Smoke alarm 3rd core, WHY ?

[jamestaylorchat]

Hello fellow sparks, how are we ?

I am slightly embarrassed about asking this but here goes,

I have never realy understood why you need a 3rd core when wiring smokes, live, neutal and earth i get, but why do you need a switch wire exactly,

what is its job ?

 

[Fin170]

Live, neutral and the 3rd is the interlink/com. It's in the manual with a free Fire Alarm sticker usually

 

[monkeyelectric]

To sound the other smokes if one is triggered

 

[amlu]

third wire is for linking them together, when one gets triggered then all of them will sound the alarm.

 

[MDJ]

the third core is the switched link to other smokes, when one smoke rings the interconnect or third wire sends a signal to the others on the circuit, Happy friday by the way.

- - - Updated - - -

haha 3 replies whilst I replied, we are quick tonight guys.

 

[jamestaylorchat]

I thought that was it but wasent sure.

Now why the trhird core when wiring a fan switch from a bathroom switch ?

 

[monkeyelectric]

For the overrun after the light has been switched off

 

[MDJ]

come on James, why do you think there is a third core?

 

[Resu]

Switched live, neutral and permanent live to supply timer.

 

[jamestaylorchat]

I just drew out a simple oneway bathroom switch with a fan switch being feed of it.

Common = per live
L1= SW Live
L2=fan switch 3rd core

Switch switched, current goes down L2 and runs fan for however long the time is set for,

correct ?

 

[NadHuh]

Even I knew this and I'm a first year apprentice

 

[MDJ]

yup absolutely love Friday's here

 

[monkeyelectric]

When you said in your first post hello fellow sparks just how much of a spark are you?

 

[onfire25]

No......you need to go from the switch to a TP fan isolator then the fan.

Common - perm live at fan isolator (brown)
S/L - S/L at fan isolator (black....remember to sleeve)
Neutral - Neutral (gray......remember to sleeve)

Then wire from the isolator to the fan!

Failing that......rtfm.....or call a professional spark

 

[jamestaylorchat]

HEY HEY HEY !!!!

Settle down Lads, there is all man and all sparks right here

Give me a bit of trunking or conduit and watch me go, but when it comes to wiring, i strugle,

 

[onfire25]

Wiring is the same.....you go from from a-b with a few switches between!

 

[Thefailsafe2012]

but when it comes to wiring, i strugle,

And spelling

Oooooh sorry geez couldn't resist

 

[Stroppy]

I've never really seen the point in putting triple pole isolators in for fans. If you need to 'perform maintenance' on something you generally isolate the circuit it is on, so why are fans different?

The half-witted ape who built and wired my bathroom (it wasn't me, before you ask) didn't put in a TPI for the fan, so when I changed it for one that worked I just isolated the lighting circuit. Easy.

 

[shagbite]

I've never really seen the point in putting triple pole isolators in for fans. If you need to 'perform maintenance' on something you generally isolate the circuit it is on, so why are fans different?

The half-witted ape who built and wired my bathroom (it wasn't me, before you ask) didn't put in a TPI for the fan, so when I changed it for one that worked I just isolated the lighting circuit. Easy.

it simply removes the inconveniences that can arise from isolating an entire lighting circuit. i always fit fan isolators - love 'em.

 

[Deleted member 26818]

A lot of people opt for TP isolators, if the bath/shower room or even toilet has no natural light.
That way work can be conducted with the light on and without having to use a torch.

 

[MDJ]

Also good practise IMO, local isolation for a moving part, maybe not regs, not sure about that will have to check, but in anycase good practise

 

[Octopus]

Yet another stupid example of the regs.

The regs for fixed equipment like fans should read "local isolation by means of DP or 3P isolation must be installed within easy reach to allow the item to be isolated from the supply circuit" Particulaly useful for fault finding and isolation when performing IR tests.

I was doing fault finding on a lighting circuit on Friday and not 1 of the 3 fans had isolation - so I had to physically disconnect each one.

Not fitting isolators is bad practice IMHO.

 

[shocking_eg]

is this a wind up ? lol

 

[D Skelton]

Ah, fans and triple pole isolators, my favourite subject!

No......you need to go from the switch to a TP fan isolator then the fan.

Common - perm live at fan isolator (brown)
S/L - S/L at fan isolator (black....remember to sleeve)
Neutral - Neutral (gray......remember to sleeve)

Then wire from the isolator to the fan!

Failing that......rtfm.....or call a professional spark

Please have a read of this if you'd like to know more about the subject and why you are not required (unless the manufacturers specify to do so) to fit a 3 pole isolator:

http://www.electriciansforums.net/e...3-pole-isolation-source-much-controversy.html

 

[MDJ]

I enjoyed the thread there Buddy, however totally confused by it, so are you saying a triple pole isolator is not required but isolation is? or is the post so long I cannot work out what is being said ?

 

[D Skelton]

Put simply, the only time a 3 pole isolator is required is if the manufacturers instructions specify that one must be fitted.

Every electrical circuit must have a point of isolation. Every electrical circuit can effectively be isolated by use of the main switch.

Local isolation is a made up term and is found nowhere in BS 7671. 'Readily accessible means of switching off' which does appear all over the BGB, is open to interpretation.


These are the main points I try to make in that post, is there anything specific you need clarification of bud?

 

[Octopus]

Putting it simply a fan is a fixed piece of equipment and good practice says that you should always install local DP or TP isolation, plus fuse down if directed by the manufacturers instructions.

 

[shagbite]

it might not be in the wiring reg's, but the building reg's says that "an extractor fan supplied from a lighting circuit for a bathroom without a window should have it's own means of isolation, as otherwise replacement or maintenance of the fan would have to be carried out in the dark. an isolation switch for a fan with an overrun facility will need to be triple-pole (switch wire, line and neutral), and must be installed outside of zones 0, 1 and 2."

 

[MDJ]

Put simply, the only time a 3 pole isolator is required is if the manufacturers instructions specify that one must be fitted.

Every electrical circuit must have a point of isolation. Every electrical circuit can effectively be isolated by use of the main switch.

Local isolation is a made up term and is found nowhere in BS 7671. 'Readily accessible means of switching off' which does appear all over the BGB, is open to interpretation.


These are the main points I try to make in that post, is there anything specific you need clarification of bud?

Oh right, so theres no reg to state a triple pole is required but down to the manufacturer? however an isolation point is required? fair enough, I just like clarification incase an engineer who I may work with tries to tell me otherwise, I always fit a triple pole if a timer fan is used, or a double pole if it is a PIR fan, But I enjoy trying to get one over engineers, It doesn't happen very often though haha

 

[D Skelton]

it might not be in the wiring reg's, but the building reg's says that "an extractor fan supplied from a lighting circuit for a bathroom without a window should have it's own means of isolation, as otherwise replacement or maintenance of the fan would have to be carried out in the dark. an isolation switch for a fan with an overrun facility will need to be triple-pole (switch wire, line and neutral), and must be installed outside of zones 0, 1 and 2."

No it doesn't, what you have posted there is a direct quote from The Electricians Guide To The Building Regulations. This book is as it says... a guide. It is simply a book, written by an individual and is not statutory in any shape or form.

 

[D Skelton]

however an isolation point is required?

And that isolation point can be the main switch if you like!

The only requirement for 'local isolation' as some like to call it is defined in 132.15.2 which to summarise states that a fixed electrical motor needs a readily accessible and easily operated means of switching off. Well I don't need to tell ya that 'switching off' is not the same as 'isolation'

 

[MDJ]

appreciate this mate, thanks for the info. another grey area considered to some I suspect, it is good to learn something new, cheers.

 

[shagbite]

No it doesn't, what you have posted there is a direct quote from The Electricians Guide To The Building Regulations. This book is as it says... a guide. It is simply a book, written by an individual and is not statutory in any shape or form.

yep, i'll concede to that. even though it's non statutory it's still good advice, but i accept your point.

what i will say is that, whilst you may be correct about the lack of any hard and fast rules regarding isolators, as the installation designer i must make an assessment of the type of equipment that is being installed and who is going to be using it. extractor fans have permanent lives, motors and moving parts; there is every possibility that something could go wrong at a later date which would require a competent person to carry out repairs. it's not beyond the realms of possibility that these repairs might need to be carried out in less than satisfactory light conditions and because of this, i believe it's good practice to provide isolation from a point other than the fuse board.

also, it might be acceptable to use the mcb for isolation in a tn installation, but what about a tt? i'd want both line and neutral disconnected. it's obviously not ideal to isolate the entire installation, so a fan isolator is the perfect solution.

 

[D Skelton]

yep, i'll concede to that. even though it's non statutory it's still good advice, but i accept your point.

what i will say is that, whilst you may be correct about the lack of any hard and fast rules regarding isolators, as the installation designer i must make an assessment of the type of equipment that is being installed and who is going to be using it. extractor fans have permanent lives, motors and moving parts; there is every possibility that something could go wrong at a later date which would require a competent person to carry out repairs. it's not beyond the realms of possibility that these repairs might need to be carried out in less than satisfactory light conditions and because of this, i believe it's good practice to provide isolation from a point other than the fuse board.

also, it might be acceptable to use the mcb for isolation in a tn installation, but what about a tt? i'd want both line and neutral disconnected. it's obviously not ideal to isolate the entire installation, so a fan isolator is the perfect solution.

I absolutely agree, you're right, there are more than enough scenarios where fitting a 3 pole isolator would be the most reasonable thing to do. I have always stated that fitting a 3 pole isolator is often good practice, my only point was that it wasn't a requirement. The whole reason I 'took a stand' so to speak to the myth that 3 pole isolators MUST be fitted was because of the amount of hear say and rubbish floating around in the ether. People talking of building inspectors failing jobs because of the lack of 3 pole isolators, 'sparks' rubbishing other sparks work, people wasting time fitting both fuses AND isolators??? I just wanted to bring some clear, consise and accurate information to the table to clear the matter once and for all.

Personally, when fitting extractors, I rarely fit 3 pole isolators as most fans that I fit require fusing down so 9 times out of ten I fuse down the bathroom light and fan together, thus killing two birds with one stone. What you choose to do is up to you, and as long as it complies with regs, isolator or no isolator, I can assure you I wouldn't be rubbishing your work

 

[dim_bulb]

Love the way the thread started out as smoke question then a slight detour onto bathroom fans and isolation