changing or swapping a MCB

[Michael stath]

Hi, I have a garden studio that is fed from the main consumer unit in the house. It is wired into a B6 MCB on a radial circuit which is fine but occasionally, if I use something that draws too much power the MCB trips. I use power tools which work fine as I only use one at a time obviously, but I have recently acquired a new Hoover which just trips the MCB when it is switched on.

There is a spare B20 MCB in the CU and I have tried to move the live from the B6 to the B20 but this just trips straight away. Would this indicate that this B20 is faulty (it's a reasonably old Steeple CU)?
I'm wondering if I would be able to just replace the B6 with a higher rating MCB?

I have attached a photo. In short I have tried moving the wiring from B6 (A) to B20 (B) with no luck. Can I just replace the B6 (A) with a higher rating MCB?

Thanks in advance.

 

[Harry Bloomfield]

Is it the RCD which trips? That will happen, if you simply move the live from A, across to B. The neutral needs to be moved across too.

 

[Rodders53]

Oh dear. Oh dear. Oh dear.

First you need to determine the current carrying capability of that bit of cable going to the garden studio by determining the cross-sectional area, etc.,.

Only then can you consider increasing the current rating of the overload protection MCB
- but don't just do that without knowing the cable current carrying capacity!

There should be two Neutral busbars inside for the two RCD 'sides'. Swapping RCDs may save relabelling if the cable is up to a 20A load. --- But what about the garden room lights vs sockets circuits and overcurrent protection then?? Is there CU in the garden room or what ???

 

[Michael stath]

Thanks for the reply guy's,

Ah, right. I'd assumed (which is a stupid thing to do, I know) that the neutrals were all connected to the same place?! I've attached another photo. The red line indicates the path of the current cable set up.

All of the cabling was in when I bought the house a couple of years ago. There is a small CU in the studio with two MCB's - one B6 for the lights and a B32 for the sockets and it is approx 10m from the house. The cable looks like 4mill.

 

[opps]

What is the rating of your vacuum cleaner? Each of my dust extractors are less than 1200w- I am not an electrician, but perhap you might need a C class MCB, it will allow a greater initial load. I will however defer to the electricians on this site to advise you accordingly.

 

[Harry Bloomfield]

Ah, right. I'd assumed (which is a stupid thing to do, I know) that the neutrals were all connected to the same place?! I've attached another photo. The red line indicates the path of the current cable set up.

Your quickest solution, is probably to simply move the B20, to the location where the B6 is - swap the entire MCB's over, leaving the cables where they are, but to do that, you need to be careful. Turn the main isolator off, before you start.

4mm on a B20 is fine, but the B32 in your sub-board is completely pointless/serves no real purpose, but not a real issue.

 

[Michael stath]

What is the rating of your vacuum cleaner? Each of my dust extractors are less than 1200w- I am not an electrician, but perhap you might need a C class MCB, it will allow a greater initial load. I will however defer to the electricians on this site to advise you accordingly.

Thanks. It’s 1400w. The previous one I had ran fine and that was 1400w also. It’s the initial load that trip it I think.

 

[Michael stath]

Your quickest solution, is probably to simply move the B20, to the location where the B6 is - swap the entire MCB's over, leaving the cables where they are, but to do that, you need to be careful. Turn the main isolator off, before you start.

4mm on a B20 is fine, but the B32 in your sub-board is completely pointless/serves no real purpose, but not a real issue.

Thanks Harry. May just do that.

And I thought the same about the B32 in the studio. We bought the house a couple of years ago so all this was already in place. It was an old rented property and apparently the landlord used to do his own maintenance. I’ve had to fix a lot of his handiwork.