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Understanding an SPD lightning arrestor


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Just got this SPD yesterday & don't really understand them. It looks like fuzes/breakers on L & N side and assuming they're open until >275V comes along, than they close sending the surge to G earth bar. This is only on the N side, the L side is plugged on the lower left.
What happens to the surge going down range on L side? And would N open again when <275V?
And to contradict things, I found this diagram online. Shows the L side (mine's plugged) going to ground also. ????  Confusing. For me anyhow.
 Thanks in advance!

Chint 1.jpg

Chint 2.jpg

ChiNT SPD.jpg

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Connect it like your diagram. The terminals on your unit are clearly marked.


It will clamp surges on both L and N down to ground.


Sometimes there is a third module L - N  but it's not essential in all but the most sensitive situations.


You are correct on the operation. Once the threshold is exceeded the device starts conducting and clamps the surge (the actual voltage it is held to depends upon the surge energy), once the surge has passed the unit returns to being open-circuit.

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1 hour ago, r136dg said:

Thank you Crossy, cap popped & grounded. 

 Puzzling why it was capped to begin with.


There should be an internal link, so no need to ground both sides.


Actually, I would remove the second ground, it may be internally configured as N-E and L-N rather than N-E and L-E.


EDIT It probably isn't N-E and L-N but one can't be too careful :)

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Just to say... while these devices will suppress transients (caused by lighting or whatever) there is NO protection from a direct/near lighting strike.  It doesn't even matter if your electric stuff is plugged in.  I have the unfortunate experience with that and virtually everything electric got fried - plugged in or not.  So, you can do this kind of protection but don't think you are invincible because of it.

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You may wish to scatter some secondary protection around too.


I bought a big bag of these little chaps, 20mm diameter 8kA MOVs from NPE http://www.mynpe.com/mynpe/more.php?data=116450101007




11 Baht each.


They are scattered around the house in every light fitting (we are all LED or fluorescent with electronic ballasts), at the power inlet of the aircons and slipped into the back of outlets serving technology (you need to sleeve the leads of course).


I will say I am a tad paranoid, we had a direct hit on the house a few years back. We lost surprisingly little technology but I still went all out to protect my investment. I think we were saved by the hit being to the roof and our roof steel being very well grounded by our driven piles (all the steel is interconnected). The roof structure actually measures as a better ground than our ground rod :smile:




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SPD is basially Surge Protection Devices and are used for electric power supply to networks like telephone networks, communication and automatic control buses etc. This is the most commonly used  for efficient type of overvoltage protection. It is connected in parallel and has a high impedance. 


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