T.p.n isolators for extract fan

[just add water sparks]

Briefly went to help a guy /Sparks first fix a job(i was agency) and he seemed to have an idea of wiring an additional spur in conjunction with a triple pole isolator for a bathroom fan.I have normally never used a spur and just used a triple pole isolator which in turn was fed from a 6amp m.c.b via various connection points.When i queried this the sparks ( young and green) he remarked that one of his supervisors said that the fans should be fused at 3amp/5amp as manufacturers warranty would be not be valid if a fault happened.I said i could see his point ,but thought it was a bit overkill and have never done this on other jobs. About 40 other jobs i have seen must been wrong then lol!!!! anyway agency workers are low lifes i think in his mind and not allowed opinions.lol

 

[telectrix]

if you read the manufacturers instructions that come with fans, you will find that most stipulate 3A fusing. on timer fans, this usually entails fusing the bathroom lights at 3A so as to fuse both the permanent and switched L's to the fan.

edit: for this reason, i either fit non timer fans, or feed separately from the light.

 

[just add water sparks]

as i said in op i see his point, but without going over old ground have installed loads TPN isolators on very large jobs designed by so called qualified consultants which have had no fusing down.Yes could fit non-timer fans but i have replaced many of these when they burnt out through being left on permanently.When you said "feed seperately from light " did you mean via a FCU?? If i remember correctly his idea ,obviously it was a d. pole FCU ,first feeding the fcu (from light) perm live, switched live & n.Then from spur to (joining switched live in connector block) to Tpn isolator,then to fan.Permanent live was fused from spur , but switched live was being joined in a connector block.As i am not aware you can obtain a fused TPN spur suitable for a one gang knockout box.Without stating the obvious, the permanent live would be fused @ 3amps(via spur) whilst the switched live would be fused at 6amps(via mcb)Does not seem quite right to me.Thanks for your input not saying your right or wrong just constructive critiscism.

 

[telectrix]

if you fuse the lights at 3A then both supplies to fan are fused. to save doing this, feed fan via a separate switch. only problem, as you say, is numpties leaving the fan switched on. my ideal solution is to use a non-timer fan, fed from lighting via FCU. client switches on light ( and fan), showers/baths, then fan keeps running while he's drying off/scratching his arse/posing in front of mirror. no need to use timer fan.

 

[sjm]

What fans were specified on these other jobs?
Most cheap fans require fusing down because they have no thermal cut out built into them.
Some manufacturers (Vortice and S & P I think) do have cut outs and therfore do not require additional fusing only multipole switching for isolation and maintenance.

 

[Guitarist]

As tel says, you fuse the supply to the light in question, then both perm and switched live are fused. This all came about several months ago after a guy installed a bathroom fan off a lighting circuit with a 6 amp MCB. The fan in question developed a fault and burnt the house down. The spark who fitted it was prosecuted for not following manufacturers instructions (in the regs), which said it must be fused at 3 amps.
So yes, there are loads of fans out there on 6 amp MCB's, but the law is unforgiving of what we think is acceptable.

 

[just add water sparks]

telectrix just looked back on other threads(should have done that before lol! i know) seems that someone had a legal implication with this one ??? by not fusing down.I am working on uni accommodation having 250 + flats and the idea of having to split just one bathroom on its own circuit on a 3amp mcb seems excessive to me with cost and time additions.Just wondering anyone have or worked through a similar situation.They dont make a fused TPN isolator which would be ideal,you would have thought the manufacturers woud have come up with this one a long time ago.How long have timed fans been out now for goodness sake lol.Another idea would be a slim in-line fuse but i don't think there would be a lot of room for this in the fans????Any other ideas lads???
sorry : Guitarist did not check your post. By using a FCU on a timed fan you will only be able to fuse one of the lives , perm or switched so no point in that really

 

[Guitarist]

My post must be invisible....

 

[telectrix]

pointless excercise anyway. you have a 3A 1362 fuse and a 6A 60898 MCB in series on the fan. a fault in the fan will cause the 6A MCB to trip before the 3A fuse.

 

[Top Cat]

Only other way of doing it would be to come off outgoing side of 3 pole isolator, mount a 2 gang grid next to it with 2 x 3Amp fuses in it. Come off outgoing side of fuses back to isolator and crimp L & SW/L back to fan (leaving neutral in isolator).

 

[Top Cat]

pointless excercise anyway. you have a 3A 1362 fuse and a 6A 60898 MCB in series on the fan. a fault in the fan will cause the 6A MCB to trip before the 3A fuse.

And that Your Honour concludes my defence!

 

[just add water sparks]

sjm not sure what was specified, as these jobs were years ago.Point taken with Vortice and s&p good info mate Thanks!!!

 

[just add water sparks]

thks guitarist did mention in prev. post

 

[just add water sparks]

interesting post telectrix , so it begs to answer the previous posts of someone being prosecuted that did not put in a 3amp fuse.Fan caused a fire as it was not fused at 3amp!!! as you say discrimination (or new 17th term selectivity i think!)wise the 60898 would trip first,so a 3amp would have made no difference?.Just for legal clarity could you give me the page no./ time characteristics on bs 7671 for the 60898 and also for the 1362 fuse if thats what i believe the crux of the issue is about.Thanks

 

[Guitarist]

sparks, u misunderstood my post. 3 amp supply to the circuit for the light in question so that perm and sw live both fused.
The electrician was prosecuted because he didn't follow the manufacturers instructions, regardless of the practicalities. Crazy, I know.