Solar switch wired in series? That's crazy. Isn't it?

[Fingers]

My solar switch burned out at almost 50% of the stated max amps & volts.



Aha! It's wired in series, and it obviously should be in parallel, I thought.


If it were wired in parallel I'd get twice the switching amps and it wouldn't burn out, I thought.

So taking a look at a few switches on ebay etc, they're all the same!


The one that I finally bought states "pole connection in series obligatory".

Has the world gone mad or am I missing something?

 

[Shimmy]

Breaking a DC arc is harder than AC; series contacts is one way to deal with that.

 

[Fingers]

The dreaded ac arc.
I get it.

Thanks.

Maybe that's the answer to another question.
I have a 100amp industrial fused switch box, rated at 415volts AC and 250volts DC, and it's a giant of a thing.
Massive two pole blades, sprung open and closed with a CRACK! I wondered why on earth it was only rated at 250volt DC.

 

[Quattrohead]

Look at YouTube videos of people pulling tremendous arcs from a single solar panel. DC loves to jump gaps where as AC is lazy 60 times a second.

 

[Fingers]

Yes I know, there are some crazy arc videos on there.
I just didn't think using multiple switches in series would be any good at arresting the spark.
I still don't understand how a puny little switch can be better than my giant grey butch box
The contacts snap closed at a heck of a rate, I would think an arc would have little chance of getting under way.

 

[Quattrohead]

Ah, you believed some fine gentleman from far away places to tell you a true technical fact lol

 

[Shimmy]

Short and long of it is that when you have three contacts in series the voltage (and arc potential) is cut by 1/3 for each. A 25mm gap can sustain (IIRC) about 100V, so 3x25mm gaps gets you safely at 250V.

For AC, the arc only lasts half a cycle at most and then self-extinguishes. It won't re-form unless the contacts are in very close proximity which the switch design inherently prevents.

 

[FightThePower]

Have you looked at the IMO brand switches? They seem really well made.

 

[Fingers]

Ah, you believed some fine gentleman from far away places to tell you a true technical fact lol

The duality of man.
We think with our eyes, then we think with our brains.

Eyes: This sports car must be one of the fastest cars in the world, it's shiny, sleek and has a red paint job.
Brain: But no engine, just bicycle pedals.

 

[Fingers]

Short and long of it is that when you have three contacts in series the voltage (and arc potential) is cut by 1/3 for each. A 25mm gap can sustain (IIRC) about 100V, so 3x25mm gaps gets you safely at 250V.

Thanks for the info.
I have gone for a 40amp 500v dc switch, with two contacts per pole, and my solar is 11amp (20amp max fuse rating), max 300volts.
Next time I will go for a switch with multiple contacts. I did look at them, and thought whats the point. Now I know

 

[bertiebassett]

your switch looks to have only burnt out on one cable connection? could very easily have just been a high resistance connection on that terminal.

i see it all the time in industrial control gear.

 

[Fingers]

Have you looked at the IMO brand switches? They seem really well made.

They look a bit like the Salzer switch that burned out. I'm listening to my eyes again. lol

 

[Fingers]

your switch looks to have only burnt out on one cable connection? could very easily have just been a high resistance connection on that terminal.

Yes, the one connector is burned out. I can see the plastic underneath the switch has melted.

High resistance; could this be from tinning the cable with solder? I do this to all my cables as it keeps damp air out, which plagues my garage.

 

[bertiebassett]

there are a lot of different opinions on tinning cable ends but i think the general consensus is to not tin them.

the clamp is designed to crush the cable for a solid and spread-out connection, tinning could mean that although done up tightly, there is only a small area actually making the connection and conducting, that would lead to a heat rise and then snowball from there.

you should be able to open the case of that switch up, then you can inspect the actual switch contacts. Depending on how hot things got you may be able to see if the heat source was the termination or the switch contact.

as a side note its good that you found it before anything tried to catch fire.

 

[HRTKD]

Yes, the one connector is burned out. I can see the plastic underneath the switch has melted.

High resistance; could this be from tinning the cable with solder? I do this to all my cables as it keeps damp air out, which plagues my garage.

If this is stranded wire, maybe use a ferrule with heat shrink.