How to minimize voltage drop caused by heavy machine?

We have a typical office environment including computers, scanners,
lights, etc. However, we also have a 14" saw. When it starts, the
voltage drops for a split of a second. This has no immediate effect
except on the scanner. Even though the scanner is plugged into an
uninterrupted power supply, if the saw starts and the scanner is in the
middle of scanning, the scanner will stop and scanning is aborted. When
the saw starts, the uninterrupted power supply produces a click sound.
It seems the protection mechanism is kicked in. Why are the computers
not affected but only the scanner?

The saw starts roughly every two minutes. This renders the scanner
useless. Is there a device I can add to the saw to minimize the voltage
drop? Thanks in advance for all the help.

That's a very significant voltage drop.
I'd start by making sure you have a large enough cable feeding that saw.
If possible, move the saw so it's wired right near the main service
entrance (breaker box).

If that dont fix the problem, (If the saw is 120V), wure it to the
opposite leg of the system on a 240V system.

If course we dont know if you might have 3 phase wiring, or if the saw's
motor is 120 or 240 volts. If that motor is 120v, it might be worth the
cost to change it to a 240V motor, which will run more efficiently.
Also, could that motor possibly be failing, or have a weak capacitor? A
draw that heavy might mean that motor is a little undersize too.

It's real hard to say whats causing this without seeing all the
components and wiring layout.

Before you invest any significant money in this, call your power company
to inspect the pole transformer and all wiring up on the pole. The
transformer might be too small. They should have a number to identify
their rating, for example a home may have a 10KVA or 15KVA transformer.
But there could be multiple houses /buildings on that same transformer.
Yours could just be too small or feeding too many other buildings.
There could also be a loose connection up at the pole, or the cables to
your building, at the meter, or in your breaker box. All of that should
be checked. Maybe the service entrance is too small for your needs.

I'd begin with the call to the power company to check the pole
transformer. They are required to do that all the way to your elec
meter. All wirring AFTER the meter is your responsibility to check or
hire an electrician to do it. But if you show the power company the
problem, they might take a look at your system and maybe suggest
something, if it's not just needing a bigger transformer.

Here is a little thing I ran across some years ago. A local auto
service garage had a very large air compressor. At the rear of the
garage was a restroom. More than once, while waiting to have some work
done on my car, I'd go in that restroom, and notice the incandescent
lightbulb get real dim when the compressor kicked on.

One day I go in there and see he changed the bulb to a CFL. The
compressor started and the CFL shut off entirely for a few seconds. I
said to the owner, "what's with that light in your restroom". He said
it's always that way when the compressor kicks on, and he's had several
of those CFLs burn out after only a few weeks.

The next time I went there, he had an incandescent bulb in there again.
(I think those surges just killed those CFLs).

A couple years ago, they got a new compressor. He said the old one just
died one day and it was time for a new one. The new one is as big if
not a little bigger than the old one. Ever since that new compressor
was installed, I no longer notice the restroom bulb get dim when the
comp. kicks on. I dont know if any wiring was changed when the new
compressor was installed, but that light dimming has now stopped. Maybe
that motor was failing or under rated, or it could be bad wiring or
other things.....

What you explain is probably shortening the life of all your computers
too.

What happens if you were to remnove that uninterrupted power supply, and
run the scanner directly? Maybe that uninterrupted power supply is weak
too. Either way, you have a problem which could damage all your
sensitive electronics. I'd not leave it like that very long.

BTW: Have you connected a volt meter to that scanner outlet and watched
what the voltage dropped to when he saw kicked on? Most places have
between 115 and 120 volts during normal use. But I've seen readings as
low as 110 and high as 124. Still fairly normal. If you see a drop
below 110, you have a problem....




This is 220 V. The transformer is 100 KVA, 3 phase. It feeds one office,
one warehouse, and one office/shop which is where I reside. The office
has lights, computers, A/C, etc. No heavy machine. The warehouse has
mainly lights. There are only two cables coming to this office/shop.
Thus, it can only be single phase. There are two breaker panels wired in
parallel. I have tried putting the saw to the other breaker panel (two
are 10 meters away) to no avail. I guess this is what is expected for
parallel panels.

Although the power is supposed to be 220 V, the needle on a refrigerator
safeguard points to something like 210V. When the saw starts, the
voltage may drop to something like 170 or 180 V (difficult to tell by a
needle.)

This is a new saw, about one month old. I hope the motor is not failing.

We have a 30 KVA generator dedicated to our building only. Next time
when it runs, I'll watch closely to see if the voltage drop happens
again. If it won't happen, I can be quite sure the incoming power lines
is the culprit. If it happens again, I don't know what to do next. Would
changing the saw cable to a bigger one (smaller gauge number) help? I
have no clue.


*You may be able to change the taps on the transformer to boost the voltage. There should be a wiring diagram on the inside or outside of the transformer. Power would have to be shut off to the entire transformer to make the change.