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Forum Index : Electronics : Suggestions for Breakers

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Downwind

Guru

Joined: 09/09/2009
Location: Australia
Posts: 2333
Posted: 01:36pm 06 Feb 2010
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No matter what you do to idiot proof something the idiot will still find a way around it.

If all you want is a protection barrier than place some blocks or posts each side and screw a sheet of clear plastic or mesh or what ever is handy over the top allowing good clearance and air flow around the sides.

A cover sheet and a couple of wing nuts to hold it in place should do.
Just a crash barrier if anything at all.

If some one is poking around under that then they should beware of the hazards.

Pete.
Sometimes it just works
 
Dinges
Senior Member

Joined: 04/01/2008
Location: Albania
Posts: 510
Posted: 03:00pm 06 Feb 2010
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Thanks for that, Gordon. 'boot lace ends'... Just translated directly from Dutch. Tried googling the correct term for them... but that's the problem with google: if you don't know the correct search terms...

KarlJ, I understand anything below 42Vac is considered to be 'safe' from a shock-hazard point of view. About a month ago I did a little experiment, slowly increasing voltage till the point where I would feel it (dry skin, dry air, not standing in a wet puddle, but wearing leather shoes). It wasn't until 65Vdc that I could feel a tingling sensation, which wasn't even unpleasant.

That said, I normally make it a habit to not deliberately touch anything above 24V. It's always good form to shield electronics from direct contact. One day, it might be *you* who accidentally drops a spanner or screwdriver in it....

Not sure what your system voltage is; personally, at 24V battery voltage I wouldn't worry too much about electrical shocks (of course, when the battery gets disconnected from a running mill, voltages can end up much higher than that). At 48V, I'd take about the same precautions to be able to touch anything directly as I'd do at 230Vac. Better safe than sorry. Even though I've got my share of 230Vac shocks and lived to tell the tale.

Telecom systems use 48Vdc system voltage and from what I've seen, don't take any extra trouble isolating things from a shock-hazard point of view.

Just my thoughts on the matter.

BTW, nitpicking a bit, but human body resistance is always about 1 kohm; it's only skin resistance that can be much higher, a few 100 kohm is possible. Wet skin has much lower resistance though. Skin has also relatively low dielectric strength: at 230V, it simply breaks down and the skin resistance disappears... leaving you with just the body resistance, which is about 1kohm; 230V/1000ohm= .23A... which Hertz....

[quote]No matter what you do to idiot proof something the idiot will still find a way around it.[/quote]
True... but I find the idiot for which I have to idiot-proof everything is usually myself....

Peter.

(PS: as usual, it depends.... 42Vac is normally considered to be safe; but I've heard that, when you're lying on your bare back in a steel boiler tank using a 42V tool (required in such cases; 230Vac is not allowed), you can still get a nasty shock from 42V.)Edited by Dinges 2010-02-08
 
KarlJ

Guru

Joined: 19/05/2008
Location: Australia
Posts: 1178
Posted: 02:37am 07 Feb 2010
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System voltage is upto 62V, I did notice when I was testing the dump loads at this voltage I was using my fingers to hold the wires on the terminals and wasn't getting so much as a tickle but you never know....

Anything that has fine wire on the ends going into screw terminals I have now soldered together, anything with a lug on it I have soldered anyway as the terminals I had werent big enough hence split them and soldered in.
Here's a pic of the isolation diode and shunt mounted on cement sheet,

I cant see any reason to mount any of the other bits on cement as they just shouldnt get that hot, I'll mount the SSR and heat sink on this piece of sheet too.

Power comes in from the mill on the left of the shunt, batt power goes to the diode and other power goes to the dump loads.
Small power wire going to the PL20 and connection is there for the huge cable going to the batts.
Luck favours the well prepared
 
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