NIC PIR Certs

[holmslaw]

So for lighting:

Nominal voltage 230v, maximum VD of 3% or 6.9v so bottom line of 223.1v
Measured voltage of 240v would then give a maximum VD of 16.9v.

Not the way I read it, the actual voltage is irrelevant as far as the regs are concerned, so max vd on lighting circuit is 6.9v. Obviously the numpty who dreamt it up thinks that one day we will have a standard voltage of 230 - and then will we have a nominal voltage of 230v.

 

[GaryMo]

Why not take it further and factor in the permitted tolerance of the nominal voltage?

Beacuse that doesn't relate to us, that's the suppliers tolerance (+10% -6%).

 

[GaryMo]

So for lighting:

Nominal voltage 230v, maximum VD of 3% or 6.9v so bottom line of 223.1v
Measured voltage of 240v would then give a maximum VD of 16.9v.

Not the way I read it, the actual voltage is irrelevant as far as the regs are concerned, so max vd on lighting circuit is 6.9v.........

With respect to the value of the nominal voltage of the installation (230v) so low figure of 223.1v in this instance.

 

[ban-all-sheds]

Yes but Appendix 12 doesn't say that the voltage shall not drop to less than 223.1V, it says it shall not drop (on a lighting circuit) by more than 3% of 230V, no matter what the actual supply voltage is.

So if we ever do get to the 230±10% supply, that means you'll be allowed at the low end to drop to 200.1V, but because of the high-end you've got to design for a %ge drop of no more than 2.73% (assuming no significant change in load resistances as the voltage changes).

And here's an interesting thought - if you plug a table lamp into a socket circuit (a regular BS1363 one), does it become a lighting circuit?

 

[GaryMo]

Yes but Appendix 12 doesn't say that the voltage shall not drop to less than 223.1V, it says it shall not drop (on a lighting circuit) by more than 3% of 230V, no matter what the actual supply voltage is.

But 3% of 230v is 223.1v...

And here's an interesting thought - if you plug a table lamp into a socket circuit (a regular BS1363 one), does it become a lighting circuit?

No, the circuit stops at the socket-outlet.

 

[ban-all-sheds]

Yes but Appendix 12 doesn't say that the voltage shall not drop to less than 223.1V, it says it shall not drop (on a lighting circuit) by more than 3% of 230V, no matter what the actual supply voltage is.

But 3% of 230v is 223.1v...

Err - yes. Don't see what your point is.

No, the circuit stops at the socket-outlet.

What if I had nothing but table lamps and standard lamps plugged in?

 

[FingRinal]

Why not take it further and factor in the permitted tolerance of the nominal voltage?

Beacuse that doesn't relate to us, that's the suppliers tolerance (+10% -6%).

So what you are saying is that if the actual voltage at the origin of the installation is 216.2V (within tolerance of Uo) because you're at the last pole, you are not permitted any voltage drop at all as 3% of 230V is 6.9V which gives a maximum lower threshold of 223.1V? Or that if the voltage at the origin is 225V, you have (225-223.1 = 1.9V) to play with (a percentage of 0.8%)?

 

[GaryMo]

If it's stated that voltage shall not drop below 3% of 230v on a lighting circuit and 223.1v is 3% of 230v then as long as the voltage doesn't drop below 223.1v then it hasn't dropped by more than 3%. But.....you knew that

What if I had nothing but table lamps and standard lamps plugged in?

Still a ring final circuit and not a lighting circuit.

 

[GaryMo]

So what you are saying is that if the actual voltage at the origin of the installation is 216.2V (within tolerance of Uo) because you're at the last pole, you are not permitted any voltage drop at all as 3% of 230V is 6.9V which gives a maximum lower threshold of 223.1V? Or that if the voltage at the origin is 225V, you have (225-223.1 = 1.9V) to play with (a percentage of 0.8%)?

No, I'm saying that voltage drop of a final circuit is relative to the nominal voltage, 230v in this case. This would all be considered at design stage where actual voltage measurements haven't been taken.

 

[FingRinal]

And what about an existing installation for which no records are available - 99.9% of domestic installations?

Even your design figures don't really care what the Voltage is at the origin, only that the voltage drop from that point to the applicable point is no more than 3% or 5%.

 

[GaryMo]

And what about an existing installation for which no records are available - 99.9% of domestic installations?

Even your design figures don't really care what the Voltage is at the origin, only that the voltage drop from that point to the applicable point is no more than 3% or 5%.

That's exactly what I'm saying. 230v is the nominal voltage used for volt-drop calculations, not the suppliers lower limit of tolerance (-6%).

 

[ban-all-sheds]

If it's stated that voltage shall not drop below 3% of 230v on a lighting circuit and 223.1v is 3% of 230v then as long as the voltage doesn't drop below 223.1v then it hasn't dropped by more than 3%. But.....you knew that

But it doesn't say that - it says it shall not drop by more than 3% of 230V.

Which is 6.9V, so if your actual voltage (what is the symbol - is it Un?) is 230 then 223.1V is indeed the lowest you can drop to.

But if we do eventually go to Uo = 230±10%, the supply voltage could be 207V, so you'd struggle to maintain 223.1V in your installation then...

Conversely if you were at 223.1V but your actual supply was 253V you'd not be OK, as your % drop would be 11.8%....

The only thing that troubles me is that if what they wanted to specify was 3% and 5% of 230V, why didn't they just put 6.9V and 11.5V in Table 12?

 

[ban-all-sheds]

If it's stated that voltage shall not drop below 3% of 230v on a lighting circuit and 223.1v is 3% of 230v then as long as the voltage doesn't drop below 223.1v then it hasn't dropped by more than 3%. But.....you knew that

But it doesn't say that - it says it shall not drop by more than 3% of 230V.

Which is 6.9V, so if your actual voltage (what is the symbol - is it Un?) is 230 then 223.1V is indeed the lowest you can drop to.

But if we do eventually go to Uo = 230±10%, the supply voltage could be 207V, so you'd struggle to maintain 223.1V in your installation then...

Conversely if you were at 223.1V but your actual supply was 253V you'd not be OK, as your % drop would be 11.8%....

The only thing that troubles me is that if what they wanted to specify was 3% and 5% of 230V, why didn't they just put 6.9V and 11.5V in Table 12?

 

[GaryMo]

But if we do eventually go to Uo = 230±10%, the supply voltage could be 207V, so you'd struggle to maintain 223.1V in your installation then...

I see where you're coming from now.
I suppose that's what happens flipping back and forth from a writing up a PIR and reading every new reply email!

 

[FingRinal]

The only thing that troubles me is that if what they wanted to specify was 3% and 5% of 230V, why didn't they just put 6.9V and 11.5V in Table 12?

They didn't which is why they haven't.