Bathroom fan wiring electrics help

FlaatusGoat

My existing fan didn't work so I assumed after 30 years it was a goner! Decided to go ahead and fit a new inline fan. Curiously, the input to the old fan was brown/black. This brown/black comes out of what looks to be a 12v power supply next to the isolator. Why would I have had one of these boxes? No idea. My ceiling rose is the usual 3 pole type.

Suffice to say the new fan won't run off the brown/black input. I guess I should bypass the 12v power supply? It's a strontronics box apparently, seemingly it works as a red light comes on when I pull the rose cord and have the isolator set on. Looking for some enlightenment please.

ThisIsWeird

12V - often referred to as 'extra low voltage' ('low' voltage apparently being 'mains' 240V) - can be used to comply with AP regs, where the extractor could be at risk of water ingress.

Yes, 12V ain't going to make a 240V jobbie spin.

And, yes, you could take the supply from the 'mains' side of the transformer.

Please do check the full wiring, tho'. The basic on/off is via a pull cord? And you know where the isolator is located? Cool. 

Does the new fan have a timer or humidistat? If so, it'll need a third wire - a 'permanent' live - to make that work after the pull cord has been off'd.

Are you 100% certain you know what you are doing? As well as testing that the power is off - ie test first when it's on, and then turn it off - it's worth turning it off at the CU.

FreeBear

ThisIsWeird said: 12V - often referred to as 'extra low voltage' ('low' voltage apparently being 'mains' 240V)

Just to give you a shock, "Low Voltage" is anything in the 50-1,000V AC and 75-1,500V DC. And domestic mains voltage can range from 216V to 253V - Be careful where you stick your fingers. These sorts of voltages can kill if there is enough current.

CSI_Yorkshire

FreeBear said:

ThisIsWeird said: 12V - often referred to as 'extra low voltage' ('low' voltage apparently being 'mains' 240V)

Just to give you a shock, "Low Voltage" is anything in the 50-1,000V AC and 75-1,500V DC. And domestic mains voltage can range from 216V to 253V - Be careful where you stick your fingers. These sorts of voltages can kill if there is enough current.

The fun of our system - at least in how the wiring regs describe things.

Extra low - up to 50V AC or 120V DC
Low - higher than "extra low" up to 1000V AC or 1500V DC
High - everything that is above low.  So that's up to 1150000V AC or 1600000V DC based on what is actually done at the moment.

Although my favourite sign was on a switch room in the basement of my university engineering department - "Danger, Medium Voltage".

casper_gutman

Signage reading "Danger: low voltage" on 1000V switchgear could lead to some interesting results....

FlaatusGoat

Fyi for those following I bypassed the deceased 12v transformer and restored the wiring back to Live SL and N. Rigged into the inline fan in the ceiling and job done! Couldn't be simpler and in theory I now have better extraction than the old jobbie that was seriously weak for 5 m of ducting

Risteard

FreeBear said:

ThisIsWeird said: 12V - often referred to as 'extra low voltage' ('low' voltage apparently being 'mains' 240V)

Just to give you a shock, "Low Voltage" is anything in the 50-1,000V AC and 75-1,500V DC. And domestic mains voltage can range from 216V to 253V - Be careful where you stick your fingers. These sorts of voltages can kill if there is enough current.

Technically 216.2V is the minimum for a nominally 230V supply!

Risteard

casper_gutman said:

Signage reading "Danger: low voltage" on 1000V switchgear could lead to some interesting results....

1kV AC is HV.

Incidentally, the term Medium Voltage (MV) does still exist in some places, although it is not recognised by the Wiring Regulations. The 1kV supply would in some spheres be described as MV rather than HV.

ThisIsWeird

What are you sparkies like!