switched live connected to neutral - but no bang?

[sparkybird]

Hi everyone

Managed to track down the problem with a clients lights yesterday - ended up that the switched live was wrongly identified and connected to the neutral in one light (and the neutral was identified as the switched live).

When it was incorrectly wired, it had the odd effect of 'dimming' another light on the circuit when switched on. What I don't understand is why the fuse hadn't blown when the light was switched on (15A fuse wire.... but even so) - can any one enlighten me?

Client very happy at being able to have full set of working lights after 1 year!

SB

 

[ban-all-sheds]

Sounds like by swapping N & SL rather than just connecting SL to N you ended up with the lights in series.

 

[sparkwright]

It sounds like the neutral wire of the 'dim' light was connected to the switched live which caused it to be wired in series, instead of parallel.

 

[sparkybird]

Wow - thanks for quick replies and explanations. Of course, I should have remembered from college that wiring lights in series does funny things to them! (it was a while ago though....)

Cheers

SB

 

[plugwash]

the impact of swapping switched live and one of the neutrals depends on which neutral you swap switched live with.

At a typical celing rose (or JB or terminal block acting like one) you have one switched live and three neutrals, one neutral from the supply, one from the next light and one from the current light (usually a flex core and therefore unlikely to be confused with anything else).

If you swap the switched live with the neutral to the current light or the neutral to the next light then you will get a bang and a blown fuse/tripped breaker.

If you swap the switched live with the supply neutral things get more interesting. The one end "the one marked as live" of the current light is now connected to the supply neutral. The other of the current light is connected to the neutral of the next light and also via the switch to live.

So when the Switch for the light in question is on the light in question would be on at full brightness (it's "live end" is connected to neutral and it's "neutral end" is connected to live but like most stuff lights don't care about polarity) and lights beyond it in the circuit would be off (BUT LIVE!)

When the switch for the light in question is off and the switch for lights beyond it are all off then the light in question would be off.

When the switch for the light in question is off but the switch for one or most lights beyond it is on then you will end up with lights in series and hence dimmed (the exact brightness will depend on how many lights are on and the relative ratings of the bulbs).