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[Darkwood]

Right ... Just been nudged to set this up by Paul.M and sounds a good idea following recent threads I've done in the Arms..

Rules....No Offensive material... edit if required before posting as this is the public arena.
Anything to do with the trade or in and around it ...H&S pic's welcome.



I've posted this a few times and this is at a mates house following a kitchen refirb several yrs ago. mg_smile:

 

[Julie.]

You can’t run a 2.5mm spur from a 32A 6mm shower.

Not matter what the Zs is. The cable is only rated at max 27A.

So unless you ran it in 6mm, which would be some effort for a 2g socket then it’s not going to be compliant.

Nope, 2.5mm^2 would be fine, the maximum load could only be 26A max for a double socket outlet, and realistically 20A , so some if not most installation methods would have the capacity, exactly the same as a spur off a RFC.

Would not have to be 6, or 4mm^2, and if it was a single socket or FCU probably 1.5mm^2 would be ok from a load perspective.

I ask the question, because one's initial thought is to object, but is it actually wrong?

I know it's unusual and unexpected, but perhaps more compliant and less unexpected than some things we see!

 

[Pretty Mouth]

App. 15 recommends keeping cookers >2kW and other similar loads (heating etc) off ring finals, to avoid overloading either leg of the ring.

It's badly worded though, and often taken out of context, leading to the pseudo-reg that all such loads should be their own dedicated circuit.

 

[Raptor0014]

Nope, 2.5mm^2 would be fine, the maximum load could only be 26A max for a double socket outlet, and realistically 20A , so some if not most installation methods would have the capacity, exactly the same as a spur off a RFC.

Would not have to be 6, or 4mm^2, and if it was a single socket or FCU probably 1.5mm^2 would be ok from a load perspective.

I ask the question, because one's initial thought is to object, but is it actually wrong?

I know it's unusual and unexpected, but perhaps more compliant and less unexpected than some things we see!

The way I’ve always had it explained to me is that a spur off a RFC is fine because they’re in a ring and the socket won’t pull more than 26A. This is assuming cable is clipped direct.

However for, in this case, a shower circuit it’s not in a ring so the full load of 32A can go down it and overload the 2.5mm.

More than happy to hear other explanations and I’ve got my annual assessment next month so I’ll make a point of asking about this very scenario with the assessor as it will be interesting to see what their take on it is.

 

[pc1966]

However for, in this case, a shower circuit it’s not in a ring so the full load of 32A can go down it and overload the 2.5mm.

Not for a single or double socket as they have the 13A fuses limiting long-term loads to 13/26A (in fact most double sockets are only rated at 20A by specification).

If you have multiple sockets then yes, the feed cable had to be rated at the supply MCB to avoid overload risk, but for a single fused load it is limited by design.

When it comes to spurs off a RFC I dislike them for two reasons:

• They break the end-end test on full continuity and resulting max R1+R2 from (r1+r2)/4
• What starts as a single/double socket spurred off might then be spurred again like a radial but now violating the '2.5mm on 32A safe due to loop' aspect.

 

[Julie.]

...What starts as a single/double socket spurred off might then be spurred again like a radial but now violating the '2.5mm on 32A safe due to loop' aspect.

This I agree with, which is why you may only take one point off on a spur, but soooo easy for a diyer not to know this.

 

[Julie.]

The way I’ve always had it explained to me is that a spur off a RFC is fine because they’re in a ring and the socket won’t pull more than 26A. This is assuming cable is clipped direct.

However for, in this case, a shower circuit it’s not in a ring so the full load of 32A can go down it and overload the 2.5mm.

More than happy to hear other explanations and I’ve got my annual assessment next month so I’ll make a point of asking about this very scenario with the assessor as it will be interesting to see what their take on it is.

As said by pc, this part of the circuit is the same as a spur, the only current which can go down it is that associated with the load on the end of it.

If that is a fixed value, or load limited by a fuse etc. Then no more than load current can flow unless there is a fault condition.

I can see us all grasping to try and back-fit some genuine, or invented regulation because it feels wrong.

I have no doubt that we all object and then actually struggle to justify why we object.

Which is why I asked the question, the example achives ads (assuming Zs is ok), has overload protection inherent due to single socket or fcu, has acceptable voltage drop, rcd etc.

So is compliant - why do we object?

 

[pc1966]

So is compliant - why do we object?

If we have to find regs to justify the general feeling of unease then:

• The ones about separation of circuits spring to mind (as clearly sockets and showers are not natural bedfellows, and it is uncommon for a shower circuit to have even two showers attached as they are normally dedicated circuits)
• The ones on general workmanship - as in it is clearly some bodge/short-cut to avoid wiring in to an existing RFC/radial that was put in specifically for socket use.

Too hungry to look them up just now as pizza has to be organised for my oven!

 

[nicebutdim]

So is compliant - why do we object?

Not usual practice and people are creatures of habit.

 

[pc1966]

Not usual practice and people are creatures of habit.

Especially monks & nuns!

 

[nicebutdim]

Especially monks & nuns!

He said to the netball team.

 

[loz2754]

In many cases the shower circuit is "designed" to it's max capability, and so would be unwise to add another load.
I guess it boils down to fundamental principles rather than any specific regs.

 

[brianmoooore]

The 2.5mm2 cable to one single or double socket isn't the problem. The problem in practice will be the size of the cable common to the shower and the socket, and the rating of the circuit protection device not being high enough for both.

 

[Julie.]

As I said in my statement of the question, cable sizing, protective device sizing, Zs, rcd, ads etc being OK.

(The question is equally applicable to an fcu with a 1A fuse added to a 7.5kw shower supplied via a 40A mcb - with 10mm^2 cable)

What is the reason we try to find objections?

 

[timhoward]

What is the reason we try to find objections?

You've got me thinking - why do I hate it? I think it's because I have a sixth sense that the unusual nature of it could create safety issues, as others have said too. Hopefully not for sparks, though we do all make mistakes sometimes especially when tired. I'm thinking more of the DIY hero, or those that know enough to be dangerous.

So how do we feel about two rather predictable regs:

314 Division of Installation
314.1 Every installation shall be divided into circuits, as necessary, to:
ii) facilitate safe inspection, testing and maintenance
vi) prevent the indirect energizing of a circuit intended to be isolated

One might easily turn off and lock off "upstairs sockets", try a few sockets, and on a bad day having found every other socket upstairs dead not check the one that matters carefully enough. This might be construed to contravene indent ii).
It could work backwards too, you check that one and assume the rest are dead.
Unless there is space to adequately label the circuit, one would not expect the Shower breaker to be energising a double socket.

Another thought is 538.2. - saying that devices for isolation should be clearly identified by position or durable marking. If a shower pull cord isolator isolates a double socket, that probably contravenes this concept.

The question is, are these nit-picking issues from the regs book which are all open to interpretation legitimate enough reasons for the situation to worse than a C3?

 

[loz2754]

As I said in my statement of the question, cable sizing, protective device sizing, Zs, rcd, ads etc being OK.

(The question is equally applicable to an fcu with a 1A fuse added to a 7.5kw shower supplied via a 40A mcb - with 10mm^2 cable)

What is the reason we try to find objections?

I agree that many of us would go into knee jerk mode when presented with a situation that is out of the ordinary, and condemn it without thinking.
That's human nature. A kind of inertia. And even a kind of laziness, because it would require a deliberate effort to come up with a justification for something that would be much easier to condemn and walk away.
Also, too heavy a reliance on a book of regulations, which, in reality, cannot possibly regulate every single situation we might come across.
In other words, maybe we (myself included) should try to have more of an open mind when we see something like a socket connected to the same circuit as shower; or a pair of ring final circuits connected to the same circuit breaker!
And judge each situation accordingly. The case Julie just presented for example, would be much less of a problem, because of the different set of parameters.