Recently, due to a severe ice storm, we had wide spread power outages in the area of Michigan where I live and work. At my small retail business the power was totally out for only a few hours but we experienced two lengthy stretches (separated by a few days) of brownouts where some of the lights and outlets had power and some did not. The odd thing was that each brownout affected different lights and outlets. Why would that be? (The HVAC system was down both times)
I’ve had similar experience with my commercial property. I think it’s part of having three phase capacity - three separate lines of power come from the street. Residential units are single phase.
My house has 240V feed, which I assume is 2 legs of a 3-phase power? (Plus ground) So if one side is low, that would affect the half the house connected to that side?
Interesting - does a brownout affect LED or compact fluorescent differently than incandescent (which would be the original “brown” out)? I suspect that would, but never have had the chance to see.
I don’t think so. Most homes have some 240V appliances like a furnace, AC, or washer/dryer. They just combine two 120V circuits on the board. Three phase is necessary for many commercial use machines; in my case a 10hp compressor and a 200W laser cutter. I think the industrial AC unit on the roof is also three phase.
I always assumed that brownouts were simply reduced voltage. Some things would not work, but the old incandescent bulbs would give out less light - hence “brownout”.
Am I wrong?
I thought brownouts were when the power company strategically cuts off certain legs to keep the whole grid from going down. And a rolling brownout was to make sure no individual neighborhood was down for more than a short time.
ETA: A quick google search says I’m wrong. It is low voltage.
Many 240 volt motors will operate at half power if one phase is out, if it can provide enough torque to reach its rated speed. There could be a number of problems that result, but a few seconds like that usually won’t harm anything. Other devices like heating elements could work if the unpowered leg provides a sufficient ground.
But doesn’t it have to be the leg that gets it cycling in the right direction? That’s always been a hang up whenever the power company mucks around in the vault on the street.
Sure, in some cases a motor could start up in either direction randomly, sometimes not at all depending on how it’s configured. The usual method is a capacitor in line on one leg to do something I can’t recall exactly, but if that leg is out the other one tries to start it in the wrong direction.
Possible, but not very likely.
Power distribution is 3 phase, but what they typically do is split the 3 phases into 3 single phases and phase 1 will run down one street, phase 2 down the next street over, and phase 3 down the 3rd street, that sort of thing. Do that with enough neighborhoods and your 3 phases get balanced out reasonably well.
Typically, a split-phase power transformer will then feed a small number of houses (3 or 4 at most). Split-phase means that they take a single coil transformer on the distribution line side of it (typically somewhere between 6,000 and 10,000 volts) and “split” the secondary coil on the transformer with a center tap. From the center tap out to either end is 120 volts, and end to end is 240 volts. The center tap is your “neutral”, and is also connected to earth ground (literally a copper rod driven into the earth) to form your safety ground.
This may help if you are having trouble picturing it:
A business powered by 3 phase will usually get all 3 phases into the building. Residential 3 phase service is different, and instead each house only gets 2 legs of the 3 phase. From either line to neutral is still 120 volts, but the line-to-line voltage is only 208 volts instead of 240. If you have 3 phase service and you have electric appliances, your oven will take longer to heat up and your clothes will take longer to dry due to the reduced voltage.
While it is possible for a small business to have 3 phase power, if it’s a small building then it could also just have a residential split-phase type of setup. It depends on how much power your business needs.
A brownout is a low voltage situation, not a complete loss of power. Brownouts can be bad because motors and pumps under load can stall and overheat, cooling fans might not provide enough cooling air and the equipment overheats, and other issues.
If you have 3 phase power, then the HVAC will likely be run off of that 3 phase power and might need all 3 phases to work. Some HVAC units will detect the loss of a phase and refuse to run to prevent damage to itself. The lights and outlets should be roughly balanced between the 3 phases, so as different phases drop out, different sets of lights and outlets will work and not work.
If your business is fed by a split-phase transformer then it’s the same basic idea. The HVAC needs 240 volts to work, and the lights and outlets should be roughly balanced between the two 120 volt lines. So if it drops either line, the HVAC won’t work but half of your lights and outlets will still work, and which half works depends on which line is dropping out at the time.
It’s the same thing in a home. Your stove and dryer (if electric) will require 240 volts, and won’t work if you drop either line. The lights and outlets will be roughly evenly split between the two 120 volt lines (just like in a business fed by 3 phase) and which ones work and which ones don’t depend on which line got dropped.
3 phase is common in large apartment buildings and in businesses, but is very rare in residential service. The last I heard, some neighborhoods in New York City and Chicago are still wired with 3 phase.
This. Years ago, I came home from work one day to find my refrigerator compressor struggling to run. I unplugged it and pulled out my DMM to measure wall voltage: instead of the usual ~120VAC, it was around 75VAC. Best guess is it was some kind of malfunction in the final split-phase transformer that supplied my house (and presumably several of my neighbors).
A few years ago I went to XXX to support a mishap investigation for the Air Force. Had an interesting conversation with an engineer there.
They were not bothered too much by a sudden disconnection of power; their system could handle it. OTOH, their system didn’t like “brownouts,” where the available power drooped to 30% or 40% or whatever for a second or two. System went wonky when that happened, and caused $$$ in damage.
I work for an industrial controls company. Back in the day we had a lot of PDP-11 and Vax computers. Blackouts were no biggie. Just reboot the machines when the power came back on. But brownouts were deadly. Once the power was restored we would go around the lab to see exactly what got killed this time around.
I’ve been advised by my electrician to switch off the breakers to all of my three phase machines whenever there is any kind of outage and leave them off until power is restored. The laser cutter has a dedicated breaker that trips whenever power is lost.
Yea, that’s the term: blackout.
The engineer at the facility didn’t fret about a blackout. A brownout, OTOH, resulted it over $100K of failed electronics.
NO ! Its done per connection, not per street. They provide different phases 1, 2, 3 down to the single phase power meters as the go down the street. Its kind of easy, if location up the pole has 1 and 2 in use, and they adding a new one, they connect it to 3.
There’s always three (or the full number) of phases in the street. Have a look at the poles… 4 wires… 3 and a neutral.
In the USA, where they need 120 60 Hz, MOST premises get 2 phases so as to get 230 (aka 240 )… Two benefits to doing that than to use three phase… 1. The device only has to be twice as powerful, three times powerful is over kill… And the items are already being made for the 240 volt 50 Hz world, so the scale of economy keeps the price down. Then where the house needs multiple circuits, they drew from different phases. See if you don’t share them out, then one phase can be overloaded, and trip, and you have a blackout, until you decide to either have a normal house, or you have a blackout except for your high power device… So they share the load onto all circuits in the house too. Being only 120 volt, they are easier to overload with a household of appliances… (esp in the incandescent past,lights.)
So really all that happenned was that he lost one phase, and therefore only some circuits (count the fuses in the fuse box. ) eg one lights, one power. He still had some other circuits,as they were run from the other phase, and it wasn’t lost.
It varies.
At my house, it’s as you stated, all 3 phases are at the pole. In newer neighborhoods (at least the few that I have seen) they’ll go street by street, as I posted. The line that goes by my house eventually splits into 3 single phase lines, and each single phase goes out a long rural road. I don’t know how common that is. I was kinda surprised to see the phases completely separated physically. I was also surprised to see that one of the lines was significantly longer than the other two. I assume that they are roughly balanced with respect to number of customers, if not distance.
For neighborhoods that get 2 lines off of 3 phase (120/208), the ones that I am aware of are also in dense neighborhoods, but they are much older neighborhoods. I always assumed that the switch to one phase per street was done to reduce the amount of wire needed.
No you are not wrong. I do not know if they still use brown outs during high demand times but at one time they were used by utilities. If I remember right the utility would drop the voltage from 120 vac to 105 vac. Lower voltage would mean resistance loads (lights) would use less power. but the lights would dim some, hence the term brownout.
In California brown outs were not used. Instead rolling black outs are used. Power is cut to neighborhoods for a period of time then cut in the next neighborhood and restored in the 1st neighborhood.
If you are loosing power in some outlets or lights then your hose is experiencing a lost phase. That is either a utility problem or a main breaker panel problem in your house. What you were experiencing was one problem in the power grid failing being repaired and another part of the grid experiencing some failure.
Businesses will also often have 208 V outlets, even if they’re supplied with all three phases. They have mid-power appliance needs as well (i.e., more than 120 V/15 A, but not all the way to 3 phase). Many appliances are designed to work fine on either 208 V or 240 V.
Brownouts as a method of load shedding don’t make much sense these days. If the load is entirely incandescent lights, brownouts make sense–the lights stay on, just a little dimmer. But now, so many devices use switch-mode power supplies that reducing the voltage doesn’t necessarily change the power use. Better to have rolling blackouts in that case.
I guess that having a managed “National Grid” is one of the benefits of living in the UK. Unfortunately, the generators are over-dependent on gas, but that is gradually changing and the new nuclear plant when it comes online in 2028 will help.