Since this has come up a few times recently, have a look at this and comment / edit as appropriate:
- posted
13 years ago
Since this has come up a few times recently, have a look at this and comment / edit as appropriate:
I think that is the spec, but in reality its maintained a lot closer than that.
Useful and interesting (as ever) stuff.
A few tiny comments from a layman:
Extra Low Voltage Add to the heading "or ELV" for consistency with the preceding "Low Voltage or LV"
Live You will probably already have spotted the typo in line 1 of "wore" for "wire".
Why is Neutral a Live wire? In penultimate line similarly a typo of "(this" for "(This"
+/- 10%I couldn't find anything which replaces the +10/-6%. And the guys at
Background to the change to 230V
Any value in adding at the end something like:
"In 1994 the legislation governing the supply of electricity[1] was amended to require 230 volts rather than 240 volts between the phase and neutral conductors; but at the same time it allowed supply at 10% above (rather than 6 %) or 6% below. The net effect was that (within rounding) suppliers didn't have to change their practice.
The legislation in 1994 was the first stage in harmonising voltages across the EU."
[1] The Electricity Supply Regulations 1988 S.I. 1988/1057
Thanks for those...
Yup, our main FAQ still contains the prediction of a change to +/- 10% for Jan 2003. Probably about time that went ;-)
It got postponed a couple of times as various CENELEC countries were not able to meet it. Last I heard, it was now up to each country to decide when to change, and no longer CENELEC (or EU) wide. I got the impression there wasn't anything much in the way of any push behind it anymore.
I would guess (educated guess!) because it can be pulled to a potential other than the local earth if there's a transformer / substation fault? I've certainly seen unsafe voltages ( > 100V) on neutral lines when things have gone Very Wrong with the local substation, even an abnormal load on one phase can pull the SS neutral to quite a high voltage and coupled with an earth fault at the SS this can result in PME earths at relatively high voltages compared to a true earth - I've measured 240V between a sink and its wastepipe once or twice!
Dave H.
Good one John.
Suggested changes:
Reduced low voltage system
A system in which the nominal phase to phase voltage does not exceed 110 volts and the nominal phase to earth voltage does not exceed 63.5 volts.
This is a system you will frequently find on building sites for supply to (110V rated) portable power tools and lighting equipment. Site supplies are characterised by the use of yellow-coloured industrial plugs, cable and transformers.
=====
Why is Neutral a Live wire?
Neutral is considered a "live" wire because under normal conditions, a current flows in the neutral wire. You may consider the earth wire "dead" in comparison because under normal conditions, no current (or an extremely small amount) flows in the earth wire.
Consequently, although the neutral is bonded to earth at the electricity substation (and is usually therefore benign) it is possible under certain circumstances to get an electric shock by touching a neutral. Conversely, unless there is a very significant (and dangerous) fault in an installation which effectively makes the earth wire "live", you should never get an electric shock from touching an earth.
ok added.
Was this a suggested replacement for the whole section or an addition to it?
Er, a replacement actually. TBH, I thought your original was too wordy, too complex an argument and out of character with the style of rest of the article. IMHO you just need a simple and straightforward rationale for the use of the word "live".
Cheers, DaveyOz
Just read this back. Sorry if it sounds harsh; I'm in a bullish mood this morning :-)
DaveyOz
Sorry. I should have known you would have been there, done that.........
In penance (and/or 'cos I'm sad) I've checked with DECC the current position on +/- 10%. They pointed me to
I am sure the fact I was reminded of "and they'll be free beer tomorrow" was purely down to my imagination.
Who was going to be free beer?
Tis ok, no offence taken ;-)
I quite liked your words, but thought of using them as an intro to (some of) my original ones!
One point I felt worth making was that while the shock risk from elevated neutral voltage was small, the current leakage to earth on a short could be substantial. This potentially has knock on effects with regard conductor heating / damage (particularly with the typically smaller protective conductors)
Sure, but shirley these are subtle points more suited to a different, more in-depth article?
I see this particular article as an easily digestible "next step up from a dictionary definition" and wouldn't want the non-technical reader to be bogged down in too much detail. However, it's your article, so go for your life!
LOL!
Themm es wot (i) cant' conttrol ther diggits, (ii) cantt chekk there tie-pin, and (iii) dough-not its Scilly too send wenn dwinking before luncheon?
(And in any event, do I get time off for having discovered before lunch that my car was nicked overnight?)
ok, have a look now - went for something between the two. ;-)
Indeed. Well done that man/men.
And another :-)
Very few people are aware that the switch live in a light fitting is live. If it was marked they wouldn't know what it meant - and they frequently aren't marked anyway.
Is it worth adding that? Or does it belong elsewhere?
Cool.
^ "exceeding ELV (see below) and"
Neutral etc.: the essential point is the distinction between /live/ (current carrying) and /protective/ (earthing and bonding) conductors rather than the touch voltage you might normally encounter on a neutral. To bring the distinction home you could mention that, although the live conductors of each final circuit should be separate from those of other circuits, 'borrowed' neutrals are sometimes encountered - with the attendant shock risk from a disconnected neutral when working (for example) on a lighting circuit you thought you had isolated.
Any mention of sleeving needs to come with a big cavet that it's so often fitted incorrectly on professional installs, that no reliance should be placed upon any sleeving found in an installation.
TBH, it would be better if it wasn't fitted in the first place, but that's too obvious to an inspector, whereas fitting it in all the wrong places isn't.
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