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Surge Protectors and Neutral

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My 3 phase panel does not have a surge protection device and recently I had some damage to devices in the property. These were random items with chargers and pcbs and I put it down to nearby lightning. Its a remote property so I wasn't there at the time but everything failed at exactly the same moment.


Now I would like to instal an SPD in the panel but I see there are two options - 1. without neutral 2. with neutral. 


I won't be installing this myself but If I can source the correct part (and not some cheap local undersized option) then maybe that gives my electrician a head start. Ideally I would like to stay with Schneider and see the following two options:


1. https://www.se.com/ng/en/product/A9L15597/ipf-k-20-modular-surge-arrester---3-poles---340v/

2. https://www.se.com/th/en/product/A9L15693/ipf-k-20-modular-surge-arrester---3-poles-%2B-n---340v/


Can someone advise which option I need and what I should consider. Its the grounding options that are primarily confusing me (TNC and TT). There is a ground rod attached to the distribution board.





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If you don't know your earthing arrangement for sure then assume TT and go for the 3 pole + N unit.


I do note that that unit is only 5/20kA. You might be better served by a 40/80kA or even a 60/100kA unit backed up by smaller plug-in arrestors on that delicate technology.


Is your panel DIN rail or plug-in? You may need a small external box to house the SPD.


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Thanks for the response Crossy.

I am fairly certain that MEN has been implemented and the electrician did instal a 2.4m ground rod to the CU. I will check this with him again but its difficult to communicate with him on technical matters (as many here have also experienced).

However to be sure I will run with the 3 pole plus N and upsize to the 60/100kA unit as you advise.

The panel is DIN rail and space exists. Thanks again.


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Thanks for the suggestion Crosby. Attached is a pic of the main board and breaker box. 

You will note that the under/ over current device is currently disconnected. 

The Schneider 3P + N MPD has been quoted at Thb12k. 
iPRD65r modular surge arrester - 3P + N - 350V - with remote transfert




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10 hours ago, Bosscat said:

The Schneider 3P + N MPD has been quoted at Thb12k. 




You can get a Tomzn (a well known Chinese manufacturer) 30/60kA device for 1k Baht 



If you prefer to stay with a known name (still made in Chine of course) how about a 160kA ABB unit for 7k Baht



We have a lot of protection scattered around, a 100kA Tomzn unit on the incoming supply, various AC and DC units on the solar and baby 5kA "disc" MOVs in all the LED light fittings. The UPSs on our PCs and TVs all feature built-in MOVs which have been upgraded with more of the disc units.



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The price shocked me also. I am OK Tomzn and ABB is also OK. 


I recall you mentioning the baby 5kA MOV's before and will also look into them. 


Could you make any sense of the grounding on the board pic and if it is MEN does that mean I can drop the +N and move to 3 Pole?

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1 hour ago, Bosscat said:

Could you make any sense of the grounding on the board pic and if it is MEN does that mean I can drop the +N and move to 3 Pole?

There is no earthing visible on the incoming supply. From the pictures it is not clear if your area has MEN. It does seem extremely likely that you have a 4 cable supply (3 phases + neutral) it also is not at all clear that you have an earth neutral link. They probably are not linked.


I can’t definitively advise on dropping the neutral, though can’t see any good reason to do it and you may have to have a qualified competent electrician inspect and advise (good luck with finding one of those here) 


FWIW you have a 3 pole supply and it may well be TT

Edited by sometimewoodworker
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