I have a surge protector in my main DB, the input into this is the grid. It’s a Dehn device like this. It’s type 2.
For the inverter I have two of these - one on the grid side, one on the AC output to the backed up circuits. Also type 2.
So what are these actually giving protection against? We are having grid over voltage in my neck of the woods today (it hit 257 this morning). AIUI these protectors will not react to that voltage.
I’m told the Dehn devices are very good. I have another one just lying around. Should I just keep it as a spare?
Protection seems to be against surges induced by lightning (not a direct hit), switching surges, and the sort of surge we can get when power is restored after load shedding
Not specifically. We have a too high grid voltage in my area right now. So I was wondering if the SPDs offer protection (though the clue is in the S), which led to thinking about what they actually do protect against.
The inverter has SPDs on both sides - so I’m guessing it’s well protected, but not all of the property is supplied by the inverter, so that SPD in the DB comes in to play.
It depends on the grid code you set it to. Not unnaturally, mine is set to “South Africa 230V”. It will disconnect if it gets 253 or up for 30 straight seconds, or within about 100th of a second (if I read the settings right) at 270.
A surge arrestor is an overvoltage detector. It has to be installed after a breaker or fuse. What it does is it changes it’s resistance when the voltage exceeds a predetermined voltage. At that point it starts heating rapidly, so they are mounted next to a spring-loaded solder joint. When they get hot enough to melt the solder, the spring will cause the device to short the input (Live to earth), which will cause the upstream breaker to trip. They can also clamp short spikes without melting the solder.
Your inverter itself also has built-in surge protection (these don’t have the melting joint part, though).
The voltage is usually high enough that they won’t trigger too easily, usually 275VAC (IIRC), which means they actually start lowering their resistance when the peak of the sine hits 390V.
The DEHNguard also has a lower voltage gas discharge tube in series with the MOV, which means it has no leakage current in normal operation. I see that it is rated at 340VAC…
Thank for you for that very clear explanation. This explains exactly a problem that I had a couple of months ago. It was when I had the extra panels fitted. When they turned the PV back on a breaker tripped straight away. They checked their wiring etc, turned the PV on - same breaker trips. Then they found that one of the DC SPDs was showing a fault (presumably the flag indicator is activated by that soldered spring).
So it’s exactly what you describe here. The SPD had been activated, was causing a short, and the breaker kept on reacting to that.
OK… I don’t know what the significance of that is. I used to think I was “technical” because once upon a time I fixed cash registers and electric organs. But I’m not really.
I’m appreciative of the good information I get here.
No leakage current just means that below the breakdown voltage, the resistance of the surge arrestor is so high that essentially no current flows. IE, nothing really “leaks”.
Breakdown on something like a MOV (metal oxide varistor) isn’t immediate either. There is a pre-breakdown area where it starts to conduct, so if you have a 275V rated MOV, and the voltage is getting into that pre-breakdown area, it will start to conduct and create some heat. Which is where the second part comes in, the solder joint. At least, that’s how I understand it.
With actual surges (aka spikes), it is pushed into breakdown rapidly, and it creates a dead short that blows the breaker. And usually itself as well.
Edit: I realise that is not the full answer so let me continue. With your gas discharge type, once the voltage gets high enough the gas ionises and starts conducting. The breakdown curve will be different. Google tells me gas discharge is slower than a MOV, but it does not have that pre-breakdown area, so therefore no leakage under some conditions.