I am looking for a bit of advice, having lost the electric supply to my
original shop (long story) I have had to move it, luckily I have another
barn I can use, only problem is the electric is taken from my house to a sub
panel. When I start up the table saw I get power dips all over, although
only for a short time. Is this harmful to my electric house lights, furnace,
etc etc. Is there any way to hold up the supply to stop the dipping??
The biggest worry that comes to mind is that of a loose connection at
some point (s) which could arc and start a fire. You haven't had
excitement at home until you've seen an electrical arc inside your
home's outlets! Dimming of lights indicates a voltage drop; that means
either an incorrectly sized run of wire(s) and/or some poor connections.
My advice is to get a qualified electrician to check out your electrical
system BEFORE something goes up in smoke. I'm not just being an
alarmist on this; this symptom is indicative of a serious problem. Don't
worry about the lights; worry about an electrical fire.
Sandie C wrote:
Most likely you are right (the sizing part). Generally, if a connection was
loose then the lights wouldn't dim only momentarily, they would dim for the
duration of the saw running. This is of course generally the case, YMMV.
Can you post specific numbers like saw HP, wire guage suppling the outlet
(if you can tell), wire guage supplying the subpanel, distance from the main
to the subpanel?
While I agree that there are other things to look at first, don't rule out a
floating neutral. I had a similar problem in the house with even the washer
agitation effected the lights. I wasn't going to build a new shop with this
problem so I posted here and an electrician threw that out. I took some
readings at the panel and was surprised - called the power company and he
was dead on. They fixed it in a few hours. No more problems and now the
new shop has 50amps to it and my Griz 1023SL which pulls 18a at 220 barely
dims the lights at all and even when it does, it's barely a flicker at
A floating neutral is a neutral that is not at ground potential but it as a
higher potental. You can test for it by measuring the voltage between the
safety ground connection (the bare wire) and the neutral. There should be
no voltage present since they are connected in the panel. If a neutral
connection is loose somewhere, it adds resistance to the neutral portion of
the circuit and thus places the neutral wire at a potential other than
ground when current runs through it. This situation can be extrememly
dangerous and should be rectified immediatly. I don't however think that
this is the case of the OP. The OP has the run of the mill undersized
service troubles most likely.
Frank, the motor draws more current when first started. When it's up to
speed current draw drops markedly, thus explaining why she complains of
the lights dimming momentarily. If she was running a constant high
current device like a space heater, then the lights would be dimmed the
entire time and that could be the result of high resistance in the wire
or a flaky connection(s).
Frank Ketchum wrote:
That's my take on it, too. You do need to be careful of damaging other
equipment, however. Some things don't tolerate undervoltage or undercurrent
too well. Many electronic products may bite the dust (one bit of the clock
circuitry of my microwave oven did in a recent brown-out...this makes the
clock/timer run about 17% fast and repair is about $200 because only the
entire module, including front panel, is sold). You'd also want to be
careful to make sure any MOTORS on the circuit don't stall as that could
cause them to overheat and burn out.
I have a pair of printers that I use, one upstairs and one downstairs
that both of them when used upstairs will draw down the lights when
they first turn on. HP Laserjet 4's are the printers and well, they
are work horses. Over 20000 pages have been through both, and I only
picked them up 3 months ago and have not put any more than 300 pages
since then. But every time I turn the sucker on, the lights dim in
THis house has wiring problems as in too many things on the same
breaker, but with everything sealed <behind the drywall> including the
basement, nothing is going to happen about it! I have just gotten in
the habit of waiting till the freezer kicks off before I turn the
printer on to not draw quite so much power at the same time.
On Tue, 06 Jan 2004 02:57:51 GMT, "Sandie C"
Try plugging the tablesaw directly into the outlet nearest the sub panel and
running it. If it still dims the lights, then the wiring to the barn is
most likely inadequate for your power needs (not really dangerous, just a
nuisance). If it is possible, change the saw from 110volt to 220volt
assuming you can and that you have 220 available. This will help.
If the lights don't dim, then most likely you just need a beefier extension
cord. Buy a heavy duty one as short as you need it and plug it into an
outlet close to the sub panel.
The answer is simple, the fix may not be. You need more power to the shop.
There are no shortcuts. Larger wire to carry more amps at a minimum,
perhaps new service if very old and small. Light bulbs are probably OK,
but other motors, computers, etc. can be damaged by it over the long term.
Panels can overheat if the draw is too high for a time also.
It is best to have the lights and the power tools on separate circuits.
Nothing more joyful than working at night, hitting the power switch on a
tool and having the place go dark.
My first little Craftsman saw was OK on a 15A circuit, but my Delta 1.5 hp
needs a 20A. First time I plugged it in to try, I had two of the three
fluorescent fixtures go out on me and the third one dimmed. Next day I
started running new wire.
It is also possible you need more power coming into the main. That
determination will depend on what exists now and what power draw the rest of
the circuits have. Talk to an electrician.
Bad news. There is *no* simple solution/fix for this problem.
Depending on "how bad" the 'dip' is, then the answer is "yes, it _could_
hurt the other electrical devices.
If the 'dip' is *only* in the barn, then only things _in_ the barn would
be *potentially* adversely affected.
Whichever situation, the _cause_ of the problem is that the wiring feeding
*to* the area that shows the 'dips' is too small for the load. *OR* (albiet
a remote possibility -- the electric utility "supply transformer" is under-
sized) There are three possible fixes for this:
1) _Don't_ run the stuff that causes the dips to occur.
2) Increase the size of the supply wiring. (or the utility transformer,
*if* that is the source of the problem.)
3) Bring in a *SEPARATE*FEED* for the shop.
For simple high-power-draw motorized tools, you could probably power them
from a stand-alone generator of adequate size. 5kw is more than big enough
for a 3hp saw.
All the responses given are correct. You are drawing lots of current
and experiencing a voltage drop in your shop wiring. Obviously the
current you are drawing is not sufficient to blow the Main breakers on
the subpanel or main panel. I am assuming the subpanel is connected to
the main breaker panel and not before the main breakers. If subpanel
is connected correctly than the light dimming is probably bad wiring
or undersized wire causing high resistance path hence power loss in
wire. Other possibility is the Voltage entering your main panel may
not be well regulated or lower than 115 - 120 Volts this is often the
case in Isolated remote rural areas.
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