ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Shout Box
Recent Posts
Tingle off the water spigot
by dsk. 10/15/18 02:36 PM
Board tester power supply?
by JoeTestingEngr. 10/13/18 12:14 AM
Voltage sag
by Trumpy. 10/12/18 06:59 PM
220/230/240V 60Hz Systems
by Trumpy. 10/12/18 06:50 PM
Linear Power Supply Quits Under Load
by JoeTestingEngr. 10/10/18 08:47 PM
New in the Gallery:
What is this for?
Plug terminals
Who's Online Now
0 registered members (), 50 guests, and 23 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Transformer wiring #199292
02/19/11 01:53 PM
02/19/11 01:53 PM
S
SJT  Offline OP
Member
Joined: Jul 2002
Posts: 241
PATCHOGUE, N.Y.
In regard to the NEC, could a 225KVA transformer be used to only feed a 200 amp/208 V 3 phase panel with a main breaker. If such a transformer was to be used, then what size primary protection would be needed? Would I wire it as if it were a 75KVA transformer and rate the primary and secondary accordingly? It's a strange request from a customer. In the future he may run the proper size primary and secondary conductors, to get the max out of the 225 KVA trans.
Thanks - Good Day
SJT

2017 / 2014 NEC & Related Books and Study Guides
Re: Transformer wiring [Re: SJT] #199300
02/19/11 05:59 PM
02/19/11 05:59 PM
G
gfretwell  Offline

Member
Joined: Jul 2004
Posts: 9,298
Estero,Fl,usa
The way I understand it you use primary protection that protects the transformer and secondary protection to protect the installed secondary conductors.


Greg Fretwell
Re: Transformer wiring [Re: SJT] #199307
02/19/11 11:02 PM
02/19/11 11:02 PM
G
George Little  Offline
Member
Joined: Jan 2004
Posts: 1,489
Michigan USA
Need to know how long the Secondary conductors to see if they qualify for the 10' rule mentioned in 240.21(C)(2) or possibly 240.21(C)(3) or 240.21(C)(3). Is it a single voltage secondary qualifying under 240.21(C)(1)? Basically if the xformer is has 225 KVA capacity and you only want to use it at 75KVA there is no problem and the sizing of the primary conductors should be sized to match the secondary load taking in to considration the voltage ratio and maybe an extra 25% would be a good idea to keep the fuses from clearing on start up. There is no need to protect the secondary of the xformer, just the secondary conductors.

Last edited by George Little; 02/19/11 11:04 PM. Reason: Edited for added thought:)

George Little
Re: Transformer wiring [Re: George Little] #199322
02/20/11 01:03 PM
02/20/11 01:03 PM
S
SJT  Offline OP
Member
Joined: Jul 2002
Posts: 241
PATCHOGUE, N.Y.
Thanks,
I never wired a large transformer to a smaller rating than what it could put out.
Sounds like I'll be OK. I have to check the connection points for the x1, H1, etc. to make sure we use the proper lugs and bolt sizes.

Re: Transformer wiring [Re: SJT] #199667
03/04/11 04:20 AM
03/04/11 04:20 AM
T
Tesla  Offline
Member
Joined: Jun 2004
Posts: 1,273
Sacramento, CA
On the economics....

A 225 kVA XFMR is huge. Regardless of the true load it will bleed energy to sustain its magnetic circuit.

Correct sizing would mean a XFMR of 75kVA.

So you're bleeding off 225/75 = 3 times as much parasitic losses as would be nominal.

Do run your calculations.

BTW 3 is the lower bound.

Power cost being what it is -- you'd very likely be much better off scrapping/ reselling the gear and downsizing to a new/used transformer.

Talk to Salinger and others in the used electrical equipment market. You'll have your eyes opened.

http://www.salingerelectric.com/



Tesla

Featured:

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

 

Member Spotlight
Admin
Admin
NY, USA
Posts: 3,516
Joined: October 2000
Show All Member Profiles 
Top Posters(30 Days)
sparky 11
Popular Topics(Views)
250,258 Are you busy
187,911 Re: Forum
177,445 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.6.1
(Release build 20180101)
Page Time: 0.026s Queries: 15 (0.005s) Memory: 0.9691 MB (Peak: 1.1087 MB) Zlib enabled. Server Time: 2018-10-15 19:23:49 UTC