20A mcb or 16A mcb

Chris_909 · 12 Mar 2025

Hi,

Got a 20A mcb radial circuit which used to power a stair lift, I’m going to get rid of that, extend the cable and have one double socket, it’ll power just a lamp and general low current things, should I downgrade it to a 16A or is 20A fine? it’ll be clipped to wall and go through a wall at some point.

ericmark · 12 Mar 2025

No real reason to alter it, just use 2.5 mm² and follow safe routes.

Jurassicspark · 12 Mar 2025

The lights will be protected by the 13A fuse in the plug.

A short circuit will trip the breaker regardless of the rating.

No need to change it.

JohnW2 · 12 Mar 2025

ericmark said:
No real reason to alter it,

Agreed

ericmark said:
just use 2.5 mm² and follow safe routes.

Probably best - but if Method C, 1.5 mm² would actualkly be adequate.

SUNRAY · 13 Mar 2025

Jurassicspark said:
The lights will be protected by the fuse in the 13A plug.

A short circuit will trip the breaker regardless of the rating.

No need to change it.

I've corrected it for you

JohnW2 · 13 Mar 2025

SUNRAY said:
I've corrected it for you

Jurassicspark · 13 Mar 2025

SUNRAY said:
I've corrected it for you

Don't be so pendatic.

Whether if it's 3A, 5A or even 13A we don't know, I just gave out a random choice for explanation and I knew someone would have pointed it out.

Harry Bloomfield · 13 Mar 2025

Chris_909 said:
Hi,

Got a 20A mcb radial circuit which used to power a stair lift, I’m going to get rid of that, extend the cable and have one double socket, it’ll power just a lamp and general low current things, should I downgrade it to a 16A or is 20A fine? it’ll be clipped to wall and go through a wall at some point.

20A, needing perhaps a 2.5mm or 1.5mm seems quite a lot, for a stair lift - so I would be inclined to double-check the size of the cable, as a first step. I'm thinking - someone might have wired it in 1.0mm and just used a 20amp MCB.

Chris_909 · 13 Mar 2025

Harry Bloomfield said:
20A, needing perhaps a 2.5mm or 1.5mm seems quite a lot, for a stair lift - so I would be inclined to double-check the size of the cable, as a first step. I'm thinking - someone might have wired it in 1.0mm and just used a 20amp MCB.

Good thought, but Just checked, they have used 2.5mm cheers

ebee · 29 Dec 2025

It’s not that long since that a 1.0 live conductor would have been a no no for a power circuit (such as a central heating boiler or an extractor fan for example - although if it was a lighting circuit with an extractor fan on it such as in a bathroom then the concern was less likely to exist) my understanding is the requirement has possibly lately been dropped anyhow!
There are other examples of how regs/considered best practice changes over time that does not always seem to make much sense.
Anyway, as a rule of thumb so to speak you should be ok with a 16A or a 20A MCB USING 2.5 t & e etc.

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20A mcb or 16A mcb

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