Do you have a pic of your dis-connector, I’m interested to see its rating and if it is fused internally. It could also weld if incorrectly specd.
I highly doubt a keto fused dis-connector will weld and if it does then the fuses are incorrectly specd.
Your biggest fear should be your batteries, the amount of fault current they carry is frightening but for instance my Keto dis-connector is rated 160A and can extinguish a fault of 120KA
Firepal FP50 portable
This is what I was referring to…
What’s in the box
1 x Firepal FP50
Well, if you open it too slowly, I can well imagine that it might weld. When I’m messing around in the garage, currents as low as 40A with a 2mm rod is sufficient to weld things together…
I imagine that with these fused disconnects, pulling them open will cause one almighty arc, and leave a few black marks, but it will do what is required.
I also see the spec sheet for the Mersen (which I’ve got) shows:
Safe on load connection/disconnection in accordance with IEC 60947-3
So it seems to be perfectly suited as a DC disconnect.
Edit: I see it is rated DC-22-B. That means it can do on-load switching of a mix of resistive/inductive loads, including “mild” overloads, up to 220VDC. The “B” part means it is not meant for frequent operation.
Its the same as your light switch, try switch it on/off really slowly, it crackles and you might see sparks.
But unless you have some nervous disorder, in an emergency you probably going to almost rip the keto switch off the wall.
edit: not comparing ac to dc, point is opening electrical contacts slowly will create arcs
The idea here is not to argue, but rather a piece of advice. I was rattled that moment and I could imagine what would have happened if it was my wife or one of the kids that had to go and open that door. To save a R1000 is nothing compared to losing my house!
@Whatyamacallit, I have a dc disconnect as well as bussman fuses for protection.
Huge humangus difference with AC, because it pass 0VAC multiple times a second (100x) for SA the arc will very quickly die out as the contacts distance increase. No such luck with high current DC, even at 50V. Arcing and burning happens fast.
DC disconnects and breakers are specially designed to rapidly blow or direct the spark (magnetically) away from the non moving contact. Those Fuse Disconnects is good for emergency use, not really anything else if it carries any current.
Groetnis.
Oh not arguing at all. Tarique had a question about his fused disconnect. That has been cleared up. I suppose I am answering a question that wasn’t really asked: Whether the Mersen/Keto type fused disconnects are good enough. Lots of people use them for the simple reason that they are at least somewhat affordable. As far as I can see, they are sufficient. I expect a nice big spark if you pull them under load, but they are designed to take it.
I’m in agreement with you that only a fuse (eg a Mega-fuse inline) is not good enough. As an example, I have a 150A fuse between my inverter and the batteries. Large enough to protect the 50mm^2 cable, larger than the inverter should ever need. But even 100A would be enough to create a lot of heat without blowing a fuse. To deal with that, 1) there is the DC-disconnect, and 2) a fire extinguisher right next to it.
How people react under pressure, we need to consider that.
I wrote a manual for the people in the house … they all lost their copies.
So now, each time I “have to” do changes, I call them all together, moan moan moan … but I have a thick skin.
Here are the panel breakers, the inverter switch, the changeover switch, inverter AC on/off, the Keto fuse, the DB’s board main breakers.
I HOPE they listen to what I show them if EVER they need to do it one day.
Ps. Once I disconnected the voltage sense wire from the inverter. Was tired, so I pulled them out from the battery side.
Big BIG mistake! Smoke was everywhere as the insulation burnt.
Bare hands … nope, just burning human flesh.
Scissors, nope.
So I sat back, watching this ongoing fiasco.
Went to my toolbox and got the wire cutters.
Problem solved.
My point: How people react under pressure, we need to consider that.
Man, I’m so tempted!!! 