Getting power in a hard to power place

Thread Starter

kuera

Joined Aug 17, 2012
36
A short overview. I'm trying to power a low power device (5v) inside a light switch fitting. The problem is that there is no neutral wire going into the switch to connect up to some kind of ac-dc power supply as the only wire going in and out of the fitting is the live supply and the load wire to the light fitting. Is there some kind of way to get a small amount of power to run a circuit in there? The only thing I can think of is some kind of transformer in series of the live going in and out of the switch but that seems like a bad idea.
Also there is an earth in there too for safety reasons but I know that's not usable. Just thought I'd add that before someone tells me my house will burn down.
 

Tonyr1084

Joined Sep 24, 2015
6,954
Classic interrupt circuit wiring. Must be an older home.

Those old switch boxes aren't very big. They have OUTLETS (not switches) with USB chargers built into them, but I didn't see any with a switch and an outlet. However, those would need a neutral; and likely a ground as well.

I put a dimmer controller in my bedroom that needed hot and ground. There was no ground, just as you describe your electrical wiring I had the same. So below the switch I installed an outlet complete with hot, neutral and ground. I then added a ground wire from the grounded outlet into the switch box and was able to put my dimmer controller in place of the ordinary switch.

It's unlikely you'll be able to fit anything more than just the switch. Besides, if you forced a transformer in there the chances would be extremely high that its metal components would cut into the wires and then become a shock or fire hazard. You're right, someone is going to tell you you'll burn your house down. I won't say it - but someone will.

Best option I could suggest is wiring in a new outlet below the switch. You're going to have to do some sheetrock work anyway. If you put an oversized box in where the switch is you COULD put an outlet with a charging port in it. But you're still going to need that neutral and ground. No way around that.
 

Reloadron

Joined Jan 15, 2015
6,822
It's only since 2011 that the NEC changed the rules for lighting switches.
When wiring lighting circuits supplied by a grounded general-purpose branch circuit, the 2011 NEC now requires you to provide a neutral conductor at nearly every switch point [404.2(C)]. The purpose for this is to complete a circuit path for electronic lighting control devices, such as occupancy sensors. For many such devices, you must provide standby voltage and current at the switch.
Your only solution is to add a neutral which can be problematic depending on the wall. More often than not easier said than done especially on outside walls full of insulation. I have played this game helping friends and neighbors with the older construction. Anyway, there is no easy way around it. No trying to place anything in series with the hot is not a solution. :(

Ron
 

ErnieM

Joined Apr 24, 2011
8,328
When wiring lighting circuits supplied by a grounded general-purpose branch circuit, the 2011 NEC now requires you to provide a neutral conductor at nearly every switch point [404.2(C)]. The purpose for this is to complete a circuit path for electronic lighting control devices, such as occupancy sensors. For many such devices, you must provide standby voltage and current at the switch.
One cannot appreciate the joy of adding smart switches to my 75 year old home. I eventually found neutral for all, though it was an adventure.

All hail the NEC for this addition.
 

Ian0

Joined Aug 7, 2020
5,839
The usual solution is to allow a small amount of power to go through the light, effectively using "live out" as the neutral as it is connected to neutral via the lamp. That was all well and good in the days of filament lamps, but with LED lamps, feeding them with a small current is just likely to make them flash.
No alternative to adding a neutral conductor, and if your wiring regs are similar to the British ones, there is still no requirement to take a neutral to a light switch when the building is installed.
 

Tonyr1084

Joined Sep 24, 2015
6,954
Adding neutral and ground in my bedroom was easy because I have a basement with easy access to power sources IN the basement. Hot and Neutral were provided from another circuit down stairs, and the ground was piggybacked from the new outlet into the existing switch box. I still had to knock holes in the wall both at the plate and at the new outlet location. No way around that for me.

SOME of my old metal boxes are connected together with a bonding wire of very small gauge steel wire. I don't see where it could provide any useful current carrying capability, but it's there. IF it were there in my bedroom light switch box I would have been good to go for the dimmer that required a ground. Win some lose some.
 

Reloadron

Joined Jan 15, 2015
6,822
One cannot appreciate the joy of adding smart switches to my 75 year old home. I eventually found neutral for all, though it was an adventure.

All hail the NEC for this addition.
You are not alone in the universe. We share the joy of ownership of 75 year old homes. Room by room as walls come out and get replaced I am putting in all new wiring including neutral through switch boxes. Gone is the old original knob and tube stuff. I also like installing wireless switches and just telling Alexa what to do. :) Wife moved into this house when she was about 13 or 14 with her parents. Today she is 74. Electric and plumbing has just been such a joy. :)

Ron
 

Tonyr1084

Joined Sep 24, 2015
6,954
Today she is 74.
When public speaking and introducing myself and family I always gave my age and my wife was "um - younger". She appreciated me not giving away her age. Of course that was around when we were in our 30's. Nearly twice that age now and my "Younger" wife probably doesn't mind so much the telling of her age. Just wondering your wife's attitude on age-dropping.

Back on topic:
Lived in a house from the late 1800's. Knob and tube wiring was everywhere. The owner of that home tried replacing part of that old system by tapping into the two wires with modern Romex cable. Trouble has always been that he never knew which line was "Hot" and "Neutral". Being AC he considered that it didn't matter. Well, I had a power supply that when I plugged it in to a grounded outlet the fuse immediately blew. Never looked into why that was, but it apparently had something to do with Hot being on the neutral pin of the outlet. The ground had an additional grounding wire, which between the neutral leg of the PS and ground there was some sort of short that blew the fuse. When I swapped the hot and neutral wires in the plug box the fuse blowing problem went away.

One has to be careful with modern electronics to get the polarity correct. Though it's AC, having it backwards (hot and neutral reversed) can be problematic to devastating to electronic equipment. I know the TS wants to make 5V available at the switch but I don't recall seeing any clarification on why he wanted that. Don't know why that would be necessary or advantageous, other than - um - did he say he wanted to light something inside the box? OK, first (and last) time we heard from the TS he said:
I'm trying to power a low power device (5v) inside a light switch fitting.
Purely conjecture, could that "device" be a video camera? A microphone? A light? (they sell illuminated light switches). Thus far we don't know what the TS plans on doing. Hate to be the guy to suggest nefarious intentions, but just why does one want a low power device (5v) inside a light switch fitting?

Will be watching for a reply from the TS on this.
 

Reloadron

Joined Jan 15, 2015
6,822
When public speaking and introducing myself and family I always gave my age and my wife was "um - younger". She appreciated me not giving away her age. Of course that was around when we were in our 30's. Nearly twice that age now and my "Younger" wife probably doesn't mind so much the telling of her age. Just wondering your wife's attitude on age-dropping.
She's fine with it. :) She may get a little upset if I call her a cougar since I lag her by almost 3 years.

OK back on topic. :)

Ron
 

BobTPH

Joined Jun 5, 2013
5,467
My lovely wife Morticia takes pride in the fact that she is hundreds of years old. I think it has something to do with her ex, who had a habit of turning into a bat. She loves bats.
 

Thread Starter

kuera

Joined Aug 17, 2012
36
Classic interrupt circuit wiring. Must be an older home.

Those old switch boxes aren't very big. They have OUTLETS (not switches) with USB chargers built into them, but I didn't see any with a switch and an outlet. However, those would need a neutral; and likely a ground as well.

I put a dimmer controller in my bedroom that needed hot and ground. There was no ground, just as you describe your electrical wiring I had the same. So below the switch I installed an outlet complete with hot, neutral and ground. I then added a ground wire from the grounded outlet into the switch box and was able to put my dimmer controller in place of the ordinary switch.

It's unlikely you'll be able to fit anything more than just the switch. Besides, if you forced a transformer in there the chances would be extremely high that its metal components would cut into the wires and then become a shock or fire hazard. You're right, someone is going to tell you you'll burn your house down. I won't say it - but someone will.

Best option I could suggest is wiring in a new outlet below the switch. You're going to have to do some sheetrock work anyway. If you put an oversized box in where the switch is you COULD put an outlet with a charging port in it. But you're still going to need that neutral and ground. No way around that.
I'm guessing you're in the US. Here in South Africa, been an old british colony we have larger fittings for that. Most of our light switch fittings in the wall are either 2"x4" or even 4"x4" and all 2" (I love how we use those measurements when we actually use the metric system :D)deep so there is actually quite a lot of space for what I need to do considering I'm ripping out all the internals and making the switches electronic in nature. The whole idea is for a system to control lighting time limits or even been able to have them go on and off at random times to simulate someone been home when you're away.
 

Thread Starter

kuera

Joined Aug 17, 2012
36
It's only since 2011 that the NEC changed the rules for lighting switches.


Your only solution is to add a neutral which can be problematic depending on the wall. More often than not easier said than done especially on outside walls full of insulation. I have played this game helping friends and neighbors with the older construction. Anyway, there is no easy way around it. No trying to place anything in series with the hot is not a solution. :(

Ron
Yeah I'm leaning toward this. It's probably the lesser evil to be honest. everything runs in pvc conduit pipes through the wall so I guess I can just use one of the live wires from the fitting to pull through a neutral (ground) and a replacement live and it solves the headache.
 

Thread Starter

kuera

Joined Aug 17, 2012
36
You are not alone in the universe. We share the joy of ownership of 75 year old homes. Room by room as walls come out and get replaced I am putting in all new wiring including neutral through switch boxes. Gone is the old original knob and tube stuff. I also like installing wireless switches and just telling Alexa what to do. :) Wife moved into this house when she was about 13 or 14 with her parents. Today she is 74. Electric and plumbing has just been such a joy. :)

Ron
I haven't got this issue haha. I built my place about....20 odd years ago and I still remember where all the wires and plumbing run through the walls =P My father hit 74 this year and he's actually the one who helped me build it. I say help but he did most of it ;)
 

Thread Starter

kuera

Joined Aug 17, 2012
36
I po
When public speaking and introducing myself and family I always gave my age and my wife was "um - younger". She appreciated me not giving away her age. Of course that was around when we were in our 30's. Nearly twice that age now and my "Younger" wife probably doesn't mind so much the telling of her age. Just wondering your wife's attitude on age-dropping.

Back on topic:
Lived in a house from the late 1800's. Knob and tube wiring was everywhere. The owner of that home tried replacing part of that old system by tapping into the two wires with modern Romex cable. Trouble has always been that he never knew which line was "Hot" and "Neutral". Being AC he considered that it didn't matter. Well, I had a power supply that when I plugged it in to a grounded outlet the fuse immediately blew. Never looked into why that was, but it apparently had something to do with Hot being on the neutral pin of the outlet. The ground had an additional grounding wire, which between the neutral leg of the PS and ground there was some sort of short that blew the fuse. When I swapped the hot and neutral wires in the plug box the fuse blowing problem went away.

One has to be careful with modern electronics to get the polarity correct. Though it's AC, having it backwards (hot and neutral reversed) can be problematic to devastating to electronic equipment. I know the TS wants to make 5V available at the switch but I don't recall seeing any clarification on why he wanted that. Don't know why that would be necessary or advantageous, other than - um - did he say he wanted to light something inside the box? OK, first (and last) time we heard from the TS he said:

Purely conjecture, could that "device" be a video camera? A microphone? A light? (they sell illuminated light switches). Thus far we don't know what the TS plans on doing. Hate to be the guy to suggest nefarious intentions, but just why does one want a low power device (5v) inside a light switch fitting?

Will be watching for a reply from the TS on this.
Well considering I live on my own with a cat and dog I'm not sure video or audio would be that interesting :D
I replied to someone else with the idea so I'll just copy paste it here for you heh.
The whole idea is for a system to control lighting time limits or even been able to have them go on and off at random times to simulate someone been home when you're away.
PS, battery and MCU.
 

Tonyr1084

Joined Sep 24, 2015
6,954
everything runs in pvc conduit pipes through the wall
YIKES!
The whole idea is for a system to control lighting time limits or even been able to have them go on and off at random times to simulate someone been home when you're away.
Thank you for the clarity. Yes, I'm in the USofA. Modern homes won't allow PVC conduit in the walls because it doesn't protect from nails or screws being driven into the plastic and potentially shorting something out.
 

Thread Starter

kuera

Joined Aug 17, 2012
36
YIKES!
Thank you for the clarity. Yes, I'm in the USofA. Modern homes won't allow PVC conduit in the walls because it doesn't protect from nails or screws being driven into the plastic and potentially shorting something out.
Brick walls here. While I know that's not a reason for protection against nails and such the pipes tend to have very straight forward lines, such as either vertical from light switches and plugs or in the case of plugs close to the floor they'll go horizontal to the next. If you dont hang something up directly above a switch you tend to be good lol. That been said I have had one or two entertaining days where I've drilled into one. It makes for lengthy repair jobs =/ even worse when you hit a copper pipe in a wall >.<
 

MisterBill2

Joined Jan 23, 2018
12,697
If the device needs to be powered when the switch is OFF, and the power is not much, then across the switch is mains voltage and 5 mA at 120 V is lots of power. Neon bulbs in a plastic switch toggle have been around at least 50 years. If power is needed when the switch is closed, then a pair of diodes, inverse parallel, will provide almost a volt of pulsating power. The diodes must be good for much more than the switch load, ten amps maybe, or at least 5 amps, Low PRV is OK because each diode is shunted by the other.
So what can work depends on the application.
How comfortable is the TS working with mains power house wiring?
 
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