Electrical Regs 2002 and earth bonding

I think it's been worded differently to confuse the cowboys (sorry, the unqualified or DIYer) a bit more, but nothing seems to have changed otherwise.

The supplier has to make sure their bit is properly bonded, because some supplies didn't meet the current minimum standards. But that's it, I think.

You know what those IEE people are like. Never get one went you want one, then three come along together and disagree with each other.

I'm not an MIET (IET=IEE). All I have is a bit of DIY experience and an EAL Level 2 Domestic Installer's qualification, which, to be honest, is pretty basic by anyone's standards.

With that stated, I'm happy to comment...

jgharston coughed up some electrons that declared:

Correct.

Yes - that's about the sum of it. There are 3 types of earthing system in common residential use:

TN-S, supplied by the network operator by means of the sheath or armour of the supply cable all the way back to the transformer, at which point it is connected to the neutral tap, or centre of the star winding. Maximum allowed loop impedance (that's phase to earth, at the meter) is 0.8 Ohm, but a particular operator may state a lower figure.

TN-C-S: Also supplied by the network operator. Earth is derived from the neutral at or near the supply head at your property. Neutral is usually bonded to earth (as in the ground) at regular intervals throughout the network as well as at the neutral point of the transformer. Max Phase-Earth loop impedance is 0.35 Ohm unless they say it's lower.

TT: You stick your own earth rod in at your property and it's your responsibility. Neutral is connected to ground via rod or otherwise back at the transformer. Common with overhead lines. You can ignore a supplied TN-C-S or TN-S if you wish and make your own TT provision.

With TT, it's usually impossible to get a low enough phase-earth loop impedance to blow out a fuse or circuit breaker under a phase-earth short circuit fault, so this is mitigated by using a time delayed 100mA or 300mA RCD directly after the meter. The time delay (so called Type S RCD) is needed to ensure that if you have RCDs on the final circuits, that they trip without taking out the 100mA RCD, otherwise your house blacks out everytime your lawnmower has a wibble.

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Do you want to ask anything specific about what you are doing - you mentioned "flats" so it sounds like a non-trivial thing that you're up to.

Cheers

Tim

Tim S coughed up some electrons that declared:

BTW - after the supplier's meter, everything will need to comply with BS7671:2008 aka the IEE Wiring regulations, 17th Edition which is a rather large tome. That's why I asked what you are actually doing.

You may well need paid-for professional advice if this involved tenants or selling flats, but feel free to ask here first.

Cheers

Tim

About ten years ago I bought a building that contains: basement workshop, ground floor shop, first floor flat, second floor flat. Picture at

When I bought the properties I rewired everything to 16th Ed (got my C&G in 1995, did the work in 1997), which required some fiddly working out for the flats, see

The first floor flat became vacant last year, so I decided, along with replacing windows, heating, kithcen, bathroom, carpets, decor, etc., to get everything properly metered on their own supplies, ie: workshop, shop, flat1, flat2, landlord, all installed where the relevant consumer can see their own meter.

The supplier quote mentioned the 2002 regs, which I hadn't come across before.

-- JGH