BT & Part P

SNIP

Your memory is wrong

Telephone line voltage is 50volts dc. Ringing is around 75/80 volts ac (or thereabouts). It is ac so as to pass current through capacitors in series with the old fashioned bell ringers. Picking up the phone closes a contact allowing a dc path which is detected in the exchange and the ringing supply is disconnected and a speech path enabled. The same dc loop is detected when making a call but most phones now use tone signalling rather than loop disconnect pulses

The line voltage and ringing systems were designed to run the early telephones with two wire transmission, and a gradual transition to modern systems meant that these basic parameters were already established and still apply.

It looks as though NICEIC have, ahem, got their wires crossed:

That's not what it says DESCRIPTIONS OF WORK WHERE NO BUILDING NOTICE OR DEPOSIT OF FULL PLANS REQUIRED

Work on -

(a) telephone wiring or extra-low voltage wiring for the purposes of communications, information technology, signalling, control and similar purposes, where the wiring is not in a special location;

(b) equipment associated with the wiring referred to in sub- paragraph (a).

And again the definition:

"special location" means a location within the limits of the relevant zones specified for a bath, a shower, a swimming or paddling pool or a hot air sauna in the Wiring Regulations, sixteenth edition, published by the Institution of Electrical Engineers and the British Standards Institution as BS 7671: 2001 and incorporating amendments 1 and 2.

QED - the NICEIC page is clearly wrong.

Well I've e-mailed the NIC's technical help desk with the benefit of my opinion. I'll post the gist of any reply received.

AAgh

Anyone touched a 'new' black wire yet ;-)

P.

NICEIC reply thus (& quicker than I expected):

That is a lot quicker than I expected as well! All credit to NICEIC for accepting the error. Can't take long to alter a webpage can it?

Looks like the kind of thing that would be a reply to the letters column in a women's magazine.

Was their next comment "Imagine my surprise when I touched a black wire in the kitchen and got a belt" ?? :-)

I was saddened to read that their new leaflet "doesn't include a kitchen" :~(

Out of interest, are there any reports or evidence of anyone ever being hurt by a belt from domestic phone wiring?

David

I doubt it. The current which would flow - even for a dead short - would be next to damn all, considering the impedance of several km of cable between you and the exchange.

Interesting hare I set running. many thanks for the response.

It only set off because I assume now that whenever I pick up a tool to work on my home I'm going to be doing something illegal, anti-social and dangerous. Trying hard to figure out how to route a telephone cable around my parent's home & assuming that was illegal, I had the bizarre thought it might be illegal for BT too.

Seems howver it is still illegal for me to fix a 2.5V battery electric clock to my bathroom wall ;-)

(and immoral)

I got quite a belt once when I stripped a telephone wire with my teeth...

You can get quite a belt off telephone wiring if working outdoors in the wet, particularly if there is ringing current on the line at the time (in theory up to 100 V AC superimposed on 70 V DC although in practice rather less).

Only ever in a secondary sense - working on an MDF in an exchange - touched a pair which had ringing on it, causing my hand to jump away, and the back of my hand slammed into the solder tags on the adjacent block!

I should think that you've got to have a severely weakened physiology to have a direct problem from comms voltages

You should have been wearing your "Protectors Hand"

:-)

If I'd worn all the equipment that we were supposed to, I'd never have got near most of the stuff that I worked on!

I once had my photo taken for BT Toady, splicing some fibres. WHen the picture was published, I had a senior manager asking me why I had an open can of coke on the work bench. It took a lot of convincing before he finally believed that it was the 'cin-bin for the fibre offcuts! (Even though it was bright yellow, and not the usual red). Still, he was a graduate entrant...

Another great story (probably apocryphal) concerning a new grad. manager, put in charge of a poles'n'holes team. At his first team meeting, he asked the team if they had any concerns. One piped up to complain about the number of D-poles (decayed poles, for those who don't know) in the network. After much earnest nodding, the new manager said 'I share your concerns. Can you give me a rough number of how many of these holes there are, and how deep they are?'

Another one, in an attempt at team-building, decided that the whole team should do one of these nude calendars to raise money for charity!

Oh, those were the days.

Define "hurt". I've had shocks of ordinary phone lines, of the "ouch WTF" sort.

Assuming you *are* several km from the exchange... The loop current required for a phone to work is around 10mA so that or more, is available at the end of the line. More than enough to kill in the right (wrong?) situation.

On 2 Dec 2005 08:33:28 -0800,it is alleged that "jim_in_sussex" spake thusly in uk.d-i-y:

Provided the clock was IP 68 sealed, and not within 3 metres of the bathtub and was securely fixed to the wall out of reach with kitemarked masonry anchors. Of course, fixing it out of reach would require a safety evaluation and scaffolding, you should be fine... provided you have signed papers from John Prescott, the Queen, and some minor bureacrat in Brussels.