I was changing a light pendant today

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Discussion Overview

The discussion revolves around an electrical issue encountered while changing a light pendant, specifically concerning unexpected voltage readings when the switch is turned off. Participants explore potential causes and troubleshooting methods related to household electrical circuits, particularly in the UK context.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant reports measuring 140V with the switch off, questioning the source of this voltage and suggesting that all lights work independently.
  • Another participant, unfamiliar with UK circuits, draws a parallel to US circuits, expressing concern about the neutral connection when encountering unexpected voltage readings.
  • A third participant shares a related experience with a CCF light that pulses when switched off, implying a similar issue may be at play.
  • One contributor explains that a high impedance meter can show voltage due to minimal current, suggesting that adding a low resistance in parallel might yield a lower voltage reading.
  • Another participant discusses the behavior of household outlets, noting that significant voltage drops are uncommon under load, and suggests that consistent low voltage readings may indicate a need for professional assistance.

Areas of Agreement / Disagreement

Participants express varying levels of concern regarding the voltage readings, with some suggesting potential explanations while others emphasize the need for professional evaluation. No consensus is reached on the cause of the 140V reading.

Contextual Notes

Participants mention factors such as high impedance measurements, capacitance, and inductance, but do not resolve the underlying assumptions or implications of these factors on the voltage readings.

Who May Find This Useful

Individuals interested in household electrical systems, troubleshooting electrical issues, or those seeking insights into voltage behavior in residential circuits may find this discussion relevant.

Emanresu
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and considered doing this with just the switch turned off. After turning off the switch I checked the voltage with a meter in A/C mode. It was 140V which I thought a tad high. When I turned the switch on the reading was 230V as expected (in the UK). So I turned off the lighting circuit at the consumer unit which brought the voltage to less than 1V as expected. So what I can't work out is where the 140V is coming from ? All the lights work independently so I don't think it is a series wiring thing.

Any ideas or trouble shooting tips ? This is the electricians forum isn't it ?

E.
 
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I am not familiar with the types of circuits used in the UK, but if I saw a similar thing in the US (i.e., say 60VAC on a normal 120VAC line), I would be deeply suspicious of the neutral. In any event, that sounds like you need an electrician.
 
I have a CCF light that dimly pulses (only visible at night) every several seconds when supposedly switched off but still plugged in, so I presume it must be the same problem (my multimeter has a flat battery just now though).
 
Emanresu:
after turning off the switch I checked the voltage with a meter in A/C mode. It was 140V
If the meter measures 140V there is 140V. The meter has a high impedance ( 1M - 10 M ), so you need very little Amps to sustain that voltage.

If you put a low resistance, say 10 KOhms, in parallel with the meter, youll probably get a very low voltage. If this is the case its all OK.

This current can come from capacitance or coupled inductance between the wires.
 
Household outlets should be able to provide quite a bit of current without a significant drop in voltage. When I run my microwave the voltage drop at the outlet is less than 5V. The microwave uses about 600W so its impedence is only about 24 Ohms. If you can repeatably get measurements at about 50% of what is the correct voltage for the outlet, then I'd agree with tvp45 and say you need an electrician.
 

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