Question Tt system

[m top]

hi all wondered what your views on using split load board on Tt,explained to customer best option would be rcbos to cover 8 cuircuits only.
gave her price oh that's to much !!!
as long as ze below 200 ohms all good
reg state all final circuits to be protected by rcd 30ma they will be.
reg 411.5.3 the disconnection time shall be that required by 411.3.2.2 or 411.3.2.4
2 secondDisconnection times will be met by above arrangement
Have I missed something here thanks.

 

[Engineer54]

hi all wondered what your views on using split load board on Tt,explained to customer best option would be rcbos to cover 8 cuircuits only.
gave her price oh that's to much !!!
as long as ze below 200 ohms all good
reg state all final circuits to be protected by rcd 30ma they will be.
reg 411.5.3 the disconnection time shall be that required by 411.3.2.2 or 411.3.2.4
2 secondDisconnection times will be met by above arrangement
Have I missed something here thanks.

What do you mean a value of 199.5 ohms is all GOOD??

An all RCBO CU is always best, be it for TT or TN installations. In reality TT systems are best protected by DP OCPD's, but you'll rarely if ever see it!! lol!!


May get a better response if you quote a price based on these material prices....


Consumer Units, Fuse Boards, Fuse Box, MCB, RCD from Wyeverne Electrical

 

[m top]

Sorry less than 100ohms just asking question a split load con complies with the disconnection times the regs state do they not and the 30ma rcds will trip quicker than a 100ma time delayed set up won't they so dis times are met.

 

[Engineer54]

100 ohm's isn't much better than 200 ohms now is it??

You didn't mention anything about 100mA RCD in your OP. It's not a question of which trips faster it's a question of the maximum mA value required to operate for the protection of persons, that being 30mA. It would however be prudent to install an up front 100mA S type RCD as extra protection to cover a non operating U/S 30mA RCD device, but it won't comply to trip times for obvious reasons....

 

[m top]

100 ohm's isn't much better than 200 ohms now is it??

You didn't mention anything about 100mA RCD in your OP. It's not a question of which trips faster it's a question of the maximum mA value required to operate for the protection of persons, that being 30mA. It would however be prudent to install an up front 100mA S type RCD as extra protection to cover a non operating U/S 30mA RCD device, but it won't comply to trip times for obvious reasons....

thanks for your reply please don't think I am not taking notice of what your saying maybe I am thinking to much ,I didn't mean install a 100 ma rcd before main switch in enclosure I was ref to 16th edition I am going to ask Elecsa about this one I will post up there reply I just can't get on my head why it shouldn't be permissible to use a split load board for this customer to keep cost down .

 

[Knobhead]

I wouldn’t have RCBO’s on a TT system or any system unless they were DP or SP+N.
SP don’t break the neutral leaving a possible N→E fault un-cleared. It seems crazy to me to have a protective device that only clears half a fault.

 

[alanl]

As above, use a plastic cased, split RCD board for a TT system.

Think about it for a while.
What if there is a neutral fault? The neutral will always be live with a RCBO, even when it has tripped.

 

[m top]

As above, use a plastic cased, split RCD board for a TT system.

Think about it for a while.
What if there is a neutral fault? The neutral will always be live with a RCBO, even when it has tripped.

Spoke to Elecsa nothing wrong with split load 30ma rcd board on tt reading page 29 30 page confirms this as long as cu has class 2 construction 100 ma rcd can be omitted.

 

[D Skelton]

Oh dear, oh dear...

:mad2:

 

[Pete999]

jimminy cricket dear oh dear again

 

[m top]

Ok i am missing something about the 100ma rcd ,is a split load insulated rcd 30ma board any different to havin rcbo on a Tt system,is double pole protection not provided by the main switch ,I understand the 100ma rcd is to protect against fire incoming tails? I was just asking for opinions or am I misunderstanding the regs.

 

[yellowvanman]

Main switch does not provide double pole protection - only double pole isolation.

When working on TT safe isolation is always DP, if you've got SP RCBOs, then to achieve DP isolation you have to turn off the main switch and everything if off.

Alternatively if you've got a split board with 2 x DP RCDs, then to work on 1 circuit you only have to turn off half the circuits, less incovenience.

 

[Jay Sparks]

The upfront 100mA time delayed rcd is for "Aditional" protection, just in case the 30mA rcd's fail.

 

[GLENNSPARK]

The upfront 100mA time delayed rcd is for "Aditional" protection, just in case the 30mA rcd's fail.

`additional`?..

come on Jamie...TT...so its fault protection..isn`t it but as eng says a 100mA s type doesn`t comply...its so if used as a mainswitch you get the discrimination...

 

[Jay Sparks]

`additional`?..

come on Jamie...TT...so its fault protection..isn`t it but as eng says a 100mA s type doesn`t comply...its so if used as a mainswitch you get the discrimination...

You are right Glenn, its bin a long day and two bottles of red wine but theres no excuse for stupidity.lol