is also acceptable since my motors can turn on and off using DCS and I can send a signal from HOA to turn the motor on and off.
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As was said A HOA is not a safety disconnect and can not be used as one since a VFD can start a motor even if the HOA is in the off position if a malfunction occurs, the only legal disconnect at the motor is an actual disconnect that disconnects the motor from its supply lines, this is also the only legal method that OSHA will accept should someone get hurt they can fine your company a lot of money if you do not have a lockable disconnect at the motor, not including all the law suits that may arise from someone being injured because of you taking this shortcut, also since most VFD's do not like to be unloaded while on you should have a micro switch in the disconnect that turns off the VFD just before the disconnect opens, you can do as you want but like I said you will be in allot of trouble if OSHA ever investigates an injury cause by this motor, also a disconnect must have a means of lock out so that your plant can use the lock out and tag out safety procedures that OSHA requires, a HOA does not allow this as it does not remove the possibility of the drive from supplying power to the motor if something in the control system was to go wrong.

Just having a HOA in the main contactor circuit will not guarantee that another maintenance person can not push in the main contactor energizing the motor and getting someone hurt as it will make the lock out tag out useless, this is also why the NEC and OSHA requires a regular disconnect at the motor for workers to lock out on that keeps others from being able to turn on the motor, so again install a disconnect at the motor just order one with the micro switch already in it, with a break before disconnect feature for the VFD drive which is what we have on all our motors on VFD's.

Sorry but we have to tell you what is required not what you want to hear.

If you have other motors that only have a HOA at the motor then they need to be updated also or you may get a big surprise if OSHA ever visits your plant, trust me the fines are not cheap and in most cases will be 10 times what it would cost installing the correct disconnects at each motor.
 
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There is nothing wrong with having local control devices near the motor. they can be handy. you just cannot substitute them for a disconnecting means. If that is required locally, then you need a local disconnecting means.
 
infinity said:
Do VFD driven motors require an in-sight disconnecting means according to the NEC?
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Possibly not, but is not prohibited to have one either.

Safety policies/codes may still require disconnect local to the motor/driven load though and would be better for the drive to have an aux contact to signal to the drive's control circuits should the switch be operated.
 
kwired said:
Possibly not, but is not prohibited to have one either.

Safety policies/codes may still require disconnect local to the motor/driven load though and would be better for the drive to have an aux contact to signal to the drive's control circuits should the switch be operated.
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I agree but that's a design issue (a good one IMO) but not a code issue.
 
I don't see how it makes any difference if the motor is driven by a VFD or not. A local disconnect is either required or it is not. Most cases in factories it probably is not. Most cases anywhere else it is.
 
petersonra said:
I don't see how it makes any difference if the motor is driven by a VFD or not. A local disconnect is either required or it is not. Most cases in factories it probably is not. Most cases anywhere else it is.
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I was thinking about 430.102(B)(2).
 
infinity said:
I was thinking about 430.102(B)(2).
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While the general rule requires a motor disconnect at the motor, around here 430.102(B)(2) Exception part (b) is used unless there is an operational reason to have a local disconnect. For example equipment that needs routine cleaning may have a local disconnect to save the time it would take to go to the MCC room and lock the motor out.
Exception to (1) and (2): The disconnecting means for the motor shall not be required under either condition (a) or condition (b), which follow, provided that the controller disconnecting means required in 430.102(A) is lockable in accordance with 110.25.
(a) Where such a location of the disconnecting means for the motor is impracticable or introduces additional or increased hazards to persons or property
(b) In industrial installations, with written safety procedures, where conditions of maintenance and supervision ensure that only qualified persons service the equipment
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petersonra said:
You are not supposed to open any disconnect switch under load. They are generally not rated for make/break.
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The following is from the UL Guide Information for "switches, enclosed" (WIAX).
Ratings of certified enclosed switches are limited to 4000 A, 500 hp, 600 V. Enclosed switches rated at more than 1200 A at 250 V or less, and switches rated at more than 600 A at more than 250 V are available in two classes, one intended for general use and the other intended for isolating use only. Switches intended for isolating use only are marked "For Isolating Use Only ? Do Not Open Under Load."
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It appears to me that standard disconnects rated 600 amps and less are suitable for use as load break devices. Switches rated over 600 amps may or may not be suitable for use as load break devices.
 
petersonra said:
You are not supposed to open any disconnect switch under load. They are generally not rated for make/break.
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The early break aux contacts ought to prevent that.
But the usual specification imposed on us is fault make load break.
It's customer driven.
 
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