On 12 Nov 2005 16:49:06 -0800, wrote:

I recently bought a milling machine with a 3hp motor. I purchased a
7.5 hp rotary phase converter and hooked it up to my mill. I have a
100 amp 220 service to my house. Unfortunity I have noticed that when
I first turn the mill on the lights in my shop quickly dim due to
starting of the mill which I understand. My problem is my electric
line is shared with my neighbor then goes to the transformer on the
pole. Another neighbor is also hooked up to the same transformer and
everytime I start the mill the neighbors lights also dim quickly...My
question is due you think I should get the power company to fix the
problem? Do I really need to get a bigger service (200amp) even
though I am only running one machine?

Thanks

You probably want to talk to the local power utility before you do
anything - they probably need to put in a larger transformer at the
pole to handle the start surge of that big a motor, when combined with
the normal loads of the other houses on the same transformer.

It's also possible that there is a dirty connection or two in the
high voltage lines coming into the common transformer, or on the low
voltage side where you and your neighbors all hook up. They can send
a lineman up there with a voltmeter to look for bad connections.

And another probable source of the problem is the service drop wires
to your house. It is common for utilities to chat rather ruthlessly
on the voltage drop of service wires - you install 1/0 TW Copper wires
up the old mast for a 100A service to allow a bit over the mandated
minimums, and they use #2 XLPE Aluminum service wire up to the pole.
Sure, there's a lot of voltage drop in the circuit from that service
wire, but they're the utility and they can do it - and save some money
on wire in the process.

Myself, I'd change the main service and riser to a 200A Copper-buss
service panel as the first step, to minimize any voltage drop problems
that may be in your equipment - and if your old panel is over 20 years
old, it's probably due anyway.

If you've done any major square- footage additions to your house,
you might even jump a notch to a 400A service, then when you get that
great deal on a Lathe you are still OK.

(I have to do that myself - bump up from an old 200A fused-switch
main service to a 400A. But I've already reworked the main breaker
panel, the 200A was a bit oversized when it was installed, and we've
converted the kitchen, water heater and clothes dryer from Electric to
Gas to ease the load. See "Shoemaker's Children Go Barefoot...")

Most home builders make the main panel as small as possible to save
money, a 100A or 125A panel, or a 70A "Crowfoot" (six breakers, no
Main) in the older days. And then over the years you've gone and
added on one or two bedrooms and a Den, and central air conditioning,
and a big swimming pool/spa with a 1.5 HP filter pump and a 2 HP spa
booster, and a microwave oven, and a toaster oven, and that big-screen
entertainment center, and a computer and laser printer...

The conversion of your garage into a home shop with the upgraded
lighting, and the fans, and the 7.5 HP rotary phase converter and 3 HP
mill, and the 50A welder outlet - that's just the last nail in the
coffin. If this sounds a lot like your house, I can guarantee that
you need to upgrade the main service.

Make sure that you generously oversize all the wires - use 4/0 or
250MCM Copper for the 200A mast riser where 3/0 THHN would do, and
oversize the wires heading into your shop sub-panel and the phase
converter the same way.

The Electrical Codes are a /minimum/ standard - there's no rule at
all against doing a better job than you have to. ;-)

And get the utility to use the right sized riser wires to the pole,
too - they'll grumble about it, but if you twist their arm you can
probably get them to break out the 250MCM or 350MCM Aluminum wire.

-- Bruce --

--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
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