ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Top Posters(30 Days)
Recent Posts
VFD MotorFeeders
by gfretwell. 10/17/17 10:01 PM
What do you do?
by gfretwell. 10/17/17 01:08 AM
Good ol' copper pipe in the fuse holder trick
by HotLine1. 10/16/17 07:16 PM
Generator Cable Sizing
by HotLine1. 10/16/17 07:13 PM
Another generator question
by HotLine1. 10/16/17 07:02 PM
New in the Gallery:
Gallery Test
Popular Topics(Views)
241,356 Are you busy
177,305 Re: Forum
168,931 Need opinion
Who's Online Now
0 registered members (), 39 guests, and 8 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
#6599 - 01/08/02 02:31 PM Motor Voltage  
Frank Cinker  Offline
Member
Joined: Jul 2001
Posts: 311
Pennsylvania
A 20 horsepower, 230 volt three phase trash compactor is being relocated from one Public Works Department location to another part of the City. The new location only has 208 volts, three phase available. Would it be acceptable to feed the motor with 208 volts?


Work Gear for Electricians and the Trades

#6600 - 01/08/02 02:57 PM Re: Motor Voltage  
JBD  Offline
Member
Joined: Jul 2001
Posts: 599
WI, USA
I would not do it for long term use. 208V is at the low end of the tolerance range for most motors. At this low voltage you can expect lower starting torque and increased running current, also the life of the motor will be shortened.

This is the perfect application for a buck-boost transformer. Your application will require two single-phase transformers connected in an open-delta configuration. Your 20HP motor will need at least 21.5KVA.
For boosting 208V to 230V (10% change) you will need 1.5KVA transformers.
For 208V to 236V (13.3%) use 2KVA.

You can get an on-line buck-boost calculator at http://www.squared.com. Then go to the Support and Resources section and choose Free Software and On-line tools.


#6601 - 01/08/02 03:08 PM Re: Motor Voltage  
Redsy  Offline
Member
Joined: Mar 2001
Posts: 2,056
Bucks County PA
The 208 would be just above a 10% tolerance (207). What was the system voltage that was previously feeding the motor, 240? In my opinion, it would be better to have a properly rated motor. Table 430.150 states that the currents listed shall be permitted for system voltages of 110-120(?), 220-240, 440-480 and 550-600. Conspicuously absent is 208. I think 208 stands alone. I see dual-rated 230/460 motors regularly, but know of no 230 volt systems. These motors may be designed to operate on 240.
BTW, table 430.150 has a column for 3phase 110 volt motors. Interesting!?


#6602 - 01/08/02 03:16 PM Re: Motor Voltage  
Frank Cinker  Offline
Member
Joined: Jul 2001
Posts: 311
Pennsylvania
Thank you for replies. In the previous location the 20HP 230 volt, three phase motor was fed 230 volts.

What is approx. cost of said boost/buck transformers?


#6603 - 01/08/02 03:48 PM Re: Motor Voltage  
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
IL
Many new motors that I have been seeing have 3 FLAs listed on the nameplate. One for 208 volts, one for 230 and one for 460.

Has anyone ever worked with a three phase 115 volts system? I've never seen it anywhere, but it must exist or there wouldn't be a column for it in Table 430-150.

Don(resqcapt19)


Don(resqcapt19)

#6604 - 01/08/02 06:35 PM Re: Motor Voltage  
Joe Tedesco  Offline
Member
Joined: Oct 2000
Posts: 2,749
Boston, Massachusetts USA
2002 NEC, See Section 110.4 Voltages.
Throughout this Code, the voltage considered shall be that at which the circuit operates.

The voltage rating of electrical equipment shall not be less than the nominal voltage of a circuit to which it is connected.


Joe Tedesco, NEC Consultant

#6605 - 01/08/02 09:11 PM Re: Motor Voltage  
SPARKSALOT  Offline
Member
Joined: Dec 2001
Posts: 28
Omak, WA, USA
Since the motor is rated for a higher voltage than available it would be legal for this app. However, it will not develope it's nominal HP at this voltage and will overwork its self if something is not done to limit the load on the motor. It is probably hydralic so if chain/sprocket coupled, change the sprocket ratio to gear down the motor. There may also be a way to reset the bypass pressure so the motor dosn't work as hard. The other thing to do is resize the overloads to protect the motor. You can make this work but be prepared for the system to be slower or at least to trip out fairly often.
Don


#6606 - 01/08/02 11:30 PM Re: Motor Voltage  
electure  Offline


Member
Joined: Dec 2000
Posts: 4,262
Fullerton, CA USA
I've got to agree with JBD. A great application for boost xfrmrs.



Member Spotlight
NickD
NickD
Amish Country, PA
Posts: 46
Joined: March 2013
Show All Member Profiles 
Featured:

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.016s Queries: 14 (0.003s) Memory: 0.7930 MB (Peak: 0.9515 MB) Zlib enabled. Server Time: 2017-10-18 09:11:24 UTC