Is a 16A mcb acceptable for a radial circuit?

[kage85]

Hi everyone,
I'm new to this forum but have read from it a lot in the past for tips and advice which I've been thankful for.

Anyway just wondering as to whether a 16A mcb obviously RCD protected is acceptable for a radial circuit (upstairs sockets). I know it's not a risk as it would only trip at a lower current, but does it trip too easily to be deemed acceptable? Only ask this as I've seen them used but in the regs book regarding ring and radial circuits only a 20A with 2.5mm and 32A with 4mm cable are mentioned in the table. Are these the only ratings accepted nowadays or could you still use a 16A and be in compliance with the regs?

Any ideas anyone?

 

[Deleted member 26818]

Yes....

 

[wade88]

Length of circuit, Zs and ref method dependent, yes


ah beaten to it

 

[Deleted member 26818]

Sorry Wade, but you're just too long winded, that's why I beat you.

 

[HandySparks]

Depends what size cable has been used to wire the circuit and the minimum current carrying capacity in any part of the circuit.

 

[Deleted member 26818]

Yes in most circumstances 20A with 2.5mm² cable or 32A with 4mm² cable is fine.
However, there would be occasions where a lower rated Circuit Protective Device would be required for such circuits, depending upon the Current Carrying Capacitity of the cables after de-rating for external influences.
That aside, any circuit that can be protected by such and such a CPD, can always be protected by a lower rated device

 

[kage85]

I'd expect 2.5's as downstairs is a ring circuit and an old 16A breaker was kept in whilst all others were replaced with RCD's added, guessing the guy was an mcb short of a consumer unit, quite literally and just changed the ring into a radial to save getting another 32A breaker but surely this would be more trouble than its worth so I'm not sure really why else it was used?

 

[bigbaddave]

Because if its a radial then 2.5mm cable is rated at 27a clipped direct therefore would need a breaker smaller than that. Depending on the manufacture the next size down is 20A (25 on rare occasions) but 16 is also fine. Maybe there has been cable calculations done in order to deem this suitable for example the cable running through insulation which would down rate the cable.. Without seeing the install or having a little more info it would be impossible to comment.

But as for putting it on a radial just so he can use a 16a sound bonkers to me. Sounds more like there was a break in the ring which has prompt him changing it into a radial

My advice if its been installed by a proper spark then dont worrk too much about it, 16a is still a lot and id be worrying more if he had put it on a bigger breaker.. If you have problems in the future then get him back to correct the ring main

 

[Rampantchilli]

If its 2.5 t&e, which you don't say, then reference methods 101,103 would require it to have 16a
ref102 and A are so close to 20A that I would use 16A for sure
the person who did the CU change may have used caution on an existing circuit as he couldn't confirm ref method throughout, or precisely the quality of the installation in the first place

 

[Tesla1980]

Is 16A acceptable for a radial ? did'nt you do that at college i did

 

[bigbaddave]

Is 16A acceptable for a radial ? did'nt you do that at college i did

I dont think the OP is in the trade bud.

 

[bigbaddave]

I'd expect 2.5's as downstairs is a ring circuit and an old 16A breaker was kept in whilst all others were replaced with RCD's added, guessing the guy was an mcb short of a consumer unit, quite literally and just changed the ring into a radial to save getting another 32A breaker but surely this would be more trouble than its worth so I'm not sure really why else it was used?

I suspect these RCD's you talk about are actually plug in MCB's for your old wylex board.

 

[kingeri]

Reminds me of when I moved into my house, all the sockets over 4 floors were on a single 16a 4mm radial circuit. Never had any nuisance tripping before I sorted it out.