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I have a single circuit breaker for all lighting circuits in my apartment unit. However I'm having severe voltage drop in my bedroom's light sockets. I started suspecting about it ever since the brightness of the bulbs became unbearably low even after recently just changing them.

My bedroom has two light sockets both with a separate switch but placed in a single enclosure. With my multimeter, I only get about 110V on each socket (we're in a 240V country). However, the voltage reading weirdly rises to about 150V when I switch on one bulb. So I get these bulbs which are very dim when only one of them is turned on but slightly gets brighter when both of them are on.

I already changed both the switches (I thought the switches are causing a high resistance fault) but unfortunately, the problem still persists. It is also important to note that this problem only occurs in my bedroom. The voltage from light sockets in my bathroom, living room, kitchen, and dining area are fine at about 240V.

EDIT 1 I'm from the Philippines and some regions have split-phase power and some don't. I'm from a region which has split-phase power. But although that's the case, using 120V is extremely rare here. So in a typical home here, all circuits (including lighting) delivers 240V in split-phase. I confirmed that my lighting circuit also has 240V split-phase after seeing that it uses a dual pole circuit breaker. I also haven't seen any neutral wire inside the switches' box.

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  • This "has always been like this" or "it changed suddenly without any electrical work being done"?
    – Ecnerwal
    Apr 26 at 15:19
  • @Ecnerwal This has always been like this like this for several months now
    – Kosho E
    Apr 26 at 15:21
  • You mean with both bulbs removed and switches on, you measure 110V in each socket, but if you replace one bulb, and both switches on, you measure 150V in the other socket? I hope I'm misunderstanding because that would be really hard, for me at least :) to explain.
    – jay613
    Apr 26 at 16:39
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    Maybe if the two were wired in series to accommodate a pair of American light fixtures with 120V bulbs ... but then you'd measure 0V if either bulb was removed and strange voltages like 150 if dissimilar bulbs were used.
    – jay613
    Apr 26 at 16:43
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    Do the lights change brightness if another appliance is switched on or off, such as a toaster or flat-iron? Does your mains have split-phase, i.e., 240 VAC - 0 (neutral) -240 VAC? If so, look for a broken neutral connection between the power pole and the entrance panel. Apr 26 at 18:06

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Whoever wired your lights did a no-no

Basically, whoever wired your lights decided to "bootleg" neutral (the 0 point in 120-0-120 split phase power) off of the grounding system (or connect two 120v loads in series), since Filipino split-phase-as-single-phase power doesn't bring the transformer center tap from the distribution transformer to the customer service point. But, dirt is a lousy conductor, so now you have a situation where this "neutral" isn't connected to much of anything solid, and thus its voltage relative to the hots wanders.

This needs to be rewired to use 240V bulbs in parallel instead, with no connections to any sort of "fake neutral", just the two hot wires.

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