TT system RCBO conflict

[adyver]

headbang I have just extended my house and my old memera 2000 box has insufficient ways for the new circuits. Not only that its a TT system with a 30ma RCD as main switch and protection on a solid board. (Fitted by the local authority before I bought the house). Consequently the whole system goes down if I get a nuisance trip. I intend to replace the CSU with an MK sentry 19 way box. It has a 100amp main switch and a I intend to fit an 80amp double pole RCD. I wish to protect a couple of circuits with RCBO's, if I get a nuisance trip on an RCBO is it also likely to trip the RCD, or can I put the RCBO's on the unprotected side of the RCD on a TT system. Guiness Drink

 

[green-hornet]

Nuisance tripping is always a problem when there is no discrimination, all 30mA will trip for instance.

You could just place a 100amp main switch and wire the cu as you would under the 17th.

Providing all circuits are rcd protected this is now acceptable.

RCBO's are viable but only if cost is acceptable.

 

[Evans Electric]

All the circuits need RCD protection on a TT . Personally I use the double split boards.

(a) Because RCBOs fill all the space up and irritate me. (B) My Loop impedance tester trips RCBOs, which irritates me . © The 17th edit. iritates me. (d) A lot of RCBOs cost a lot of money which iritates me.

 

[green-hornet]

ROTFWL

Guiness DrinkGuiness Drink

Same here.

However on smaller properties I fit RCBO's because I can control the size of the cu better this way.

 

[adyver]

Nuisance tripping is always a problem when there is no discrimination, all 30mA will trip for instance.You could just place a 100amp main switch and wire the cu as you would under the 17th.

Providing all circuits are rcd protected this is now acceptable.

RCBO's are viable but only if cost is acceptable.

Thank you for your reply.

As RCBO's only disconnect the supply are they OK to use on a TT system in replacement of an RCD which disconnects live and neutral.

 

[Evans Electric]

Are we not supposed to break both poles on a TT ? I have been told that RCBOs are single pole , hence my Kewtech 42 trips 'em out.

 

[Andy™]

TT should have DP protection. dual split is the best way to go. and i have no idea why people call it 'nuisance tripping' - its tripping because there is a fault, and it tripping could be the RCD saving your life

 

[adyver]

TT should have DP protection. dual split is the best way to go. and i have no idea why people call it 'nuisance tripping' - its tripping because there is a fault, and it tripping could be the RCD saving your life

I agree, the RCD is doing its job, but its still a B!!!!! nuisance when you cannot find the offending appliance or circuit as it happens so infrequently and all the usual fault finding methods return normal results.

 

[green-hornet]

TT should have DP protection. dual split is the best way to go. and i have no idea why people call it 'nuisance tripping' - its tripping because there is a fault, and it tripping could be the RCD saving your life

This is where people get confused.

Nuicance tripping is not derived from any fault on the circuit that is disconnected but a result of a fault on another circuit that has a joint connection to a RCD.

Which is why under the regulations no 16th edition board, or even 17th edition boards are technically within the regulations.

No fault on one circuit should be able to take out another!

Like the compare the meercat advert SIMPLES.

 

[batty]

I thought nuisance tripping is if you have something like a cooker or immersion going through an RCD and because the insulation is down a bit on the elements and with the other circuits connected it will intermitently trip out. Thats a good reason for using Rcbo's on these circuits.

Batty

 

[Andy™]

This is where people get confused.Nuicance tripping is not derived from any fault on the circuit that is disconnected but a result of a fault on another circuit that has a joint connection to a RCD.

Which is why under the regulations no 16th edition board, or even 17th edition boards are technically within the regulations.

No fault on one circuit should be able to take out another!

Like the compare the meercat advert SIMPLES.

but like everything else, its how much they want to spend