Old house electrical question here – the outlets in my home office are on the same circuit as the outlets. When the fax/printer powers up it makes the lights flicker. The electrician I had look at it measured the maximum power draw at about 10 amps – the circuit is not overloaded. He checked thoroughly for loose wires and didn’t find anything.
He suggested that the fax/printer is creating harmonics which interfere with the rest of the circuit and that the way to solve this is to run a separate circuit for the fax printer. Unfortunately, the office is on the 3rd floor and it would require a pipe up the outside of the building – likely $1,500 or so. Seems like a lot to extend the lifespan of a $300 printer and avoid the lights flickering (although he did mention that my computer could be affected too).
I’ve seen that there are filters for harmonics – does anyone know if this is a reasonable residential option? Would a very high quality surge protector solve the problem?
Thanks!
Replies
When the fax/printer powers up it makes the lights flicker.
If it's a laser printer, there will be a fair amount of current drawn during start-up. The Dell color laser printer in my home office causes the lights in the room (same circuit) to dim *slightly* when it starts. I'm assuming that we're talking about incandescent lighting.
A surge protector won't help with this, although it's a good idea to have one. As for the computer, the switching power supplies in them are pretty tolerant of voltage variations. Other than with prolonged extreme under- or over- voltage conditions or large spikes, I wouldn't worry too much about that.
Bob
I would think a proper sized UPS would correct the problem. If you don't know, a UPS is an uninterruptible power supply. They provide power by batteries to the devices plugged into them during brown outs and total power outages. If you are pulling 10 amps, you'd need around a 1200 VA UPS. I'd probably get a bit larger one just in case you'd want to add you computer to it, too. here is one that would probably work well http://www.cdw.com/shop/products/specs.aspx?EDC=1243470&cm_sp=Product-_-Specs-_-Main+Tab.
No. When the fax/printer comes on heaters in it very briefly draw a high current. That's causing the flicker. Harmonics won't cause lights to flicker (unless you've got some REALLY bad harmonics on the line).
If it's just the lights flickering I'd say live with it. Won't hurt the computer. If you really HAVE to end the flickering then you need a separate circuit.
Is that 10 amps the current load on the entire circuit, or is it just the laser printer? As has been suggested a UPS wouldn't be a bad idea if you don't already have one, but chances are you won't need that big 1500va model for $700....
I have the cheapest UPS I could find, an APC brand 350va model that cost around $40 at the local Circuit City. My computer, monitor, cable modem and laser printer are all plugged into it and it works fine.
Unfortunately only the most expensive and commercial class UPSs actually run the load through the batteries and/or regulate the voltage. The cheapies, even the $1-2k UPSs just have the circutry to fail over to the batteries during a loss of AC. I wouldn't think that the load of the printer/fax should make a big difference anyway, like others I get the dimming lights when I turn on my laser printer.
There is one option if you're worried about it, you can pickup a voltage regulator/line conditioner. Just do a search for that and you'll see some products that might help.
Maybe a 120 to 120 transformer?
Forrest
A sola style transformer can be a solution to isolate the non-linear power supply, harmonic and dv/dt filters need to be tuned to the harmonics being generated which require someone with a fluke scope meter.
Have someone check the neutral, office cubicles have had to go to oversize neutrals to accomodate all the non-linear power supplys [fax,pc,calculators, etc] to keep from overheating.
You might try running a piece of 10/2 from the panel to your equipment by a surface route just to see if it "cures" your problem. What you want is a larger neutral or both a larger conductor and neutral.
Oversized neutrals are really only needed on 3-phase circuits feeding digital equipment. There may be a slight increase in neutral current with "2-phase" (split 240V) circuits, but not enough to notice. With regular 120V circuits there's no way that the neutral current can exceed "hot" current unless there's a serious wiring error somewhere.
If your view never changes you're following the wrong leader
If you look a current multiple cubicle power connection you'll find dedicated circuits with individual oversize neutrals, all non-linear power supplies create harmonics which create heating on the neutral, this holds true whether it is single phase or three phase power. NEC 310-10 prohibits using a conductor in such a matter that its operating temprature is exceeded hence the oversizing of neutrals.
We have come close to burning a few buildings down because the modern office has so many non-linear switch-mode power supplies including single phase services.
Another place that has become a really big problem is installing lt. fixtures with electronic ballasts into older homes on existing wiring.
Fluke used to do a cool demonstration of this with a standard calculator and one of their meters hooked up.
There is NO WAY for neutral current to exceed "hot" current in properly-wired 120V circuit, even instantaneously. The harmonic heating that you're talking about occurs in 3-phase circuits, since switching power supplies generate an approximation of the 3rd harmonic of the 60-cycle power. Anyone selling oversized neutral for single-phase circuits is simply blowing smoke.
If your view never changes you're following the wrong leader
And, BTW, for the past 5-10 years the "Energy Star" standards that virtually all computer manufacturers adhere to have limited 3rd harmonic current waveforms to "reasonable" levels.
If your view never changes you're following the wrong leader
So why do computer makers block the triplens harmonic if there is no possible way it will create heating on the neutral.
Are the makers of electronic ballasts,arc welders,vfds,microwave ovens,battery chargers,light dimmers, calculators, printers,ups, fax machines, and every other source that contain solid-state non-linear switch mode flat-topping power supplies blocking the the harmonic, some, not all.
When we create harmonics of different freq.they can subtract or cancel each other out anything below 60 Hz is called a sub-harmonic and one real problem with sub-harmonics is light flicker.
If the magnitude of the sub-harmonic current is high enough, the result will be a noticeable flickering of lights, which can cause headaches, nausea and, depending on the frequency of the flicker and a person's susceptibility, seizures.
Retrofitting light fixtures requires the installation of low THD ballasts electronic ballasts
Neither house systems or industrial plants are free of harmonics, in the EU the regulations are much stricter on harmonic generation,with many of todays larger household appliances contain vfd speed controls.
Much of what is being made today is indeed power factor corrected and reflect a very clean harmonic distortion thanks to the adoption of iec 1000-3-2 and, of course the US has proposed an admendment 14 to the standard that will weaken it and allow more harmonics. Due to the natural change out of equipment modern offices and data centers have gotten much better were as home system don't get changed as often though we do continue to buy more things with flat-topping power supplies.
If a UPS is used in conjuction with the equipment it can cancel out or eliminate the harmonic. The single phase APC Symetra eliminates neutral currents entirely.
Of course I agree this problem is much larger in a 3 phase system, particularily shared neutrals, but now we are seeing neutral busbar heating in single phase residential services. The days of the reduced service neutral are coming to an end unless we stick to the cleaner regulations.
> So why do computer makers block the triple harmonic if there is no possible way it will create heating on the neutral.Because 3rd harmonics CAN cause excessive neutral current in 3-phase setups. Most larger offices are fed by 3-phase. Once you split out to just two wires, though, there's no chance of harmonics causing excess neutral current.
If your view never changes you're following the wrong leader
I'd like to see some documentation of the neutral bus bar heating in residential 240V setups. It's vaguely possible with a combo of highly reactive and non-linear loads, but you certainly wouldn't see that in a residence with primarily incandescent lighting, and it's hard to believe that fluorescent lighting could draw enough current in the typical residence to be an issue.Remember, of the big loads in a typical residence -- range, dryer, water heater, resistance heating, et al -- only the AC is going to be reactive.
If your view never changes you're following the wrong leader
You're right it's not the connected load in the light fixtures and there are no freq. drives in modern washers and dryers. And that cam operated valve based pulse tube generator isn't coupled to an invertor drive in your refrigerator is it?
I apologize for the complete wrongness of my statements. All single phase services and properly designed single phase circuits never see any harmonic generated neutral heating from non-linear solid-state switch mode flat-topping power supplies in everyday electronics. I hate this, now I'm going to have to quit my job as the project engineer on the largest data center currently being built in the US.
Gosh, I bet the rest of this group found this exercise really interesting.
rest of this group
Well , you di use some terminology used that is not very often used (non-standard topology descriptions) in the power electronics industry. <G>
FWIW, some discussion of similar topics from 1994.
Show me how, in a two wire circuit, the neutral current can ever be different from the "hot" current. You need at least three wires to have a problem, plus a voltage phase difference between two of the wires that's neither 0 nor 180 degrees.
If your view never changes you're following the wrong leader
Dan,I don't see how a switching PS can NOT cause a strong signal to be generated back down the AC transmission line without some serious engineering to prevent it.This signal will send back with as steep a trailing edge as the input transformer will allow. As you know, this steep edge is composed of the odd harmonics of the input frequency. The steeper the edge, the more power present in the higher harmonics.Anytime the current through an inductive device is abruptly interrupted there is a ringing flyback effect as the magnetic field collapses. This flyback signal can possess much more power than the input signal and the frequency is determined by the reactance of the input circuit and not the 60hz input. The 60hz signal is merely determining how often the spikes occur.Disregarding the 120VAC 60hz signal from the POCO, the line still has a strong 120PPS Variable high frequency signal present from the switching PS. PPS = Pulse Per Second for those of you trying to follow this. The timing of this signal in relation to the waveform of the 120VAC 60hz signal varies by the load on the switching PS. Combine two different strong 120PPS Variable HF signals on a shared wire and there will be harmonics that could upset the larger system of loads on the 120VAC 60hz networkA switching PS Switches the load on the input transformer during both halves of the input cycle. SamT
I agree that there are harmonics which can (if strong enough) cause power factor problems, in addition to causing interference with other devices. But that's not the issue under discussion.The issue here is neutral current -- the claim (bogus in my opinion) that there can be abnormally high neutral current (without identically high "hot" wire current) in a single-phase 120V circuit. Unless there's an enormous amount (10s if not 100s of farads) of capacitance to ground, the current on the two wires MUST be essentially identical. And any such capacitance to ground would tend to REDUCE neutral current (at the expense of increased ground current), not increase it.
If your view never changes you're following the wrong leader
As Sam stated the only place these harmonics generated by the switching power supplies [and vfds in appliances] have to go are on the return path, the neutral, along with the fundamental waveform.
These additional waveforms are "competing" with the fundamental 60 hz sine wave for electrons causing it to heat the wiring and distort the waveform and sxcrew up the power factor, all from the power supply notching.
There is more to this then the triplens, a homeowner added a new arc welder to his shop causing the traffic signal at the end of his block to trip into emergency flash mode evrytime he used it.
I recently looked at a small vet clinic in a converted house, a few desk top pc, copier/fax machine, some specialty equipment that had small budget vfds.... you could not strip the insulation off the denergized neutrals of the branch circuits. The neutral bar was many colors of the rainbow, and the insulation on the reduced size service neutral was goo. The electrical contractor had retrofitted all the lighting to electronic ballast plus added ballasted recess cans to the existing wiring.
Light flickering resulted in the utility company replacing their pole transformer, when the 2nd transformer was needed we were called in.
Much of what we do in the field is benign but occasionally we have this perfect storm of harmonics and eddy currents.
But Kirchhoff's Current Law, the most fundamental law in electricity, says that current in == current out. In other words, with only two wires of presumably identical material and diameter, heating and voltage drop will be identical in the two. So there's no need to make the neutral larger unless you're also making the "hot" larger.Once again, I'm not disputing that harmonics can cause problems, only your assertion that they can require the neutral to be larger than the "hot" in a two-wire circuit.
If your view never changes you're following the wrong leader
I'm sorry I'm Irish and think only in Whitworth.
You and Bill are valuable resources here and I'm not trying to be a mister smarty pants and alienate anyone, just relay what I'm finding in the field, strange things the last generation of electricians never had to deal with. As you've often said the NEC is the minimum requirements for electrical installations, we can always do a little better.
Now let's move on to something fun like getting 2.5 meg generators to start up into a leading power factor waveform or medieval torture devices like the"'keep".
Well, I'm just trying to figure out the root cause of your misconception here. There's no argument that the 3rd harmonic nature of electronic devices kinda suprised the industry, with regard to buildings wired with 3-phase and the distribution systems feeding them. But the problem of overloaded neutrals (without accompanying overloading of the "hot" line) can simply not occur in a 2-wire circuit.
If your view never changes you're following the wrong leader
a homeowner added a new arc welder to his shop causing the traffic signal at the end of his block to trip into emergency flash mode evrytime he used it.
Would love to see the waveforms and the traffic light circuitry, either brute force or subtle effect.
BTW, I once had the meter pulled from a house and got pretty big sparking when both the white and bare wires were either cut or pulled from terminals. Looked like neither the pole or the other 5 houses had a good ground, every leakage current from the other 5 houses found it's way to the good ground in the house with the meter pulled. Probably some white and bare wires crossed in one of the other houses also..
Junkhound,You mentioned this in your post: "BTW, I once had the meter pulled from a house and got pretty big sparking when both the white and bare wires were either cut or pulled from terminals. Looked like neither the pole or the other 5 houses had a good ground, every leakage current from the other 5 houses found it's way to the good ground in the house with the meter pulled. Probably some white and bare wires crossed in one of the other houses also."I have heard that this phenomenon was a good reason not to have a Ufer ground in an older neighborhood hooked up, for two reasons: 1. The Ufer will be the best ground in the neighborhood, so all the leakage current from the surrounding homes will go to ground through your foundation. The EMF's of all that neighborhood current returning to ground through your slab foundation can be harmful to health.2. All that discharge can corrode the rebar of a foundation to nothing in under a decade, eliminating the tensile reinforcement completely.Bill
The issue doesn't arise until the are two switching PS signal sources. Their signals are not nice, 180* out of phase, sine waves.The signal from either PS is present on both it's hot and it's neutral. Kirchoff is happy. The neutral is carrying one side of both PS signals and those signals do not oppose. One end of this 3 conductor romex is connected to a center tapped transformer. The other end is connected to many simplex transformers that are feeding uncoordinated signals to it.SamT
Yeah, you're talking about a 3-wire setup, right? No way for it to happen with two wires.
If your view never changes you're following the wrong leader
Explain what those harmonics do in a neutral?And how does that different from what they do in the Hot?.
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Nah, we reeaaaly like reading the same old poli-flames and "what kind of foam insulation should I use for months on end.
Mind you, I always find it amusing when two obviously smart guys have totally opposed takes on something....
My brother had this problem and replaced all his flourescent light ballasts and the problem didn't go away. His electrician couldn't figure it out and it took a long time for him to determine that his laser printer caused the problem.
Apparently this is very commonplace. See:
http://www.google.com/search?sourceid=navclient&ie=UTF-8&rlz=1T4GGLR_en___US208&q=laser+printer+light+flicker
Billy
It should be noted specifically (given the long discussion above) that the problem with desktop laser printers IS NOT due to harmonics, but due to the large resistance heater in the unit. When it's fully on as the printer starts up it's a purely resistive load with essentially no reactive component and negligible harmonics.I'm guessing that the heater is controlled by an electronic switch of some sort and will develop more harmonics as the unit heats up and is "dimmed", but by then the current draw is much lower.
If your view never changes you're following the wrong leader
Dan,
I think you're correct. It is amazing to me that this is apparently a common problem with laser printers, but no one seems to do much about it.
Does the fact that florescent lights (with electronic ballasts) are flickering point to a current draw problem and low voltage, or does it point to a noise problem with the switch controlling the resistive heater/fuser in the printer? Or could it be something else?
Thanks.
Billy
I wouldn't say it's a "common" problem -- probably 95% of laser printer users don't see it. But folks with modestly deficient wiring and specific brands/models of printer do. It's done in an attempt to optimize that "first page" output time that is an advertising point -- pour about 1500 watts of power (or maybe even 2500) into a heater very briefly. (Some printers may actually have a configuration option to control this.)They can get away with overloading the line cord and the breaker because the load only lasts for a second or so. It's kind of like a motor-starting transient from an AC or refrigerator causing flicker.It's hard to say why electronic ballasts would be upset by it. Certainly it's a brief "brownout" (given sufficiently deficient wiring), but there may be some superimposed high-frequency stuff that's especially bad with electronic ballasts. (Magnetic ballasts wouldn't be fazed by high-frequency noise.) Dimmable electronic ballasts would be especially likely to be affected, interpreting any noise as a "command" to dim.
If your view never changes you're following the wrong leader
From the early 80's through the late 90's, I was in charge of computing for several university departments. A typical office might have as many as a half dozen PCs or Macs and one or more laser printers (typically HP ). These offices were fairly new but built before the advent of personal computers, so all the PCs and printers ran off of existing university 20 amp circuits. While the lighting was overhead fluorescents, many offices had incandescent desk or floor lamps. I never experienced any problems with the lights flickering. While I fought my share of gremlins, I never saw anything in any of the offices or any of our instructional computing labs that would have indicated adverse effects from generated harmonics. Granted, my only experience with third order harmonics came from doing Fourier analysis as an electrical engineering class exercise.It might be interesting (for at least a few of us) if the guys saying their can be major problems with third order harmonics would write would write a Wikipedia article on the problem.
Like I indicated, the problem with 3rd harmonics only occurs in large office buildings with 3-phase distribution internally, and the problem has been greatly reduced from the early days, due to the redesign of power supplies and the generally lower power of modern computer equipment.
If your view never changes you're following the wrong leader
I think the key is in " old house problem". While 10 A maybe well below circuit limit, on the old wiring it cause significant voltage drop. So called "fuser" on printer is drived by switching power supply to maintain constant temp. That's why flickering. UPS, even on-line kind will not fix the problem- it may change flickering of the lights into dimming when printing and is expensive. Another solution is to replace wiring. But simplest and cheapest is to change printer to inkjet.
I've never seen the problem with my HP laser, but then the wiring here is fairly kosher -- 15A circuit on #14, maybe 20 feet to the panel.
If your view never changes you're following the wrong leader
As I said, old wiring. It could be in the walls, on the panel or as in my old house on the pole outside. It is enough to have bad contact at one point: outlet, panel or in my case neutral on the pole. In your case short connection directly to the panel and probably good one, that why it works. I saw this problem in old buildings few times. Long circuits with connections on outlets even they seems to be ok, amount of connections, oxidations of contacts will cause voltage drop.