I live on the East Coast in the area that has been having a heat wave these last few days. During the afternoon, with temperatures hitting 100+ the electic power has been dropping badly. Voltage to our house on Tuesday afternoon dropped down to 107 volts. Is this what a "brown out" is defined as, if anyone knows? And do you know at what point the voltage is low enough to start to overheat compressors in refrigeration equipment? Our normal supply voltage is 122+ but not during the late afternoon recently. I haven't had any pumps or motors quit, but I wonder if they are being damaged in any way?

-- Gordon (gpconnolly@aol.com), July 07, 1999

Answers

They'll be running hot, which is never good for life expectancy. Whether they are running inside design spec, outside spec but inside good engineering rule-of-thumb tolerances, or simply on good luck, is down to the design of your particular equipment. 107 is (just below) 10% down on a nominal 120, which may well be the maximum permitted normal supply deviance (ie what a utility company may do on purpose when demand peaks, and what equipment is supposed to be designed for). Also isn't a lot of the USA on 110V, meaning your equipment will be designed for 110-120 nominal? In that case it's hardly under- voltage at all.

I don't know if there is an official definition of "brownout", but I thought it referred to the situation where for a few seconds the voltage drops *dramatically* and the lights go dim. This can be more destructive than black-out, especially if longer than a few seconds. Usual cause is same as a black-out: catastrophic failure of electricity company plant. Happened locally here a few years ago because of a substation fire; popped a lot of computer power supplies (some immediately, several more over the next couple of months).

-- Nigel Arnot (nra@maxwell.ph.kcl.ac.uk), July 07, 1999.

I saw the brownout too.

My PC's UPS started beeping, thinking the power had gone out, although everything else in my office was OK (including another UPS).

-- Anonymous99 (Anonymous99@Anonymous99.xxx), July 07, 1999.

Nigel,

Thanks for your response. I'm sure you are right about having to trust to luck as far as the various motors being within good design specs. To the best of my knowledge, all power in the USA is kept at a nominal 120 volts. If I remember correctly, Japan supplies it at 110 volts, but not here. I was halfway expecting the power to go off as the utility shed some loads to stop the driftdown. Due to concerns about Y2k I had purchased a couple of plug-in-the-wall voltmeters and was watching it unfold as the afternoon dragged on. I did use a good digital voltmeter to verify the analog plug-ins were correct.

-- Gordon (gpconnolly@aol.com), July 07, 1999.

Valid question.

What IS a brownout? And what does it REALLY do?

I'd like to hear from Robert Cook, or someone who can shed even more perspective on the issue too.

Like when it starts... what's the best thing to do with the 'puter. Unplug the wall socket a.s.a.p. even if on a surge protector?

Diane

-- Diane J. Squire (sacredspaces@yahoo.com), July 07, 1999.

Interesting thread, because we have been experiencing brownouts here for several months. I assume they are brownouts. Lights dim; UPS goes off; a/c and fans slow down and our oscillating fans bearings are now making alot of noise. We keep most things unplugged to minimize problems.

Our EMC : Coweta-Fayette EMC in GA. announced on their website that they will be testing after June 30th. Guess what? The problems have magnified 100 fold. Power was off/on..off/on..off/on, as much as 10 times a day the past week, and off for several hours at a time at least 4x.

Driving us CRAZY! I have a question:

Can the power company install a whole house surge protector? I can't afford a surge protector for every outlet in the house! I'm waiting for a call back from their repair dept, so any answer would be appreciated.

-- gale (gale@home.com), July 07, 1999.

I live in Maryland and BGE our local power utility will install a whole house surge protector . We also have a device on our central ac unit that the power company can cycle power on and off to that device when brown outs are threatening this area. They will only do this for short periods of time.

-- John D Pusinsky (beagles3@ix.netcom.com), July 07, 1999.

We lost power for no apparent reason yesterday, as well, in Central Texas. Parts of NY is out.

Anybody else lose power yesterday?

-- Lisa (lisa@work.now), July 07, 1999.

From a poweer company's web site:

"Brownout: A reduction in voltage and/or power when demand for electricity exceeds generating capacity. The term BROWNOUT is misleading because customers generally do not notice the reduction, except when it affects sensitive electronic equipment."

Jerry

-- Jerry B (skeptic76@erols.com), July 07, 1999.

The utilities try to avoid brownouts, but they are stretched to limit the past few days. As load increases, at somepoint, they cannot create enough current to meet demand. Whenthis happens, tey can either shed loads (up to 20% may be mandated to be dropped) or reduce voltage to everybody so the resulting reduced current can be supplied. (voltage (V) = current (I) * resistance (R)) Each load is a small part of the total resistance your electric company sees.

Technically, a brown out happens when power is maintained, but when voltage drops below 10% (12 volts) lower than the normal 120 volts. Frequency stays at 60 hz, it very, very rarely ever slows down lower than that - to the point that you and I see an effect.

Lower than 108 volts, then, is a brownout. It's called a brownout because at severe drops (lower than 100 volts) the incandesent light bulbs actually are visibly dimmer.

Effects: on steady "heater" type loads like light bulbs - less energy is used, less light or heat is generated, and the appliance or process (like an oven or industrial kiln or drying oven) has to stay "on" longer to get to the same temperature, if the temperature can be maintained at all.

On computers - the power supply converts AC to DC at 12 or 5 or 3 volts DC. There is little effect. On TV's and VCR's, other consumer electronics - it varies, but no effect is really very good. few absolute failures if the voltage stay constant - the trips and restarts are a major failure mode though. More on that (surge protection) later.

On monitors - can't tell. I think very severe - can somebody help here? - This is because the monitors uses 120v directly in the cathode tube, not converted to 12 v. Laptops - no effect, everything runs off the internal power supply from the convertor.

On motors - worse effect of all. The motor's windings have a constant resistence, and this resistance (the copper) doesn't change with voltage. However, the reduced voltage leads to a slower otation speed and much less induced counter force from the magnetic fields internally. At a constant load, then the motor turns slower, and current increases proportionally to the relative voltage drop.

The increase in current increases heat load by the square of the loss in voltage drop (I^2R losses) inside the motor, and in bad cases, burns up the motor windings. Service life is significantly decreased in industrial motors such as pumps and elevators, cranes, hydraulic power supplies, air compressors, presses, etc. the increased current increases the needed load from the utility too. But not as much as the reduced current from other efects.

-- Robert A. Cook, PE (Kennesaw, GA) (cook.r@csaatl.com), July 07, 1999.

Have lived in this small Arkansas town for 6 years, never had any problems, until the last few months. Last month especially, power out for 16 hours total. One day was over 7 hours. OG&E usually has it back up in minutes but not anymore. It was a terrible 7 hours, total electric home, kids upset. Found out how addicted we are to electricity. Needless to say we decided to get more serious about preparation. We are so spoiled!

-- (stillwondering@prodigy.net), July 07, 1999.

Then what's that "dimming" effect called?

Diane

-- Diane J. Squire (sacredspaces@yahoo.com), July 07, 1999.

Thank's Robert,

(Posting at the same time).

So the visible dimming would be one indicator of a brownout... yes?

Diane

-- Diane J. Squire (sacredspaces@yahoo.com), July 07, 1999.

The brownout effect is real visible for an incandescant light that's on a dimming switch. The dimming switch is clipping a chunk of each wave, 60 times a second. On full brightness it allows the full wave through, but on minimum brightness it's only allowing a little lens-shaped chunk at the peak of voltage. So any small reduction in voltage will drop that peak down below the dimmer's threshold, and the light goes off completely.

When you turn a dimmer up from the minimum setting, you have to turn past the minimum and then you can back it down a little. Well, if a dimmer cuts off because of a voltage drop (and if the dimmer was at the minimum to light the bulb) the voltage won't come back up far enough to turn it on. So if you've ever left a room with a dimmer on minimum and come back to find it out completely, it was probably a voltage drop. Maybe just your house, maybe the neighborhood.

-- bw (home@puget.sound), July 07, 1999.

--bw,

Thanks for that explanation about dimmer switches. I have noticed that behavior for a number of years, but never knew why it was so. When I have the dimmer set to a low light setting I will often notice that it sometimes dims a lot further down then comes back up. I figured it had something to do with a voltage fluctuation and that the dimmer was just amplifying the situation.

-- Gordon (gpconnolly@aol.com), July 07, 1999.

As a former residential and commercial electrician, now running my own consumer electronic repair (TV, VCR, Stereo) repair business, I'd like to say Mr. Cook is mostly correct, especially about the motors.

The only motors that would have little problem with reduced voltage are the smaller ones not requiring much torque, as in household fans and clock motors. The motors having the most problems would be in high torque needs such as compressors,which could easily burn up.

As for modern electronics most TVs VCRs, computers, and monitors are being built with SWITCH MODE power supplies which will, up to a limit, put out a constant output voltage even if the line voltage is low. There may be a small lag-time though for the supply to adjust. SOME of these supplies will work at full output voltage with a line input as low as 30 Volts. Operating them for long periods that way would overwork them fairly quickly though, so if you see the lights dim, I'd still unplug them, but they should be able to weather small brownouts OK.

The other type of power supply found mostly in cheaper TVs is the linear regulator supply. These should be mostly OK if the line voltage doesn't go below about 105 volts.

Over-voltages and surges are another thing. These may occur not only during storms, but upon reenergizing of the lines after a power outage.

If anyone would like a more technical explanation, let me know.

-- christa (christamike@hotmail.com), July 07, 1999.

Last night we had a power outage in at least 3 towns in Idaho. It lasted almost 3 hours. First the lights dimmed. I plugged a voltage meter into a socket and it read as low as 95V for an extended period of time before the blackout.

I think that this was probably caused by the sudden arrival of hot weather.

-- Brown Black (nosee@em.com), July 07, 1999.

95 volts is a really bad situation. I am planning to start shutting off refrigerators, freezers, air conditioners, water pump, at anything below 105 volts just to be safe. Even at 105 volts, if it went on too long I would probable start trying to save these motors. In case anyone wants to be able to watch this voltage, I got my plug in voltmeter at an outdoor camping store. It is a nice small unit that is meant to monitor the voltage in RV trailers and such, since some campgrounds have voltage problems. I paid $20 for mine. However, I see that Radio Shack just started advertising the same kind of plug in meter for $10 so you could check that out too. I'm glad I have one, in fact I bought two. Anyone planning to use a portable generator should have at least one of these to monitor the voltage.

-- Gordon (gpconnolly@aol.com), July 07, 1999.