TN-S earth connection upgrade

[John Rumm]

As a general rule, do the electricity suppliers worry if one improves the state of the earth connection to the cable sheath on a TN-S supply?

I was looking at someone's install the other day where all the earthing and bonding in the house had obviously been brought up to standard at some time in the relatively recent past, but the final connection from the main earthing block to the cable head end was the original rather feeble bit of bare steel stranded conductor that was probably no more than 2mm^2 csa. It kind of made a nonsense of the nice new 16mm^2 running from the block to the CU etc.

[Dave Stanton]

Well I upgraded mine to 16mm^2 a while ago and no one complained. There again I doubt meter readers would know or care. This was of course pre Part P ;-)

Dave

[Andrew Gabriel]

On two I've done which required reconnecting the TN-S earth, I left the original cable clamps in place. On one, an original

1955 installation, the earth clamp is a nice substantial brass thing of much higher quality than todays clamps. On another, the clamp screw seemed to have squashed into the lead sheath very substantially, and I didn't fancy the incommer blowing up on me, so I used the same clamp with a new earth cable connected.

[Stephen Dawson]

Strictly speaking the earth clamp on the cable is the property of the distributor and should not be touched. Give you local electricity co's emergency number a call and they can point you in the right direction to get it replaced. The standard eath clamps from the shed should not be used as they may squash the cable and cause an explosion!!

Regards

Steve Dawson

[Dave Stanton]

On rereading the OP I take it to mean the cable from the headend earth connection to the CU. I don't think he means hes going to change the actual sheath connection.

Dave

[John Rumm]

In this case I was not going to change anything since it is SEP! - just more curious whey the original sparks who upgraded everything else (I presume), had left that one last weak link...

There was no obvious clamp to the lead sheath - it almost looked like it was soldered to it (although the connection was at the back of the cable and under tape - so not immediately obvious).

The wire connected to the sheath was in turn connected to a modern 6 way earth block, thence a couple of CUs and the main bonding to gas and water pipes.

[Roger R]

I found the clamp had changed the incoming cable shape from circular to eliptical and the screw had made a similar significant indentation in the flattish side. I too was quite worried about shorting out the cable on refitting, so chose a different position away from the damage.

This... from BBC4 TV programme 'Take one museum'

- Manchester Museum of Science and Industry. Presenter (Paul Rose) described that to get the go ahead for building the first electric power station in the uk, the proprietor had to prove the distribution system was safe.

This was done by driving a cold chisel into a large energised distribution cable - the power station proprietor was not the one holding the chisel! Apparently all went well and the cable was shorted out with no serious injury to those involved and the go ahead was obtained. The section of cable and the chisel may be seen in the museum.

Roger

[Steve Firth]

Roger R wrote: [snip]

The first (public) electric power station in the UK was at Godalming in Surrey, it was a hydroelectric generator and I'm bemused by the story above since I can't see any direct link between Manchester and Godalming in this respect. Nor can I understand why, if the tale is true, the chisel is not located at Godalming museum.

[Cicero]

=============== The generating equipment was probably made in Manchester.

'Metro-Vick', 'Mather & Platt', 'Ferranti' (and many others) are all famous manufacturers in the area. The demonstration cable and cold chisel mentioned above were probably cut out after the demonstration and taken as a trophy to the manufacturer's HQ.

Cic.

[Steve Firth]

Nice theory but rather at odds with the facts. The Godalming generation scheme was commissioned by Calder & Barrett in 1881 and the alternator was provided by Siemens AG.

[Cicero]

================== In that case it would appear that the Godalming museum was a bit slow off the mark in collecting exhibits. As far as I know the Manchester museum is sometimes referred to as a 'national' museum of industry which might put it ahead in the pecking order for exhibits or maybe it was established earlier than the one at Godalming.

Cic.

[Dave Stanton]

I was lucky, mine had a proper 2 x screw terminal.

Dave

[Roger R]

The tale was as I recollected it from the programme broadcast only a couple of weeks ago on Tuesday 28 February 2006, 8.30pm, BBC Four.

You can hear the audio that accompanied the programme by scrolling down to the Manchester museum on this page:

to the accuracy of 'the first electric power station', that might depend on the type and nature of the prime mover and generator and who, how, or what it supplied, etc, etc.

Havn't had a chance to hear the programme again yet and get the detail

- if specified.

Roger

[Roger R]

Listened to the audio last night. (section 4 of the unzipped audio) The presenter says that around 1880 electrical power generation was limited to individual private systems powering their own equipment. (Direct current systems?)

Mr Ferranti's idea was a central generating station providing a public supply of alternating current over a distribution network to consumers. This was to be the first public A/C supply and there were concerns about the safety of the distribution.

To answer these concerns Mr Ferranti had developed a line circuit breaker that he claimed would protect the public, the line and the generating equipment in the event of a short on a cable.

A public demonstration was arranged as was the norm for placating public concerns about new technology. The chisel was driven into a cable energised with 10,000 volts A/C. The presenter does not say where the demo took place.

The Manchester connection is that Mr Ferranti was a mancunian, and I would think his factory was in Manchester, which is probably why the museum has the artifacts.

Roger

[Cicero]

================ To confirm what you say.

The museum exhibit is actually named, "Ferranti's chisel" and the presenter (Rose) actually states this in the programme.

Ferranti is located in Oldham which is now I believe part of Greater Manchester.

The actual demonstration probably took place at Deptford power station - see here: