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..??

 

[not clever]

What do you think you should or shouldn't do?

 

[9regnac]

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

 

[not clever]

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.

 

[9regnac]

8 circuits

Wylex

Could i put a 100a 100ma type s in an enclosure before the board then leave the rest?

 

[9regnac]

Or i could just as u said put rcbos in and change rcd to 100a 100ma type s.

 

[jaydee81]

as all circuit need rcd protecting just change the cu for a dual rcd no advantage of using 100ma time delayed rcd as main switch even if you did fit rcbos if all circuit have 30ma (whats it protecting?)

 

[ackbarthestar]

8 circuits

Wylex

Could i put a 100a 100ma type s in an enclosure before the board then leave the rest?

Not advisable. You will have lost all the additional protection to your sockets, buried cables, outside circuits, bathroom circuits.

Better to leave it as it is since it has both fault protection and additional protection.

However, if you choose to upgrade then you will need a 100mA 'S' upfront to give earth fault protection and then either use a parallel split load board or individual RCBOs.

That of course may throw up other faults, but that's something else.

Now, It is pointless to add a 100mA 'S' RCD upfront if you are going to leave the 30mA RCD.

 

[jaydee81]

if u used dual rcd consumer unit with 30ma rcd protection to all circuits then 100ma s rcd is pointless 30ma rcds and rcbos will give you earth fault and additional protection your 100ma s rcd is protecting nothing as 30ma would always trip first

 

[MDJ]

just have a double pole switch for the board isolation and every circuit protected by individual RCBOs, providing the money is there.

 

[9regnac]

So mdj u would say just buy a wylex rcbo loaded board and put that in with a 100 dp main seitch and that would do the trick. Then no need for a 100ma type s really appreciate this guys.

 

[MDJ]

Buy a BG board with a 100 amp double pole main switch and have all individual RCBOs they are £91 at City electrical with all the RCBOs included, ridiculous price really, and perfect for a domestic TT system.

 

[jaydee81]

no need at all

 

[Engineer54]

if u used dual rcd consumer unit with 30ma rcd protection to all circuits then 100ma s rcd is pointless 30ma rcds and rcbos will give you earth fault and additional protection your 100ma s rcd is protecting nothing as 30ma would always trip first

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....

 

[MDJ]

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....

you are quite right actually, however individual RCBOs on each circuit with a double pole switch to isolate the board is fine in a domestic situation, of course if the DB did have the 100ma S type as the main switch and then all individual RCBOs then it would be even better of course, lets hope the customer will pay for it, one didn't even want to pay for a DB change I noticed in an earlier thread even with a wooden backed old wylex board, the problem with the set up mentioned is price, however on this occassion you are right.