tt system

[9regnac]

Customer has a tt system with a 30ma rcd as main switch on cu. would you upgrade this board and put type s in or..??

 

[Amp David]

Really!!!! So what is protecting any of these circuits when either one of the RCD's fail in a dual CU, or if any of the RCBO's fail in an all RCBO CU??

We don't know what the Ra value of this installation is, but it's a pretty sure bet, that the usual single short thin twig has been employed as the earth electrode. So were probably talking of an unstable made electrode with an Ra value hovering around this magic 200 ohms. So let's hope that none of these RCD'S/RCBO's fail!!! The 100mA S type up front RCD will give a TT installation additional protection it needs....

Just another reason to spend the time and effort (and cash also) in trying to install a good reliable source of earthing, rather than being quite happy with 200ohms Ra

 

[Smart Sparks]

All, less than 100 ohms is not that hard to achieve in most areas. It doesnt take too long to drive a decent earth rod in. I got 28 ohms the other day from an earth electrode that was driven in around 4ft.

 

[richy3333]

Fair play.
How many circuits?
What make is the board?
Change the 30mA for 100A 100mA s type & plonk in 30mA rcbo's for circuits................or change the board for a dual rcd board.

Do the Regs say you have to fit a 100mA S type RCD? I know the onsite guide shows one, or used to show one, but do the Regs stipulate it?

 

[Smart Sparks]

for additional protection it stipulates 30mA, all TT systems are required to have RCD protection to my knowedge. However there RCD rating for fire protection is higher, I think 100 mA from memory.

 

[GLENNSPARK]

Customer has a tt system with a 30ma rcd as main switch on cu. would you upgrade this board and put type s in or..??

Personnaly i would upgrade but looking for advice as not long tome served and i knew someone could help me on this. And if ur not sure better to ask some one with more experience

why an S type?.....

 

[GLENNSPARK]

look....
if you have a garage.....and wish to give the garage 30mA RCD (for fault) at the garage end......then you would typically use an armoured to feed the garage of ov a 100 mA S type top end .......so whats the meanin of feedin the house c/u with a 100 mA S type as an `upgrade`.....lolffs..

 

[9regnac]

Ra is 70ohms

 

[MDJ]

Do the Regs say you have to fit a 100mA S type RCD? I know the onsite guide shows one, or used to show one, but do the Regs stipulate it?

no I haven't seen that, if I'm wrong then apologies Richy, basically all circuits need protection, if they are split up as individual RCBOs then I cannot see any reason why a 100 amp S type is required by regulation, I bet there is one though LMAO, engineer actually has a good point of course, if an RCBO fails at least there is the S type to still maintain protection, but the customer if trained properly by the electrician can be more than capable of pressing the test button monthly and if it fails they can call a spark.

Mike

 

[Knobhead]

You haven’t said what make of board it is and what you think is wrong with it.

Or is this a wheeze to extract money from an unsuspecting customer?

 

[MDJ]

Hi-Tony

he said it was a wylex, however no mention how old or what type, maybe wrongly I think he means the old type, maybe even wooden backed, however thats a complete guess of course, it may be more modern, we will have to wait for another reply first.

 

[Engineer54]

look....
if you have a garage.....and wish to give the garage 30mA RCD (for fault) at the garage end......then you would typically use an armoured to feed the garage of ov a 100 mA S type top end .......so whats the meanin of feedin the house c/u with a 100 mA S type as an `upgrade`.....lolffs..

Only on a TT system Glenn. It's 100mA and time delayed because of discrimination, and it'll be looking at the total/combined leakage of both RCD's in a dual board or all RCBO's of an all RCBO board. To my mind all domestic TT installations should be full RCBO boards!!
The S type, basically backs up the standard RCD devices that fail to operate... Given that most UK TT systems have been installed around that numbty 200 ohm Ra, it's more than prudent NOT to totally rely on two single 30mA RCD devices for the installation, or circuit (RCBO's) earth fault protection.

 

[ackbarthestar]

Only on a TT system Glenn. It's 100mA and time delayed because of discrimination, and it'll be looking at the total/combined leakage of both RCD's in a dual board or all RCBO's of an all RCBO board. To my mind all domestic TT installations should be full RCBO boards!!
The S type, basically backs up the standard RCD devices that fail to operate... Given that most UK TT systems have been installed around that numbty 200 ohm Ra, it's more than prudent NOT to totally rely on two single 30mA RCD devices for the installation, or circuit (RCBO's) earth fault protection.

and, of course you are offering fire/fault protection to the tails with a 100mA 'S' RCD

 

[Engineer54]

300mA is the recognised value of RCD for fire protection. But using a 100mA, it'll be that much of a closer fire protection!! lol!!

 

[Amp David]

Just goes to show they teach sod all during these nifity 5 week courses LOL

Sounds as though every new comer to the trade either can't read or because they undercut everyone to get the work, can't afford a copy of the regs:rant:

 

[Elmer BeFuddled]

Just goes to show they teach sod all during these nifity 5 week courses LOL

Sounds as though every new comer to the trade either can't read or because they undercut everyone to get the work, can't afford a copy of the regs:rant:

I got mine! Off eBay, sealed, 32 sobs. Bargain! (Oh, and OSG, GN3, d'led Part P and other pertinent bits as per building regs guides, but I'm a smug bugger!! :biggrin5