Connection issue with swa

[davesparks]

2.5mm on a 32A ocpd sounds a little bit on the non-compliant side of things.

 

[telectrix]

oops.missed that. needs a 20A OCPD or go up to 6mm.

 

[Ian1981]

Depending on the fixed load a 2.5mm off a 32amp mcb is no different than spurring off the ring final directly from the Mcb at the consumer unit.
If overload protection isn't required then all the 2.5mm needs is fault protection which the mcb will give.
I personally would size the mcb so Ib<In<Iz but it wouldn't necessarily be a non compliance

 

[buzzlightyear]

but would it be better to run a radial 20amp mcb or rcbo 2.5 mm cable own circuit if possible if a problem with out side fixed load with out knocking of main circuit .

 

[Ian1981]

Think he's planning a radial buzz , just off a 32 amp mcb.
I'd go 20amp but just saying that what he proposed isn't necessarily non compliant.

 

[westward10]

Why you would use a 32A device on a 2.5 cable to supply a 13A, which I assume to be a socket, is beyond me.

 

[Ian1981]

Outdoor isolator according to the op.
Makes little difference I suppose.

 

[buzzlightyear]

ian 1981 , I see don't look back in hanger and mad for it. are at it about Manchester concert .

 

[Dave OCD]

3kw design current I'd use a 16a B type RCBO. Might as well is nothing else is on the circuit.

 

[telectrix]

if his SWA tails come straight through the wall, not buried <2" in plaster, no need for RCD protection unless it's TT.

 

[Dave OCD]

Ok in that case a 16a MCB. But if it's going straight to an external rotary isolator you'd need the RCD protection at source for the tub.

 

[davesparks]

Depending on the fixed load a 2.5mm off a 32amp mcb is no different than spurring off the ring final directly from the Mcb at the consumer unit.
If overload protection isn't required then all the 2.5mm needs is fault protection which the mcb will give.
I personally would size the mcb so Ib<In<Iz but it wouldn't necessarily be a non compliance

It is different to a 2.5mm spur from a ring, this is a dedicated circuit to a single appliance and the spur from a ring is one point out of a number of points for general use. The ring circuit relies on loads being spread around the circuit to work correctly and it is advised that fixed loads greater than 2kW aren't fed via a ring circuit.

Yes you could prove by calculation that the mcb will provide fault protection for the cable, but this seems like an over the top and unnecessary thing to do for a domestic installation. Especially when you can guarantee that anyone who looks at this installation in the future will label you as a cowboy for having done it that way.

Far simpler to install an ocpd which is better matched to the load.

 

[davesparks]

Depending on the fixed load a 2.5mm off a 32amp mcb is no different than spurring off the ring final directly from the Mcb at the consumer unit.
If overload protection isn't required then all the 2.5mm needs is fault protection which the mcb will give.
I personally would size the mcb so Ib<In<Iz but it wouldn't necessarily be a non compliance

It is different to a 2.5mm spur from a ring, this is a dedicated circuit to a single appliance and the spur from a ring is one point out of a number of points for general use. The ring circuit relies on loads being spread around the circuit to work correctly and it is advised that fixed loads greater than 2kW aren't fed via a ring circuit.

Yes you could prove by calculation that the mcb will provide fault protection for the cable, but this seems like an over the top and unnecessary thing to do for a domestic installation. Especially when you can guarantee that anyone who looks at this installation in the future will label you as a cowboy for having done it that way.

Far simpler to install an ocpd which is better matched to the load.

 

[Ian1981]

It is different to a 2.5mm spur from a ring, this is a dedicated circuit to a single appliance and the spur from a ring is one point out of a number of points for general use. The ring circuit relies on loads being spread around the circuit to work correctly and it is advised that fixed loads greater than 2kW aren't fed via a ring circuit.

Yes you could prove by calculation that the mcb will provide fault protection for the cable, but this seems like an over the top and unnecessary thing to do for a domestic installation. Especially when you can guarantee that anyone who looks at this installation in the future will label you as a cowboy for having done it that way.

Far simpler to install an ocpd which is better matched to the load.

I hope you do realise that I'm not suggesting that it's spurred from the ring circuit, more suggested that if it was supplied from a 32 amp mcb on its own dedicated radial then as it's a fixed load it not necessarily no compliant as people are suggesting.
As stated I wouldn't use a 32 amp on a 2.5 , mearly suggesting it's no different being protected by a 32 amp as a spur is directly from the consumer unit when overload isn't a factor.
And yes the mcb will protect against fault protection you don't need a calculation to work that out.
Even a generic I2t let through value from a manufacturer will tell you that for a disconnection time under 0.1 of a second

 

[westward10]

Is a hot tub a fixed load.

 

[Ian1981]

It will I imagine have a maximum draw if you like
If it's rated 13 amp it's not going to pull 20 is it?

 

[davesparks]

It will I imagine have a maximum draw if you like
If it's rated 13 amp it's not going to pull 20 is it?

It will under an overload fault, it will not be a simple resistive load.

 

[Ian1981]

It wo

It will under an overload fault, it will not be a simple resistive load.

why will a 13amp supply overload a 2.5mm swa?

 

[davesparks]

It wo

why will a 13amp supply overload a 2.5mm swa?

That is not the question I was replying to, you asked if a load rated at 13A could draw 20A, which it could under an overload fault.

 

[Ian1981]

That is not the question I was replying to, you asked if a load rated at 13A could draw 20A, which it could under an overload fault.

Okay