230v or 240v

[seasickstevie]

... Plug tops are the covers that screw on to cover the terminals.

Strange that!

I quite agree. But have never understood why so many people - just about every spark I've worked with in ** years - has called them plug tops.

 

[dormermike]

Voltage in my house varies between 249 and 253v

 

[EFLImpudence]

Voltage in my house varies between 249 and 253v

Then you will need bigger cable for your shower.

 

[dormermike]

Voltage in my house varies between 249 and 253v

Then you will need bigger cable for your shower.

Sorry dont understand... Whys that? Amps lower as a result surely?

 

[EFLImpudence]

Whys that? Amps lower as a result surely?

No, got caught like that myself the other day.

Resistance of element is the constant, not the wattage.

 

[echoes]

Voltage in my house varies between 249 and 253v

Then you will need bigger cable for your shower.

Sorry dont understand... Whys that? Amps lower as a result surely?

Because I = V/R (current proportional to voltage) when R is constant.
Doh!

 

[JohnW2]

Voltage in my house varies between 249 and 253v

Then you will need bigger cable for your shower.

Sorry dont understand... Whys that? Amps lower as a result surely?

No, got caught like that myself the other day. Resistance of element is the constant, not the wattage.

That's all true, but I think the saving grace is that I believe the regs expect/allow current carrying capacity to be determined under conditions of nominal supply voltage (i.e. 230). If that were not the case, cable sizing would always be on the basis of the maximum possible (permitted) supply voltage, namely 253V.

Whether that is 'good design practice' if one knows that (as for most of us) the supply voltage is well above 230V (mine in usually 242-245V) is a different matter - but I think it's what the regs intend/allow - or am I wrong in that interpretation?

Kind Regards, John.

 

[EFLImpudence]

That's all true, but I think the saving grace is that I believe the regs expect/allow current carrying capacity to be determined under conditions of nominal supply voltage (i.e. 230). If that were not the case, cable sizing would always be on the basis of the maximum possible (permitted) supply voltage, namely 253V.

Whether that is 'good design practice' if one knows that (as for most of us) the supply voltage is well above 230V (mine in usually 242-245V) is a different matter - but I think it's what the regs intend/allow - or am I wrong in that interpretation?

I would agree that it is 'allowed for' in our 'European' nominal voltage.

Shower manufacturers, as said above, still tend to use 240V.

I only posted as dormermike was enquiring about his shower recently and stated that he has voltage on the high side.

 

[JohnW2]

I would agree that it is 'allowed for' in our 'European' nominal voltage. Shower manufacturers, as said above, still tend to use 240V. I only posted as dormermike was enquiring about his shower recently and stated that he has voltage on the high side.

Yes, I undertand that. However, if I understand the regs correctly (maybe not!), even if a manufacturer quotes power (or current) at 240V, one can recalculate the current at 230V for the purpose of determining required cable sizing.

However, as before, if this is true, I really do have difficulty in calling this 'good design practice', whatever the regs may say. As always, the saving grace is probably a lot of 'safety margin' built into the CCC figures we work with.

Kind Regards, John.

 

[dormermike]

That's all true, but I think the saving grace is that I believe the regs expect/allow current carrying capacity to be determined under conditions of nominal supply voltage (i.e. 230). If that were not the case, cable sizing would always be on the basis of the maximum possible (permitted) supply voltage, namely 253V.

Whether that is 'good design practice' if one knows that (as for most of us) the supply voltage is well above 230V (mine in usually 242-245V) is a different matter - but I think it's what the regs intend/allow - or am I wrong in that interpretation?

I would agree that it is 'allowed for' in our 'European' nominal voltage.

Shower manufacturers, as said above, still tend to use 240V.

I only posted as dormermike was enquiring about his shower recently and stated that he has voltage on the high side.

You have a great memory! Thanks

 

[EFLImpudence]

Yes, I undertand that. However, if I understand the regs correctly (maybe not!), even if a manufacturer quotes power (or current) at 240V, one can recalculate the current at 230V for the purpose of determining required cable sizing.

I suppose, strictly speaking, that is correct but as calculating @ 230V will give a lower current rating while the actual voltage and current will be nearer that which the manufacturer has stated would there be any point

If allowance is made in the CCCs given, it would seem to have been a rather silly exercise merely reducing the nominal voltage and adjusting the CCC to compensate.

However, with something like a shower, should we use 250V just to be safe? Probably equally unnecessary for the same reason.

More ambiguity?

However, as before, if this is true, I really do have difficulty in calling this 'good design practice', whatever the regs may say. As always, the saving grace is probably a lot of 'safety margin' built into the CCC figures we work with.

Yes.

 

[JohnW2]

More ambiguity?

Quite. Given the fundamental importance of cable size calculations in electrical design, one could be forgiven for hoping that the Wiring Regs would at least be clear and explicit about the operating conditions (supply voltage) one should use for determing the design current! Ah,well.

However, as before, if this is true, I really do have difficulty in calling this 'good design practice', whatever the regs may say. As always, the saving grace is probably a lot of 'safety margin' built into the CCC figures we work with.

Yes.

I don't know about you, I find this all rather intellectually displeasing - so many uncertainties seem to have been dealt with by building 'margins' into the figures we work with. Intellectually, I'd prefer to be able to remain in control - do 'proper calculations', refer to 'proper tables' and hence be in control of the margins being incorporated.

Kind Regards, John.

 

[ban-all-sheds]

Perhaps somebody with access to a copy of BS 6004 (possibly via their library) could tell us what currents they really have to withstand are...

 

[EFLImpudence]

I don't know about you, I find this all rather intellectually displeasing - so many uncertainties seem to have been dealt with by building 'margins' into the figures we work with. Intellectually, I'd prefer to be able to remain in control - do 'proper calculations', refer to 'proper tables' and hence be in control of the margins being incorporated

Agreed.

I've asked before but did not receive an answer but...

can anyone tell me at what current would, say, a 2.5mm² conductor actually be rendered unusable and then finally melt ?

 

[JohnW2]

Perhaps somebody with access to a copy of BS 6004 (possibly via their library) could tell us what currents they really have to withstand are...

That would be interesting - and I suspect that we might be quite surprised by the answers!

Kind Regards, John.