Local Start/Stop for VFD driven Motor

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kwired

Electron manager
Location
NE Nebraska
Isn't putting the motor into the circuit when the drive is already providing output a bigger issue with the drive then removing the motor from the drive while it running?
 

Aleman

Senior Member
Location
Southern Ca, USA
Maybe so because of the inrush current. Either way I don't think it's good to use disconnect switches to break loads.

As far as the original post goes, I wouldn't work on a motor if the power wasn't locked out. A HOA switched to off does
not make it safe to work on.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
  • Per the definition in Section 420.2 a VFD (actually an ASD, Art 430, Part X) is a controller. Technically, a hard contactor or switch isn't necessary; it only has to make or break the motor current. Hoe that is accomplished isn't specified.
  • Section 430.108 requires every disconnecting means to meet the (fairly extensive) requirements of Sections 430.109 and 430.110. The Ampere Rating and Interrupting Capacity requirements are listed in Section 430.110.
 

kwired

Electron manager
Location
NE Nebraska
So is it OSHA or company policy, or old wives that require a visible contact break for some conditions?
If contact break is required to be visible, you need a open style switch. Molded case circuit breakers/switches, and even snap switches generally do not have visible contacts and there are a lot of these used as disconnecting means.
 
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