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Author Topic: Getting 5V D/C from single live wire A/C light switch  (Read 3200 times)
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Left Coast, CA (USA)
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How do I tap 5V D/C from a single live wire A/C from a light switch without turning on the light ?

Something like the attached picture ...


In many cases, the neutral wire, or a neutral wire will be available in the junction box along with the hot wire.

That is just an assumption. Many times the main power branch cable will go to the light junction box first and then a separate run from the light to the remote switch junction box, so it will only have just the line or just the neutral run to the switch, not both line and neutral.
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That is just an assumption. Many times the main power branch cable will go to the light junction box first and then a separate run from the light to the remote switch junction box, so it will only have just the line or just the neutral run to the switch, not both line and neutral.

If anyone runs just a neutral to a switch, they should be hung, drawn and quartered! Switching off the neutral will still leave the fitment live [hot].

The only time a neutral can be switched is if it's on a double pole switch, where both live and neutral are switched together.
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That is just an assumption. Many times the main power branch cable will go to the light junction box first and then a separate run from the light to the remote switch junction box, so it will only have just the line or just the neutral run to the switch, not both line and neutral.

If anyone runs just a neutral to a switch, they should be hung, drawn and quartered! Switching off the neutral will still leave the fitment live [hot].

The only time a neutral can be switched is if it's on a double pole switch, where both live and neutral are switched together.

I understand that, I was just making the point that if the power feed first goes to the light then there will not be both a neutral and line wire available at the switch box.

Lefty
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How do I tap 5V D/C from a single live wire A/C from a light switch without turning on the light ?

Something like the attached picture ...


In many cases, the neutral wire, or a neutral wire will be available in the junction box along with the hot wire.


That is just an assumption. Many times the main power branch cable will go to the light junction box first and then a separate run from the light to the remote switch junction box, so it will only have just the line or just the neutral run to the switch, not both line and neutral.

Yeah, hence the qualifier manysmiley  If OP's circuit is wired that way then they can take advantage of it.
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I understand that, I was just making the point that if the power feed first goes to the light then there will not be both a neutral and line wire available at the switch box.


Yes. The two wires going to the switch are live [line] and switched live [line]. The usual way of wiring lights in the UK is to take both live and neutral to each lighting box and then run a cable to the switch. In Ireland, the system is slighly different, as they use single, not twinned cable, which allows for more flexibility in the wiring. There, the live [line] wire may be run between switches and only the switched live goes to the lighting box. I understand that it's similar in Germany.
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Regarding getting the 5VDC from a wall switch. As has been already reported it is:
1 Dangerous if you do not know what you are doing, and
2 Typically a switch may not have a neutral wire available, and
3 Both the wires attached to the switch terminals are on only one leg of the AC.

It can be done, however, in certain circumstances with something similar to this diagram. This circuit will work by running a small amount of power through the light itself (caveat: this circuit was designed when all lights were incandescent, probably will not work with flourescents). The wall wart power module can be wired across the switch and as long as the switch is not turned on the power for the wall wart will be obtained through the light acting as a very low resistance inline resistor. The power consumption must be tailored to the needs of the wall wart without affecting the light.

This circuit was used in a film developing lab to prevent someone opening the door to a darkroom unless the inside light was on. Just do not install the two extra switches and instead of a transformer and bell use a wall wart DC adapter.

Again, if you are not sure, DO NOT DO IT.

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1 get money,
2 Call electrician,
3 Explain the job,
4 Wait for him to do job,
5 Pay up.


or

1 do it yourself
2 Get electrocuted
3 End up in hospital
4 Hope they can save your life!

As people have said - If you don't know how to do it, don't do it!
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Sorry for the noobish post but my knowledge is 10 years out of date!

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