Electronics Electrical Safety

Hi Again!!! all,

As we all know (im sure) house hold electrical equipent is not prohibited in part where hazordous amount of water my be present, such as the bathroom which is split down to electrical zones in the regulations.

What Id like to know if what type of high safety can I incorporate in to a circuit/setup to ensure that NO danger could be present.

the thing Im running is of fairly low power anyway, just a TFT screen, but obviously this need power. One thing I was think with the power is to store the power tranformer out the room, like the loft, and only have the low power cable section entering the room, which will be behind the wall so out of reach anyway.

What about circuit breaker, protection, eathing, etc

Thanks all

 

cant you power it from a shaver scocket.

or do as you suggested and have a 15v lead powering it.

 

I can do as I suggested with the cables behind wall, but electric regulations are very tight when it some to bathroom/kitchen, etc. And I want to put as many safety devices in to ensure it above regulations, so need some idea's?? Like the feathertouch buttons, these will hopefully be a nice brushed stainless steel effect and fair enough to power a button its hardly any voltage/ampage at all, but if a 240v wire accidently touched that cable powering the buttons while someone was touching it then bang.....ya dead so need some safety involed. Ok the chance of that happening is about 1 in a billion, but thats how regulation inspectors etc, think, plus I want it to be completely safe....cause I tend to be that 1 in a million!!! hahaha

 

All of my sockets have a GFCI built into them.

So when I get spastic and drop the electric razor, it trips the socket and doesn't burn my house down.

I'm not sure what they are rated out, but they trip really quick.

 

and these sockets are regulation acceptable yes????

I wont be having sockets as all the wiring will be hidden, but if I can install one where the mains will be pluged in for the screen then that extra safety

Thanks Fronzel

 

I don't know about the regulations outside the USA. You would do best to ask an electrician.

But anytime you have A/C near water, you need either a GFCI on the socket or one between the socket and the electrical device. You can get the ones that are a retrofit. They plug into the socket, and the device plugs into them.

You should be able to pick one up at a local hardware store or shopping center.

 

If you don't already have a high quality RCD on your mains electricty then upgrade

RCDs work by making sure that the current going out on live, is the same as the current comming back on the return line. If you have one of these installed on the mains side + proper sheilding, you should have no difficulty.

You could make a similar own for low-voltage devices with a couple of FETs mesuring the vd over some resistors, but i wouldn't ever trust an anologue circuit designed by me

I would recomend covering every wire/connection in welders flux once you have your project working, and if your too cheap to have proper RCD AND earth leakage on your lines, then buy one designed for a hedge trimmer or somthing for £10!

 

Again, this is US stuff, in case it's valuable to someone.

GFCI's (Ground Fault Circuit Interruptors) sense the difference in current between the phase (hot) wire and the neutral, any difference means the current is entering the hot terminal and is then finding another way to earth instead of the correct path, which is via the neutral wire.

If this difference is greater than 4-6 milliamps or so, they will shut off all power to that socket, and any downstream. They do it in milliseconds, thus they are capable of saving not only equipment (which is what breakers are for) but lives as well.

You can get these devices to replace existing receptacles, or you can use temporary devices, usually another device that you plug in which has integral GFCI protection. You can even get GFCI breakers, usually expensive, but they're a snap in solution to protect a whole circuit.

You do not need a grounded circuit to install a GFCI receptacle, this is a misconception, the ground is not used in the sensing or disconnecting circuitry, although when installed in a non-grounded circuit, they are required to be marked "no equipment ground"

I sure would be interested in what the lowdown over the pond is, I find it all terribly (sadly) interesting...

EDIT: Wait, you already posted it... I imagine RCD is Residual Current Device?

 

Americans, taking english and making it sound funny.

 

SELV (lower than 24V) is perfectly acceptable in the bathroom according to the IEE wiring regulations, so if you have your transformer elsewhere (i.e. not in the room) and run the 15V to your device you will be ok.

Shaver sockets are isolated from the mains (via an isolation transformer) so that if you did drop your device in water the earth leakage trip would not switch off since the live is not referenced to ground. However, only touching the one of the outputs from an isolated shaver socket would not result in shock anyway - you need to touch both.

Usually 30mA needs to pass through ground before an earth leakage trip will switch off, since many appliances in the home leak current to earth as part of their normal operation (switched mode PSU's are very bad for this).

 

How many amps at 15v are we talking about, bucause if you can supply it with an oversized transformer to prevent it from heating too much, and you want good security, put a small hole or two in the housing and fill the thing up with RTX silicone to make it impossible for a high voltave lead come into contact with a low voltage line. Though that is what a double insulated transformer is meant to do. You can tell if it is double insulated by there being a square within a square symbol on it.

You were talking about feather touch buttons, do you mean a touchpad that requires very little pressure, like the ones on a microwave oven? Or the buttons that use capacitive touch sensing like the QT110? (I think that is the name) If you use a stainless touch area on it, the stainless cant be grounded, and non grounded metal casing are a no no. But a small plastic area for the touch sensor would work. You could use a small stainless touch area if you can isolate it, just make sure that there is no HV lines near the circuitry or the sense line going to pad.


oh and

What up with that. In the weld shop at school the only flux i've seen is borax for brazing or when you do blacksmithing work, and that was a powder. What purpose would it serve, you have me interested in this one

 

arr well, thats another questions I had once I get set up with every thing. I cant seem to find any feathertouch buttons on maplin or RS for my design, can anyone point me in the right direction

Thanks for all your help guys

 

i know i hadn't seen welders flux before i went to secondary school, where they had it in a very very old tin, i was un-able to buy it in the UK (it was american packing) so i just got given a tin by secondary school, and i've still some left

 

A good SMPS will have a ground-leakage rating just as good as the linear ones.

 

But what purpose would it serve to cover the project in it? Powdered borax could probably be melted on it with a heat gun, but you might blow a cap if you aren't careful.

I also thought that borax would eat at the insulation of the wire.

Edit: Looking at post below, you must not be talking about borax. knd of funny though, most methods of welding provide their own shielding, be it a coating on the electrode or a shielding gas. The only thing I've heard of a seperate flux being used, was for Oxy-Fuel welding of aluminum (read it in an older text book) and that didn't exactly take off now did it .

 

Welders flux is easy to apply goes on cold, sets hard, clear etc, its a resin, dosen't interfear with the presant insulation its great, a must have if your soldering connectors.

 

I can't think of any commonly used configuration of linear power supply that would leak any current to ground under normal operation.

I'm assuming the TFT display in question has some form of flourescent backlight. The high voltage generated for the use of these backlights is probably something that should be addressed in a high humidity environment.

In my opinion, the best idea would be to build the display into some form of waterproof box, or set it back into the wall and cover the front with acrylic. Either capacitive or waterproof buttons could be used.

IRRC vandal resistant buttons are acceptable for use in damp environment...

 

There's always stray capacitance.

 

We use a seperate flux where I work on fire safety release valves for gas bottles. There are stainless steel and the solder that comes in is just rough strips with no flux in. So we use a seperate flux which is around 100 pounds for a small tub. Is also corrosive and a high irratent!!!!!.

Correct, I dont have RCD!!! Tut Tut naughty. But I am going to upgarde in the next few weeks, just change over the consumer unit to an RCD one.

Im not too familiar with how touch sensitive buttons work so if you can guide me to the right product it would help. I was hoping for a stainless steel touch pad cause obviously it look neat and wont rust in the high humidity. But I didnt know you could not earth it, how come???
Would the high humidity cause any problems for touch sensitive switches??

I was indeed planning on setting the TFT screen back in to the plastered layer of the wall. and then covering with a piece of glass screwed to the wall and sealed round the edges with silocon. Only thing Im wondering, is would the coldness of the walls and the high humidity and temp of the room cause the glass to steam up quickly????


Thanks for all you help guys

 

Not sure Im looking in the right place, but just had a look on RS for some capacitive switch and found these
Switches

Please tell me that you can get much much cheaper ones for a fiver or something, cause these are some serious money, Id be spending about a 1000 pound on them alone!!!!!!