BATHROOM ELECTRICS

[falcon16]

I AM FITTING A SHAVER SOCKET INTO ZONE 3. DO I NEED TO RUN A BOND BACK FROM THE EARTH T0 THE THE HOT AND COLD BONDING IN THE AIRING CUPBOARD.
ALSO AS I HAVE TAKEN OUT THE ELECTRIC SHOWER FROM OVER THE BATH AND REMOVED ALL CABLES. IS IT OK TO RECONNECT THE CEILING SWITCH AND USE IT TO RUN THE EXTRCTOR FAN (NO TIMER) INSTEAD OF FROM THE SWITCH CURRENTLY POSITIONED IN THE AIRING CUPBOARD? AS FAR AS I CAN SEE IT WOULD THEN ONLY REQUIRE THE EXISTING CABLES TO BE CONNECTED TO THE CEILING SWITCH.

 

[dingbat]

The protective conductors of all power and lighting points within the zones must be supplementary bonded to all extraneous conductive parts in the zones (OSG, Fig 4d refers)

Ideally you run a 4 sq mm bonding conductor from the protective conductor of the circuit to the nearest metalwork capabale of introdcing a potential, but in practice this can be difficult to achieve; if you can run your to the bonded pipes in the airing cupboard then this is good enough. Remember that what you are trying to achieve is that all conductive material in the zones is at the same potential. If your pipework is all metallic there's a good chance you will have achieved this. By the way there should be no [edited] earth connection to the secondary side of your shaver socket as it uses an isolating transformer.

Yes, you can use your old shower switch for your fan, so long as the circuit cabling is suitably protected from overcurrent at the circuit origin. Using over-sized switchgear is not a problem - just overkill!

Oh and please don't SHOUT!

 

[Damocles]

Why should there be a connection to the secondary side of the shaver isolating transformer? After going to all that trouble to isolate the voltage, you want to un-isolate it again?

 

[L.Spark]

There should be no connection to the primary side of the shaver outlet, it's an isolation transformer as said, the only connection to earth should be where the mains goes in..

 

[dingbat]

Why should there be a connection to the secondary side of the shaver isolating transformer? After going to all that trouble to isolate the voltage, you want to un-isolate it again?

Sorry, typo - 'on' = no in my post. I meant what L.S said [better than I did ].

 

[Griggsy]

The protective conductors of all power and lighting points within the zones must be supplementary bonded to all extraneous conductive parts in the zones (OSG, Fig 4d refers)

Ideally you run a 4 sq mm bonding conductor from the protective conductor of the circuit to the nearest metalwork capabale of introdcing a potential, but in practice this can be difficult to achieve; if you can run your to the bonded pipes in the airing cupboard then this is good enough. Remember that what you are trying to achieve is that all conductive material in the zones is at the same potential. If your pipework is all metallic there's a good chance you will have achieved this...

Would it be ok to use the earth terminal in a junction box (in the loft above) that supplies the light switch, light, shaver socket and extractor fan to bond all the electrics in a bathroom to pipework? Or must a seperate cable join each item?

 

[dingbat]

Well they are all on the same circuit, aren't they? So a single bonding conductor from the junction box to the nearest pipework should do nicely. Then, as you've also bonded all exposed conductive parts to this pipework there's no chance of a difference in potential appearing between any two conductive bits of your bathroom.

 

[Griggsy]

In that case, why can't you just use the MET as a bonding conductor?

 

[Damocles]

Your house is supposed to form an equipotential zone, which means all possibly earthy things are wired together where they enter the house.

The idea with bathroom bonding is exactly the same, but on a smaller scale. All earthy things should be wired together where they enter the bathroom. Connections should therefore really be inside the bathroom at the point of entry, but nearby is considered ok. They are supposd to be available for inspection if someone wants to check.

 

[dingbat]

In that case, why can't you just use the MET as a bonding conductor?

Because, although all the circuit protective conductors and main equipotential bonding conductors should terminate at the MET, there is no guarantee of electrical continuity between the incoming water (and/or gas) supply pipe and all the extraneous conductive parts in the bathroom.

 

[Griggsy]

Cheers guys, does anyone know how far from a tap or shower a bonding clamp can be placed?

And is it ok to have clamps underneath floorboards and under a bath or must they be visible?

Also if the toilet, bath, sink and shower are all fed by a few metres of copper pipe with soldered joints, does each item need a seperate bonding clamp or can one be used to bond the whole lot?

 

[dingbat]

'Judgment call' (horrible expression) on all of that really. Ideally all connections should be accessible [and under the floors isn't, really] but on the other hand most people will happily sacrifice safety for beauty.

In an ideal world you'd ascertain the resistance of all possible paths between conductive bits and position clamps and cables accordingly but as the vast majority of households neither have nor have even heard of supplementary bonding you're doing more than most just be considering how to go about it!

Do the best job you can do while keeping your bathroom usable and attractive. A BS951 clamp on the common cold water pipe, one on the common hot water pipe and one on either of the pipes serving your radiator will do the job and under the bath is ideal.

 

[Griggsy]

Is it common practice to use ring lugs to attach earth cable to the earth clamps?

 

[dingbat]

Is it common practice to use ring lugs to attach earth cable to the earth clamps?

If you mean eye (or eyelet) crimps then yes, but it's also a good idea to keep bonding conductors continuous, so many will advocate removing an inch or so of insulation, then forming a loop in the exposed conductor which you use to screw to the clamp. That way, no matter how many connections are made, if an intermediate connection is lost the bonding is still in place to all other points.

 

[falcon16]

Thanks for the replies to my recent questions, they have been much appreciated. One further one though. I now wish to fit a pull cord chrome light fitting that is marked as suitable for zone 3 in bathrooms . It has no earth connection as it is double insulated. Do I still need to bond it and if so how can this be achieved.