extractor and shaver socket in bathroom.

[scotsparky]

The regulations say all circuits in a special location have to have rcd protection. So its lights,shower,anything else. Sorry.

 

[ban-all-sheds]

shower is going to be mains pressure hot water so no electrics there

 

[ColJack]

why are you sorry scot?

the OP has already said that he's wiring the lights, shaver socket and extract fan from an RCD spur, that there will be no elextric shower, and that there will be no other circuits in there besides the afforementioned circuit, so that covers everything and it will be RCD protected from the RCD spur..

 

[RF Lighting]

As for Supplimental bonding in the Bathroom If you can get your hands on an good low reading Ohmeter use a long lead from the main earth in the D.B and go round all exposed metal parst such as heaters metal taps and such. if the reading is under 0.05 ohms your suplimental bonding should be ok.

That is just plain and simply wrong.

Do you actually understand the purpose of supplementary bonding?

 

[scotsparky]

R.F i do understad the reason of suplimentary bonding and if the reading is down to 0.05 on exposed metalwork then your tounch voltage will be well down if you can there is a handy table on page 106 of the electricians electrical installation design guide it gives maximum legns and maximum readins for all suplimentary bonding on all sorts of mcb sizes. on a 100A type c mcb its states 0.05. as this is going to be your worst case sinario in a domestic property as the main HRC fuse is unlikely to be over 100A more like 63A then your covered.

 

[RF Lighting]

Why would you measure the ECPs back to the MET?

The resistance to the MET, and metal work actually being earthed for that matter has nothing to do with supplementary bonding.

How can there be different readings for different MCBs??

 

[scotsparky]

RF lighting. here is an example.
Using the long lead test measure from the main earth terminal to the exposed metalic pipework at the sink. the lead resistance is cancelled out pre test the resistance is 0.1 ohms
If the largest circuit in the installation is a 50A type c then the fault current Ia would be in the event of a short would be 500a. If you then cross refrence to Appendix 3 of 7671 the time current charts you will see a 50 a type c will disconnect in 0.4 seconds with a 500A fault current. so your disconnection time is satisfied. If it is not then Supplimentary bonding is requiered to improve the earth path mack to the MET. If you are using this to work out if suplimentary bonding is required then always use the worst case of the largest circuit. Or as the largest main fuse installed in a domestic property will be 100A use that.

 

[RF Lighting]

Oh, so you don't understand the point of supplementary bonding then.

 

[scotsparky]

ok you tell me the information i got was from the my 2391-02 course and advice from the electrical safety council

 

[scotsparky]

RF read REG 411.3.2.6 as well at OSG p30 as well as if your interested reg 54.2.6

 

[ColJack]

If it is not then Supplimentary bonding is requiered to improve the earth path mack to the MET

don't mean to put words into his mouth, but i think it's this bit he means..

it's NOT to improve the earth path back to the MET..

it's to make sure that all exposes metalwork is all at the same voltage during a fault so that you don't get a shock from having one hand on a tap and reaching for a tower off the towel radiator if the heating element in it chose that second to short to earth..

 

[RF Lighting]

Yup

 

[scotsparky]

but by creating those earth paths the resistance is lower and so higher current on fault and lower touch voltage
i also have already said that when your checking it test all exposed parts

 

[ColJack]

still not the point though..

it could all quite happily sit at 230V with respect to earth and as long as part of you doesn't touch something with a different voltage with respect to earth, you wouldn't get a shock..

it's true that a side effect of sup-bonding is that you create paralel earth paths and lower the resistance back to the MET, but that's not the reason for doing it..


side note.. strange how this weekends arguments seems to be all about earthing..
we ought to make a weekly argument topic to discuss... pick a theme each week...

 

[RF Lighting]

But the purpose of supplementary bonding is not to reduce the touch voltage. It is to ensure that every part of metal work in the room is at the same potential.