A Switch Circuit that Could Be Electrifying!

Posted: September 20, 2013 in Piano

skematic.player1

This is the power circuit for a player piano that is currently in the shop. I had posted a question to several people to learn what the unknown device was.

Now for the long story….

This morning I woke to find a note on the kitchen table. “The A/C is out…” <signed by wife>. A great way to start the day. It was 82 in the house. Thermo is set at 78. A/C is blowing hot air. I switch the unit off and make a note to call the repairman.

After checking in with e-mail, my daughter rises and says the power is off in the back part of the house. GREAT! Just what I needed. I checked the house fuses. All are good. I reset all the breakers anyway. No change.

The A/C man arrived in 30 minutes. He checked the A/C compressor. It was good. Next, he checked the main. It was dropping 118 instead of 220. Problem solved. The house was only receiving one phase of the 220 power from the street.

“Okay,” I said to the A/C man, “But that does not explain why the power went out in part of the house.”

He said, “No problem. The A/C comes off the 220, but you have no 220 coming in. You have one phase (wire) working, so you are getting your 120 side okay. The way your A/C circuit is wired, it has an extra line coming off of the A/C which powers one circuit in the home. So that is working okay — until you turned off the A/C unit in the house, which made the lights go out.”

“Oh,” I said.

I continued, “What about this…” I gestured towards the shop and took him to the player piano. “Explain this?” I asked.

He asked, “Paper…?”

I gave him some paper and he drew a schematic, shown below.

skematic.player

The two wires on left (power in) are both hot (not hot/common as one might expect since a standard power cord is being used). They are coming off the hot side of the motor and form a series circuit. The unknown device is actually a variable resistor (dimmer switch) with a switch. Last, there is the switch which is triggered when the roll is at end and is flapping. The paper hits a piece of rubber tube which causes the circuit to be interrupted. Two switches in series. Twist the wires and the switches are by-passed.

Makes perfect sense.

Forty-five minutes later the power company shows up. I explained what I was told by the A/C man, “Not receiving one phase of the signal.” I went to get a sandwich at the local DQ and when I returned, the power man said that one line of the main line had been rubbed by a tree limb.  The insulation was gone and the live wire had fused to the common wire.

Two hots, and a common. I revisited the player unit. Two hot wires, twisted together would bypass the switches (and electrocute anyone who touched the bare wire while the unit was running.) Why would someone twist the wires? One of the switches must have gone bad. I make a mental note to check the continuity of the switches.

The power man (meanwhile) spliced a new wire to the bare wire and restored the power.  The lights came on. Soon the A/C was chilling the house again.

Now earlier (last month when I discovered an electrical anomaly in the house circuit), I wrote my father-in-law and said that my daughter’s hair dryer was causing the lights to get BRIGHTER in the house. That is highly unusual. Usually a hair dryer will cause a decrease in current (and thus performance) from other units on that power circuit.

So I posed this question to the power man, “What’s up?” He said that when the hot wire fused to the common wire, it was dropping current to the common ground (common to both hot wires), but that when extra current was drawn from that line in the house, it was “borrowing” current from the other hot main wire — sometimes.

“A fused power line does strange things,” he explained.

I said, “I was just explaining to my daughter that if you touch a hot wire with your right hand, the electricity will take the least path of resistance to ground – which would be down the outside of your right leg. However,” I continued, “If the current is great enough, it will sense the ground felt by your other leg and go down that leg too.”

The power man agreed, “That is what happened with your main power line. Under normal usage the current flowed through the good line fine. But when you turned on the hair dryer, it drew so much power that it “borrowed” current from the other main line which was fused to the common line. That gave a power boost to the good line which made the lights in your house get brighter.

I had a lot of things to do today. Suffice to say I did not get any of them done. But I did get a very valuable lesson in electrical circuitry which provided the added benefit of solving the problem with the player piano.

Often, that’s the way I roll. (By the seat of my pants!)

lol.

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Comments
  1. Linda Moore says:

    this was the most unbelievable post ever! how could it possibly be the same problem in the house as the player piano.