100/30ma rcd question for tt

[gary38]

hi.
i am replacing an old earth trip on a tt insulation.
i should had got a 100ma rcd, but by mistake i have a 30ma.
if i fit the 30ma rcd and it causes no problems is it ok to leave it or MUST it be a 100ma.

 

[dingbat]

hi... by mistake i have a 30ma.
if i fit the 30ma rcd and it causes no problems is it ok to leave it or MUST it be a 100ma.

If there really are no problems then there is no regulation that says you cannot have a 30mA RCD as your main switch, but... All your lights will go out if you plug in a faulty appliance that causes the rcd to trip, or if you get a socket wet.. or any other accessory for that matter. 30mA RCD's are for supplementary protection from electric shock, but are prone to nuisance tripping, which is why most modern installations have a split load consumer unit. It's up to you, but I'd get a 100mA RCD for your main switch.

 

[plugwash]

a 100ma rcd on its own is *NOT* ok on any TT system that includes sockets

while there are no wiring regs that prevent useing a 30ma rcd for the whole install it is considred very bad practice and may fall foul of other regs (stuff about continuity of supply to fire alwarms)

best practice with a TT is to use a time delay rcd (usually 100ma) for everything and a normal 30ma rcd to cover *ALL* sockets and any other high risk cuircuits

 

[dingbat]

Sorry, you're quite right, Plug. ALL sockets on TT install must be 30mA RCD protected. Having mentioned a split load unit I was (wrongly) continuing down that route. Thanks for the correction

 

[gary38]

ok,
will get a 100ma rcd and make that the main incomer and then i can still use the 30ma to feed a couple of mcbs with the rings on.

 

[plugwash]

just make sure that the 100ma rcd is a type S (time delayed)

this is to aviod a fault tripping both rcds at once