Any thoughts on surge protection? BS 7671 now requires SPDs unless you can either show that a risk assessment deems them unnecessary (perhaps unlikely if you're next to a lake - doesn't sound "urban") or the value of the installation is so low as not to justify them economically (again feels unlikely). SPD considerations might influence your choice of RCD location (or type) too.

   - Andy.

Hi Andy, we are very urban! The substation is about 200 yards away and the 11kV transformer about half that. 80 dwellings in our road.

Mike

Hi Andy, we are very urban! The substation is about 200 yards away and the 11kV transformer about half that. 80 dwellings in our road.

Mike

Of far greater concern should be induced currents on external antenna feeders, which if your antennas are to be any good, will be at a significantly greater height than the incoming underground mains (!), and likely to bring in far more in the way of  atmospheric static and thunderstorms. Depending how much you intend to transmit, gas discharge devices across the coax or from any open line feeders to ground , at the main access panel or earth marshaling point, or the base of the antenna if it is a vertical tuned against ground, are worth considering. They are pennies to those of us who can solder  The Three legged ones are very good for balanced open wire line, the single cartridge ones are better for coaxial cables.

Be aware though that you need to have GDTs with a breakdown voltage a lot less than the peak RF that will appear on the lines, or they will suddenly light up mid transmission and short the PA, which is not good for the kit or the continuity of the QSO.. If you are not considering long bursts of unattended operation, then a sacrificial  relay that shorts all the antennas to ground when the shack mains is off is  a simple belt and braces expedient.

I'd also suggest that an RF filter rather than the BS7671  type surge suppressor will be more use for a radio shack- it will keep any stray RF  of yours out of the mains cable (reducing the risk of domestic conflicts), and put a bit of a damper on any mains born interference coming to you, as well as smearing out and flattening any short duration spikes into a lower amplitude longer duration 'ring' without lifting your local earth potential.

(the standard surge suppressor simply dumps the KV surge into the local earth which in your case, where there is a mix of inside and outside, is not so good.)

Mike.

I thought the requirement for an SPD didn't apply to individual domestic properties? In the 40 years I've lived in this road there gave been no lightning strikes (I can't even remember the last time we had a power cut). Given the intended use of the garden building it wouldn't be occupied during a thunderstorm so the risk to life is low.

My antenna is an HF end fed half wave fitted with a lightning arrestor that is connected to an earth rod. I propose to move the arrestor to the building and connect it to the mains earth rod.

Mike

it is a requirement to consider it.  You may consider it, to be spurious on this case ;-)

The sort of consideration you are supposed to do is

This includes a simplified assessment for when SPDs are required, stating that:

“Protection against transient over-voltages shall be provided where the consequence caused by over-voltage:

1. Results in serious injury to, or loss of, human life or
2. Results in interruption of public services and/or damage to cultural heritage or
3. Results in interruption of commercial or industrial activity, or
4. Affects a large number of co-located individuals.”

Maybe a shack full of gear that is unplugged or DP isolated when not in use does not really need this.

Mike

A rather long but interesting doc - but bear in mind written largely by the makers of the things.

The current rules for fitting SPDs are:

Must, if loss of life etc as listed in (1)..(4) above; else

if single domestic and cost outweighs value of stuff protected, then can skip;

else if can't be bothered to do risk assessment, then Must;

else if risk assessment says yes [this isn't a subjective thing - it's the calculation based on location in the country and the characteristics of last km of supply - except plus the dodgy urban/suburban distinction] , then you Must, else can skip.

The domestic exception is becoming mostly meaningless these days, as the value of TVs, laptops, LED lighting, boiler controls etc are almost always going to far outweigh £60 for an SPD.

The assessment includes the arrangement of the HV feeding the sub-station, and a lightning strike can be quite far away and not directly hitting the supply and still cause a transient.

I'm pretty certain a RA would conclude it's not necessary but if they really are £60 then the hassle would outweigh the cost. Where is the SPD installed - house or garden building?

And please tell me I don't need an AFFD ...

Mike