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#57752 - 10/20/05 02:13 PM Changing Shop Voltages
measervices Offline
Junior Member

Registered: 10/20/05
Posts: 2
Loc: Belle Chasse,LA,USA
A friend of mine owns a machine shop and she's attempting to install a few new CNC machines as well as switch all the voltages on her machines from 3 PH 240 to 3PH 480. She said that the utility asked her what size xfrmrs she needed on the new relocated pole outside of her facility. Assuming that she can change all of the voltages on her equipment from low to high, I'm guessing that her amperage draw will be reduced with the higher 3 PH voltage. How should I go about adding up the total loads and identifying the proper size xfrmrs for the utility company? I'm also guessing that they'll probably over size it anyway, based on what she asks for, right? Any help would be greatly appreciated.

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#57753 - 10/20/05 05:29 PM Re: Changing Shop Voltages
HotLine1 Offline


Registered: 04/03/02
Posts: 6805
Loc: Brick, NJ USA

The utility(s) here do the xfr sizing based on info submitted by the client for the electrical equipment being served. BTW, based on calculations that I do, they 'undersize' their equipment; as they are not subject to the NEC, but the NESC.

Unless your lady friend is a qualified electrician, she should seriously consider hiring an appropriatley licensed and qualified person or company to modify the machinery; there's more to it than switching the taps!!


#57754 - 10/20/05 05:55 PM Re: Changing Shop Voltages
frenchelectrican Offline


Registered: 02/06/03
Posts: 938
Loc: Wi/ Paris France { France for ...
i will agree with Hotline1 with this sisuation.

to change over from 240 to 480 volts system it will take more than simple set up.

have to set up with 480 volts breaker [ they cost more than 240 v breakers are]

change wire circuits to reacmmuated with 480 volts [ some circuits can use the same wire but i will not recomned at all]

add a step down transformer for 120 volt plugs and 120 volts lighing circuits and some 240 or 208 v [ single or 3 phase ]

the electrical load the poco will figured out for correct size transformer by load demand usage not the main breaker rating unless hevey loaded

on most machinines when you change over to 480 volt the mmagatic starter or contractor have to change and the same thing with heater strips for overloads , motor reconnection etc etc

so there are some condersation you have to take a look at it not only on electrical side but the machery also for how much time to take to change over alot of items to work on proper votage

Merci , Marc
Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)

#57755 - 10/20/05 07:51 PM Re: Changing Shop Voltages
e57 Offline

Registered: 05/27/03
Posts: 2837
Loc: S.F.,CA USA
Why not leave all the 240 alone, and just add have them add service for 480? Or have a step up just for the 480 stuff? Might be better to check billing rates first.
Mark Heller
"Well - I oughta....." -Jackie Gleason

#57756 - 10/20/05 08:18 PM Re: Changing Shop Voltages
measervices Offline
Junior Member

Registered: 10/20/05
Posts: 2
Loc: Belle Chasse,LA,USA
I haven't even been up to see EXACTLY what she's dealing with, but I do recall some mention of alot of the machines working on the 240 with step up xfrmrs, so some will work just fine with the 480. She also stated that she has purchased a new distribution panel, so that's promising. In South MS, you would not believe the caliber of electrical services. I wired up a trailer house for one of this lady's employees after Katrina and most of the local electrical supply houses did not know that you should bury conduit 36" when running from the main on the pole to the trailer. They believe kicking some dirt over it will suffice. I've only agreed to offer some advice on the work her electrician will be doing, but I believe him to be cut from the same rural cloth as the shade tree electricians at the supply house. I'm very careful to reference NEC when providing consulting work to family/friends. I work for a major utility and safety is a serious part of my livelyhood. I appreciate all of your input and kudos to a great forum for information. I've learned a lot from simply browsing through these posts and many of the safety-related stories reiterate some things that I have witnessed, like a complacent 20 yr veteran by-passing a voltage check in a disconnect before tightening an allen screw.
Thanks again!


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