Type 1 Surge Protection - Second opinion required

[Dannyspark]

Hello chaps,

With the advent of amendment 1 and Surge Protection playing a big part now I need a second opinion on a job I'm quoting for at the moment. I'll admit my experience with these devices is zero apart from the usual Type 3's that are common place now in homes.

I am rewiring a church (TT system), which obviously has a lightning conductor on the spire. The electrics look like they haven't been touched in 50 or 60 years......I can't even recognise the board as anything I've seen before! (I wish I'd photographed it). The installation is a simple 3 radial lighting, 2 radial sockets circuits set up so no concerns with that side of it.

Anyway my plan is to install a Type 1 SPD just after the distributors main cut-out via a Henley block keeping cable lengths to an absolute minimum.

This is the SPD I am planning on using http://www.farnell.com/datasheets/640099.pdf. Now my confusion is coming due to the recommended OCPD rating that is listed in the datasheet for the SPD, as it says that it should be a minimum of 125A! This sounds excessive to me but am wondering if you guys who work on large industrial installations and are used to using these bits of kit think it is okay? Also the suggested minimum cable csa is listed as 6mm but for this MCB I would expect to be using 35mm!

I have found a suitable MCB here http://www.expert-electrical.co.uk/...Current-MCB-Double-Pole-125-Amp/prod_985.html but would like your opinions on this if you would be so kind.

Thanks in advance.

 

[spark 68]

You can get different size SPD's, some are fused at 63A with supply cables max of 16mm, but I have only used the TP+N versions, I have not used SP ones yet.

Google for Furse, I think Tony had a link on here some where.

 

[malcolmsanford]

Danny not sure what the manufacturers mean by that and they only specify a gL fuse as well, may be worth a call.

The reduction of CSA for the connection is simply because you need preferably to keep the tails below 0.5m as per reg 534.2.9 and should never exceed 1m, so by doing this your adhering to regulation 434.2.1.

Can I ask if your installation as lasted 60 yrs without Surge Protection, why now?

 

[Dannyspark]

Can I ask if your installation as lasted 60 yrs without Surge Protection, why now?

Thanks for the replies. The reason I considered SPD on this installation was due to following the flow chart on page 33 of OSG (2011). On 3.7.2.2 it states that Surge protective devices should be considered in the following circumstances: The low voltage supply to the installation, at some point, is provided by bare overhead conductors at risk of direct lightning strike, and the building requires or already has a lightning protection system (LPS).

Now I realise the key word is "should", so I was airing on the side of caution. Do you think that it is unnecessary Malcolm? As I said SPD's are all new to me and as this has only been live since January this year it seems that it could become a big issue now.

 

[spark 68]

The low voltage supply to the installation, at some point, is provided by bare overhead conductors at risk of direct lightning strike

Hi Danny,

Looking at reg section 443.2, in 443.2.2, under external influences, in the UK we are AQ1, or less than or equal to 25 thunderstorms a year, so SPD not required under that criteria (above), and using the alternative risk assessment in 443.2.4, Churches are under consequences iv) which on the face of it SPD is not neccessarily required, unless you want to do the calcs, length of DNO power lines etc...etc., I think I would prefer to base it on AQ1.

As you say this is a completely new section.

 

[malcolmsanford]

Hard to give a direct yes and no to be honest Danny.

Section 443 in the regs do now cover this and regulation 443.2.2 covers your risk assessment on overhead lines. Of course there have been instances in the past of lightening strikes, but a good indication for you would be the current condition of the installation. As you have pointed out it could be over 50 yrs old, that would tell me that there have been no incidents of strikes.

Also what are you protecting with the SPD to be honest, a couple of socket circuits and a lighting circuit, hardly NASA is it.

Without researching more into the area, how many strikes it as a year, it's impossible to say yes or no, but for me an indication of the existing installation would be my guide

 

[Dannyspark]

Many thanks chaps,

As it seems a vague area at the moment and when reading through the regulations it suggests that it is recommended as opposed to required, I think I will defer to the client and ask them if they want to pay the extra £2-300 to have it installed and then note it with the certs.

Thanks again for your opinions.

 

[malcolmsanford]

Well Danny we all know how that decision is going to pan out, 2-300 notes and left to the customer

 

[spark 68]

I was thinking exactly the same thing Malcom, a church shelling out an extra 300 notes that they don't see the need to, lol.