Regulation clarification

[Guitarist]

What do you think might happen to a socket outlet supplied via 2.5mm2 cable protected by a B32A MCB ?

The point of only having 1 single or double socket from a 32A MCB as a spur is that the plugtop fuses will be essentially protecting the cable. Granted, you could have 2 lots of 13A connected meaning 26A (very close to the 27A limit of Ref method C), but the point is that the cable IS protected.
You could also do 150mph down the high street and something bad would probably happen, but it's unlikely you would....

 

[Jimmy Boy]

It's always shocked me how you can do that under the regs, considering how ---- some of the regs are, rarely is a cable not de-rated for some reason or another or fused at 16/20

 

[spark 68]

It's always shocked me how you can do that under the regs

Bear in mind the regs will have a relatively large safety margin built in, they will certainly not be right at the limits of CCC even at the worst case scenario.

 

[Guitarist]

Bear in mind the regs will have a relatively large safety margin built in, they will certainly not be right at the limits of CCC even at the worst case scenario.

I believe that 100% margin is the norm. Feel free to correct me.

 

[Jimmy Boy]

what do you mean the adjustments for rating/de-rating ? whats the margins built in ?

 

[spark 68]

When the powers that be, and the bods who draw up the cable current capacity tables and max Zs etc..etc..,they will build in a safety margin, the regs that we follow will not be at the absolute maximum ratings.

This does not mean that we can ignore the regs or under estimate a size of cable, but by following the regs we will be under the limits by a comfortable margin.

So if the regs say 2.5mm cable is good for 27A, and guitarist says it is a 100% margin (I honestly don't know), the cable will likely in reality be able to take about 54A, we would never risk running it that high though as we follow the regs.

The regs take into account a lot more than we realise you see.

 

[ackbarthestar]

So if the regs say 2.5mm cable is good for 27A, and guitarist says it is a 100% margin (I honestly don't know), the cable will likely in reality be able to take about 54A, we would never risk running it that high though as we follow the regs.

The regs take into account a lot more than we realise you see.

I wouldn't want to push the cable that far for too long. But I agree that there is a safety factor built into the regs and by following them blindly, as many sparks do, you will always be on the safe side rather than the 'dark side'.

Now,

The point of only having 1 single or double socket from a 32A MCB as a spur is that the plugtop fuses will be essentially protecting the cable. Granted, you could have 2 lots of 13A connected meaning 26A (very close to the 27A limit of Ref method C), but the point is that the cable IS protected.
You could also do 150mph down the high street and something bad would probably happen, but it's unlikely you would....

I don't agree with this in its entirety.

The regulations allow us a safety margin, so where a non-fused spur is taken from the origin of the circuit the allowance of 1 single or 1 double socket is acceptable.
The cable is protected from both ends. A B32A MCB will provide S/C protection at the origin and the BS1362 in the plug top will provide O/L protection at the load end. Since by definition, it is impossible for the cable to overload without a load being attached. Also the MCB will disconnect much quicker than the BS1362 cartridge fuse.

The problem arises when more sockets are added to the spur, then an accumulation of normal full loading at each socket will cause an overload in the spurred cable, which is what I assume you mean by traveling at 150mph? The spur now running hot will be reliant on the O/L protection in the MCB, which by my reckoning, will have to be somewhere in the region of 60A for 3 mins or higher for a shorter period of time.

This is not an acceptable situation and is discouraged.

 

[Geoffsd]

The problem arises when more sockets are added to the spur, then an accumulation of normal full loading at each socket will cause an overload in the spurred cable, which is what I assume you mean by traveling at 150mph? The spur now running hot will be reliant on the O/L protection in the MCB, which by my reckoning, will have to be somewhere in the region of 60A for 3 mins or higher for a shorter period of time.

But more sockets should not be added to the spur - and won't be by anyone who knows what they are doing.

You cannot predict nor allow for stupidity.

If the circuit complies when you do it then what someone may do in the future is not foreseeable.

Your example could arise if it was a perfectly acceptable 4mm² radial - the CCC is only 37A instead of 27A.

 

[Guitarist]

Adding more sockets to that single spur is no different to breaking any other reg. We can't plan for it, as Geoffsd says.
Personally, I believe the combined knowledge and experience of the guys who write the regs is higher than mine, so I will stick to what they advise for now

 

[Risteard]

I think you are all correct it's a 'does not comply with 7671'
I have emailed the nikky spark (who I get on with really well) and see what he says

Which Regulation does it not comply with?

 

[Jimmy Boy]

Read my first post strictly speaking its a final circuit to each way in the board ? but then someone chips in with definitions and it all goes pear shaped..so you tell me