Part 18 Surge Protection

IET 18th edition?

Not heard the "within 1km of a church" wording anywhere else, sounds like bollox

In any case, SPDs don't apply to single dwellings

No,he is reading it wrongly. There is a risk assessment that needs to be satisfied. TBH, not much has changed, but the IET are making people aware of the changes to the Regs, and increased the scope of the chapter on lightning etc. The local Church tower is not relevant, it states : 'this section deals with direct strikes to the supply systems .... it does not specify protection against...direct or nearby strikes on the structure'.

The RA goes into some detail, and gives a map of strikes per year per km/2., the figure for which is used in the calculation. Overhead supplies are more at risk than underground. It also has 4 examples that should be protected, all of which make sense - 'protection.. shall be provided where the consequence .. could be..1, injury or loss of life.2, interruption of public services or damage to cultural heritage, 3, interruption of commercial activity, 4, affect a large number of colocated individuals.

The course I went on went into some detail about this. 1 is self explanatory,but it is hard to see how to mitigate it, unless you do the RA. 2, government/council buildings/museums that could have their electic systems damaged by a lightning strike in the area, 3, self explanatory, 4 blocks of flats. But what is a large number - 10? 100? Typically, the above should all be designed to make sure the people are safe, and little damage will occur if there is a strike on the feed cables.

It then says 'protection shall be provided.. except for single dwelling units where the value of equipment does not justify such protection'.

OK, this came up on the IET forum, with a solid argument that the majority of houses will not need it. There is a one in a 50,000 chance of a strike in your area (just an example). 50000 houses at £100+ each to fit an adequate SPD will be £5million. Then what is the cost of a few electical appliances being burnt out by a strike? Far less overall than the total cost of fitting the devices. So, on a purely risk based assessment, you would not fit one in a typical house.

That is still being debated. Many say they should be TT, others says you then have earth gradients to the house TN system. Say you are using a hoover plugged into the house to clean the car while it is plugged into the charger.Different earth voltages, and the risk of a shock when touching metalwork between the 2 devices. No easy solution, but, the present situation of a mixture of earthing hasnt led to multiple deaths yet.

No, it will not be done. Its another one of those pie in the sky things that are impractical to achieve and in any case, I have yet to see proof that any kind of surge protection is going to stop problems from lightening. Remember I was almost struck by it twice, but the buildings nearby were trashed from all wiring and electronics points of view, however many others nearby were not affected, so its a variable feast indeed and trying to achieve some utopia here is crap. Brian

The equipment manufacturers seem to have realised that leaning on the IET to force adoption of arc fault and surge protection products is more fruitful than trying to convince people to buy them.

taking their lead from the "eco" central heating pump manufacturers.

I've seen this more and more in the last few IET regs. Used to regard them as a excellent document, but less so nowadays - too much industry just trying to push their products into the regs.

Looking after some radio and comms sites earthing and lightning protection is more to do with 'eff off size earth conduction and shunts rather than surge devices..

sounds like someone had nothing better to do that to spout some bollix to sell more devices that are questionable in effect anyway:(..