Light flickered when turning it on for about 2-3 seconds then flickering would stop and not resume until it was turned off and on again. It just happened a few times and we stopped using it, until I could check it out. Well, today I checked it out. The light would not turn on at all. The voltage at the light was 4.3VAC. I opened the switch and the voltage was zero. I disconnected the switch and the voltage at switch wires was still zero. The voltage at light was now zero(switch disconneced). I reconneced the switch and while off the voltage across the switch was still zero. The voltage at the light was now 70 volts(with switch on). So I checked back at the switch and voltage was zero. I disconnected the switch and it was still zero volts and with the switch disconneced the light voltage was zero. I reconnected the switch and it still had zero volts across it, but now the light had 119 volts. I installed the bulb and the light behaves like it did when we stopped using it(flickers for 2-3 seconds, then just works perfectly, until it is turned off and on again).
What gives???
Paul
PS: I do have a good understanding of house AC. I have modified house wireing, installed new circuits, etc. I have done this off and on as needed for over 30 years. I have made no recent changes to this house wireing.
Putting a voltmeter across a switch will result in zero volts reading because you are placing the voltmeter in-line rather than across the line. If you are reading from hot to neutral and getting zero, that’s a different kettle of fish.
I suspect a faulty switch. If you have an ohmeter, remove the switch from the circuit completely, then test for resistance across the switch terminals. It should read zero when the switch is on, infinite when off. Turn the switch on (or have someone do it for you while you hold the leads), and jiggle it around a bit. Is the ohmeter needle remaining on zero or is it bouncing around? If the latter, you are making intermittant contact, which means the switch is faulty.
If you don’t have the appropriate test equipment, I would replace the switch. They’re cheap.
Arrogant one, here. First question: does the switch box only have two wires in it, or four, not counting grounds?
If two, it is a switch leg, as power feeds to the fixture box first, and thence to the switch box. Connections in the fixture box should be examined.
If four, then power is fed to the switch box first, the white (neutral) wires are nutted together, and the black (hot) is switch controlled.
Beyond that, I’ve seen deterioration in lamp sockets from age, corrosion, and heat from overlamping (putting too large wattage bulbs) in the fixture. If the socket is loose or shows discoloration at contact points, replace it, ASAP.
High resistance and/or arcing contacts are a significant cause of residential fires.
Another electrician weighing in (my c-wrench is pretty useless underneath the sink).
I had a very similar problem on a single pole switch that ran the overhead light in my bathroom. Exact same symptoms as you described. It was just a bad switch. A $5 replacement and all was fine. Given that you say you’ve had experience with household wiring I would suggest just trying to replace the switch. If that doesn’t work, call in someone you trust to take a look at it. It may be a slight blow to your ego, but there may be something bigger going on that you’re not seeing.
If we are talking incandescant, well it can happen that there is a break in the filament that touches and and allows the lamp to work intermittantly and this can give the same initial symptoms.
I expect by now you have already replaced the lamp by now.
How about replacing the flexible wire that leads to the lampholder, it would be my next most likely culprit.
Your next most likely scenario is a loose terminal, in the switch, or in the lampholder, I have come across the occasional oddity where a part has been replaced, however the installer fastened the terminal screw down on the insulation so of course there is still a break in the circuit.
Beyond that, you perhaps need to think, have you had done, or has anyone esle done any electrical work at all in the house lately ?
Individual circuits are often looped across various consumer outlets, especially lights so it is possible that someone has broken the circuit elsewhere.
If you have replaced the lamp, the lamp fitting, and the switch, and you are sure all the terminals are correctly installed, then its time to start checking the continuilty of all the wires, it might be that there is an internal break in one, the insulation may be sound but the copper within may have parted.
This will most likely occur at any point where you flex and bend anything, say to get wires into a terminal.