Power Outage Question

Factual Questions
1

I’m in Chicago during the current blizard, and have run across an unusual power outage situation. Basically, only half the house is out of power–pretty much everything on one side of my circuit breaker panel. It’s as if one of the two power lines to my home has been disconnected and I’m running on one phase of power (between the hot and the ground return). I checked the circuit panel and as much of the power feed as I can running back to the meter, and I don’t see any switch or similar point where only one of the lines could be broken. I spoke with a neighbor and he has full power.

I’ve reported my issue to ComEd, but with understandably-more-urgent outages in the city I doubt I’ll get a response anytime soon. What I’m wondering is, is it worth calling an electrician to see if the problem is in the house? Has anyone on the board seen this type of power company outage?

2

It sure sounds like it would have to be inside the house. When a power company runs power to your pole, you typically(I don’t think I’ve ever seen it) will not have two separate pulls of wire coming in.

Do you have a big enough house to require your own transformer?

3

Something similar is happening to me right now. I’m getting normal power on one circuit, but only about 60 - 70 V on the other circuit. I can mostly get by ok with the good circuit, but apparently this is not good enough for the water heater of my condo building. :frowning: Still, I think I’m fortunate that I still have partial power.

This seems to be a fairly common failure mode in my area. This has happened a few times before, both at home and at my former workplace.

4

Typically it’s 2 hot lines braided around the neutral. All three are separate wires. Most common thing I’ve seen is during stormy weather the burndies(connectors) bounce against each other or the house. If they are old or lack insulation eventually they will short out and blow the connection. Sometimes this is spectacular with obvious damage other times you can’t tell until you are on a ladder inspecting them.

A failed connection at the transformer is also possible.

I’d recommend just waiting for the power company to take a look.

If you feel the need you could have an electrician come out and investigate earlier. They could handle the problem if it’s at the connection to the house or anywhere in the house. If nothing else they could at least shuffle the breakers to get power to the things most important to you.

5

Most homes these days are fed from a center tapped transformer. You have two “hot” lines and a grounded “neutral” center tap. You get 120 volts from either hot line to neutral, and 240 volts from hot to hot. In a typical breaker box, the breakers alternate the hot lines.

In other words, if you call L1 and L2 the two hot lines, each side of the breaker panel looks like this:

L1
L2
L1
L2
L1
L2

So, if you want a 120 volt circuit, you just plug it into one of the slots. If you want a 240 volt circuit the breaker is bigger, and it takes up two adjacent slots, so it will connect to both L1 and L2.

Typically, when you lose one of the lines coming into your house, half of the house will work and half won’t, because either L1 or L2 will be dead. Your 240 volt stuff like your dryer or oven probably won’t work either.

When you say that everything on one side of the breaker box is broken, the first thing I think of is that you have one of those boxes that has a separate neutral connector for each side (as opposed to a box that has a single neutral bar at the top of the breaker box where neutrals from both sides are connected) and that the connection between the neutral bus bar and the main house neutral has gone bad.

If you lose one line coming into your house, then it is much more typical that the things connected to every other breaker on both sides of the box will be not working.

It is very easy to have a broken connection that you can’t see. For example, I had the connector inside the meter go bad. There was nothing visibly wrong from the outside, but I lost power to half of the breakers in my house. Another common possibility is that the main breaker for that line has gone bad.

The only way I could see this being a problem from the power company’s side is if your house is fed from two legs of a 3 phase line. Most homes these days are fed from a center tapped transformer attached to a single phase, but you do occasionally find the other configuration. This is fairly easy to identify, because in a typical single phase configuration you have 120 volts from either hot line to neutral and 240 volts from line to line, but if you have 2 lines from a 3 phase system you have 120 volts from line to neutral but only 208 volts from line to line.

6

that is symptomatic of a your neutral wire connection being bad. it happens more frequently in winter with ice in the connectors.

the voltage on one hot side will go up and the other hot side will go down.

you might have devices able to tolerate the high voltage on the side going high. though it could swing higher or to the other side and damage devices. the more current you draw the worse it will be.

have the utility check your line.

7

If the voltage on the other line is still 120 volts then it’s not a bad neutral connection. It’s more likely to be a bad line connection somewhere.

If the voltage goes up on the other line though as johnpost said it indicates a bad neutral connection.

Either way, this is the type of problem that can burn your house down and needs to be fixed ASAP.

8

I’ve checked the other line with a multimeter, and they’re at around 120 V.

Anyway, things seem to be back to normal now, and I’ve just taken a nice, long, hot shower. Hurray!

9

Has to be the transformer. Here’s a very scientific diagram. As you can see, there’s no way a power company outage could affect just one side of the secondary. Do you still have 220?

10

The house could also be fed from 2 phases from a 3 phase system, in which case the transformer looks more like this cheesy diagram:

http://www.equitech.com/images/rep1-3.gif

In this case, losing one of the incoming phases from the power company will cause one of the line voltages to drop.

In either case, the problem doesn’t necessarily have to be anywhere near the transformer. The broken connection could be in the wiring, at the meter, at the breaker box, or could be a faulty main breaker. In some homes there may also be a cutoff switch somewhere, which is another potential location for a failure to occur.

11

I don’t understand 3 phase at all. According to the diagram it starts with 480V at 60 hz? and then…?

It does seem clear though that measuring the voltage would diagnose what is wrong.

12

Ignore the 480 part of that diagram. There are a lot of different places where 3 phase power is used. A house will not have 480 volts on the high side of the transformer. Residential distribution voltages are much higher than that. I just picked that diagram because it seemed to illustrate the point.

In 3 phase power, the voltage on each phase (or line) is a sine wave that is 120 degrees out of phase with the next line, compared to a center tapped transformer which has 2 phases that are 180 degrees out of phase with each other. The neat trick about 3 phase is that if you add these 3 sine waves together, you get zero. This means that if you have a perfectly balanced 3 phase system, you don’t need a return wire since it would be carrying no current. In the real world you can never get the system perfectly balanced, but even if its not perfectly balanced the return wire will still be carrying much less current than the line wires. This means that you can make the return wire a lot smaller, which saves you a fortune when you have to run miles and miles of wire. When you look at power lines, if you see 3 big wires and 1 small wire, it’s usually 3 phase.

Power companies use 3 phase power all over the place. These days, when they get to your neighborhood, they split the phases up and distribute them as evenly possible to all of the houses. Each house gets a transformer that comes off of one of the phases.

It isn’t very common these days, but they used to sometimes give you 2 phases out of a 3 phase line directly into your house. You still find this occasionally in older systems or in large cities, which is why I mentioned it as a possibility since the OP said they were in Chicago. The power company would install a 3 phase transformer like the one in the diagram, and would then take the lines to different houses in the area, with each house getting only 2 of the lines. They would balance how many houses were attached to each line as much as possible so that they would continue to get the 3 phase benefit of a smaller return wire.

The disadvantage of doing it this way is that your line to line voltage is reduced from 240 to 208. Your 120 circuits are all still 120 though, so they aren’t affected. Things like your oven and clothes dryer tend to run off of 208/240 though, so in houses with 208 it takes a bit longer for your oven to heat up and longer for your clothes to dry.

13

Nit pick
high voltage three phase utillity power does not have a return or neutral line. The primary is delta wound, no center tap.
Each house will not have a single transformer in the city. Each transformer will serve several houses.

14

thanks for the explanation. Looking at the diagram it looks like 3 lines going into the same coil winding on the input side and, and 3 coils on the output side.

15

I’ve just measured the line-to-line voltage of my A/C outlet: It’s 213 V. Yup, so I guess I’m on one of those older distribution systems.

16

FOLLOW UP: The discussion here has been illuminating. However, in my particular case, it turned out one of the two mains feeding the home was indeed broken (at the pole across the alley). I didn’t spot it myself, but the ComEd guys did.

This is one case where I have to applaud ComEd for their service. This was admittedly a minor problem given the scope of the blizzard, but ComEd was out the next day after we called and the linemen tramped thru 4-5 foot drifts in the back alleyway to get to the pole and restore full service. By contrast, the electrician took a day to return my call, and he couldn’t come out until a day after that. ComEd’s speedy response saved me a $49 service call.

If engineer_comp_geek is still around, I understand from your description of the circuit breaker box that what I should have expected was every other circuit in each vertical column of breakers should have been out, rather than all the ones on one side. I admit I didn’t check every breaker on the “out of service” side, but it sure looked like most of them were out when I lost one of the mains. Is this an unusual configuration, and if so should I be worried?

17

There have been breaker boxes made that have one phase on one side of the panel and the other phase on the other side of the panel. You don’t see them very much these days, but there’s nothing wrong with it. Was your house built in the 50s or 60s?

18

CJJ*, do you have any 240 volt appliances? If so, how are they breakered?

19

Mine was, and one side of the panel came loose during wind. As a result, half the house had power, the other half not. The electric company scrambled to get out with lights flashing on their vehicle when I called it in. It must have been especially dangerous, I guess. I honestly don’t know.

20

I Googled a question about losing power to every other circuit in my breaker box and I found the thread that engineer_comp_geek had replied to a similar question from CJJ. I have a small gift shop that lost half of our breakers today. I was impressed with your answer, and I’m fairly certain after speaking with the utility company that I have one of two problems - either it is bad line coming in or a bad bus. Should find out in the morning.

I have another question for you -

A couple of years ago my neighbor’s home burned. The fire marshal ruled it to be a problem with the HVAC (outside unit). My dad is a HVAC contractor and he said that was nearly impossible.

Well, we were renovating our home and had not moved in at that point. Several days later I was working with a power saw and I noticed that the house would surge each time I used the saw. I called an electrician and he told me I had lost my neutral - which could “burn my house down.”

The utility company came and found no problem. I called again and they sent a supervisor - he freaked out and wanted to know how I knew what the problem was when their lineman had missed it.

Turns out my neighbor and I were on the same transformer, and the utility company did find that the neutral bus had gone bad at a junction box that fed both my home and the neighbor.

FYI the fire marshal never changed his ruling.

Anyway, ever since then our home had a flicker that is noticeable most of the time, but particularly in the winter - it drives me CRAZY!

I have had several visits from the utility service and they say it is not their problem. They have checked the neutral bus, cleaned the connectors, put a machine called “the Beast” on the line, hook a monitoring computer to the house for 24 hours, and still nothing. Every lineman and supervisor has seen the flicker, but they declare my feed is uniform and constant.

I have a friend who is an electrician and he has tested every circuit, outlet, switch, etc in the house.

My suspicion is that we have a bad transformer, or at least a bad connection at the transformer. However, the utility company has even checked the transformer and they claim there is nothing wrong.

My other idea is that when I lost the neutral to my house it fried my breaker box, or at least a portion of it. They say it isn’t their problem.

Another theory I have is that there is a problem with the under ground from the junction to the house - but that does not seem likely since the utility company checked both ends.

To give the utility company credit they did come out several times, and they did fix every problem they found.

What do you think is going on?

Any advice is appreciated!