Table 41.1 and Reg 411.3.2.2

[sm1thson]

I repeat - the nominal supply voltage in the UK is 230 volts.

This is a matter of European harmonisation - it would breach an EU Directive if it were not.

Look here under amendment 4

http://www.opsi.gov.uk/si/si1994/Uksi_19943021_en_1.htm

Now the voltage at your house could be 240V or even 250V that does not matter - the nominal voltage is 230V.

I believe it use to be 240V +-6% then when we moved down to 230V and mainland Europe moved up it became 230V +10% -6% for us (and i think 230V +6% -10% for them) . i believe at present the average voltage in the uk is 238V.

edit 1: (i didnt check the values but Im sure if there not right there in the right ball park)

edit2: if the average supply voltage is turned down 3.4% from 238 to 230 then resistive loads will take 3.4% less and the supply companies will make 3.4% less money (on resistive loads)! i dont think they are in a rush to do it!

 

[holmslaw]

..

 

[NotHimAgain]

Smithson - spot on - thats why the disconnection tiime is 0.2secs not 0.4 secs.

The disconnection time for a normal TN system in the UK, as per table 41.1, is 0.4 seconds. If you disagree check it out with the IET or the NICEIC or NAPIT or who ever you like.

 

[RF Lighting]

Yep, it doesn't make a blind bit of difference what the actual supply voltage is. It is the NOMINAL voltage which counts, and must be used to determine the disconnection time.

 

[holmslaw]

..

 

[RF Lighting]

Do you know what Uo means?

 

[NotHimAgain]

Do you know what Uo means?

Homslaw

Look at the text under table 41.1 - last sentence.

Uo is the nominal a.c. rms or d.c. line voltage to earth.

Now follow the link I gave you for the law relating to supply voltage.

In the UK Uo = 230 volts.

 

[SgtTrojan]

Ok.. Consider these two examples for TN systems only.

1. Each installation in the UK is designed around our nominal supply being 230V. Every installation will be the same (assuming shock protection and thermal contraints are met, etc) and will be required to disconnect within 0.4 or 5 seconds.

2. Installations are designed to the supply characteristic at the initial design stage (ie the measured voltage is the voltage used). This wouldn't account for any fluctuations in voltage drop over different times and could mean that two identical installations in different parts of town could be installed to different standards. (ie to disconnect in 0.2 / 0.4 and 5 seconds just because there is an 8 volt difference in supply voltage)

For me, option one is what we are required to do as it creates a more standard installation.

Anyone a member of NICEIC so they can get confirmation?

 

[SgtTrojan]

I was just scooping through the 16th Ed and found this

16th Ed - 413-02-08 below old table 41A.
Note 1. For voltages which are within the supply tolerance band (230 +/-10%V) the disconnection time appropriate to the nominal voltage applies

So I assume that we are still following the same direction? Hence using 230v and 0.4 seconds (not 0.2)

 

[ban-all-sheds]

Ok.. Consider these two examples for TN systems only.

Where did #2 come from?

Anyone a member of NICEIC so they can get confirmation?

Why do you think that NICEIC have any say in the matter? They can have an opinion, and they can confirm what their opinion is, but they have no role in confirming what the requirements actually are...

 

[Spark123]

Uo is the nominal line voltage to earth, the nominal value for a normal supply in the UK is 230v.

 

[SgtTrojan]

Sheds,

#2 is hypothetical and seems to be what a couple of the chaps above are implying I think.

Re: The NICEIC, I was under the impression that they know their stuff and read the regs to their kids at bedtime

 

[ban-all-sheds]

#2 is hypothetical and seems to be what a couple of the chaps above are implying I think.

Ah - OK. That does seem to be a suggestion in some quarters.

Re: The NICEIC, I was under the impression that they know their stuff and read the regs to their kids at bedtime

Sorry to disappoint you, but....