I have a bunch of computer/computer related things getting power from
the same two outlets. The list goes:
--Compaq Presario computer
--an older (circa 1999) HP computer
--a 19-inch monitor
--Samsung laser printer
--Canon photo printer
--HP flatbed scanner
--speakers with subwoofer
--charging cradle for a cordless phone
--a Linksys router
--charging cradle for a USB price swiper
--power adapter for a USB hub
Just wondering if all this together will stress my wiring or otherwise
be dangerous? I'm running all of this off a power strip and an APC
UPS (which I guess draws a bit of power on its own).
One 15 amp circuit in the USA will support 1800 watts of resistive
load (15 x 120)00. Computer equipment is a complex load with less
than 100% power factor. Let's assume your p.f. is 80% so now you are
limited to .80 x 1800 or 1440 of real power watts. Derating this
further, will give you even less since you never want to load up one
circuit to 100% ampacity.
If you had a simple device like Watt's Up, you could measure your
actual load just before the UPS. It will vary depending on what
printers are powered up, but for the most part, the devices you
mentioned present pretty much of a constant load. If you don't have a
true power Wattmeter, you can get a very rough approximation by adding
up the watts for each device as stamped. Just a guess here, but the
laser printer probably consumes the most power when warming up and
actually printing, the computers and the monitor will come in 2nd,
espcially if it's an older CRT monitor. Put your hand on the top and
in the back. Does it run hot? The heat you feel indicates heavy
power use and possible wasted power. Printers only consume
significant power when they come off standby. The hubs, cordless
phone, and router, have minimal power consumption.
I have similar equipment in my office. Based on a long life of
experience with this stuff, you would be much better off with two
circuits for your office equipment. If you are just limited to the
one, however, it probably won't be dangerous. The question is...
What else is on that circuit (bathroom lights, window air
conditioner?) If you a tripping the breaker due to overloads, you
will need to do something about it.
20 Amp circuits are also common and preferred whenever possible. You
will have a 33% increase in capicity to 2400 resistive watts vs. the
15 amp circuit. The ampacity of the circuit is listed on the breaker
Thanks much for your reply. Since I live in an apartment I doubt my
landlord would let me have an electrician wire a second circuit.
Maybe...I've been here 5 years, plan to continue living here...so he
might. The reason I ask is that sometimes the lights in my
office/spare bedroom will dim when the laser printer starts up. That
Samsung is a new addition, and I guess it put me close /over to what
my wiring/circuits can handle.
I'm not sure what else is on the circuit, but I do not get dimming
when my A/C (which is is another room) comes on, or when I turn
lights on. The dimming also doesn't happen when I use the
photo/inkjet printer, but of course it's a much smaller printer.
You mentioned monitor age might be a factor; mine is a KDS
purchased in 2003, I think. It's a CRT.
Oh, I have not had any breakers tripped. Just the dimmed lights
On Sat, 04 Jun 2005 07:05:46 GMT, not email@example.com (Beachcomber)
Overload or not, that flickering when the laser printer's fuser starts
cycling on and off can drive you nuts. Try to get a dedicated outlet for
that if possible. Also, The laser printer is your largest load on your list
of equipment when it's online and printing. Also, since most of your
equipment uses Switch-Mode Power Supplies, there is a large non-linear
component to your load; an instrument like the aforementioned "Watts Up"
will not give your accurate results because it measures RMS. It will not
indicate the full actual load applied. Additionally, the NEC requires
circuit ampacity to be rated for 125% of the rated load when the load is
continuous plus the non-continuous portion:
"Branch-circuit conductors shall have an ampacity not less than the maximum
load to be served. Where a branch circuit supplies continuous loads or any
combination of continuous and non-continuous loads, the minimum
branch-circuit conductor size, before the application of any adjustment or
correction factors, shall have an allowable ampacity not less than the
non-continuous load plus 125 percent of the continuous load."
I had the exact same issues (dimmed lights) when I got my first Apple
NTX Laser Printer way back around 1994. That sucker had the pickiest
power requirements I've ever seen and I had to give it its own
circuit, even it meant running a heavy duty extension cord across the
room. I believe it had something like 7 separate power supplies
within and God help you if you wanted to run it on an alternative
source of power like an alternator.
The new Watt's Up claims to be fairly accurate, even with complex
loads. It will also give you a value for the power factor. If you
don't have a $3000 precision scientific wattmeter just laying around,
it's certainly better than just guessing.
Also, if you need to find out what else is on your office circuit,
just flip the breaker off and see what else has stopped working.
When you design your own house, put in two dedicated isolated ground
20A circuits for your office equipment. You can even have the funny
looking hospital grade orange receptacles with little pilot lights in
them for the ultimate in coolness.
You can go with the load calcs, or , if you have your own circuit
breaker panel inside your Apt. without bthering the LL, you can have
someone place an ammeter on the circuit with all you're equipment on,
and measure just how much draw you have on each circuit and take it from
there. 1 Solution is, If the conduit used in the apartment is Pipe (EMT)
it wouldn't be too difficult to upgrade the circuit to accomodate your
demand., but there are other solutions like changing the light fixture
wires to another unloaded circuit, Or Easier yet, try placing a Compact
Fluorescent Bulb on it and see if it still dims when your laserjet kicks
On Sat, 04 Jun 2005 10:45:37 -0400, firstname.lastname@example.org wrote:
Just another thought... If it were me, I would remove the laser
printer from the UPS and plug it a separate outlet (ideally on a
different circuit and perhaps use a good surge protector device).
The function of a UPS is mostly to keep your computer going during a
power failure and give you time to save your open files and do a
normal shutdown. A laser printer on that line is going to take up a
lot of the capacity of the UPS with no real benefit to you.
I run my monitor, main PC, router, and cable modem off the UPS.
During the one long power outage I've experienced since I've had
the UPS, the UPS battery lasted about 10 minutes. More than enough
time to log out of my work VPN, save things and power down gracefully.
On Sat, 04 Jun 2005 15:25:00 GMT, not email@example.com (Beachcomber)
As others have noted, little power consumption with all
those devices together. The wall receptacle is probably rated
for 15 amps. Moreso, it is probably powered by a 20 amp
circuit. With so many devices, then a power strip is probably
being used. That $3 power strip (that should have no surge
protectors as even the UPS manufacturer suggests) must have
the one component essential to power strips - a 15 amp circuit
breaker. IOW long before ae load can cause wiring problems,
that circuit breaker would trip. Again, a power strip without
that circuit breaker: replace it for human safety reasons.
Do incandescent bulbs dim or brighten when powering up this
system or any other heavy appliances? If not, the you
probably have a very healthy wiring system. But again,
multiple appliances on one receptacle should be powered
through a power strip that has an all so necessary 15 amp
Trevor Smithson wrote:
|> Are 20A breakers and 20A wiring that prevalent? Most panelboards I see|> (North of the USA) are chock full of 15A breakers.|>
| Here in the South USA, typically 15A for lighting circuits and 20A for
| (Thats the way I install them, and what I have seen in almost all the homes
| that I have worked in anyway.)
I see that in lots of homes around here in WV (considered by some to be
part of the south).
My plan for my future house is to just go with 20A across the board, while
still keeping all lighting on separate branch circuits apart from all the
receptacle branch circuits. Switched receptacles intended for table lamp
use will be on the lighting circuits.
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
The circuit breaker will protect the wiring as long as the circuit breaker
is good and the wiring is done well (e.g. no loose connections in wiring, no
loose connections where cords plug into outlets, etc.). The circuit breaker
is probably fine. If you have, and are comfortable using, a voltage tester,
you could plug in some big loads (some 300W - 500W torchiere lamps, heater,
hair dryer, etc.) on your power strip and see how much your voltage changes
at the power strip with the load ON versus with the load OFF. Post the info
here (Watts & type of load, voltage with load OFF, and voltage with load ON)
and you can get some opinions on whether the numbers sound reasonable or
not. You could also give some indication of how far the outlet is from the
panelboard. If you use lighting as a load for this test, you can also try
shaking and wiggling cords and connectors and watching to see that the
lighting stays constant. This is a mild indication that there is not some
intermittent connection that may cause trouble if your cords gets
bumped/disturbed as they likely will with normal use.
Laser printers are notorious for causing light dimming. They will draw huge
current (30A is a number I believe I've heard kicked around) for brief
periods for internal reasons (heating toner I believe). Apparently many of
them will do this regularly, every 20 - 60 seconds. That huge current draw
will cause a brief voltage drop at the load end of the circuit, which can
cause lights on the same circuit to dim. Your a/c will be on a different
circuit, which is the reason you don't see it causing dimming of those
lights. If you want to find out what all is on your computer outlet
circuit, turn off the breaker. Obviously, the lights on the circuit will go
out. A voltage tester or portable lamp (or portable anything) will tell you
which outlets are on the same circuit. You may want to keep them in mind,
and not plug a heater into one of those outlets some day.
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