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.
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!!
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! mea