SPDs - retrofitting practicalities?

Given the dubious value of SPDs as being currently provided, I'd opt for the cheaper ‘Replace as you go’ approach to your consumer electronics.

AJJewsbury: 
Or is it all just too hard to do properly, and should I just give up and resign myself to occasionally replacing the odd bit of electronics?

There was a time when it was considered wise to unplug a television during a thunderstorm, but in those days we could cope without for most of the time. Alternatively, disconnect the aerial lead. I wonder whether an aerial in the loft space would be safer than outside? Of course some might say that an aerial is out of date nowadays.

Andy, I think that you have answered your own question, but I suspect that it is more a matter of whether it would be cost-effective than doing it properly.

It is tricky, and in a case where the external services do not all enter solidly glanded through a common access panel (nuclear bunkers do this, and they really are surge proof) it has to be a compromise.

What are you protecting - 

a)mains connected equipment just on the mains, damaged by spikes between the mains wires? or 

b) mains powered equipment connected to the antenna? or

c) mains powered  equipment connected to the phone lines ?

The strategy varies. 

The sort of thing that goes in the CU only really covers ‘a’ well.

Earthing the coax of the antenna to the cpc of the circuit supplying ‘b’ close to its point of use protects that but may introduce a problem for ‘a’ that was not there before.

In a similar way, ‘c’ is best projected by spark discharge or varistor devices between the phone lines and also between the phone lines and the CPC of the circuit supplying equipment ‘c’.

This to may introduce a problem for ‘a’ that was not there before.

Of course if you answer ‘all of them' then you have to loop the telecom cables from their point of entry, via the power MET, and only then onwards to the equipment they supply - now you are in effect creating the same condition as the common access panel in the bunker. This is not often very convenient.

Mike.

Robin Earl from Dehn UK is the person I would ask about anything surge related. He does the presentations at the Elex conferences. JP may know him better than me. His email is easily found. Just copy and paste what you have written above, and I'm sure he will advise.

And please repost what he recommends.

Thanks.

Thanks guys.

This to may introduce a problem for ‘a’ that was not there before.

Indeed - the more I think about it the worse it seems. SPDs seem easy enough when there's only one connection to a piece of equipment, but once you get two or more, especially heading off in different directions, it seems to get much much uglier - with far more risk of (a portion of) the surge current being drawn right through the equipment you're trying to protect.

Fig 534.1 (the concentric circles of lightning protection zones with external services heading off in all sorts of different directions) looks good on paper but seems to rely on the bonding forming each circle having near negligible impedance … but given that most of us don't live or work in something akin to a landlocked submarine, that doesn't seem particularly realistic.

As you say, having everything enter at a common point makes things a lot simpler … but isn't particularly practical, especially with PV & aerials on the roof and main services coming out of the ground. Maybe for a new build or major renovation it would be possible to arrange things that way (PV d.c. cables coming down the outside wall to an inverter next to the intake, likewise phone and TV aerial), but isn't going to wash for me now.

The only simple policy I can see that might work would be to have SPDs on all connections immediately next to every piece of equipment you're trying to protect (with a common PE connection) . So for the PV I'd need SPDs on the d.c. side right before the inverter, then another set on the a.c. side - both connected to the same c.p.c., then another two sets in the CU - one on the bus-bar and another after the PV circuit's RCBO (if I didn't want it to be subject to the surge current). Likewise the TV aerial system would need SPD both fore and aft of the distribution amplifier and then again on both the aerial and mains at the TV. Cost and convenience count strongly against that approach however.

I do wonder about the value (or indeed the costs) of adding SPDs to the LV installation without considering everything else in the building.

   - Andy.

Once we all have fibre-to-the-home internet, the problem of surges on the phone line will disappear.

I think solar should be pretty safe unless you take a direct hit from lightning, in which case a few SPDs aren't going to do much good.

Simon Barker: 
Once we all have fibre-to-the-home internet, the problem of surges on the phone line will disappear.

Oh yes, super-fast fibre optic all the way to the green box. Then copper.

Or as they are rolling out  new connections now, fibre overhead on poles in a high tensile plastic pipe, and then down the side of the house and into a mains powered box in the living room.

EMC and ESD issues not perhaps helped in cases like my parents where parallel to the fibre runs the twisted pair for the phone. 

But BT Openreach do claim they will be turning off the copper telephone lines in 2025. I expect that deadline to be missed, like all big infrastructure projects, but it is certainly on the cards at some point..

Their current timetable is here.

Mike.

There's always the Wi-fi in water pipes system.

Chris Pearson: 
 

Simon Barker: 
Once we all have fibre-to-the-home internet, the problem of surges on the phone line will disappear.

Oh yes, super-fast fibre optic all the way to the green box. Then copper.

There is a company (and it's not Openreach) rolling out fibre across my town at the moment.  The down-side is that a phone then becomes an optional extra, as you need to get a VOIP box to plug the phone into, and then pay extra for the service.