NIC PIR Certs

[ban-all-sheds]

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.

Do you mean because Uo might not be 230?

 

[NotHimAgain]

Dear me we do love to complicate things don't we .

Some comments:-
The nominal supply voltage between line and earth (Uo)is 230 volts - this is by EU directive and anyone that says this is not the standard will be arrested and cast into a dungeon - never to be let out again .

I believe that the +/- 10% tolerance is now in force, but I may be wrong about that.

Those that draft regulations are usually quite fussy about the use of 'shall' and 'should' - you will not find shall used in Appendix 12 because its status is informative - it is not normative. Appendix 12 is only 'deemed to satisfy' so if you are competent you may choose different limits.

Voltage drop is rarely a 'safety issue'.

The reason a percentage is quoted is probably because the nominal supply voltage is dictated by the EU, and could be changed.

The different percentages reflect the fact that the rate of change of light output with voltage (from many types of light source) is considerably greater than, say, the rate of change of heat output from heaters.

Appendix 12 mentions that voltage drops may be determined from Appendix 4 - so that's easy then - when you are doing a PIR just look up the design calculations - what do you mean you have never seen any - surely not.

Another thoroughly thought through new requirement.

 

[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.

Do you mean because Uo might not be 230?

It might not be. I've seldom (if ever) measured a nice crisp steady 230V or 400V. If you're at the last pole, Uo might well be at the lower end of the tolerance, or even below (the REC probably wouldn't care - something people actually suffer from).

 

[FingRinal]

Another thoroughly thought through new requirement.

Wait for Amendment No1:2009

 

[GaryMo]

It might not be. I've seldom (if ever) measured a nice crisp steady 230V or 400V. If you're at the last pole, Uo might well be at the lower end of the tolerance, or even below (the REC probably wouldn't care - something people actually suffer from).

Nominal (being such in name only) and not measured. Uo is 230v.

 

[FingRinal]

It might not be. I've seldom (if ever) measured a nice crisp steady 230V or 400V. If you're at the last pole, Uo might well be at the lower end of the tolerance, or even below (the REC probably wouldn't care - something people actually suffer from).

Nominal (being such in name only) and not measured. Uo is 230v.

fair enough - let's then say 'actual voltage at the origin within the prescribed tolerance of Uo'...just seems such a mouthful and tediously long to type. Can we agree on a shorthand and call it 'Actual Uo' to save people's fingers and keyboards?

 

[ban-all-sheds]

If you're at the last pole, Uo might well be at the lower end of the tolerance, or even below (the REC probably wouldn't care - something people actually suffer from).

No - it doesn't matter where you are, or what actually trickles off the last pole - the Uo of the single phase public supply in this country is always 230V.
You can't have "Actual Uo" - that's an oxymoron.

Uo is not the actual voltage (although the actual voltage may sometimes have the same value as Uo), it's the nominal voltage.

The distinction is very important, because that's what the whole question of what voltage drop is allowed to be hangs on.

It is allowed to be up to 3%/5% of the actual voltage, or is it allowed to be up to 3%/5% of the nominal voltage?

Edited to fix use of completely the wrong word.

 

[FingRinal]

It is allowed to be up to 3%/5% of the actual voltage, or is it allowed to be up to 3%/5% of the nominal voltage?

What do you think?

 

[ban-all-sheds]

I used to think it was 4%, and now 3%/5%, of the actual voltage.

But 525-01-02, and now Appendix 12, categorically state a %ge of the nominal voltage.

Given that they've had several chances to change it, nominal voltage must be what they mean.

So for a single phase supply, VD must not exceed 6.9V/11.5V, no matter what the actual measured voltage is.

 

[FingRinal]

There is hardly any difference btwn calculating as a % of permitted tolerance or calculating as a % of 230V.

So one has to wonder if it really matters whether you use a % of actual voltage or the figures 6.9V and 11.5V.

The spread could be 246.1V to 209.3V for 3% and 241.5V to 204.7V for 5%. I guess you could specify lower limits - 209.3V and 204.7V but then people might just ask 'why?'. And all the hard work of the harmonization committees would go unrecognised.

Using 6.9V and 11.5V keeps the values in the 'middle' of the range so on average everyone is happy.

 

[ban-all-sheds]

There is hardly any difference btwn calculating as a % of permitted tolerance or calculating as a % of 230V.

For 5% circuits at the maximum permitted voltage drop based on Uo, the final voltage for a 230±10% supply will range from 195.5V to 241.5V.

If the 5% is taken off the actual voltage not the nominal then the range becomes 196.65 - 240.35.

So one has to wonder if it really matters whether you use a % of actual voltage or the figures 6.9V and 11.5V.

Apparently not, when looking at the absolute values, but it does mean that you can't design for 3% and 5%. If you were to assume linear resistive loads then it's a PoP to design for a VD of a %ge of your actual voltage, but when your VD is a fixed limit you have to assume worst case, so to achieve no more than 6.9V when your actual voltage rises to 253V means designing for a % drop of 2.73%, not 3, and for 11.5V circuits for 4.55%.

The maths is then just as much a PoP, you just have to remember not to be seduced by 3%/5%.

Unless you're allowed ±10% on your voltage drop, like the suppliers are allowed on their supply....

 

[FingRinal]

a 230±10% supply

Can you confirm if ESQCR 2002 has been updated to increase the permitted tolerance to +/- 10%?

BS7671:2008 states not, according to App. 2.

I wasn't aware that things had changed at a national level. Certainly there would be no need for us to change things as the permitted tolerance stated in ESQCR 2002 would automatically mean that we comply with the wider pemitted tolerance 'proposed' for 2003 detailed in BS7671:2001.

 

[holmslaw]

According to the 17th the tolerance is +10% -6% it does mention a 3rd stage of harmonisation - but thats it - it just mentions it with no details.

Perhaps the 3rd stage is "forget it nominal voltage is 240v".

ESQCR 2002 also states the same tolerance.

And a reminder to all, supply companies have until 2013 to remove all protective devices in neutrals. So if your supply company cannot confirm complete compliance with ESQCR all isolation and switching devise must comply with chapter 53. ie sp isolation unacceptable.

 

[securespark]

TLC's VD calculator....

I've used that, too. It gave me the all-clear.

 

[FingRinal]

So if your supply company cannot confirm complete compliance with ESQCR all isolation and switching devise must comply with chapter 53. ie sp isolation unacceptable.

I bet they're all losing sleep over it.