Motor Load protection - Electrician Talk - Professional Electrical Contractors Forum
CLICK HERE AND JOIN OUR COMMUNITY TODAY, IT'S FREE!
Go Back   Electrician Talk - Professional Electrical Contractors Forum > Electrical Trade Topics > PLCs, VFDs, Motors and Controls


Reply
 
Thread Tools Display Modes
Old 12-06-2011, 10:46 AM   #1
Junior Member
 
Join Date: Nov 2011
Location: Minnesota
Posts: 26
Rewards Points: 25
Default Motor Load protection

I had some chiller loop pumps installed and noticed that the pumps name plates read 29.9 amps (34 Amps FLC according to Table 430.250) for a 25 HP 480v motor. If you take 125% of 34 amps you will come out with 42.5 amps for continuous use for Overload Protection. The electricians installed a 70 amp breaker in the load center. Is that the correct protection? FYI: There is one backup pump for each loop. So a set of pumps for each.
CelticElect is offline   Reply With Quote
Join Contractor Talk

Join the #1 Electrician Forum Today - It's Totally Free!

ElectricianTalk.com - Are you a Professional Electrical Contractor? If so we invite you to join our community and see what it has to offer. Our site is specifically designed for you and it's the leading place for electricians to meet online. No homeowners asking DIY questions. Just fellow tradesmen who enjoy talking about their business, their trade, and anything else that comes up. No matter what your specialty is you'll find that ElectricianTalk.com is a great community to join. Best of all it's totally free!

Join ElectricianTalk.com - Click Here JOIN FOR FREE


Warning: The topics covered on this site include activities in which there exists the potential for serious injury or death. ElectricianTalk.com DOES NOT guarantee the accuracy or completeness of any information contained on this site. Always use proper safety precaution and reference reliable outside sources before attempting any construction or remodeling task!

Sponsored Links
Advertisement
 
Old 12-06-2011, 02:08 PM   #2
Senior Member
 
Bulldog1's Avatar
 
Join Date: Oct 2011
Location: No where, USA
Posts: 2,367
Rewards Points: 1,000
Default

Quote:
Originally Posted by CelticElect View Post
I had some chiller loop pumps installed and noticed that the pumps name plates read 29.9 amps (34 Amps FLC according to Table 430.250) for a 25 HP 480v motor. If you take 125% of 34 amps you will come out with 42.5 amps for continuous use for Overload Protection. The electricians installed a 70 amp breaker in the load center. Is that the correct protection? FYI: There is one backup pump for each loop. So a set of pumps for each.

If you are asking if the feeder overcurrent protection is sized correctly you take the largest breaker and add the FLA of the other motors to it.

For example if the largest breaker was a 40 amp breaker and you had 2 additional motore with a FLA of 30 amps then it's 40+ 30 + 30 = 100 amp breaker for OCP.
Bulldog1 is offline   Reply With Quote
Old 12-06-2011, 02:29 PM   #3
Junior Member
 
Join Date: Nov 2011
Location: Minnesota
Posts: 26
Rewards Points: 25
Default

Quote:
Originally Posted by Bulldog1 View Post
If you are asking if the feeder overcurrent protection is sized correctly you take the largest breaker and add the FLA of the other motors to it.

For example if the largest breaker was a 40 amp breaker and you had 2 additional motore with a FLA of 30 amps then it's 40+ 30 + 30 = 100 amp breaker for OCP.
Each pump is individually fed. There aren't any other loads attached to these pumps. We are feeding one 25HP 480v pump at 70 amps. When I think it should be fed at 45 amps. Is the 70 amp breaker wrong?
CelticElect is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 12-06-2011, 02:36 PM   #4
Senior Member
 
Bulldog1's Avatar
 
Join Date: Oct 2011
Location: No where, USA
Posts: 2,367
Rewards Points: 1,000
Default

Quote:
Originally Posted by CelticElect View Post
Each pump is individually fed. There aren't any other loads attached to these pumps. We are feeding one 25HP 480v pump at 70 amps. When I think it should be fed at 45 amps. Is the 70 amp breaker wrong?

Look in 430 I don't have a code book with me. You can go up to either 175% or 250% for OCPD I believe. I believe the article says 250%. If so then a 70 amp breaker is the correct size.

Last edited by Bulldog1; 12-06-2011 at 02:40 PM.
Bulldog1 is offline   Reply With Quote
The Following User Says Thank You to Bulldog1 For This Useful Post:
FCR1988 (12-08-2011)
Old 12-06-2011, 02:49 PM   #5
Junior Member
 
Join Date: Nov 2011
Location: Minnesota
Posts: 26
Rewards Points: 25
Default

Quote:
Originally Posted by Bulldog1 View Post
Look in 430 I don't have a code book with me. You can go up to either 175% or 250% for OCPD I believe. I believe the article says 250%. If so then a 70 amp breaker is the correct size.
Found it! They are using "varying duty" from Table 430.22(E) which is 200% of FLC. Vetting duty is found in Artical 100 under "duty" for it's definition.

Thanks
CelticElect is offline   Reply With Quote
Old 12-06-2011, 02:53 PM   #6
Senior Member
 
Bulldog1's Avatar
 
Join Date: Oct 2011
Location: No where, USA
Posts: 2,367
Rewards Points: 1,000
Default

Quote:
Originally Posted by CelticElect View Post
Found it! They are using "varying duty" from Table 430.22(E) which is 200% of FLC. Vetting duty is found in Artical 100 under "duty" for it's definition.

Thanks

No problem. I can never remember those %. Glad I could help.
Bulldog1 is offline   Reply With Quote
The Following User Says Thank You to Bulldog1 For This Useful Post:
CelticElect (12-06-2011)
Old 12-06-2011, 07:05 PM   #7
Senior Member
 
Join Date: Apr 2009
Location: Northern Kentucky
Posts: 1,359
Rewards Points: 1,620
Default

Unless the breaker is a very expensive class, 70 amps is about right to handle the inrush of a 25 HP motor. If using time delay fuses, 45 or 50 amp would usually be correct.
varmit is offline   Reply With Quote
Old 12-06-2011, 08:03 PM   #8
Senior Member
 
Join Date: Jul 2010
Location: IL
Posts: 3,838
Rewards Points: 1,224
Default

The breaker in a motor circuit only provides the ground fault and short circuit protection. The wire is required to be sized at 125% of the current as shown in tables 430.247 through 430.250. A thermal magnetic breaker used for the short circuit and ground fault protection is permitted to be sized at 250% of the current shown in the tables. The motor overload device must be sized based on the motor nameplate current and not the current shown in the tables.
don_resqcapt19 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Overcurrent protection - motor circuit Mike in Canada Canadian Electrical Forum 7 03-26-2012 04:47 PM
AC Electric Motor under no load. PsiMan84 General Electrical Discussion 5 10-26-2011 04:11 PM
Motor overload protection Gamit NEC Code Forum 12 12-05-2010 10:37 AM
How to calculate No load current and No load torque in DC Motor AMIanna General Electrical Discussion 3 05-21-2010 09:15 AM
3 phase motor protection te12co2w General Electrical Discussion 8 09-09-2008 04:22 PM


All times are GMT -4. The time now is 07:48 PM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.1
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Our Pro Sites Network
ContractorTalk.com | DrywallTalk.com | HVACSite.com | PaintTalk.com | PlumbingZone.com | RoofingTalk.com