does this comply?

[ianmacd]

Because, again, sockets are not suitable for overcurrent protection of preceding cable. 433.2.2 states that.

 

[wozz]

hmmm read it and see where u are coming from, i read it as sockets installed along the length of the cable and not on a branch.

As a side point 433.2 is about the position of overload protection, the first line states except where 433.3 applies where we are talking about omitting overload due to the load characteristics.

 

[Andy™]

I would find it impossible to design two radial circuits sharing one mcb.

a radial can have a branch at any point, including the MCB, so technically, its still only one circuit

 

[Andy™]

Im going to state this again,anyone that designs a circuit with a cable capable of carrying 27Amps(at most) and protects it with a 32Amp device is at best unable to grasp the theory of :-

load current < design current < cable current

and at worst simply incompetent

so that would be everyone who has added a spur to a ring main.

 

[Andy™]

Because, again, sockets are not suitable for overcurrent protection of preceding cable. 433.2.2 states that.

but ive alreayd said before - sockets come under 433.3 - omission of overload, since the actual circuit doesnt contain the overload protection, the equipment plugged in does.

 

[ianmacd]

[quote name='Andy

 

[Badger]

so tell me then as im not quite getting how a 27 amp rated cable can comply with a protective device rated at 32amps:|

 

[steptoe]

[quote name='Andy

 

[ianmacd]

In the compliance agreement posies' defence there steps, they claim that the fuse int he plug will protect that piece of structured cable.

 

[wozz]

because quite simply it has been designed as a ring(compliant with regs) and a spur has been added(complying with regs)but can someone please explain to me how you can design a circuit to the following equasion and still comply

load current < design current > cable current

and eletrically the difference is? wheres your overload protection for your single 2.5 with a DSSO on the end?

 

[ADS]

Could you explain this from a design stage?I would find it impossible to design two radial circuits sharing one mcb.

In all, regardless of what anyone thinks its just not good practice, I would have to read up on the science though.

Maybe Manator can enlighten us?

No, as I've said in earlier posts, I couldn't think of a single reason why I would design or install it this way.

BUT

Let's say, for arguments sake, that the said scenario came about because the two 2.5mm radials were once spurs off a 4mm radial.

For whatever reason, someone saw fit to remove the 4mm radial without changing the 32 A RCBO.

If I then turned up to do a PIR on the installation, I couldn't justify coding it a 1, and thereby failing the whole installation - it hardly presents an immediate danger.

And, as has been shown in previous posts, I wouldn't even code it a 4, doesn't comply with BS7671, because it does

 

[ianmacd]

and eletrically the difference is? wheres your overload protection for your single 2.5 with a DSSO on the end?

We are compliant due to reg 433.1.5

 

[ianmacd]

No, as I've said in earlier posts, I couldn't think of a single reason why I would design or install it this way.BUT

Let's say, for arguments sake, that the said scenario came about because the two 2.5mm radials were once spurs off a 4mm radial.

For whatever reason, someone saw fit to remove the 4mm radial without changing the 32 A RCBO.

If I then turned up to do a PIR on the installation, I couldn't justify coding it a 1, and thereby failing the whole installation - it hardly presents an immediate danger.

And, as has been shown in previous posts, I wouldn't even code it a 4, doesn't comply with BS7671, because it does

You have never shown this because you can not accept that a socket can not provide protection to the preceding cable. Even the IET agree to that hence have pointed out it doesnt comply with the regs too.

 

[wozz]

and 433.1.5 point you to 433.3.1 for compliance, omission of overload.

 

[a1]

In the compliance agreement posies' defence there steps, they claim that the fuse int he plug will protect that piece of structured cable.

I haven't read all the pages to this thread, and neither am I going to.

Going on what you state above; Ian, The fuse in the plug will protect the appliance and cable that it is attached to, Yes. Has this thread turned into a wind up?

 

[a1]

On the New version of the forum, I am going to add a "Mod" that will show thw original OP on the top of every page.

It will be ideal in this situation where it has gone through many many pages, and would be easy to scroll to the top and look at it.

 

[batty]

I am afraid threads like this boare me to death. The way I see it a cable that is rated at 28 amps in perfect conditions should not be used on a 32 amp circuit simple if you do its poor design of circuit and why would you want to do it anyway when you could use a 20 amp circuit breaker or two.

 

[ADS]

I am afraid threads like this boare me to death. The way I see it a cable that is rated at 28 amps in perfect conditions should not be used on a 32 amp circuit simple if you do its poor design of circuit and why would you want to do it anyway when you could use a 20 amp circuit breaker or two.

So, once again, how do you explain the regs allowing a 2.5mm, un-fused spur, off a 32A ring final or radial??

This isn't a 'special' allowance (as some are trying to point out), it is allowed because 'overload' protection for the 2.5mm cable is provided at the socket outlet when a device is plugged in.

I haven't got the exact definition to hand (maybe someone else can help out), but it goes something like -

Overload : An overcurrent occuring in a normally operating, healthy circuit.

This excludes 'fingers in sockets' or 'un-fused' plugs, because they aren't normally operating circuits.

With this in mind, explain to us how the two radials in the scenario could possibly be overloaded under normal operating conditions?

 

[Riggy]

I am afraid threads like this boare me to death. The way I see it a cable that is rated at 28 amps in perfect conditions should not be used on a 32 amp circuit simple if you do its poor design of circuit and why would you want to do it anyway when you could use a 20 amp circuit breaker or two.

I find many threads on the forum boring, I would never comment on them to say so, I assume they are of interest to other members.

I believe the OP was wishing to start an intellectual debate, and on the whole he achieved this. I'm fairly sure he didn't want a solution, I suspect he is more capable of designing a better circuit than the one he describes than many of those missing the point of the debate.

 

[Lee321]

the reason were a bit alien to this is economics.

i.e we don't design circuits to have a single point of use.

we'd end with 24way cu's and much bigger cable install costs.

for me the thread is done and pretty sure ALL of us are in agreement that we wouldn't do it and the majority accept it is actually acceptable to 7671.

Amen