just a quick one

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spin london, can you back this up with regs please? i cant find this anywhere and as far as i can tell from readin up a 100ma td rcd is no longer required as was under 16th edition not 17th?

i am going to be replacing the consumer unit i think and use it for major and minor works for NICEIC assessment so it may require the td RCD

 
ok for arguments sake, im going to get the customer to have rcbo.s fitted to all circuits therefore there have 30ma protection. i have all books in front of me and cant find a reg that says it must have 100ma Rcd aswell

 
My regs are in the van,,,,

but don't you need to have DP RCD protection at some point for all circuits on a TT installation?

This gives you a couple of options

a twin RCD CU or

a 100mA TD RD main switch with SP 30mA RCBOs

 
My regs are in the van,,,,but don't you need to have DP RCD protection at some point for all circuits on a TT installation?

This gives you a couple of options

a twin RCD CU or

a 100mA TD RD main switch with SP 30mA RCBOs
i cant find anything in the regs, just states that all circuits require 30ma protection.

the only mention of 100a 100ma Rcd is for "cables in walls or partitions have an earthed metal covering or installed in earthed conduit". this property is not the above.

 
I think it's something along the lines of TT installations requiring DP fault protection.

Imagine you have a faulty circuit and the SP RCBO has operated; now that will only disconnect the Line conductor, the Neutral will still be connected and could very easily be at a different potential to the earth conductor due to the fact that they are not physically connected together.

 
It's got nothing to do with DP fault isolation as DP RCBO's are readily available.

 
On domestic TT installations generally all circuits will require 30mA RCD protection so a main switch consumer unit with RCBO's for 3 circuits will be the best option. Only certain TT installations will require double pole RCD protection but as this is domestic this is not required. As long as main switch is double pole that is the only double pole isolation you will need.

 
thanks batty. i have similar advice from yourself and lurch, and this is also my understanding of the situation. if i get picked up on it hopefully NICEIC GUY, will go easy on me

 
spin london, can you back this up with regs please? i cant find this anywhere and as far as i can tell from readin up a 100ma td rcd is no longer required as was under 16th edition not 17th?i am going to be replacing the consumer unit i think and use it for major and minor works for NICEIC assessment so it may require the td RCD
Not certain what you mean?

The requirements for discrimination between RCD devices in series has not fundementally changed between the 16th and the 17th. There is some change to the wording, such as changing from indirect contact to fault protection. Apart from that both 531-02-09 and 531.2.9 are the same.

 
On domestic TT installations generally all circuits will require 30mA RCD protection so a main switch consumer unit with RCBO's for 3 circuits will be the best option. Only certain TT installations will require double pole RCD protection but as this is domestic this is not required. As long as main switch is double pole that is the only double pole isolation you will need.
Fair enough, as I said RIV...

Whenever I do a TT board change I tend to use a twin RCD CU, 5 + 5 for larger installs and 3 + 3 for smaller installations...

 
thanks batty. i have similar advice from yourself and lurch, and this is also my understanding of the situation. if i get picked up on it hopefully NICEIC GUY, will go easy on me
Not sure what NICEIC rules are but on an assessment a few years back I used a Contactum consumer unit with RCBO's on TT system and my assesor said that was fine as the Main switch provides the DP isolation.

 
Not sure what NICEIC rules are but on an assessment a few years back I used a Contactum consumer unit with RCBO's on TT system and my assesor said that was fine as the Main switch provides the DP isolation.
once again a big thanks to all who has helped on this matter, appreciate the help

 
Just drifting back in the thread a bit, i believe the CU should be of "all insulated construction", and that includes terminal and bus bars etc.

 
ITS UP TO YOU OR WHOEVER WANTS TO INSTALL THIS,

(sorry about the caps!)

TT requires DP fault protection,

SP RCBOs do NOT provide this,

the easy way is to have a front end 100mA RCD, td if you wish.

otherwise you must fit DP RCBOs,.

you can freely ignore this advice at your own peril and have someones insurance company widening your ass sometime in the future,

no skin off my nose.

 
ITS UP TO YOU OR WHOEVER WANTS TO INSTALL THIS,(sorry about the caps!)

TT requires DP fault protection,

SP RCBOs do NOT provide this,

the easy way is to have a front end 100mA RCD, td if you wish.

otherwise you must fit DP RCBOs,.

you can freely ignore this advice at your own peril and have someones insurance company widening your ass sometime in the future,

no skin off my nose.
steptoe, i appreciate your comments, however i do not feel this can be backed up by regs? i may be wrong, however i have read through regs over and over and cant find where it says requires dp fault protection? all books show a normal 100amp dp pole main switch, and then rcbo.s on each circuit which are sp and not dp?

im not doubting you , am however just trying to get the facts straight on what is required.

 
DP RCD'S are required on certain special installations IE caravan parks and jetty's they are made for the job. But as said I am unaware of a reg saying DP RCD protection is required on all TT installations. The regs do say that you do need to isolated all poles and phases and neutral on three phase though maybe this is were the confusion comes in.

 
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