100mA / minor works

[monkeyhanger]

A domestic TNS installation has a 100mA RCD main switch and 'Type 2' MCBs.
I Need to move a kitchen socket away from a hob, install an additional one, install a fused spur unit for an extractor hood, and move two light switches to the other side of a room.

The customer is a right pain and it needs doing as CHEAPLY as possible because my kitchen fitter mate can't get any money out of her for electrical work as she was lead to believe (by the person who passed the job on to him) that it was included in the estimate
.
What is the minimum I can do in this situation?
I was thinking of mounting 2x stand alone 30mA RCDs to the side of the consumer unit and feeding the circuits from these (RCDs fed from old MCBs in board)
May have trouble testing the new RCDs though due to the 100mA RCD.

Discrimination wouldn't be clearly provided but they are existing circuits.

Would it be at all possible to just do the work and leave the existing protection arrangements as they are and note that it was recommended to upgrade CU on the certificate but that the installation is no worse off safety-wise?

Hmm

 

[Deleted member 19807]

your work needs to comply with 17th so 30ma is a must, however i would be tempted to change the 100ma for a 30ma and leave it at that, if it neusance trips just tell her that the designer said to do it that way to keep the cost down.

 

[Jimmy Boy]

The problem here seems to be your being faced with making decisions based on the fact a mate has got himself in bother by virtue of having his pants pulled down by someone else, rather than making the decision how to do it based on what is best for you and the customer, when they get nuisance trips every time a bulb pops your be called the cowboy, in fact your doing everyone a favour and end up getting shafted, I'd tell you mate it's £x to do right and put his hand in his pocket if you want to do the labour for free that's noble, but I would prefer to stick a small board next to the old with a MS and two RCBO's fed from supply that way it's a proper job and testable, I do however have empathy with being put on the spot by 'mates' ..it's awkward.

ATB Steve

 

[telectrix]

agree with hifly. as cost is a limiting factor, change the 100mA for 30mA. and hope you don't find any leakage

 

[Deleted member 9648]

I dont see why testing the 30ma rcd's would be a problem....on a 1x test the 30ma's should trip in the required time without the 100ma tripping.On a 5x test no doubt the 100ma will trip as well, but in the end as long as the meter shows <40ms all's well.....that said I would change the 100ma to a 30 as well,gotta be the cheapest option if thats what they want.

 

[Jimmy Boy]

But if both the 100mA and the 30mA trip at the same time how do you enter this ? You need to demonstrate the 30mA has tripped <40ms for x5 how do you prove this or record it ? It's messy.

ATB Steve

 

[Deleted member 9648]

Cant see it,,,as long as the circuit has tripped @ 150ma within 40ms it matters not which rcd did the deed....just enter the actual recorded time,that would be my take on it.

 

[Jimmy Boy]

I know where your coming from but how do you demonstrate that either/or one of the RCD's tripping times meet the regs ? your placing reliance on one of them to do the deed, not knowing if on an individual basis if they work in accordance with the regs ?

 

[Deleted member 9648]

I know where you are coming from as well!!....but as far as I'm concerned if an RCD test is carried out on the circuit and it disconnects within 200ms@30ma and 40ms@ 150ma the regs are satisfied.....I accept your point that it may not be technically correct but it would be good enough for me.

 

[Jimmy Boy]

I'm sure you OK with that but where do we enter the disconnection times ? Either on a Minor or a EIC ?

Where do we enter the info ? Where ? I am not being picky I just want to know where you suggest we enter the data ?

ATB Steve

 

[Deleted member 9648]

I'd enter it on the RCD trip times for the circuit....where else?...On a minor there is a box for rcd trip times which is for one circuit...and on an EIC the rcd trip times are entered in the schedule of test results for each circuit.

 

[malcolmsanford]

If your really concerned about tripping that 100mA on a x5 test you can always for the 30ma test bypass the main 100mA RCD.

That way you can prove your disconnection times for the new 30mA. After you completed the tests reconnect the 100mA and re-do the 30mA tests and see if the 100mA will in fact trip on the x5 test.

It's not ideal but in real life is anything that straight forward.

 

[Deleted member 9648]

Funnily enough had just this scenario today on a rush job wiring up site huts for a civil engineering co at a water board site.We ran a distribution circuit from the intake (TNCS) to an insulated DB in one of the site units and split the earth to a TT there....from there we ran out SWA's to the various site units,the SWA's we protected with a 100ma RCD main switch in the DB,and each site unit had it's own DB with a 30ma RCD main switch.
Testing the 100 ma rcd in the main DB it tripped @24ms.....testing each 30ma RCD in each of the site units at both 1x and 5x they all tripped within the required times and none of the tests @5x (150ma) tripped the 100ma main switch...the 30ma units were too quick and tripped before the 100ma unit reacted.