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.
Sounds like you're doing construction. How about a long heavy duty
extension cord for the scanner until you get to a circuit not affected
by the saw. Or, find a receptacle possibly closer to you for the
scanner that is not on the same phase as the saw. (110 volt saw?)
That is, which uses a breaker that is on the left half of the breaker
box if the saw uses a braker that is on the right half. This assumes
you have receptacles on both sides of the breaker box. Check back if
you only have lights on the other side. I don't know how big your
building is or how many boxes there are.
Or put the saw on a long heavy duty extension cord, but that's my second
choice because the saw must use a lot more power and might be impeded by
a long extension cord. (Although I have my lawn mower on a 100' foot
heavy duty (but I forget what gauge) extension cord, which is plugged
into an 8 foot light duty extension cord, and I have no problem. (well
it mows the grass well.)
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
What you explain is probably shortening the life of all your computers
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....
On 27/01/2015 11:27, firstname.lastname@example.org wrote:
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
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
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.
It may or may not be the incoming lines. I'd say though, that wiring at
some point is not up to the job as you are trying to suck a lot of juice
through a small straw. It could be the lines to the panels. I've seen
similar situations when a power tool is on too small of a line even
though there was plenty of power coming to the panel from the stret.
Moving things around to distribute the load properly and assuring the
individual lines are adequate is the way to start. If you are not
familiar with tracing loads, get an electrician and he can do it for you.
*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.
We rent this place. Power cables go from the transformer to landlord's
office building. Everything has to go through the landlord. Anyway, last
week an electrician came, checked the system, and claimed the system has
no problems. There is nothing he can do. Well, I don't know how much I
can trust the electrician. The government (Burma) doesn't have electric
code and doesn't issue licenses for electricians. Virtually anyone can
be an electrician.
On 1/26/2015 11:35 PM, email@example.com wrote:
I don't understand this at all.
The purpose of a UPS is to prevent that from happening.
You need a better ups...or maybe the batteries are just weak
and not really doing their thing.
Maybe you can put the scanner and the saw on different circuits?
Depending on the wiring of the building that may or may not help.
Having your ups restart every two minutes sounds like "asking for trouble!"
I don't understand it either. A computer, monitor, and the scanner are
plugged into the same power strip which, in turn, is plugged into a UPS.
I don't know why the computer is not affected. Perhaps it has something
to do with the power supply of the computer.
I'll try piggybacking one UPS to another to see if that helps.
Well, the 1st thing I'd try is to plug the scanner directly into the
power and not through the UPS. Most UPSs actually switch the output
from the mains to the inverter built inside. Some UPSs actually run the
load on the inverter all the time. This would probably be good in you
case, however, those UPSs are getting fewer and farther between.
Computer power supplies tend to have enough storage to hold during the
switchover, however, most scanners use a small wall wart power supply
and may not have enough capacitance to hold over during the switchover.
If that doesn't work, I'd try replacing the wall wart. Some are
switching power supplies (more are going this way now) and some are
analog. That probably doesn't make a difference as it's all in how much
capacitance (holdover capability) it has. So, if the plug to the
scanner is a generic plug, changing the wall wart should be easy.
This email has been checked for viruses by Avast antivirus software.
On Tuesday, January 27, 2015 at 2:56:19 AM UTC-5, mike wrote:
It sounds like the UPS is no good. If it can't handle a voltage drop,
what's it going to do with a power loss, etc? First thing I'd do is just
try plugging the scanner in directly, no UPS and see what happens. It's
possible the UPS senses the power drop, then screws up in the response.
The scanner might tolerate the momentary drop in voltage. IDK why you need
a UPS on a scanner anyway.
Aside from that, some investigation into the sizing of the conductors,
what circuits loads are on, what the root cause is, would be worthwhile too.
Just measuring the steady voltage while the saw is operating does not
tell the whole story. The saw probably has a high peak start-up current
that might be 3 or 4 times the running current. Even without the
scanner problem, you seem to have excessive voltage drop.
Your scanner may be sensitive to power fluctuations, but a good UPS
should take care of that. Try unplugging the UPS, and see if it keeps
putting out voltage. Plug a lamp into it to provide a load. It may
just have weak batteries.
If you replace the scanner, consider one that is powered from the
computer's USB port such as a Canon LIDE. A computer's power supply
should provide buffering from power fluctuations.
It is actually a printer/scanner.
Yesterday, the saw started while the printer was printing. The printer
aborted the first page half way into printing it but the printer then
printed starting from the first page again and printed the entire
document even though the saw had started at least twice during that
time. This time, the printer/scanner was plugged directly to an outlet,
not to a UPS.
Seems like that should be adaquate for the transformer and wiring.
I'm not sure how that refrigerator setup is wired, but if it's reading
the voltage directly off the source wires, you have a BIG PROBLEM.
You're dropping nearly 50V below the required voltage.
Now take a plain multimeter, set it to AC Volts, 250V or higher scale.
Then SAFELY measure the voltage at the mains. If you're not comfortable
doing this, find someone who is or call an electrician.
An electrician will have equipment to measure current draw too, which
would be helpful.
Anything is possible, but ot's less likely with a new saw.
Shuting off the GRID power and running the generator would be a good way
to check to see if the same problems occur. If not, then you know there
is a problem with the power source from the GRID.
I think you have a bigger problem than the saw cable. Too small of a
cable would starve the saw motor, leading to eventual motor damage. It
should not drop voltage in th building by 50v.
BVut just to know, what is the amperage of that saw? What gauge is the
cable (cord). How long is the cord? Are you using an extension cord?
(what gauge is the ext cord if you have one). What size breaker is
feeding that saw?
Besides what I already said, the NEXT thing you should do is call your
power company. After all, part of the reason you pay them, is to
maintain PROPER power for your needs. They should not charge you to do
an equipment check. Maybe you have everything on one leg of the 3 phase
and the other two are sitting idle???? (Unbalanced load).
One other thought. You have that 30KVA generator. There has to be a
switching device that completely isolates the generator from the GRID.
(REQUIRED by code to prevent backfeeding into the GRID.)
There could be some sort of problem with that switching device.....
On 27/01/2015 18:46, firstname.lastname@example.org wrote:
The electric system in this country is notorious. Every house that can
afford a generator has one. When there is a power outage, you hear
generators humming everywhere. Some people have stabilizer also because
the power from the grid may be only 180 or 190 V.
I have a 30 KVA 3 phase stabilizer. Not sure if it will help or can be
used in a single phase environment.
My multimeter is also analogue. I still have to rely on the needle to
tell the voltage. What I said about 50V drop is just my guess. It is
difficult to tell the actual number from a small needle pointer.
The saw is 2000W, 8.8A. The wire feeding the saw is slightly less than
13 gauge (2.5 mm2 cross section).
The switching device for the generator is a simple double knife switch.
It needs to be manually switched between grid and generator.
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