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yes , very Good Ian :) The Discussion has however, moved on to a point regarding the difference in Installation design considerations between TNCS & TNS systems.. I think you would agree with the points made by me in refernce to this. If we do go back to the original discussion then...

Infor. Yes I did mention the on site guide, but that is not the Regs, its a means of compying with the regs without having to do too much design work -calculations etc. If you read back on my post you will see one of the things I refered to was PIRs. So if you did a PIR and there was for...

Hi Batty what are snaplites..? have you got a link please a1 Spark

Is it not true that on a TNS system the Main Bonding can be 6mm ?, whereas on a TNCS system it has to be min. 10 mm. so : It doesnt really matter if its TNS or TNCS. is not correct. I see what you are saying i.e err on the safe side [ On-site goide etc] and you cant go wrong but from a...

32A TYPE 1 MCB . -1.88 ohms. Max Zs/ a1 Spark

Hi Infor , It would matter if it Was a PIR that was being carried out, or planned additions to the installation though wouldnt it ?....Different criteria on sizing of Main Bonding Springs to mind.....Ze lower limits is not the only consideration between the two systems.

Or maybe someone else has been messing around with the system since the PIR ?

OPB see edited post and infor post !

Infor is correct OPB 559.6.1.5

Not me .but BS 7671 2008 Does :D

AND a TNCS SYSTEM

You are right about the temperatures [ of the cables ] ,I touched on that above... but thankls for your input mate ! a1 spark

[quote name='Andy

Not specific related to downlights, but may regs relate to installation of equipment & luminaires in general The Electricians guide to the building Regs gives some useful advice also. a1 spark

try : www.esc.org.uk/business-and.../best-practice-guides.html Guide No 5. gives all the guidance you require a1 spark

If you meen you are replacing the one way light switch operation to a PIR controller then a three core run from the light to the controller and then as above stated --permanent live in.......neutral in .....and switched live out....... cpc usually parked at relevant location at controller...

Yers Sparky B. your right there , but what the OP was enquiring over was why bother to give the non adjusted figures in the first place why not just give the on-site adjusted figures .I was trying to give my thoughts as to the requiremets for both sets...obviously the non adjusted figures are...

Fair question maybe someone can expand on this. I see it as the tables are a base level from which to start and the 0.8 figure is an averaged figure applicable for all cable type..70 degree - 90 degree , protective conductor combined ----protective conductor seperate etc. If a more scientific...

Are you trying to avoid the joists,,,i.e when installing downlights from beneath a ceiling , or are you trying to fix a standard type of light from below ?

Hi, The formulae in Appendix 14 is used for calculating the acceptable in-service value where the circuit will be under load and therefore its resistance will be higher , thus the nominal 0.8 factor has to be applied to the max values of those given in tables 412-41.4