TT System RCD protection

[charliefarli]

Hello electrical mafia, Just a quick one for you on this fine evening…..been asked to do the electrics for a hot tub install, house is a TT system and has no upfront RCD the ZE reading is 12 ohms. Would I be ok to split tails in a henley block and feed hot tub from a garage unit that has a 30ma RCD main switch or does an upfront 100ma need to be fitted to whole install swell as this. I haven't had much experience of TT systems and thought I would ask the finest bunch of sparks about for there wisdom.Thanks

 

[uksparks]

I'd be enclined to do a bit of upselling...

 

[uksparks]

Also, id probably just tell them to pay WPD for s PME conversion for £75 or whatever it is.

 

[charliefarli]

Thanks for the reply,really appreciate it.The guy used to be my accountant and is tight as aresholes,lol!!Can you get away with just the 30ma RCD on the garage board and no upfront protection if just putting a test on the hot tub circuit?and make a note on test it is recommended that upfront rcd is put in for whole install?

 

[charliefarli]

the main house board is 17th edition and has 30 ma RCD protection on all circuits by the way!!

 

[Simonslimline]

Also, id probably just tell them to pay WPD for s PME conversion for £75 or whatever it is.

If it is available in the area.

 

[Leesparkykent]

The fact its TT makes an easier job Imo. New circuit from MCB protected by one of the 30mA RCDs to rotary isolator....jobs a goodun.

 

[charliefarli]

Thank you for reply.I would of deffinetly done that but the main board is choca block with no spare ways, sorry i should of added that before. So a 100ma Upfront RCD is not needed because all circuits are protected by 30ma RCDS?Is this correct?

 

[Leesparkykent]

Thank you for reply.I would of deffinetly done that but the main board is choca block with no spare ways, sorry i should of added that before. So a 100ma Upfront RCD is not needed because all circuits are protected by 30ma RCDS?Is this correct?

Yes but its also not a bad idea to have a 100mA time delayed up front. You could install the 100mA in the tails to provide a single point of isolation. Out of this to a double pole Henley block then feed existing board and new board...alternatively talk the customer in to a new board.

 

[charliefarli]

Great reply, thank you. I am afraid this customer is one of those, "get it done the cheapest possible as long as its working" mob! I will advise him but am sure he will say no when I say it is not a necessity. So 100ma upfront RCD's are not needed on TT systems if all circuits are already protected by 30ma RCD's via the board but it is good practise and advisable to do so?

 

[crawf]

When you say 17th edition is that amendment 3??

 

[Leesparkykent]

Great reply, thank you. I am afraid this customer is one of those, "get it done the cheapest possible as long as its working" mob! I will advise him but am sure he will say no when I say it is not a necessity. So 100ma upfront RCD's are not needed on TT systems if all circuits are already protected by 30ma RCD's via the board but it is good practise and advisable to do so?

Yes as provides as a back up when relying on an RCD as I doubt any customer ever tests their RCD quarterly..also with dual RCD amendment 3 boards the 100mA S type provides protection for the flexible links feeding the RCDs.

 

[charliefarli]

Morning everyone, No the board there is not amendment 3 but has dual RCD'S so is earlier 17th board. There is one circuit that has been put on the main switch which is a 16mm t and e on a 50 amp breaker which feeds a massive outhouse, there must be a junction box on the outside wall which converts it to armoured unless it goes through a ducting. This should be protected though and I will be advising customer its unsafe and if he refuses to put up front RCD I will mention it in test on comments on existing installation. The garage board I will be putting in will be amendment 3 metal Wylex board with a metal blank. Thanks all for your help, have a good day