Hi,
Got a home office and had my sparky set it up with its own 20A circuit. Runs a desktop computer, large monitor, scanner, and printer.
Just replaced my old printer and this new color laser I’ve noticed is causing the desk lamp to flicker when I turn it on and when it prints–even sometimes when it appears to be “idling.”
Printer says 11 amps on the back.
Am I stressing the other equipment on the circuit? Everything has surge protection, but I wonder if that printer is drawing so much juice that it’s causing voltage drops and spikes to impact the other stuff. Will this wear out the other equipment? What’s the best solution?
Thanks.
Replies
Laser printers have a large fuser heating element. I have never seen the specs on just the heater, but they have a large inrush current. I would not be surprised at an additional 10- 30 amps. But it is only for a second or fraction of a second. The duty cycle is low enough that it average current is at or less than the 11 amp nameplate.
They keep it on standby when the printer is not printing, but probably at a lower temp. That is why you sometimes see this during idle cycles.
The power supply in the equipment will not be affect by this.
Just ignore it.
Just some swags here;
1amp standby on the scanner + 5 amps inrush when it lights up
1 amp standby, printer, + 30 amps inrush
5 amps, computor
3 amps, monitor
Someday the printer and the scanner will light up at the same time = 45 amps. (Murphy says so.)
SamT
But a 20A circuit should easily handle a 45A inrush. (And I think you may be overstating the scanner inrush.)
I'd say don't worry about it. Fluorescent lights tend to be more sensitive to voltage fluctuations than many other devices, and computers in particular are designed to handle substantial voltage fluctuations without "losing it". I've had a laser on the same circuit as my main PC for maybe 10 years now and never had a problem due to it.
That is what is great about time inverse circuit breakers.
Have you ever seen the curves on those?
>>That is what is great about time inverse circuit breakers.
>>Have you ever seen the curves on those?
No. Do they look something like crossing logrythmic(sp???) curves? Got a copy you can post?
Samt
I found this on discussion on Mike Holts.
NEMA AB4, Guidelines for Inspection and Preventive Maintenance of Molded case Circuit Breakers Used in Commercial and Industrial Applications, Table 5-3, Values for Inverse Time Trip test, states that the maximum trip tome in seconds for breakers of a continuous current rating of 0-30a up to 250v shall be 50sec at 300% of Rated current of the circuit breaker.
It would take a 20a breaker with a 30a load significantly longer. Just for grins I dug out a trip curve for a single pole breaker for frames less than 50a. At 150% of its rated current the minimum trip time was about 1 min. and a maximum of 25-30 min which may raise an few eyebrows. I could understand that but most are familiar with published breaker trip curves and what they mean.
Another thing that has a huge affect of breaker trip times is ambient temperature. Sense it is not uncommon for a panel to be located in a cool basement this would add to the trip time. Warmer ambient temperature would be less.
Some place on SQ D and/or CH's web site they have some actual curves from test data, but I don't have time to find it.
Edited 6/2/2004 8:54 pm ET by Bill Hartmann
Thaanks bill
I've got Mike Holts in my favorites too.
SamT
For a fully equipped home office I usually pull in two 20A circuits. Large printers, multifunction devices and a possible foot warmer heater under the desk together can run up the amps. On too small a circuit these loads can sometimes cause voltage fluctuations. These fluctuations are unlikely to cause damage but they can cause minor glitches and instability.
If it is just a standard computer setup 20A should be good enough. The rule of thumb is to add more receptacles and circuits than you think you would ever need. Running a additional circuits to the same location while your pulling in one is relatively cheap as long as there is room in the panel.
Adding an uninteruptable power supply, UPS, down stream from the surge arrestor can save trouble by smoothing out voltage drops.
Bill H. is right about the heavy power draw from the heater in photocopiers and laser printers, but that's only half of the story.
Copiers and laser printers use an electrostatically-charged drum to pick up the toner and transfer it to the paper. Then a heater fuses the toner to the paper. To maintain the charge on the drum, whenever the copier is on, a large current is drawn once a minute or so, for a fraction of a second. I'm talking several times the average operating current.
I had a service call to an office where two big laser printers and a medium sized copier were being run off of one branch circuit (20A). A computer had been added to the circuit, and its UPS kept beeping periodically, meaning that the branch circuit voltage was dropping below ~110V. The building owner swore that the machines were on separate circuits, based on what his electrical contractor told him.
I used a recording voltmeter/logger (Fluke 189), and when I looked at the voltage vs time plot, saw an interesting pattern of inverted spikes. I could see the voltage drop associated with each machine's drum charging cycle, as well as the heater draw when the machines were in use. When all three of the charging cycles coincided by chance, the voltage really dropped--like to 90 volts. If I find the data on my laptop tomorrow, I'll try to post it.
A couple of dedicated circuits took care of the problem.
I recommend a dedicated 20A circuit for each medium size laser printer or copier.
Cliff
"I used a recording voltmeter/logger (Fluke 189), and when I looked at the voltage vs time plot, saw an interesting pattern of inverted spikes. I could see the voltage drop associated with each machine's drum charging cycle, as well as the heater draw when the machines were in use. When all three of the charging cycles coincided by chance, the voltage really dropped--like to 90 volts. If I find the data on my laptop tomorrow, I'll try to post it."
Back in the dark ages when I was in grad school I worked on an air craft naviagtion system.
Our test plane was a steam powered DC-3. We had on of the first mini-computers that used integrated circuits so it was fairly compact. About the size of PC tower, but it only had 4k of memory. But the memory was magnetic core so that it kept the program when power was off.
The program was loaded from paper tape using an ASR-33 (teletype). We set all of this up in the plane and loaded the program. Got everything working, got the signals, and zero'd or position. Then went to take off and by the time the plane was lifting off the computure had crashed and taken the program with it.
After doing some testing we found that the planes 120 volt system, whcih came from a mot-gen set on the 24v system would drop to about 90 volts when the enginers where pulled back to idle when the plane stopped at the end of the taxi way to clear the traffic.
We put the computer on a variac in the lab and afound that at about 105 volts that the low voltage detect properly shut the computer down. But the idiots that designed it used a relay so that about 90v the relay released and the computer started backup. But the supply was too low for it to run correctly.
I have a big home office setup. Laser printers should each get their own breaker. Two or 4 computers on a 20 A circuit is OK, but I'd share nothing on the same circuit as a laser printer. Mine is a little overkill, but 5 circuits. Lights, Window AC, Laser, Computers, Printers. UPS for each computer.
Definitely put the laser on its own breaker. If your other stuff is not super heavy-duty, it can all probably share a circuit. I recommend a whole-house surge protector on the panel as well as individual ones for each major item. UPS units don't need one; its built in.
You say to put the laser on its own breaker. Is part of your concern the impact the voltage fluctations might have on the other equipment sharing the circuit?
My CPU, monitor, and scanner share a small UPS unit with surge protection. Laser just has surge (only 3 outlets on the UPS!).
I'm actually using a spare bedroom as an office temporarily until I can build my shed/barn/workshop with office space above. Based on what I'm hearing here, I'll definitely have plenty of independent 20A circuits on hand.
But I'm just wondering if in the meantime I'm shortening the life of my other computer equipment by having it on the same circuit (at a rental a few years ago I used to cringe every time the frig. kicked on and made my desk lamp flicker).
No, if the computer is "solid" and isn't dropping out on sags, you aren't experiencing any additional "wear" due to the sags. The power supply of a computer is actually a mini-UPS (with a "battery" good for a fraction of a second). It regulates the output voltage such that your computer sees either in-spec voltages or zero volts -- nothing in-between.
Monitors may fluctuate, but their power supplies and high voltage circuitry are no more complex or damage prone than regular TVs.
Probably your fluorescent light is taking a bigger "hit" than anything else.
My laser is big. About the size of a floorstanding office copier. Draws 20 amps when the fuser is on and 5 when its off. Definitely needs its own circuit. Newer printers are less demanding. An IBM color laser draws 10 amps peak and 5 amps average. Most of the new desktop machines draw even less. This won't cause any physical damage to computers if the line voltage gets drawn down too far, but it might cause an annoying reboot. Newer computer power supplies have minimal energy storage and only a couple cycles below 90 volts can be enough to reset them. This is why a UPS is so important.
Most PCs these days have about a 250 watt power supply. They're quite efficient and would draw 3 amps maximum. Usually much less since you rarely have enough stuff inside to reach the 250 watt level. Unless its a server or something with a ton of hard drives in it. Monitors can be pretty variable. Some only a hundred watts. Some big ones like my old 20 inch draw closer to 5 amps. I run my monitors on one UPS and the computers on another. The monitors draw way more than the PCs. I'm out in the country and power is flakey. By doing that, the monitors may go out but the computers stay up. Peripherals that would not need to be running if the power is off do not get put on the UPS at all. Scanners and a couple printers just go off if the power drops. I might lose a few minutes of work, but no data loss. The point of the UPS is just to give enough time to shut down or ride out momentary blips. If the power is off for more than a minute or two, I begin shutdown. I have a pair of 2 KW UPS units. That gives me about 10 minutes run time. Takes about 5 to shut down.
My system is fairly big. 5 PCs, 2 monitors, ledger-size 30 PPM laser, inkjet plotter, small printers, scanners, etc. In the last 5 years I've lost 2 modems, 2 fax machines, a laser and an inkjet due to lightning, but never anything hooked to the UPS. Anything hooked to the phone line is at higher risk. I only use external modems. Maybe not any safer, but it makes me feel better.
I don't think you have any concern about shortening the life of your equipment the way you're doing things. Scanner probably only draws an amp, but I wouldn't bother putting it on the UPS. The main issues are loss of data and lightning and surge protection. Don't try to run a laser on a UPS. You'd need a really big one. Easily costs more than the printer for that size. Typical home office would do really well with 3 20A circuits. Laser, computers, and misc. office stuff. Maybe a 4th if you have a window AC unit or portable heater. Never put one of those on an outlet strip. Always directly into the wall socket.