Help with discrimination

[mainebankelec]

Just been at Church hall with 3p TT supply, My query is we carried out a PIR on it,it has no 100ma rcd protection of church metal consumer units mentioned on cert but we are only certifiying church hall.

Church hall has 100ma 4 pole rcd up front onto metal switchfuse 3036 60A protection on to 16mm4c swa with separate earth to metal consumer unit fitted with an other 100ma rcd in it and rcbos on some circuits.

My problem is on testing the 100ma in the church is quicker than the one in church hall therefore need a 100ma 4 pole time delay rcd but cannot seem to find any stockists of these. Would it be acceptable to fit a 300ma upfront to protect complete installation even this this mainly for fire protection?

Thanks

 

[Deleted member 26818]

What's the RA of the earth rod?

 

[IQ Electrical]

What is your Ra value?

 

[mainebankelec]

Ra - 57.4 ohms

 

[Deleted member 26818]

Should be fine.

 

[IQ Electrical]

Should be fine.

I'll second that.

 

[mainebankelec]

At present there is no main isolation for the complete building also so to overcome all these problems fit 300ma upfront of everything then to escos to split of for single phase church metalclad consumer units?

 

[mainebankelec]

Sure there would be no point in making it time delayed either?

Many thanks

 

[IQ Electrical]

You should make it time delayed, that's the ONLY way of achieving discrimination with RCD's.

 

[mainebankelec]

That will do thank you very much for your help cheers

 

[Deleted member 26818]

You should make it time delayed, that's the ONLY way of achieving discrimination with RCD's.

I'll second that.

 

[Engineer54]

There's more than a decent chance that any one of those 100mA RCDs will also take out a non S type 300mA RCD. The only real way of achieving discrimination between RCDs is via A time delay on the upstream RCD!!!

 

[IQ Electrical]

There's more than a decent chance that any one of those 100mA RCDs will also take out a non S type 300mA RCD. The only real way of achieving discrimination between RCDs is via A time delay on the upstream RCD!!!

Like in post 9 lol

 

[Engineer54]

Like in post 9 lol

I was called away while replying to the post, so by the time i got back and posted .... there was a few posts confirming the same thing!! lol!!!

 

[MarkieSparkie]

All enclosures of RCDs or consumer units incorporating RCDs in TT installations should have an all-insulated or class 2 construction, or additional precautions, as recommended by the manufacturer, need to be taken to prevent faults to earth on the supply side of the upstream 100mA, S type, RCD.