Electrical issues.

Hi everbody. I've a couple of issuesregarding my home electrics. The mains supply is via overhead cable, and so is presumably a TT system. There is a 63A, 100ma RCCD covering the whole installation, but the consumer unit is a fuse wire type. There is a additional 30ma RCD protected circuit which supplies an outside shed/workshop via a 6mm overhead T&E cable.

First issue is the earthing - as far as I can see the only local earthing is via a spike connected to the earth by the shed. Since this is via the T&E cable earth wire, which I measure as about 1mm2, this looks a little inadequate - my understanding that the earth in a TT system should be 16mm? I'm very happy to install a new earth cable/spikes if necessary myself, but presumably this is not really possible under the new regs?

Secondly, I need to arrange an additional external supply for sewage treatment plant. About 80W. The simplest way to do this would be via an RCD protected spur off the downstairs ring. Is this OK, and again, can I do it myself without falling foul of the new regs?

SR.

Reply to
SR
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Does this help?

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are a garage and a shed, but does outline acceptable connection methods to the house circuits.

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the searchable bit - some earthing matters mentioned.

I don't want to answer directly as your TT earthing is totally outside of my experience.

Yes you can do it all yourself, notify Building Control. There is a prescribed test for an earth rod. Can be done in theory with a couple of meters and a car battery plus resistors but the pros have proper test gear for this.

The testing is particulalry important, because, unlike a new bit of typical fixed wiring, it is difficult to say "it looks right", ground conditions are too variable.

You can phone the electricity supply company (the REC, not the billing company) to confirm what they think your earthing arrangements are.

HTH

Tim

Reply to
Tim S

Your earth rod will have far higher resistance than the 1mm wire. You have an RCD to deal with this limitation of TT systems. 1mm is small, but wiring a high impedance earth with 16mm would be pretty pointless. On a new install it would not be done the way yours is, but in the grand scheme of real life problems I'm not sure it really features in the top 1000.

would work fine.

NT

Reply to
meow2222

The supply to my house is overhead but we are TC-N-S (PME). Just because it's overhead does not necessarily mean it's TT. The supply co have put a label by my meter actually saying "PME installation"

Best thing is to contact the supply co and they will tell you.

Roy

Reply to
RzB

It shouldn't be too difficult to tell by looking at the installation around the incoming feed, company fuse and meter.

Reply to
usenet

The FAQ tells you how...

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Reply to
Andrew Gabriel

That would have been my assumption - I calculate 20M of 1mm2 to have a resistance of less tham an ohm. However, the advice at:

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16mm, so that's what I assume I really should have.

SR

Reply to
SR

Reply to
Dave Plowman (News)

The earth electrode resistance (its "resistance to the general mass of earth") will be much higher than that of a few metres of 1 mm^2 wire, yes. (Typically 20 - 200 ohms, depending on the soil conductivity.)

Did you think he meant the resistance of the rod itself?

Reply to
Andy Wade

That's what he wrote. ;-)

Reply to
Dave Plowman (News)

or more direct connections to earth."

Being devil's advocate that implies a rather nasty short-circuit, but I'm sure that's not what is really meant.

Phil

Reply to
Phil Addison

Did you see the previous paragraph? ... "Note that in these descriptions, 'system' includes both the supply and the installation, and 'live parts' includes the neutral conductor." These definitions of 'system' and 'live parts' come from the wiring regs. The actual derivations of all these letters is unfortunately missing from the wiring regs which is why I thought it particularly good to explain in the FAQ. The original document on earthing types was a French standard. TN is Terre Neutre (earthed neutral), IT is Isolée Terre (insulated from earth), etc.

Reply to
Andrew Gabriel

In that context "live" means "current carrying," and is not the opposite of neutral, IYSWIM. In wiring-regulations-speak "live conductors" refers to the current carrying conductors of a circuit, as opposed to the protective (earth) conductor, and therefore includes the neutral.

In colloquial usage it is common to use "live" to refer to a phase conductor (sometimes called "line") - but it will usually be clear from the context what interpretation should be placed on the term "live."

Nevertheless a better description of the first letter "T" might be something like "indicates that one or more points of the source of supply is directly earthed."

Reply to
Andy Wade

Oops must have been in my blind spot, transfixed by that apparently contradictory definition. It would be nice to see it written out in plain English avoiding any confusing (for non-professionals) terminology.

I appreciate that but we don't have to perpetuate it. Maybe quote the regs definition then explain it in everyday language.

That extra information, the French bit, is very helpful. Code letters that I can't penetrate give me a mental block.

Phil

Reply to
Phil Addison

So some neutrals are both live and earth at the same time.

NT

Reply to
meow2222

Hmm, that comment is rather ambiguous and misleading. Depends whether it was made in wiring-reg-speak or electrical-theory-speak.

As a generalisation, it always used to be the case that for private installations the neutral conductor may *not* be used for protection against earth leakage currents (PME) without the express written approval on an individual basis of one or other Secretary of State - can't remember which one. I'm assuming that is still the case

Reply to
The Wanderer

Not within the Consumers installation - i.e. downstream of the service cutout

Reply to
John

This is just playing with words really. When the wiring regs talk about "the live conductors of a circuit" they mean phase and neutral, colloquially called live and neutral.

So in that sense the neutral is a live conductor (but not a 'hot' conductor in the sense that Americans us the word).

Reply to
Andy Wade

Yes, it's still expressly forbidden and is an offence. Chapter and verse follows:

Statutory Instrument 2002 No. 2665 The Electricity Safety, Quality and Continuity Regulations 2002

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The Secretary of State, in exercise of the powers conferred on her by sections 29, 30(3) and 60 of the Electricity Act 1989[1], hereby makes the following Regulations: -

General requirements for connection with earth ---------------------------------------------- 8(4) A consumer shall not combine the neutral and protective functions in a single conductor in his consumer's installation.

Offences -------- 35. [...] and any consumer who fails to comply with regulation 8(4) or 34(2) shall be liable on summary conviction to a fine not exceeding level 5 on the standard scale.

Reply to
Andy Wade

Your snipping loses the context of what I wrote. I replied to the comment that sometimes the neutral wire doubled up as Earth. Nowhere did I say that Neutral could not be considered a live or current carrying conductor

Your point being?

Reply to
John

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