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can someone with a regulation book please help me?I don't have.Concerning isolation reg 537.2.2.1(I think)The requirement to have in a TT installation isolation of all live conductors.Does this mean all switches,sockets,and spur units,and circuit breakers should be double pole?or is the regulation met if the main consumer unit switch alone provides this?
 

ian.settle1

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Mentor
Arms
can someone with a regulation book please help me?I don't have.Concerning isolation reg 537.2.2.1(I think)The requirement to have in a TT installation isolation of all live conductors.Does this mean all switches,sockets,and spur units,and circuit breakers should be double pole?or is the regulation met if the main consumer unit switch alone provides this?
If it included light switches you would have a problem with any two-way lighting circuits as the are no 2-pole 2-way switches suitable for domestic properties I think you will find.

Don't have the BRB handy at present but think you will find it only applies to the main incoming switch. All CUs are two pole switches anyway.
 
L

L&B Electrics

Hi there,

if you were to put 2 pole on everything one it would cost a fortune and 2 you cant due to lighting, this is only for the DB board
 
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  • #4
Hi there,

if you were to put 2 pole on everything one it would cost a fortune and 2 you cant due to lighting, this is only for the DB board
I know that when we were fitting isolators to 3phase air con units we were told to use 4pole switches as opposed to 3 pole,but I would think that in the case of light switches these would be classed as functional switches as opposed to isolators,isolation being provided presumably by rcbo.But as I say I haven't got the book yet.
 
W

WarrenG

Main Isolating switch.

The Isolators you talk about for the fans you were fitting would have been to isolate the supply for mechanical maintenance.
 
S

Spudnik

The reason the neutral needs to be switched is:

537.1.2
In a TNS or TNCS system the N need not be switched or isolated where it can be regarded as being reliably connected to earth.

In a TT system this is not possible as the earth is provided via rod.

Therefore, if you are working on a circuit on a TT system you should at least isolate via the local RCD for that circuit.

So in essence, yes a DP main switch or RCD will comply along with 537.2.2.1

I hate TT systems and so i get them PME'd where ever possible.

My local DNO do it for free if its available.
 
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  • #7
Main Isolating switch.

The Isolators you talk about for the fans you were fitting would have been to isolate the supply for mechanical maintenance.
yes,warrenG,this is what i'm on about-isolators for mechanical maintenance.So a fuse in a spur unit wouldn't be sufficient then in aTT system for isolation,for instance to an oil fired boiler,where a plumber could safely work?I don't know how isolation can be provided on a lighting circuit without double pole mcbs or rcbos,without having to knock off the main switch,which is often not practicable,especially if it is in a commercial context,your client cannot be left without anypower.
 
W

WarrenG

Well the FCU would be isolating both the phase & Neutral which is the requiremnts for Isolation in a TT system and I would therefore expect that to be surfficient to isolate the load it is supplying to safely work? Could be wrong? Could always remove the fuse?

As for lighting circuits for true isolation then I would say that the main DP switch (or as Jason has said the local RCD for that Circuit) would have to be switched off to achieve true Isolation of the supply.
 
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  • #9
Well the FCU would be isolating both the phase & Neutral which is the requiremnts for Isolation in a TT system and I would therefore expect that to be surfficient to isolate the load it is supplying to safely work? Could be wrong? Could always remove the fuse?

As for lighting circuits for true isolation then I would say that the main DP switch (or as Jason has said the local RCD for that Circuit) would have to be switched off to achieve true Isolation of the supply.
I'm pretty sure FCU's only switch the live only.I know we could always fit a 20amp dp switch or even a tp switch which I think is what british gas insist on(as there can be a perm live and a switched live and neutral)But I am wondering if people normally would fit a dp/tp switch in addition to a FCU. I understand that isolation can indeed be provided in an entire installation,by the main switch(rcd) ,but am thinking this may not be really practicable for instance if power is needed,perhaps for power tools/temp lighting,or the client not wishing you to knock his power off to the intire premesis.I know that if necessary true isolation can also be achieved by physically removing the live and neutral at the consumer unit, but what I am trying to get at here is the point that we shouldn't be using spur units to provide isolation in a TT,system.(most of my work would be of a commercial nature).I think this may be the reason why recently we have been required to use(for example)a dp key switch instead of an unswitched FCU for local isolation to fire alarm panels.
 
W

WarrenG

I have always been under the impession that a FCU was a DP switch and switched both Live & Neutral and therefore can be use for local Isolation purposes ?
 
S

Spudnik

DP key switches for alarm panels, i would suspect, are needed as an anti tampering isolator?

As for DP FCU, i think most of them are nowadays, especially decent branded ones.

They are normally marked on the back.

Mind you, if most of your work is of a commercial nature, then i wouldn't have thought you would come across TT that often
 
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  • #12
I have always been under the impession that a FCU was a DP switch and switched both Live & Neutral and therefore can be use for local Isolation purposes ?
we must have been useing cheap and nasty ones with sp switch only
 

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