Upgrading shower circuit from 6mm to 10mm

[JohnW2]

What else?

I mean that it's not just numbers - hardly appropriate for Europe.

I know what you meant - but shouldn't everyone in Europe (and the rest of the world) learn English so that they can understand labels written in the most ubiquitous Western language?

Have since thought more about the reducing of nominal to 230V and CCC. Perhaps the regulation writers also thought that current would increase with lower voltage so there would be even greater safety margin.

I almost made that suggestion myself earlier, but felt it would be disrespectful to suggest that regulation writers would be capable of that!!

Kind Regards, John

 

[EFLImpudence]

It's the thought that counts.

 

[ban-all-sheds]

I do not know why CCC was not similarly adjusted .

Probably because CCC is voltage-independent.

 

[JohnW2]

I do not know why CCC was not similarly adjusted .

Probably because CCC is voltage-independent.

Indeed so - but, as I presume you understand, that's not what EFLI meant. Zs is also voltage-independent, but that didn't prevent themn revising their tables when the nominal voltage changed.

As you will understand, the point is that the regs appear to allow one to calculate the load current (for comparison with cable CCC) at nominal voltage (even though voltage will often be higher than this), just as they allow CCC to be compared with In of an MCB, even though 1.45*In may flow for up to an hour before the device operates. In these cases, it is apparent that there are presumably substantial margins built into the tabulated CCC figures. When nominal supply voltage was reduced, this will have eaten into those margins (if people calculate was load current would be at 230V, rather than at 240V), but they seemingly didn't see the need to revise their CCC figures to restore the previous level of margins.

Kind Regards, John

 

[bhm1712]

The very fact that the voltage harmonisation was a paper exercise only has caused these issues.

The UK should never have harmonised with the rest of Europe on such things. I have never measured voltage at a domestic socket outlet and found it to be anything less than 239 volts. Usually around 243 volts in my area.

There was no need to harmonise anything. But we have to live with it now. Calculate for whatever is on the data plate of the device. If the device says 240v calculate for that. If 230v then calculate for that.

However having said that, the voltage tolerances are there for that reason as well. Dont forget that even if a manufacturer has stated the figures at 230 volts, they will have taken into account the tolerances as well....

 

[bernardgreen]

Calculate for whatever is on the data plate of the device. If the device says 240v calculate for that. If 230v then calculate for that..

What does the calculation give ? It gives the current that the load will take at 230 volts. If that value is then used to select the cross section area of the cable and the rating of the protective devices then there is a possibiity that the current taken when the voltage is higher will become an overload. It is said that the cable ratings take this into account by setting a maximum safe rating that is lower than the actual safe carry current.

But how much lower is the rating ? How much tolerance is there ?

Is the tolerance enough that a design with a current design value based on 230 volts will still be safe when the actual current is higher than the design value due to the supply voltage rising to the maximum of 252 volts ( 230 +10% )

 

[JohnW2]

The very fact that the voltage harmonisation was a paper exercise only has caused these issues. The UK should never have harmonised with the rest of Europe on such things. I have never measured voltage at a domestic socket outlet and found it to be anything less than 239 volts. Usually around 243 volts in my area.

Indeed. They obviously actually wanted real 'harmonisation', but that would have been so unbelievably impractical/expensive that they undertook this basically silly paper exercise. Like you, my supply is usually within a volt or two or 245V - I've never seen it even as low as 240V - and I suspect it will be that way 'for ever'..

There was no need to harmonise anything. But we have to live with it now. Calculate for whatever is on the data plate of the device. If the device says 240v calculate for that. If 230v then calculate for that.

It's not really that simple. For a start, as EFLI has pointed out, plates sometimes bear ratings for multiple voltages these days. Furthermore, if the plate does say 230V, although it's seeming what the regs want/allow, it's clearly not all that appropriate to determine what the current load would be at 230V if one knows that the supply is usually around 245V.

However having said that, the voltage tolerances are there for that reason as well. Dont forget that even if a manufacturer has stated the figures at 230 volts, they will have taken into account the tolerances as well....

Yes, but we're not tallking about the voltage tolerances of the equipment. We're talking about determining the current draw in order to ascertain whether the installation's wiring has adequate CCC - that's nothing to do with the manufacturer. However,as is being discussed, the IETs CCC tables clear have large 'margins' built into them .... if one works out current assuming 230V supply, that current will be 1.1 times greater at 253V, and cables have to be able to tolerate 1.45 times the In of a Type B MCB for an hour. In other words, when the tables say that a cable has a 'CCC' of, say, 20A, and can therefore be protected by a 20A Type B MCB, they are recognising that there may be a current of up to 31.9A flowing in that cable for up to an hour.

Kind Regards, John

Kind Regards, John

 

[bhm1712]

Agreed. So maybe it should be the case that the installer of a piece of equipment should calculate the current draw and thus MCB and cable sizing based on the maximum allowable voltage within the tolerance of the UK supply.

Lets not forget that the MCB is to protect the cable not the equipment on the end of it.

As an electrician, maybe the manufacturers ratings and cable/mcb sizing recommendations should be taken just as that - a recommendation. It should be down to the individuals knowledge and experience of electricity and how it works which dictates a safe and suitable installation.

 

[ban-all-sheds]

Zs is also voltage-independent, but that didn't prevent themn revising their tables when the nominal voltage changed.

The maximum permitted Zs is not independent of supply voltage - you still need the same current to operate a protective device, so with fewer volts you have to have fewer ohms.

but they seemingly didn't see the need to revise their CCC figures to restore the previous level of margins.

No, because CCC is voltage independent, and the margin needed to accommodate the supply voltage rising to the maximum changed so little that it did not lead to a change of the tabulated values.

 

[JohnW2]

Agreed. So maybe it should be the case that the installer of a piece of equipment should calculate the current draw and thus MCB and cable sizing based on the maximum allowable voltage within the tolerance of the UK supply.

That would obviously make electrical sense but, as you know, it is not what the regulations require. However, if one did that, it would be appropriate to use 'actual/real' CCC figures for cables (if one could find them), rather than the highly conservative ones, with seemingly massive 'margins', provided by IET in the regs. The fact is that the regs have decided to adopt the approach of allowing cable sizing to be based on the current that would flow with a 230V supply, and the actual In (not 1.45*In) of an MCB and to build these large margins into the CCC tables to allow for that.

As an electrician, maybe the manufacturers ratings and cable/mcb sizing recommendations should be taken just as that - a recommendation. It should be down to the individuals knowledge and experience of electricity and how it works which dictates a safe and suitable installation.

Yes but, as above, that one would require one to know the actual/real safe current carrying capacities of cables, under all possible installation methods (not easy to find) and to be prepared to justify one's calculations. For an electrician whose time is money, it's far simpler just to comply with the 'deemed-to-satisfy' provisions of BS7671.

Kind Regards, John