Ring circuit cable length

[Richard Burns]

A 100mA RCD might trip before a 30mA RCD depending on the type of fault and the characteristics of the RCDs.
To ensure discrimination the 100mA RCD would need to be time delayed i.e type S.
If I were installing I might tend to go for an upfront time delayed 100mA RCD and then a split load Dual RCD board, though obviously RCBOs would be better if you can get them in double pole versions.

If you had good Ufer earthing and the resistance to earth was then low enough to trip your MCBs then you would be OK with just RCBOs.

 

[Deleted member 26818]

You can use single pole RCDs with TT.
There just has to be Double Pole isolation somewhere.
The 100mA should be an S type to be used with 30mA RCDs.

 

[Yr ys]

How low would the resistance to earth have to be to trip a neutral to earth fault? My home has a radial foundation 50cm thick concrete and rebar. I'd have to break the concrete to access the rebar and then connect a 16 mm2 earth cable about 2 meters from my consumer unit. Then reseal the concrete to prevent corrosion.

My power is coming from a 10000kva inverter with a 60 meter long 16 mm2x2 10mm2 earth cable just for your info.

 

[Deleted member 26818]

10 million VA?

 

[Yr ys]

Correction, 10000VA

 

[Yr ys]

How would I go about bonding copper earthing wire to the rebar, isn't this going to corrode (more) quickly due to the potential between different metals?

 

[ChipFanDave]

Can you use Wylex double pole RCBOs to avoid an upfront RCD ?

 

[Yr ys]

We don't have wylex here. I only found hager single pole rcbos. I put a 100 ma rcd infront of the rcbos. So I'm thinking the 30 ma rcbos should trip before the 100 ma rcd.

 

[ChipFanDave]

We don't have wylex here. I only found hager single pole rcbos. I put a 100 ma rcd infront of the rcbos. So I'm thinking the 30 ma rcbos should trip before the 100 ma rcd.

TLC sell them online if you need them in the future.