Is this circuit safe?

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cyberblak

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Hi all,

Just curious, do you guys think that this touch switch circuit could be approved for safety (UL or eq.)?

I thought that the only circuits that could be directly connected to the mains are the ones a user cannot access (in a plastic enclosure or something else)...

What are your opinion?

Thanks,

cyberblak

oups... forgot to upload the file... Here it is!
 

The circuit has 4.4 Megohms between the touch switch and the mains. This could put a mA or so through a body. I would not risk it. Can you put a plastic film over the touch switch?

[edited part: I did a math error. the 4.4 Megohms and the line voltage is in the uA range as calculated in the posts below.]
 

Sensor current is only 28µA. Usual mains live wire testers have currents about 150µA. And they are selling it.
 

Those main live wire tester put the user directly in contact with the mains through the circuit or they are enclosed in a plastic case?

With this touch switch circuit, the user must touch a metal plate that is connected directly through the circuit (no isolation).

As for the use of a plastic film, I really don't know. Would the capacitance added by the finger would still be added to the circuit??

Good question...

cyberblak
 

An old tester is nothing but glow bulb in series with resistor mounted in screwdriver made of insulating material. When connected to liwe wire and other end is touched by hand glow bulb lights.
 

If we neglect the base current of the transistor and take the 4 resistors in series, we'll find that the current is only 2.5uA.

Also the body needs over 50V potential difference to be shocked.

Please, Correct if I'm worng.
 

Current through sensor or body is about 28µArms.
I=120/4.4E6
 

That make me think that the circuit is safe indeed... I agree that the two 2.2M series resistors reduce the available current to a safe value.

Thanks all
 

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