TT supply sytem RCDs

[JGH1948]

When a property is supplied by a TT system with its own earth electrode should the 100mA RCD cover all circuits including lighting or just the socket rings?

 

[plugwash]

you need to have some form of RCD protection on everything. Some people put everything on one 30ma RCDs but this is generally considered unacceptable because it means that a fault on a socket circuit can take out your lights, smoke alarms etc.

the most commonly reccomended setup i've seen is a time delay 100ma RCD as mainswitch feeding a 30ma RCD for higher risk circuits (sockets etc). The trouble with this setup is that time delay RCDs are expensive. Another possibility is to have a main switch feeding two seperate RCDs.

 

[JGH1948]

They certainly are a little expensive - around £69. Many thanks for the advice.

 

[Spark123]

The other acceptable method is to use a split board which has 2 RCDs, a 100mA for lighting etc, 30mA for sockets etc. Both RCDs are covered by a main switch, I think Hager make them.

What are you looking at for £69? Seems pretty cheap for a CU with 100mA TD RCD and 30mA RCD?

 

[plugwash]

I assumed he meant £69 just for the time delay RCD on it's own.

 

[JGH1948]

Yes - it was just a standalone RCD which is fitted between the meter/cuttoff switch and the CU (from www.tlc-direct.co.uk) plus you have to buy a box for it.

For a pre-assembled, 6+6 Split Load Consumer Unit with 10 x Type B 6kA SP MCBs. BS EN 60439-3: 1991. 100A DP isolator, 63A 30mA RCD; 1 x 40A, 4 x 32A, 2 x 16A, 3 x 6A, 2 x blanks for £58 go to Pre-assembled, 6+6 Split Load Consumer Unit with 10 x Type B 6kA SP MCBs. BS EN 60439-3: 1991. 100A DP isolator, 63A 30mA RCD; 1 x 40A, 4 x 32A, 2 x 16A, 3 x 6A, 2 x blanks see www.screwfix.com/app/sfd/cat/pro.jsp?cId=A331827&ts=07721&id=82204.