Multi RCD testing

[170OL]

I’m getting myself confused a bit.
I have a feed that goes from the house CU (RCBO protected) out to the Workshop CU, where there is another RCD. When I come to test it I’ve done all the tests on the cable from the house CU to the workshop including testing the RCBO. BUT to test the circuits in the workshop should I temporally replace the RCBO in the house CU with an MCB and then carry on as normal tests in the workshop? my reasoning is then I'm just testing the Workshop RCD with out the risk of the RCBO tripping in the house
Is this right?!
Bit confusing but I hope people understand it!!

 

[Octopus]

What is the cable feeding the workshop?

 

[Darkwood]

What is the workshop supply wired in
What is the nature of the supply
What is the mA rating of the supply rcbo

Their shouldn't be 2 rcd's in series if they are rated the same... you wont achieve discrimination ....more info pls

 

[Octopus]

And who installed this "solution"?

 

[170OL]

The cables have been in for several years by the looks of them, but all tested OK. There is a 20A 30mA RCBO in the house. It then goes along 6mm SWA cable about 30m to the workshop. In the workshop is a lighting circuit 6A, and a ring socket circuit, on this second RCD. Only standard power tool use so not a massive amount of power required. Would the best be to remove the RCD in the workshop as its not really needed (as two in series as darkwood mensioned is pointless)

 

[Octopus]

The cables have been in for several years by the looks of them, but all tested OK. There is a 20A 30mA RCBO in the house. It then goes along 6mm SWA cable about 30m to the workshop. In the workshop is a lighting circuit 6A, and a ring socket circuit, on this second RCD. Only standard power tool use so not a massive amount of power required. Would the best be to remove the RCD in the workshop as its not really needed (as two in series as darkwood mensioned is pointless)

Only if you want to run back to the house each time the workshop trips the rcd.

Are you a sparky?

 

[telectrix]

or replace the one in the hous with an MCB, as long as none of the cable going to the workshop requires RCD.

 

[Sintra]

Are you a spark? If you are you should know the easy solution to this.

 

[170OL]

Still learning. thanks for the replies. Walking back to the house it OK. The whole thing has to be RCD protected. In all the time using it the RCD hasnt tripped (apart from during testing) Also have emergency lighting, so not plunged into total darkness

 

[tony mc]

Bit confused has a question been asked and answered?

 

[davethsparky]

Why does the whole thing need the RCD protection?

The presence of emergency lighting is irrelevant to the question, there is no regulation allowing the use of emergency lighting as an alternative to proper installation design!

 

[Darkwood]

To the OP the supply is swa its serves its own mechanical protection if terminated correctly just swap the front end for an MCB and have the rcd protected DB doing its job its designed for without risk of rcd discrimination issues .... cost probably less than a tenner and you get a free rcbo to you stock list ...

Your profile states Technician but not from which area- as well as part P qualified IMHO the part P should mean you are at a level to know this.... what scares me is your technician status because if that's Electrical Technician who is advanced in electrical knowledge and able to design complex large commercial and industrial projects yet you have just asked the most basic of domestic questions without realizing the fact that the set up in i contravention of BS7671 the very issue that you have got confused .... so entertain me and correct my assumptions ..... if you enter an Electrical Forum and state your a technician this hold a reservation of a member who should be spending his time on the forum giving advice not asking for advice a year 1 student could be expected to.

 

[170OL]

Hi Darkwood, just checked "my profile" which is wrong, I correct it after this. My job title is a technician but not electrical as in domestic stuff but of design of electronics and circuit boards, the sort that go in computers etc. I am currently training as a domestic electrician, I was using the power supply to my workshop in the garden as an example to answer some of my college questions, when I saw the problem. Thanks for any advice you can give on future questions

 

[Darkwood]

Hi Darkwood, just checked "my profile" which is wrong, I correct it after this. My job title is a technician but not electrical as in domestic stuff but of design of electronics and circuit boards, the sort that go in computers etc. I am currently training as a domestic electrician, I was using the power supply to my workshop in the garden as an example to answer some of my college questions, when I saw the problem. Thanks for any advice you can give on future questions

If you are still training then in that case the question may be justified as also you have explained the technician part....

Apologies for the assumption but its the impression your profile gave.
My comment still holds though if the swa is correctly glanded then the supply cable (sub-main) itself dosn't need rcd protection just swap the rcbo for an appropriately rated mcb.

 

[170OL]

Thanks will do.