Intermedate switch wiring question

I have four lights in a hallway. They are controlled by 2 2-way switches and 1 intermediate switch, which is in the middle. The circuit is not working, after I hired a contractor to replace ceiling.

I disconnected all four wires from the intermediate switch and then checked the 2 2-way switches and the wires. One 2-way switch has no hot wire coming in. The other 2-way switch has one hot wire coming in. There are four wires going into an intermediate switch. Let me name them A, B, C, and D. Here are the voltages between the wires:

A-D 115

A-C 184

A-D 219

B-C 58

B-D 72

C-D 0

How could a 220 V circuit have 184, 115, 72, and 58 Volt? I believe the contractor, when re-connecting the wires, connected them incorrectly somewhere. If I knew how the wires were mis-connected, I might be able to correct them.

BTW, the hot wire on the 2-way switch is 113 volt.

winsoe said:

I have four lights in a hallway. They are controlled by 2 2-way switches and 1 intermediate switch, which is in the middle. The circuit is not working, after I hired a contractor to replace ceiling.

I disconnected all four wires from the intermediate switch and then checked the 2 2-way switches and the wires. One 2-way switch has no hot wire coming in. The other 2-way switch has one hot wire coming in. There are four wires going into an intermediate switch. Let me name them A, B, C, and D. Here are the voltages between the wires:

A-D 115

A-C 184

A-D 219

B-C 58

B-D 72

C-D 0

How could a 220 V circuit have 184, 115, 72, and 58 Volt? I believe the contractor, when re-connecting the wires, connected them incorrectly somewhere. If I knew how the wires were mis-connected, I might be able to correct them.

BTW, the hot wire on the 2-way switch is 113 volt.

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This is a UK forum and I assume by your use of the terms hot wire & 220v circuit you are not UK based?  Your apparent 'strange' voltages are because I would guess you are not actually using any fixed 0v reference point, (earth or neutral) to measure from. Dependent upon the physical switch positions some of the wires you are connecting too at the point of your testing may be connected to nothing,  just another open or off switch terminal. And the type of meter used for taking your measurements is most probably not suitable either.  

Doc H.

You are right. I'm not in UK. I'm in Burma. Thanks for the reply. Here, all the switches has only hot wires (how do you call that in UK?). There is no neutral and no grounding wires. I'll measure the voltages again if I can find a grounding wire nearby. But then, how do I tell if the grounding wire is really grounded?

There is usually a big clue.

"I have just had the ceiling replaced"

Stop looking for faults at the switches, you will find your fault at a light fitting where the ceiling contractor has wrongly re connected a light fitting.

winsoe said:

You are right. I'm not in UK. I'm in Burma. Thanks for the reply. Here, all the switches has only hot wires (how do you call that in UK?). There is no neutral and no grounding wires. I'll measure the voltages again if I can find a grounding wire nearby. But then, how do I tell if the grounding wire is really grounded?

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Various terms 'Live', 'Phase', 'Line' have been used to describe what you call 'hot'. general the average UK person would call it Live. As ProDave said unless the switches were also replaced then that wiring should be correct. If not you do need an understanding of how the wiring should be connected and a continuity tester with the power turned off is probably best to verify all the switch connections are correct. A quick google cut & paste may help you understand how all of your 'hot wires' should connect through the switches. But you can also see on the image if you were measuring between some of the intermediate switch terminals whilst one may have a connection back to the supply, others are just floating open and another would be back via the lamp to neutral (or ground).  So any voltages you measure without a fixed reference point will be quite random to say the least. 

Doc H.

By "fixed reference", do you mean the same reference is used for voltage measurement? In other words, should I measure the voltage between a wire and that same reference? Seems I need a long wire to reach the two 2-way switches. OK. I'll re-measure the voltages tomorrow.

ProDave said:

There is usually a big clue.

"I have just had the ceiling replaced"

Stop looking for faults at the switches, you will find your fault at a light fitting where the ceiling contractor has wrongly re connected a light fitting.

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Frankly, I can't imagine how the fitting wiring can go wrong. As depicted in Hudson's diagram, there are only two wires for each light, one in, one out. Even if they are connected reversely, the light should still work.

winsoe said:

Frankly, I can't imagine how the fitting wiring can go wrong. As depicted in Hudson's diagram, there are only two wires for each light, one in, one out. Even if they are connected reversely, the light should still work.

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Well, newly created faults are nearly ALWAYS in what's been disturbed, rather than elsewhere.  There is plenty of scope for error;  a wire not inserted into a terminal, or put into a "spare" terminal by mistake, a core broken within the insulation by excessive bending.

OR  Were the switches dismantled at the same time as the ceiling wiring?  In that case the chance of error is equal all round and all you can do is trace the circuit through. 

Forget measurements made with a high impedance digital meter. They are meaningless

some options:-

1/ nail through cable

2/ disturbed a junction box above ceiling

3/ cut out cable that was 'in the way'

as said above, it's unlikely to be a problem at the switches, but something above the ceiling.

winsoe said:

Frankly, I can't imagine how the fitting wiring can go wrong. As depicted in Hudson's diagram, there are only two wires for each light, one in, one out. Even if they are connected reversely, the light should still work.

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Have you checked how many wires are at the light fitting? there could be several if the supply is looped in and out at the light. You don't actually say what symptoms are with the light? e.g. Not working at all, Stays on all the time, Only works in certain switch permutations.  That drawing is only one illustration of how intermediate circuits could be connected, there are other methods that will also work. It all depends upon where the supply is brought to, switch/light/concealed joint elsewhere? Did the contractor actually remove any switches during his work?

Doc H. 

Doc Hudson said:

View attachment 10426

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Just want to clarify one thing. The terminal at the upper-right hand corner of S1 should connect to the terminal at the upper-left hand corner of the intermediate switch, right? As it is in the diagram, the two terminals are not connected.

Doc Hudson said:

Have you checked how many wires are at the light fitting? there could be several if the supply is looped in and out at the light. You don't actually say what symptoms are with the light? e.g. Not working at all, Stays on all the time, Only works in certain switch permutations.  That drawing is only one illustration of how intermediate circuits could be connected, there are other methods that will also work. It all depends upon where the supply is brought to, switch/light/concealed joint elsewhere? Did the contractor actually remove any switches during his work?

Doc H. 

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I have unscrewed two fixtures. Both of them have only two wires. None of the lights works. I searched the net and found at least three different ways of connecting an intermediate switch but the one you showed uses the least amount of wire as one of the 2-way switch is six meters to the left and the other ten meters to the right of the intermediate switch.

Oh, I didn't see how the contractor worked but I do know that after the work was finished, the light, which has nothing to do with the hallway lights, in the next room did not work. When the switch was flipped on, both the incoming and outgoing wires were live but light just didn't work. It turned out one of the neutral was not connected correctly (by the contractor).

If there are only 2 wires at each light, then you will find somewhere, up above the ceiling, there is a junction box.  I will be a connection in there has been disturbed. You have already said that is the case an a light in an adjacent room stopped working and was found to be a missing neutral.

Get an electrician to find that junction box and find the messed up connection.

 Turns out one of the 2-way switch is faulty. That one is less than two years old. I thought switches would last at least 20 years. Thanks to everyone who helped.

winsoe said:

 Turns out one of the 2-way switch is faulty. That one is less than two years old. I thought switches would last at least 20 years. Thanks to everyone who helped.

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Thank you for the update. Basic tip for any future fault finding problems, is to always assume everything is faulty until you have proved otherwise. Or "Do Not Assume Anything", irrespective of what your brain is saying is or isn't working correctly.

Doc H.