Neutral at dimmer switch?

[JohnS888]

Evening all

I went to someone's house today to look at a lighting circuit for them that's is tripping rcd. While there on a circuit as far as I can make out at moment that is not interconnected in anyway to offending circuit they have 230v at a switch between switch feed and what I think should be switch live. I know there is some intelligent dimmers/switching that requires neutral but this really shouldn't be present should it??? This is second dimmer they have tried to connect into and now isn't working although they said first one did work for quite a long time. Looks to me like light got to be dropped and reterminated into SL?

 

[freddo]

That wouldn't explain the RCD tripping.

 

[littlespark]

What other cables are at the switch? Sounds like customer has changed a switch to a dimmer and mixed up the cables

 

[westward10]

Need some pics or more info.

 

[JohnS888]

It's just a red black and cpc. It does seem like they have have mixed SL with neutral but apparently they haven't touched any connections for light in while surprised me the first dimmer worked for so long. As for tripping I know this is probably totally unrelated. At moment where that circuits concerned have disconnected and proved with r1 +r2 and r1+rn the correct cables at db. The readings for L to N and L to E are about 0.15M ohms as soon as try to terminate cpc rcd trips had pretty limited time today but think? Next port of call is to switch of all lights to rooms, disconnect fire alarm and take readings again. There's only one dimmer in this circuit. The fact I am getting low L to N is concerning me think switching lights off shouldn't really resolve this? Looks like might have to break circuit at rose at what thinks about half way in and test away from this?

 

[westward10]

Sounds like you have red line in switched live black out so a standard dimmer should function. Are you insulation testing between line and neutral, if you have a tripping rcd this is pointless.

 

[JohnS888]

Sounds like you have red line in switched live black out so a standard dimmer should function.

Yeah but I'm getting 230v between the 2 of them if this was the case I shouldn't get this should i? It can only be if it's a neutral no?
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That wouldn't explain the RCD tripping.

I think your right Freddo. See above post for IR fault description. Where the dimmer is concerned do you agree that if getting 230v on black and red it looks like a neutral? Cheers

 

[James]

You will get 230 between perm live and switched live when the switch is off, as long as there is a lamp in the fitting.

Edit,

Remember, sw live is connected to neutral through the lamp filament that has a low enough resistance to tell your meter it is at 0v.

 

[westward10]

Why do you think black is neutral.
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Do you understand the so called three plate wiring system.

 

[James]

Go back to basics, change dimmer to normal light switch, that rules out any problem with the switch.

If problem remains, check ir between n and e then L and e with the sw on and again with it off. ( disconnect circuit from dB first)

 

[JohnS888]

You will get 230 between perm live and switched live when the switch is off, as long as there is a lamp in the fitting.

Edit,

Remember, sw live is connected to neutral through the lamp filament that has a low enough resistance to tell your meter it is at 0v.

Cheers James for clearing up my proper doughnut moment. Have you got any thoughts on why the dimmers seem to keep failing after a while?

 

[Andy-1960]

What type of lights are you trying to dim and what’s the total load?

 

[JohnS888]

What type of lights are you trying to dim and what’s the total load?

Not had proper look but they look like maybe standard incandescent ones about 4 or 5 of them maybe as much as 20W each is it imperative that these lights are manufactured as dimmable. LED ones are manufactured as so maybe advise to change for these?

 

[telectrix]

if they are filament lamps they are dimmable. 20 watts seems low for a filament lamp.

 

[JohnS888]

if they are filament lamps they are dimmable. 20 watts seems low for a filament lamp.

I'm round there bit late I'll check. Telectrix you got any thoughts on the low IR readings I'm getting I posted above. Does my plan for finding problems seem best way to go? Cheers mate