17th edition board TT system high integrity board what size RCD front End?

[electro]

What size Rcd should you use as main switch for a high integrity board on a 17th installation. 16th was a 100mA type S, could you use a 300mA RCD without the delay?
I understand if you use a split 17th edition board you don't need a front end RCD...

[Shakey]

Originally Posted by electro

What size Rcd should you use as main switch for a high integrity board on a 17th installation. 16th was a 100mA type S, could you use a 300mA RCD without the delay?
I understand if you use a split 17th edition board you don't need a front end RCD...

well if you installing to the 17th, assuming buried cables, socket outlets, bathrooms etc, then use use twin or triple 30mA RCD's, you wont need a front end RCD

the 30mA will provide additional protection and protection against fire

interesting how theres no mention of it in the 17th, cant wait for the OSG to come out!

[electro]

Hi shakey
I'm using is a high integrity board which allows three circuits to be none RCD which leads me to think it needs a RCD main switch. The high integrity board I'm using is 3 none RCD and 5+5 RCD.


regards

[Shakey]

what is a 'high integrity' board?

anyway, just treat every circuit as a normal circuit, regardless of it being a TT

if a circuit requires 30ma, because its got buried cables, socket outlets, or bathroom, then it needs 30mA, TT has nothing to do with it

so the non rcd protected ways can either be for surface mount cables (or protected cables), and if they still meet their disconnection times then you are ok, if not, just RCBO's

you should do this for your smokes anyway, unless you are gonna surface mount/ or put you lights and smokes on a seprate RCD to the sockets

[electro]

we have some medical equipment in bedrooms that we dont want on rcds. i think that part of the system should be protected against fire on a TT system?

[Shakey]

Originally Posted by electro

we have some medical equipment in bedrooms that we dont want on rcds. i think that part of the system should be protected against fire on a TT system?

yes it shoulf be protected against fire, which under the 16th was a 100mA RCd (s type if main switch), under the 17th its up to 300mA, but either way, it means an RCD, so the stuff in the bedrooms WOULD be an RCD

do the circtuits meet their disconnection times - I have worked on TT's with very low Ze (only a couple of ohms), so things like the lighting circuits still comply
, but if the Zs is too high (because of the earth spike) then you have no choice but to RCD it

[electro]

Nice one shakey thanks for your info. just one last question does the 300mA have to be a delay type to meet the discrimination from the 30mA downstream RCDs

[Shakey]

it would have to be a time delay if used as the main switch