Adding non protected MCB to a duel RCD board

[Traineeboy]

Is it possible to add a non protected MCB to a duel RCD Board. A non protected circuit would serve a mini garage board that has its own RCD.

The chap i was with today was quoting to put a garage feed up to the top of the garage. He said that as they have a Duel RCD board it can’t be done and they would need to change the board. Really ? 

Would it not be acceptable to have a MCB next to the main switch ( linked with a piece of busbar) and the incoming line obviously going into the top of the MCB, but the questions is where would incoming neutral go as there is only 2 N bars not 3 as it’s only a duel RCD board. Can it be done properly or would the board have to be changed ?

Thoughts 

 

[Fleeting]

Fit a garage board which doesn't have an rcd.

 

[Andy™]

depends on the board. some have an additional neutral bar on the non-RCD and a busbar to allow this. most dont. those that do are usually advertised as 'high integrity'

but if you only have 2 neutral bars then no good

either change the board or split the tails

 

[Traineeboy]

Fit a garage board which doesn't have an rcd.

If you have a garage board with a main switch not an RCD but then if it is supplied from a MCB from the house CU that Is on a RCD. Would this not be poor selectivity/discrimination as if the garage had a fault it would knock out half the house ? That’s what the chap I was with said or is he being over the top ? 

 

[Andy™]

If you have a garage board with a main switch not an RCD but then if it is supplied from a MCB from the house CU that Is on a RCD. Would this not be poor selectivity/discrimination as if the garage had a fault it would knock out half the house ? That’s what the chap I was with said or is he being over the top ? 

its poor design doing it that way. ideally everything should have its own RCD as you are wanting to do. ignore the cowboys

 

[Fleeting]

This is very true but you could argue this for any circuit. Creating a high integrity board from a dual rcd board would require alterations above the manufacturers original intention and as you say requires an additional neutral bar, the circuit description bar on the front cover would also become out of kilter. Sometimes you can only do what you can unless you completely replace the board. If they only require small power and lighting in the garage you may as well put in a radial with a spur for the lighting. 

 

[binky]

Is it possible to add a non protected MCB to a duel RCD Board. A non protected circuit would serve a mini garage board that has its own RCD.

The chap i was with today was quoting to put a garage feed up to the top of the garage. He said that as they have a Duel RCD board it can’t be done and they would need to change the board. Really ? 

Would it not be acceptable to have a MCB next to the main switch ( linked with a piece of busbar) and the incoming line obviously going into the top of the MCB, but the questions is where would incoming neutral go as there is only 2 N bars not 3 as it’s only a duel RCD board. Can it be done properly or would the board have to be changed ?

Thoughts 

It can be done but is a right pain in the neck as you need an extra neutral bar, and then the link cables that run between the main switch/ RCDs/ neutral bars etc etc. It would be easier to convert to RCBOs if the board has enough room above the MCBs. 

 

[Sidney]

What is the intended use of the garage? A couple of sockets and a light for basic use or something more akin to a DIY workshop/minibar/sauna?

 

[Badger]

its poor design doing it that way. ideally everything should have its own RCD as you are wanting to do. ignore the cowboys

Yes I've now decided for future consumer changes that dual rcd boards are not the best and so will. Reccomend rcbo boards every time much neater to install and much better for protection for the property 

 

[Andy™]

Yes I've now decided for future consumer changes that dual rcd boards are not the best and so will. Reccomend rcbo boards every time much neater to install and much better for protection for the property 

arguably dual splits dont comply anyway, i.e if there is an earth fault on a circuit then you have no selecivity between MCB on the offending circuit and the RCD protecting multiple circuits

 

[poni]

Would it not be acceptable to have a MCB next to the main switch ( linked with a piece of busbar) and the incoming line obviously going into the top of the MCB, but the questions is where would incoming neutral go as there is only 2 N bars not 3 as it’s only a duel RCD board.

you would not be using the board as the manufacturer intended,

 

[Traineeboy]

What is the intended use of the garage? A couple of sockets and a light for basic use or something more akin to a DIY workshop/minibar/sauna?

a couple and sockets and a some lights 

 

[Traineeboy]

Thanks for your thoughts chaps. He spoke to customer and they will just have a main switch board in the garage , 1 circuit for sockets and another for lights. Then he will just come off a MCB for one of the existing RCD. Yes ideal to use RCBO or Board change but the above will do the job. At least the garage unit can be isolated if there is a fault so it won’t keep knocking half the house out.