×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Motor disconnect switch NEC 430.109

Motor disconnect switch NEC 430.109

Motor disconnect switch NEC 430.109

(OP)
Hi, as I reading NEC Sec 430.103, regarding operation of the disconnect means for motor, I was puzzled why it stated disconnect mean must be rated for the locked rotor current, in case when the motor controller fails, which has its own overcurrent protection elements.  If I only have a small motor unit (like a fraction HP fan coil unit), will using a simple single pole switch (within sight of the equipment)comply with the intent of the code, as the intent of the within-sight disconnect mean is only to disconnect the ungrounded phases of the equipment.  However, in 430.109, it listed only 7 types of switch that is considered acceptable, a simple switch is not listed as one of those.  I would think a simple switch would not be acceptable for motor disconnect.

RE: Motor disconnect switch NEC 430.109

Only if it says "rated for xxxHP" which, by implication, means it has been tested at the requisite Locked Rotor Current for that rating. You can buy cheap junk toggle switches that have little or no HP rating, and you can buy better one's that do have it.

You get what you pay for.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln  
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies  

RE: Motor disconnect switch NEC 430.109

(OP)
Hi thanks for the input.  Obviously you get what you pay for.  But from the compliance standpoint, apparently NEC art. 430.109(B) allows the circuit breakers to be served as the disconnect for motors size 1/8hp or less, and therefore the simple switches are just for turning on/off the fan coil units, which is the designer intended.  Thanks.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources