Peter McCarthy Electric Co., Inc. - Specializing in Older Buildings in Chicago
Adventures in Old House Wiring....

The Anantomy of a Service Call (For those of you who really dig the technical stuff!)

Electrical Repairs ChicagoElectrical Repairs Chicago
Electrical Repairs ChicagoElectrical Repairs ChicagoElectrical Repairs ChicagoWe had a service call in a high rise here in Hyde Park several weeks back. A long-time client has a condo that he is renting out. I did my first job for him in 1988. He is now retired and living in bucolic New England. When his number came up on my caller ID I was so pleasantly surprised. I had not spoken to him in years. After my congratulating him on his retirement, he told me about the problem his tenant was having at an outlet that was supposed to feed a 220V AC unit. He had already replaced the unit, thinking it may have a short because it was very old. But the problem persisted. There was power out in several outlets, the refrigerator went off when the short happened, and the 90+ temperatures were making it pretty uncomfortable in the unit. They were afraid to plug in the new AC unit lest they lose the fridge again.So they were very happy when we got there.

In the course of solving this problem, I was trading emails with the out-of-town owner. As a result, I have a very complete "blow-by-blow" narrative of the entire service call, showing our thoughts, reasoning, methods and how we solved the problem. I know this will put a lot you you to sleep. But I'm sure some of my readers will really enjoy it, the more technical folks in the crowd. So if you wish, skip it. If not, here is where we pick up the story:



I hope you are enjoying your retirement and the fresh clean air up there.

Yes, I missed his calls this morning. It has been hectic here.  We were finally able to co-ordinate with the tenant and we got back in there last week. I had been there on a service call to check everything out originally about 3 weeks ago after you called me. The subsequent delay was trying to co-ordinate with the rental agent and then fitting things into our schedule here. It was a bit of a challenge.

As I told your husband, the wiring was messed up and showed signs of a non-electrician making some sort of modifications to it somewhere along the line. Tracing the various wires down, opening switches and outlets to see what passed through where and what had been spliced or tapped off, and what was no longer hot took a good amount of time and effort. In order to trace/identify the wires at their source, we needed access to the panel. The cabinets had been installed over the panel cover, making it impossible to remove.  At first I thought we would need a carpenter to take down the cabinets, but as that became increasingly more complicated to find, I came up with the idea of leaving them in place but cutting them further to allow us to remove the panel cover to see all the wires, what was coming off each breaker, what wires were emanating from the panel in which pipes and going to the perimeter of the apartment through the ceiling or floor, ect. We also needed the cover off to test the fuse blocks themselves, to verify that current was indeed passing through the fuse holder and that they were not damaged somehow. So I called your husband back to get permission to cut the cabinet as neatly as we could, with the understanding that we were not woodworkers and could not guarantee perfection. But all in all, it did not come out too badly.

The wiring in the bedrooms was very messed up as I said. Whoever had last modified it clearly did not understand what they were doing. The way the wiring was supposed to be was that there was a blue hot wire and a white neutral wire (15 Amp 120V circuit) that came into the Peg's bedroom via the floor. That 120V blue and white circuit was to power the general outlets, the lighting and the 120v receptacle portion of the combination 120/240 outlet in the wall adjacent to the AC unit. It was not intended to be a part of the 240V power to the AC units. There were also 2 red wires and 2 black wires coming up in the same pipe as the blue and white. When I came out the first time, the 120V outlet was not working and the 240V for the AC was tripping and cutting out kitchen power when it did. The refrigerator was going out with it. A very confused mess. At that point, when I arrived, the 120V portion of the combination outlet had the blue connected on one side of it and one of the red wires connected on the other. There was another red attached to the 240v line along with a splice off the blue. Obviously, this had been jerry-rigged. I opened a few other outlet boxes and saw that the blue was providing general 120V power for the bedroom. I was able to rewire the 120V side of the combination 120/240 outlet by attaching the blue to the hot side of the outlet and taking a new piece of wire and making a "pigtail" from the neutral and attaching it to the other side of the 120V outlet. This restored power to the 120V portion of the circuit. The most basic rule of our work is that you need a "hot" and a neutral wire to power a 120v outlet. The fact that the red was attached and the white neutrals were splices together but had no wire intended for the receptacle was a clear indicator that an unqualified person had last modified this wiring. After that, I had the 2 reds remaining. One was hot, the other was not. The blacks were passing thru the box uninterrupted. That was as far as I could go without having access to the open panel.

When Matt and I cam back the second time, he started working on cutting out the cabinets and I went back to opening the junction boxes to see where we stood. At that point we had no way to know where these wires came from. Since one red was hot and the other was dead, it stood to reason that they were passing through one or more junction boxes in between when they left the panel and when they appeared at the location we were dealing with. They may have been cut, disconnected, connected inadvertently to a switch, or who knows what. I opened several boxes in Peg’s room in exploration. I also opened up the other 240V Air Conditioner outlet in the bedroom opposite from Peg's to see what was going on there. That AC unit had been working according to the tenant.  I noticed on this side, the 2 black wires that passed through the box on Peg's side made their way here, as well as the blue and the white. I also noticed that the blue wire was tapped to provide one side of the 240v AC circuit, and one of the black wires was attached to provide the other side. The second black wire was dead and capped off. At least on this side, they had the neutral wire attaching to the 120V outlet so that it was working, as opposed to in Peg's room.

After a lot of drilling, cutting, and subsequent sweeping and vacuuming wood chips and sawdust, we got the panel cover off. Upon opening the panel cover, and pulling out all the wires to see what circuits went where, we were able to do more investigation. One mystery was "Why would the kitchen and fridge go out when the AC outlet blew a fuse?" Clearly they would not have originally put the 120V kitchen counter outlets and the refrigerator on the same circuit as the 240V AC unit circuit for the bedrooms. That could not have ever been in the original design; another indicator that we could find literally anything here, and that we needed to throw out "looking for normal" and really have our thinking caps on.  After we got into the fuse panel and could test everything, we found that all the fuse terminals were intact. Each one that had a fuse in it was "delivering power" out of it. Once we had the panel cover off and pulled the jumble of wires out enough to see the pipes that were exiting and bringing wires (circuits) to the various locations in the apartment, we could start to piece the evidence together. Of course, the panel cover was not marked, so there was no clear identifier as to what fuses controlled what loads in the house. It was all a matter of trial and error combined with our experience and ability to look at what was there and ask "well, what could they have done? What would they have done? What would I do if I were setting this up?" I had a sense that originally, before the goofy modifications were made, the proper wires had been in place to power the loads in the correct manner. We were not sure if any wires had been cut off or pulled out, but it did not look like any new ones were added. So at some level, I reasoned, unless they removed something, (which I guessed was not too likely) the pieces were still all intact. We just had to figure out how to put them back together again.

We found a pipe that was leaving the panel with 2 reds, 2 blacks, and one blue and one white. Most likely, that was our feeder. By process of elimination then, by tracing those wires to their terminations in the panel, we could start to figure out what was what.  We noticed right away that there were unused fuses in the panel, fuse blocks that had fuses in them but had no wires attached to them. The blue wire was attaching to a fuse that was double-tapped. That means there were 2 wires (i.e. 2 circuits) connected to one fuse terminal that was originally intended for only one wire. (Again, another red flag that there had been foolishness going on here. While double-tapping is against the code, from time to time you find it when the panel is completely used up and there are no additional places to put additional circuit wires. Having a double-tap set up in a panel that has empty unused fuses indicate a very severe lack of understanding on the part of whomever was here last)  I screwed in and unscrewed the fuse controlling the blue wire and the double-tap, while Matt read the voltage at the bedroom location. It came on and off, so we knew for sure that was our pipe and these were our wires. I heard the refrigerator come on and off as well when I screwed in and then backed out the fuse. So that solved one puzzle. The original kitchen counter circuit that had the fridge on it was the other wire of the double tap. Thus, when the fuse was blown by the blue wire being connected to a short or subject to an overload, it would take the refrigerator circuit down with it. Remember, the 240V AC outlet when I originally got there was set up with one of the red wires on one side, and the blue was spliced to power the other side. Thus, the 120V blue circuit, which was intended to only carry lights and outlets in the bedrooms, was "cannibalized" and tapped to provide one side ("one leg") of the 240V power to the AC outlet. I'll get back to this in a minute.

A little electrical background theory may be in order here.  The electrical service to the panel is 120/240V. That is achieved by providing two individual 120V main power wires to the panel from the meter closet, as well as one main neutral wire. (They are run in conduit that is concealed in the concrete walls and floors. You would never see them, per se.) These three main cables "feed" the fuse panel. Each one of the cables provides 120V when it is paired up with a neutral wire. Each main service hot wire (which we call a "leg") gives power to half of the fuses in the panel. Thus when you take a "hot” wire from one fuse, and run it to a location with a neutral wire connected to the main neutral bar in the panel, you have a 120V circuit. When a 240V circuit is needed, there is (usually) no neutral required, but instead, one "hot" wire from each side of the panel is run to the location. The 120V "hot" from each "leg" of the service provides a 240V circuit when combined like this.  In this type of panel it is very easy. All of the fuses on the left side are fed from one hot leg and all the ones on the right are fed from the second hot leg. So when you run 2 hot wires to the location, one from say the bottom left side fuse and the other from the bottom right size fuse, you will have a 240V circuit. This was the way it was originally set up, as was standard procedure for the era it was originally installed. 

After we verified that we had the correct pipe and could positively identify the wires at both ends, we were able to start to understand what was going on. The blue "hot" wire had been double-tapped, (meaning two individual "hot" wires both placed illegally under the terminal screw of one fuse rather than separate individual fuses. Hence those two blue wires that originally would have comprised 2 individual circuits, in essence, were combined into one circuit, because they were both dependent on that same fuse.) so every time it caused the fuse to blow, it took out the refrigerator and other kitchen appliances. Most likely, the blue had been moved from its original fuse and put on this one. We identified one of the unused fuse holders and re-located the blue wire to there so that it was separated from the kitchen circuit. Now the blue hot wire was on its own circuit. (Even though it was still connected to one side of the 240v AC outlets in both bedrooms.) In the panel, where the wires came out of the pipe, the 2 blacks and 2 reds both had only one of the pair connected to a fuse. The other was just disconnected in the panel.

At this point it became clearer what the situation was. The 2 red hot wires had originally been the 240v circuit for Peg's bedroom AC. The two black wires had originally been the 240V circuit for the AC on the other side of the wall. All 4 of them came up in the pipe directly from the panel, and entered the junction box in Peg's room. (The blue and white also came from the panel in the same pipe.)  The 2 reds stopped in Peg's room, the 2 blacks passed through along with the blue and white to the other side, where the 2 black wires stopped. The Blue and white spliced again, and continued on to other locations. So it was clear to us that the 2 red hot wires had been the original 240V circuit for Peg's room, (with one red originally being fed from each respective side of the panel, thus creating a 240v circuit) and the 2 black wires had been the original 240v circuit for the other room. But for some inexplicable reason, one of the 2 reds and one of the 2 blacks had been taken off of their original fuses. Remember, when I first got there one red wire was "hot" and the other one was "dead." How it got like this, or why, is beyond anyone's guess. When all the evidence was in, it made no sense whatsoever. Never-the less, at each AC outlet, only one red and one black was hot (obviously, because the other one had been disconnected from the fuses. So the last person to work on the system must have been unable or unwilling to go into the panel (Maybe by that time the inside of the panel had been rendered inaccessible by the cabinets?)  to see if the 2 reds and 2 blacks were indeed still intact at the opposite end, and if so, why were they not hot. Instead, (presumably) he realized that he could use the one "hot" red wire for one side of the AC outlet, and he could make a splice and tap off the Blue "hot" wire to connect to the other side of the AC outlet. This created a 240V power source at the AC outlet. He did the same thing on the other side of the wall. One side of the AC outlet was connected to the one black wire that was "hot" and the other side was tapped off of the 120v Blue that was supposed to be the 120v circuit for the lights and outlets in the bedrooms.  So when we arrived, that blue hot wire was powering half of each AC unit, the lights and outlets in the bedrooms, and was sharing a fuse with the kitchen counter and refrigerator. Amazing.

We were able to re-configure the wiring properly after that. We located 2 opposite leg fuses for the reds, and two more for the blacks, so that those 240v circuits are set up again as they were intended. The panel cover is marked to show which 2 fuses control the AC in Peg's room and which control the other one. Of course, we put the 2 black wires on one 240V outlet and the 2 red wires on the other one. The blue circuit is no longer co-mingled, and it has been put on its own fuse as well. It is no longer double-tapped with the kitchen circuit. When we were done, I gave Peg a little tutorial on how the fuses work, what to look for if something stops working. The whole job took 5 man-hours, which at 95.00 comes to 475.00   The first visit was one hour. I normally charge 150.00 for the first hour of labor as the service call charge, and 95.00 after that. But I know you are retired so I'm waiving that as a senior citizen discount (ouch that hurts, I know....) and just charging the 95.00 for the first visit. The second visit was for 2 hours of clock time for 2 men, myself and Matt, hence the 4 man-hours. There was no material involved.

That was the email I sent him. I hope you enjoyed it!

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