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custom90



Member Since: 21 Jan 2010
Location: South West, England.
Posts: 20316
United Kingdom 
This is quite an interesting thread!
After reading through what does PME actually stand for?

We have a commercial installation here, and when it comes to the underground SWA. (Steel wire armoured.) cable the power line company said it can be put in on its own.
(Can't imagine any conduit would do any harm bar added cost only add even further protection.)
But* it must be at least xx depth. (Figure eludes me.) and xx distance above use SWA live cable yellow warning tape that you bury underground above the cable. The tape is BS xxx (again I can't recall the number.) standard marked and designed just for the job.

We apparently need this year to get the Consumer Unit. (MK) changed to a metal one to meet new regs.
Inc testing already done total about £800. Shocked

Hate to think what a line in, inc meter install now costs plus whole Consumer Unit install and hook up.

Brands wise always liked MK, BG & Steinel for outdoor lighting sensors.
Not a Crabtree brand fan though..

Straying off of the OP's original question. (Hope he doesn't mind a touch OT. Off Topic)

We have overhead HV lines outside which power feeds are brought down from to houses.
There isn't any transformer in sight that close that I am aware of, as the feeds are tapped off which I would imagine two live lines and two neutrals. (Unless I'm assuming wrongly.) with the 4x lines.
How is the voltage reduced down to the 220 - 240v range when reaching the house? I can't imagine the lines up there are such low voltage as that or is there some form of voltage trickery I'm missing literally closer to Home?

I find it an interesting subject, I would imagine they are somewhere between 6 KV and 32KV, 4 lines per pole mounted vertically one above the other.
There are some further away that are 3x lines mounted on a horizontal bar, I would imagine these are higher voltage again as these sometimes have transformers mounted just below also.
All are timber poles.

The power network company have been inspecting a lot with the helicopter of recent years.
I take my hat off to the linesmen that deal with all the HV network that we all rely on so much!

Thumbs Up ⭐️⭐️God Bless the USA 🇬🇧🇺🇸 ⭐️⭐️
Post #726382 30th Aug 2018 11:45pm
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dorsetsmith



Member Since: 30 Oct 2011
Location: South West
Posts: 4554
PME Protective multiple earthing



Last edited by dorsetsmith on 31st Aug 2018 11:22am. Edited 2 times in total
Post #726392 31st Aug 2018 7:15am
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blackwolf



Member Since: 03 Nov 2009
Location: South West England
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custom90steve wrote:
This is quite an interesting thread! ...
Agree Thumbs Up

custom90steve wrote:
We have overhead HV lines outside which power feeds are brought down from to houses.
There isn't any transformer in sight that close that I am aware of, as the feeds are tapped off which I would imagine two live lines and two neutrals. (Unless I'm assuming wrongly.) with the 4x lines.
How is the voltage reduced down to the 220 - 240v range when reaching the house? I can't imagine the lines up there are such low voltage as that or is there some form of voltage trickery I'm missing literally closer to Home?


That sounds to me more like a 415V three-phase supply. Perhaps you are getting your mains from one (or more) phases.
Post #726393 31st Aug 2018 7:19am
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Caterham



Member Since: 06 Nov 2008
Location: Birmingham
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/\ as you say either it's not HV or it's 400v (415v is old school Smile ) or there is a transformer somewhere - and it's usually fairly obvious.
Post #726395 31st Aug 2018 7:32am
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Caterham



Member Since: 06 Nov 2008
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[quote="apt100"]
Rashers wrote:

Just to add about 30mA RCD...
Many people call the green/yellow wire "earth", but there is usually a voltage difference between it and true earth. Inside a building it doesn't usually matter. When you take it outside it can be dangerous. If you have a PME supply, and there is a broken neutral in the supply network, then the green/yellow wire (and anything metal connected to it) can be close to the full 230V supply voltage above true ground. And an RCD won't be any help at all.
Hence it is illegal to have PME supply at eg caravan parks and marinas. And usually not recommended for supplies to outdoor buildings.


Would I not be right in thinking without a neutral supply the RCD will trip ie there'll be a potential difference between the phase and neautral?
If not then a guess there's no need to worry because you'll be no worse off than 95% of people in this country and guess there's also the questions of whether your looking to carryout an install that meets current regs or looking to overcome every possible eventuality?
not trying to have a dig here but more concerned that what little knowledge I have / had as either gone or become rusty Thumbs Up
Post #726396 31st Aug 2018 7:45am
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dorsetsmith



Member Since: 30 Oct 2011
Location: South West
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RCD

Under normal circumstances, the current flowing in the two wires is equal. When an earth leakage occurs due to a fault in the circuit or an accident with the equipment, an imbalance occurs and this is detected by the RCD, which automatically cuts off the power before injury or damage can result.
Post #726410 31st Aug 2018 9:32am
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Caterham



Member Since: 06 Nov 2008
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/\ exactly.

an inbalance (fault) will cause the RCD to trip. an overload which is generally a different type of 'fault' will not trip an RCD but should take out a fuse or MCB. Thumbs Up

30mA RCD for protection to life
100mA RCD for protection of property
(typically)
Post #726413 31st Aug 2018 9:36am
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leeds



Member Since: 28 Dec 2009
Location: West Yorkshire
Posts: 8580
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apt100 wrote:
.
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.
.
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Hence it is illegal to have PME supply at eg caravan parks and marinas. And usually not recommended for supplies to outdoor buildings.





Going OT and just to satisfy my curiosity what is correct/legal/conforms to part 17/18 way of earthing/providing electrical safety at caravan parks?

Just curious as we sometimes plug into outdoor supplies on caravan sites.

How are caravans protected electrically?


Brendan
Post #726424 31st Aug 2018 10:13am
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Caterham



Member Since: 06 Nov 2008
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I believe you'll find it's via an RCD.
Post #726425 31st Aug 2018 10:16am
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Retroanaconda



Member Since: 04 Jan 2012
Location: Scotland
Posts: 2639
Scotland 
As far as power distribution networks go, usually (but not always) if you have wires mounted vertically above one another than it's a low-voltage circuit (i.e. 230/415v). The lines with the wires mounted in a line horizontally will be HV so most likely be 11kv minimum, potentially 32kv. If you trace your vertically-hung wires back you will get to a transformer on the HV line somewhere. The three lines can also sometimes be combined into one three-core insulated wire.

When I put the power supply in to my workshop I dug the trench, laid the conduit, pulled the cable (10mm^2 SWA) through and mounted the workshop consumer unit. Then the sparky hooked it up to both consumer units for a few hundred quid. I did all the subsequent circuit wiring inside the workshop. That's for a 40A supply from the house.

The requirement to use a Part P certified electrician doesn't exist in Scotland however, everything just has to be done to the correct standard.
Post #726429 31st Aug 2018 11:03am
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Intercept



Member Since: 27 Feb 2017
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Re: Power Supply to Garden Workshop
Rosco wrote:
Mrs Rosco is having a garden workshop to do her arty wool dying delivered this weekend, which will then need kitting out, insulating, etc, etc and will need a power supply running too it.

https://www.tlc-direct.co.uk/Book/7.14.1.htm has useful information for this and other types of installation.
Post #726437 31st Aug 2018 11:45am
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custom90



Member Since: 21 Jan 2010
Location: South West, England.
Posts: 20316
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Thumbs Up Interesting. I'm no expert on it so many of you probably know a lot more than I do.
We have quite a nest of overhead lines here!

There are some very large NG metal pylons out in Wilts and South Glos. Some of which are networks across the Severn Bridge and Avonmouth etc.
Such large pylons that the have a large V formation of insulators on them and you can hear them buzzing especially in damp weather in the winter with a high load. Corona Discharge basically. Rather un-nerving if your close especially knowing they are 250kv upward minimum.

NG have a map I think on their pages somewhere. ⭐️⭐️God Bless the USA 🇬🇧🇺🇸 ⭐️⭐️
Post #726468 31st Aug 2018 2:49pm
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custom90



Member Since: 21 Jan 2010
Location: South West, England.
Posts: 20316
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Interesting photo Corona Discharge 500kV:



Click image to enlarge

Further info:
https://en.m.wikipedia.org/wiki/Corona_discharge ⭐️⭐️God Bless the USA 🇬🇧🇺🇸 ⭐️⭐️
Post #726469 31st Aug 2018 3:13pm
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Retroanaconda



Member Since: 04 Jan 2012
Location: Scotland
Posts: 2639
Scotland 
The biggest transmission lines (line the one across the Severn at Aust, by the bridge) are 400kv. With the rest of the transmission network being made up of 275kv and 132kv. Distribution then generally takes over for lines at 33kv, 11kv and low voltage (230/415v).

The bigger the line, the more important it is. There are two lines feeding from Scotland into England, and the capacity of these lines being exceeded is often the reason why windfarms are required (and paid) to turn off up here. Most of the grid demand is in England after all. I heard a while back that a new third link via subsea cable in the Irish sea was being considered.

Try phoning them up and asking if they can shut down the 400kv western England/Scotland link so you can fell some trees alongside it - worth a laugh for their response Laughing
Post #726470 31st Aug 2018 3:17pm
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custom90



Member Since: 21 Jan 2010
Location: South West, England.
Posts: 20316
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Rolling with laughter ⭐️⭐️God Bless the USA 🇬🇧🇺🇸 ⭐️⭐️
Post #726471 31st Aug 2018 3:28pm
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