Need to replace mk 100ma rcd (6160) with 30ma one

[Eddiesparks]

Sorry, in a rush...,Will any mk 30ma one do? Thanks loads guys

 

[Engineer54]

Afraid people just don't THINK, before they start altering things that were based on much earlier regulations. To do this job correctly, the CU needs to be changed out for a 17th dual RCD CU, or remove the existing 100mA RCD and protect the circuits via RCBO's. But you can bet your bottom dollar it won't be!! lol!!

 

[tony mc]

You say 16th edition CU. Can you clarify that the CU has a main switch and a 100mA RCD protecting the FRC etc and you are replacing that unit to a 30 mA unit.

 

[Eddiesparks]

The way i look at it i need MY kitchen radial to comply with regs so an existing 16th ed. board with 100a main switch and non sockets not rcd protected then all sockets protected. Existing broken ring was on rcd side. Rewired a 4mm radial then when i tested i got through all other tests and did rcd test which was when i noticed the 100ma rcd. Yes to do the job completely a board change would be ideal but you couldnt argue my method isnt by the book! ?!?!

Could also be that there could be faults on rcd side that are not being 'noticed' by 100ma rcd so it could be opening a bit of a can of worms! Fairly unlikely, not a hugely old install

 

[tony mc]

Its Sunday and I don't understand your reply. Do you have a 100 Amp main switch with a 100 mA RCD in place of a 30 mA unit on the split board?

 

[Engineer54]

A 16th ed CU did NOT employ a 100Ma RCD on split configurations, it was always a 30mA RCD. Only as i remember, on the earlier 16th's or was it 15th, that used an upfront 100mA RCD in CU's that covered all circuits....

 

[tony mc]

I think but I am often wrong that the split CU here has a main switch and a 100mA RCD in place of the 30mA unit but the reply does not clarify that!

 

[Eddiesparks]

Thats it tony you're correct

 

[Engineer54]

Thats it tony you're correct

If that's the case, as i stated before the 16th ed split CU's had the protected side fitted with a 30mA RCD as standard
...

 

[Eddiesparks]

Thats what i was getting at. It had layout of 16th board but some (builder) person had put a 100ma rcd in there. Kitchen was a broken 2.5mm ring on 32a with a lot of load on it. In the end it stopped working altogether hence the rewire.

 

[Eddiesparks]

If 30 as standard then why had it been changed?

 

[Engineer54]

You'll probably find out why when you install the 30mA RCD!! lol!! Have you done any testing to find out if there is any problems waiting for you??

 

[Eddiesparks]

Haha yes i probably will haha! Had spent long day rewiring tricky kitchen, it was right at the end of the day!! I will do some IR tests on the other protected circuits before sticking in the 30ma one!! I worked out once with ohms law (could've made a cock-up!!)that a L-E fault of 0.007M ohms would trip a 30ma rcd but that's assuming 230v whereas the pot. diff between N-E is v small so working it out is harder. I suppose under 2M ohms (as per bs7671) is a safe bet.

 

[not clever]

The way i look at it i need MY kitchen radial to comply with regs

So put in a stand alone rcd on that circuit?

 

[Eddiesparks]

Put 30ma one in no probs. thanks for input everyone