Is it safe to add DC circuit inside AC electrical wall box - Page 1
Forum section: electronics / beginners

author: symbianas
author_rank: Regular Contributor
timestamp: May 04, 2025, 12:07:05 pm
content: Hi, I want to addHi-Link power supply(which I soldered on the board) and ESP32 with gas sensor inside electrical wall box, but I was wondering is it safe to do so? I am thinking about AC interference?

author: themadhippy
author_rank: Super Contributor
timestamp: May 04, 2025, 12:30:44 pm
content: Dont just cram the bare board in there, put it in a box,if your worried about interference use metal and earth it,also any wires should have insulation rated for the highest voltage present.

author: bostonman
author_rank: Super Contributor
timestamp: May 04, 2025, 01:18:29 pm
content: I wouldn't add it to the same box.If the supply gets hot, blows up, etc... then you're at risk of damaging the AC wires.My suggestion (this isn't by code or by any safety codes, just an opinion) would be to place another box aside of it so you isolate the two.Most likely you need the AC power present to power the power supply, so another box will still have AC mixed with DC, but I'm assuming the existing box has wires for other circuits in the house; hence why I don't think mixing is a good idea.Your best and safest would be to have an outlet for the DC power supply rather than try to hard wire everything.

author: Analog Kid
author_rank: Super Contributor
timestamp: May 04, 2025, 06:06:42 pm
content: No, absolutely not. Don't even think about doing this!No electrical code that I know about allows this.The only exception would be outlets that contain a 5-volt supply for USB charging, which are UL or other agency approved.

author: symbianas
author_rank: Regular Contributor
timestamp: May 04, 2025, 08:19:29 pm
content: Quote from: Analog Kid on May 04, 2025, 06:06:42 pmAnd what about those smart switches which mounts in there?

author: Analog Kid
author_rank: Super Contributor
timestamp: May 04, 2025, 08:27:20 pm
content: Quote from: symbianas on May 04, 2025, 08:19:29 pmThose are also purpose-designed and certified, unlike whatever you're trying to stick in there.Those regulations exist for a reason.

author: amyk
author_rank: Super Contributor
timestamp: May 04, 2025, 09:13:44 pm
content: Legally not, practically likely yes.

author: Analog Kid
author_rank: Super Contributor
timestamp: May 04, 2025, 09:20:06 pm
content: Quote from: amyk on May 04, 2025, 09:13:44 pmYes, but this is one place where I'd definitely err on the side of caution.Especially since the OP lives in 240-volt land.House fires due to electrical faults are pretty much avoidable.

author: CaptDon
author_rank: Super Contributor
timestamp: May 04, 2025, 09:52:31 pm
content: What gas are you trying to detect and what would the level in the room look like as compared to the gas finally reaching your sensor with no apparent air movement being shoved into a wall? If you were trying to detect the LEL of a combustible gas you would probably launch the room into orbit by the time the sensor sensed any apparent level. If you are trying not to suffocate from things like cold dry nitrogen in the room the sensor should call the undertaker to remove your already dead body. Probably a fail on many levels?

author: floobydust
author_rank: Super Contributor
timestamp: May 04, 2025, 10:22:59 pm
content: How does OP expect WiFi to work with the ESP32 inside a metal junction box?Does the PSU have a fuse? Any safety agency approvals? Unfortunately that chinese stuff is risky in the first place.The cheat of running 5VDC wires outside of the junction box is not legal.

author: bostonman
author_rank: Super Contributor
timestamp: May 04, 2025, 10:35:55 pm
content: QuoteGood call, I didn't notice this when I replied.

author: SteveThackery
author_rank: Super Contributor
timestamp: May 05, 2025, 09:32:43 am
content: I would add a new plastic wallbox alongside the existing one and and put my electronics in that. You can feed the mains to it from the existing box by treating it like a spur.It's quite a quick job to cut an additional square out of the plasterboard and sink a new back box. Once fitted, a little bit of filler to tidy it up and a dab of paint, job done.

author: symbianas
author_rank: Regular Contributor
timestamp: May 05, 2025, 01:36:57 pm
content: Quote from: CaptDon on May 04, 2025, 09:52:31 pmIt's temperature/humidity/pressure/gas sensor BME688. I would still add it to similar place, so its good enough. But I have noticed that it pickup ESP32 temperature and shows 27C instead of 22C - that's maybe an issue if I want correct temperature reading.Quote from: floobydust on May 04, 2025, 10:22:59 pmWiFi is working great in the wall with 50% strength - already tested. Junction box is plastic.Quote from: Analog Kid on May 04, 2025, 09:20:06 pmAnd whats the difference for safety to have ESP32 with power supply running in the electrical wall box compared to ESP32 with power supply running in the kitchen cupboard or similar (on wooden furniture etc...).I would expect wooden furniture to be more dangerous for fire compared to wall box?Maybe only the heat dissipation is the advantage if it is running in more open space than wall box.

author: SteveThackery
author_rank: Super Contributor
timestamp: May 05, 2025, 01:49:21 pm
content: Quote from: symbianas on May 05, 2025, 01:36:57 pmIt is arguable, I agree. For me, it's mostly about space. Here in the UK, at least, those back boxes are usually extremely cramped. The terminal screws and terminal holes are not protected from electrical contact, merely recessed. Anything else you put in there needs to be completely insulated, of course. And also able to withstand quite a lot of pressure: cramming the front plate onto a back box which already has six 2.5mm solid core wires in it often requires quite some force until you've got the two retaining screws engages.No, it's much more elegant to add an extra back box and blanking plate. Plus you can safely drill ventilation holes for your gas sensor.

author: themadhippy
author_rank: Super Contributor
timestamp: May 05, 2025, 03:00:05 pm
content: Quoteif its a plasterboard wall use a dry lining box,no need for any touch up.

author: symbianas
author_rank: Regular Contributor
timestamp: May 05, 2025, 03:03:19 pm
content: I would not add power socket on top of the sensor if that's how you understood. It would be empty/no socket like this (black dot gas sensor).

author: symbianas
author_rank: Regular Contributor
timestamp: May 05, 2025, 03:06:12 pm
content: Quote from: themadhippy on May 05, 2025, 03:00:05 pmThe wall is from bricks and cement with the plastic junction box.

author: Sorama
author_rank: Frequent Contributor
timestamp: May 05, 2025, 03:07:46 pm
content: i don't think it would be legal to put that in a wall.

author: symbianas
author_rank: Regular Contributor
timestamp: May 05, 2025, 03:10:00 pm
content: Quote from: Sorama on May 05, 2025, 03:07:46 pmI think a lot of DIY things are not legal if you look at it that way.

author: Sorama
author_rank: Frequent Contributor
timestamp: May 05, 2025, 03:44:12 pm
content: Quote from: symbianas on May 05, 2025, 03:10:00 pmthat's exactly the reason why you should not do it, although I'm pretty sure you will.Unless you do care much about the people or houses near you.

author: symbianas
author_rank: Regular Contributor
timestamp: May 05, 2025, 04:59:15 pm
content: Quote from: Sorama on May 05, 2025, 03:44:12 pmWell, I will do it outside wall box then, on/in the furniture, but not sure if that's safer.

author: JoanBS
author_rank: Contributor
timestamp: May 05, 2025, 06:22:29 pm
content: It's no more dangerous than any AC outlet. I wouldn't worry at all... but it's necessary to install a suitable fuse to protect the power supply!

author: SteveThackery
author_rank: Super Contributor
timestamp: May 05, 2025, 07:14:08 pm
content: Quote from: JoanBS on May 05, 2025, 06:22:29 pmOf course it is. There is additional stuff in the box, so additional failure modes, some of which might be safety related.Nobody can make a definitive pronouncement because nobody has yet performed a risk assessment on the real device.

author: JoanBS
author_rank: Contributor
timestamp: May 05, 2025, 08:23:47 pm
content: Quote from: SteveThackery on May 05, 2025, 07:14:08 pmIf we compare this circuit, which contains a 3W low voltage sealed power supply, with, for example, a 500W triac dimmer for recessed switch boxes, there is no color!Most of these old dangerous dimmers burned out, and I don't know of any place where they've been banned.

author: Analog Kid
author_rank: Super Contributor
timestamp: May 05, 2025, 08:46:19 pm
content: Quote from: JoanBS on May 05, 2025, 08:23:47 pmReally?I was handyman for many years, saw lots and lots of dimmers in people's houses, and never once ran across one that was burned out.They are, after all, UL approved (in my country). Which means they have been tested.

author: SteveThackery
author_rank: Super Contributor
timestamp: May 05, 2025, 11:26:54 pm
content: Quote from: JoanBS on May 05, 2025, 08:23:47 pmI wasn't talking in the context of banning things. I merely wanted to point out that cramming a homemade gas sensor behind a wall socket increases the possible failure modes, some of whichmighthave safety implications. I'm also mindful of how much squashing of rather stiff 2.5mm solid core wires might be needed, depending on how big the sensor module is.That's why I recommend installing an additional back box and putting the gas sensor in there. Plenty of room, air vents if required, nothing sharing the original backbox.

author: JoanBS
author_rank: Contributor
timestamp: May 06, 2025, 09:00:17 am
content: Quote from: Analog Kid on May 05, 2025, 08:46:19 pmI've replaced a lot of these regulators, both for domestic and industrial use, most of them blown due to short circuits or overloads, although luckily none of them caused a fire.Whether they're certified or not doesn't guarantee anything, believe me.

author: JoanBS
author_rank: Contributor
timestamp: May 06, 2025, 09:11:33 am
content: Quote from: symbianas on May 05, 2025, 03:03:19 pmQuote from: SteveThackery on May 05, 2025, 11:26:54 pmI understand he's talking about plugging the sensor into an empty outlet, without any socket.In some countries, rigid solid cables have been banned for electrical installations for over 50 years.I agree that if it's possible to install an additional box, it would be a good solution.

author: Analog Kid
author_rank: Super Contributor
timestamp: May 06, 2025, 06:27:33 pm
content: Quote from: JoanBS on May 06, 2025, 09:11:33 amNot sure what you're referring to here: you can't mean cable with solidwires, can you? Because all of our NM (non-metallic, aka "Romex") cable has such wires.What exactly are "solid rigid cables"?

author: JoanBS
author_rank: Contributor
timestamp: May 06, 2025, 07:07:05 pm
content: Sorry, English isn't my language. I was referring to solid copper wire. Flexible copper cable is used for low-voltage electrical installations.

author: SteveThackery
author_rank: Super Contributor
timestamp: May 06, 2025, 07:12:41 pm
content: Quote from: JoanBS on May 06, 2025, 09:11:33 amHi, @JoanBS! Perhaps you are right about plugging the sensor into a wall socket. I thought he meant installing itinsidethe box. When he asked about AC interference I assumed he was intending to cram it into a box that already has a socket installed.About the cables: here in the UK, at least, we wire our domestic sockets using three core cable, comprising three solid conductors, the live and neutral of which are 2.5mm2cross-sectional area, connected as a ring main.We also have sockets wired radially in more modern installations, which use 2.5mm2conductors or 4.0mm2conductors, depending on distance and anticipated current draw.

author: SteveThackery
author_rank: Super Contributor
timestamp: May 06, 2025, 07:16:20 pm
content: For what it's worth, I wish the UK allowed stranded cable for domestic installations, because the solid core stuff we use is actually very stiff. You typically have six conductors connected to each socket, and it is pretty hard to push them back into the back box when screwing on the socket, especially when it's a shallow socket.

author: Analog Kid
author_rank: Super Contributor
timestamp: May 06, 2025, 07:39:17 pm
content: Quote from: SteveThackery on May 06, 2025, 07:16:20 pmSurprised you can't use stranded wires over there.Here stranded wire of adequate gauge (12/14 AWG) is certainly allowed under the NEC (Nat'l. Electrical Code). In fact, it's what you need to use if you're running wire in conduit; solid wire can be difficult or impossible to get through those pipes.And of course most of the wires for the "last inch" (i.e., connectors to lamps, etc.) are all stranded, and in fact a good deal thinner gauge than the conductors that feed them.Yep, I know all about trying to stuff wires into boxes ...

author: Monkeh
author_rank: Super Contributor
timestamp: May 06, 2025, 07:40:01 pm
content: Quote from: SteveThackery on May 06, 2025, 07:16:20 pmThere's no rule against it.

author: TimFox
author_rank: Super Contributor
timestamp: May 06, 2025, 08:51:28 pm
content: Normal house wiring in the US does use AWG12 or AWG14 solid wire.Before retirement, our electrical guys often used fine-stranded (more than the standard 7 or 19 strands) large gauges (e.g. AWG8 as 160 strands of AWG30) in "liquid-tight" conduit for flexibility and ease of manufacture.The infamous "back-stab" outlets are only rated for solid wire, but stranded can be used otherwise. UL requirements:https://code-authorities.ul.com/wp-content/uploads/2014/08/NovDec2008.pdf

author: themadhippy
author_rank: Super Contributor
timestamp: May 06, 2025, 10:11:53 pm
content: Quotewho says you cant? look hard enough and youll find stranded 2.5mm T+E,although its only 7 strands.https://www.cef.co.uk/catalogue/products/2326330-h6242y-2-5mm-pvc-twin-and-earth-stranded-core-cable-grey-100m-drum

author: TimFox
author_rank: Super Contributor
timestamp: May 06, 2025, 10:48:53 pm
content: For power wires, 7 and 19 strands are common.

author: SteveThackery
author_rank: Super Contributor
timestamp: May 07, 2025, 09:53:02 am
content: Quote from: themadhippy on May 06, 2025, 10:11:53 pmThanks, @themadhippy and @Monkeh, that's good to know. I guess the almost universal use of solid core mains wiring in the UK is mostly about cost. Thanks again.

author: themadhippy
author_rank: Super Contributor
timestamp: May 07, 2025, 12:46:14 pm
content: Quotecould be ,i think there was something in older regs that prohibited flex for fixed wiring,but thats vanished. Personally i don't think you'll gain much,if anything by using flex for sockets ,2.5mm is still 2.5mm,plus with flex the earth will also be 2.5 instead of 1.5mm found in most T+E. With T+E the secret to getting the box back is to bend the cables so they naturally fold into shape,flex tends to go wherever it wants

author: Haenk
author_rank: Super Contributor
timestamp: May 07, 2025, 01:02:04 pm
content: I would also suggest to put it into a box, and add a fuse.Use something like this:https://www.amazon.de/dp/B0DJY7QXTQ(something like this; check for CE, so it does not catch on fire in the worst case. Brick wall should be pretty safe and should be unaffected if the supply catches fire or explodes...)Of course this is still not a safe or compliant installation, but "good enough" IMHO.

author: tszaboo
author_rank: Super Contributor
timestamp: May 07, 2025, 02:44:48 pm
content: Quote from: amyk on May 04, 2025, 09:13:44 pmI had the same question a few years back about a product.I think the electrical consultant informed me that it's against the current Belgian regulations for a residential installation to mix AC and DC in certain situations, and we should do it differently.

author: Langdon
author_rank: Frequent Contributor
timestamp: May 07, 2025, 03:28:24 pm
content: Use a separate box.Better yet, just use a metal enclosure of some sort.Stoves often have an auxiliary 120V outlet.Just tell UL you are building a stove with external heating elements (which you don't actually plan to add) and you will get certification (I'm kidding).

author: Monkeh
author_rank: Super Contributor
timestamp: May 07, 2025, 04:34:58 pm
content: Quote from: themadhippy on May 07, 2025, 12:46:14 pmNot that I know of, but 521.9 is often misinterpreted.QuoteI don't believe that's gone anywhere in newer revisions.

author: themadhippy
author_rank: Super Contributor
timestamp: May 07, 2025, 04:43:22 pm
content: QuoteIm thinking back to my apprenticship days when the 15th was the new kid on the block

author: Sorama
author_rank: Frequent Contributor
timestamp: May 07, 2025, 06:48:08 pm
content: In Belgium, multi strand wires cannot be used in fixed installations (walls, Floors,…)Strictly forbidden!

author: Monkeh
author_rank: Super Contributor
timestamp: May 07, 2025, 06:53:38 pm
content: Quote from: Sorama on May 07, 2025, 06:48:08 pmSo nothing above about 4mm² for you, then. Get the pipe bender out..Daft restrictions are daft.

author: Sorama
author_rank: Frequent Contributor
timestamp: May 07, 2025, 07:04:09 pm
content: Let’s not forget those cables need to be ECA or CCA depending on the situation like height of building.Safery comes at a cost.I can only hope that those who are EE amongst us here will respect the regulations.Those who don’t are lost cases and might become famous in a local newspaper when things burn down.

author: themadhippy
author_rank: Super Contributor
timestamp: May 07, 2025, 07:37:58 pm
content: QuotePyro is always single ,not stranded conductors,but 25mm is about the largest youll find in 4 core,anything bigger is singles.

author: Monkeh
author_rank: Super Contributor
timestamp: May 07, 2025, 08:05:18 pm
content: Quote from: Sorama on May 07, 2025, 07:04:09 pmPerhaps you can explain why stranded wire is a problem? It seems to me those who blindly follow regulations without pondering the reason are lost.

author: voltsandjolts
author_rank: Unknown
timestamp: May 07, 2025, 08:32:38 pm
content: IMHO I don't like putting electronic stuff behind the plasterboard (drywall) because it bypasses the 30min fire rating (or whatever for the stuff you have) that is supposed to protect timber frame structures long enough for people to realise there is a fire and make their escape. All these USB PSUs etc. in wall sockets is placing cost-optimised electronics with one-hung-low electrolytics in situ's where they are likely to be left for a decade or more, potentially powered long term if the wall socket is left switched on. A metal back box will likely prevent fire spread, but I still don't like the idea. Just use a plug-in wall wart.

author: themadhippy
author_rank: Super Contributor
timestamp: May 07, 2025, 09:04:49 pm
content: QuoteIf you need to maintain the fire rating use a fire rated box ,but even the bog standard dry lining boxes are flame retardantQuotewot with the multitude of fixing holes in em?

author: Haenk
author_rank: Super Contributor
timestamp: May 07, 2025, 09:17:38 pm
content: Quote from: voltsandjolts on May 07, 2025, 08:32:38 pmHe talks about a brick wall. With the right enclosure (aka "non flammable"), I don't see a risk of anything bad happening.Btw. I have drywall double-upped, in the upper floor of my house, which is essentially fire-proof (A2). It's Fermacell boards, metal beams, glass wool filling and glass fibre wallpaper. I made the bathroom from Fermacell Powerpanels - which is A1 class. The risk of fire is just a matter of using the right construction material.

author: JoanBS
author_rank: Contributor
timestamp: May 08, 2025, 01:12:24 am
content: I think too much nonsense has already been said in this thread.There are gas sensors and many other things that can be installed in flush-mounted electrical boxes (approved, of course), such as the one shown in the following link:https://www.simonelectric.com/intl/75861-30-detector-of-toxic-and-explosive-gases-for-flush-mounting-with-led-service-status-indicator-white.htmlThis specific model requires a 12 VDC power supply, which can also be installed in an identical box:https://www.simonelectric.com/intl/75870-30-12v-power-supply-for-flush-mount-detectors-with-led-service-indicator-white.htmlhttps://www.simonelectric.com/intl/al50-junction-box-for-use-of-universal-frame-holder-mechanisms-in-columns-with-1-or-2-sides-simon-500-cima.htmlInstalling a non-approved sensor does not necessarily pose any risk if installed correctly, with minimal precautions and common sense. I worked as an electrician for many years and have never seen a fire caused by a properly installed electrical outlet or recessed electrical device. Recessed outlet boxes don't usually cause fires; electrical fires are caused by improperly wired outlets, faulty cables, or faulty installations with inadequate componentsRegarding the installation cable, in most EU countries it is mandatory to use flexible multifilar cable, not multi-core cable! In English it's easy to confuse the words. Approved for 750 V, with flame-retardant insulation, and currently, it is also mandatory for it to be halogen-free:https://www.amazon.es/ROLLO-CABLE-H07V-K-5MM2-AZUL/dp/B071CNSGNK/?th=1Likewise, single-core copper cables are not generally used:https://www.amazon.es/EBROM-Cable-alimentaci%C3%B3n-longitudes-seleccionada/dp/B077D7SPG9/?th=1except perhaps in the UK, where everything is the other way around (also, the UK is not part of the EC).The cables prohibited for residential electrical installations are multi-core cables with poor insulation and cross-sections below the minimum permitted 1.5 mm², such as the one shown below:https://www.leroymerlin.es/productos/cable-electrico-rollo-100mts-cable-paralelo-2x0-5-mm2-blanco-cca-87202055.htmlIt is true that AC and DC power lines should not be mixed, but DC devices or plugs can be installed, for which separate conduits and boxes must be installed, respecting the vigent regulations in each country.What I'm not so sure about is that the power supply proposed at the beginning of this thread won't cause interference on the power line.I hope everyone can understand my Googlenglish.

author: voltsandjolts
author_rank: Unknown
timestamp: May 08, 2025, 08:30:53 am
content: That picture shows the fire on the correct side of the plasterboard/drywall. Thanks.

author: voltsandjolts
author_rank: Unknown
timestamp: May 08, 2025, 08:33:28 am
content: Quote from: themadhippy on May 07, 2025, 09:04:49 pmYou missed the word 'likely'. As-in most of the surface area is enclosed by metal, significantly reducing the risk of fire spread, not eliminating it.

author: tszaboo
author_rank: Super Contributor
timestamp: May 08, 2025, 10:05:59 am
content: Quote from: voltsandjolts on May 08, 2025, 08:30:53 amIt's also staged, with some flammable material placed on the plug packs and set on fire.

author: SteveThackery
author_rank: Super Contributor
timestamp: May 08, 2025, 11:13:10 am
content: Quote from: JoanBS on May 08, 2025, 01:12:24 amOf course! It's brilliant fun speaking authoritatively about stuff we know very little about, presenting opinions as facts, arguing about which came first: angels or pinheads, changing the subject to our current beef about politicians/young people/wokeism, brandishing our intellect for all to admire.... you get the idea.It's very hospitable of Dave to provide this online coffee shop for us. 😄

author: Monkeh
author_rank: Super Contributor
timestamp: May 08, 2025, 07:29:00 pm
content: Quote from: JoanBS on May 08, 2025, 01:12:24 amNo it's not. Solid, stranded, flexible. Class 1, 2, 5. All of which are suitable for and permitted in fixed installations.

author: symbianas
author_rank: Regular Contributor
timestamp: May 10, 2025, 11:06:45 am
content: Well, since the sensor picks up ESP32 heat and shows incorrect temperature, I have abandoned the idea to put it inside the wall box. I will use it outside the box.

author: Sorama
author_rank: Frequent Contributor
timestamp: May 10, 2025, 11:36:12 am
content: Quote from: Monkeh on May 08, 2025, 07:29:00 pmNot in Belgium !

author: Monkeh
author_rank: Super Contributor
timestamp: May 10, 2025, 12:01:58 pm
content: Quote from: Sorama on May 10, 2025, 11:36:12 amAnd perhaps you could explain why in particular class 2 conductors are strictly forbidden and horrifically dangerous?

author: SteveThackery
author_rank: Super Contributor
timestamp: May 10, 2025, 03:00:54 pm
content: Quote from: Monkeh on May 10, 2025, 12:01:58 pmGive him a break. That's a question you need to direct to the regulators, not an end user.

author: TimFox
author_rank: Super Contributor
timestamp: May 10, 2025, 03:59:21 pm
content: Quote from: SteveThackery on May 10, 2025, 03:00:54 pmThe answer may be “because”.

author: bostonman
author_rank: Super Contributor
timestamp: May 11, 2025, 12:48:55 pm
content: QuoteThese types of statements are exactly why "accidents" happen. My dog has played with people for many years and never bit anyone. Well, it has now happened and someone got severely injured.Once an accident happens, reverting to the statement of "it's never happened" is useless when the person/people have been injured.I'd like to point out that we all live in different countries/states/etc... all with different electrical codes. Therefore we may have different opinions based off this.The bottom line (in my opinion) is that while it "can" be done, why do it? Unless the device/box/etc... is rated for such, why mix DC with AC when proper (and legal) ways exist?QuoteI fully agree.

author: JoanBS
author_rank: Contributor
timestamp: May 11, 2025, 02:47:36 pm
content: Quote from: bostonman on May 11, 2025, 12:48:55 pmMore than a statement, I'm simply stating a fact, which doesn't mean it can be considered an absolute truth.If during my life as a professional, or even as a user, I had encountered many "accidents" of this type, I would surely have a different opinion. The truth is that the only "accidents" I've witnessed are those caused by human negligence (poor installations or lack of maintenance, non-compliance with regulations, etc.), which is why I said what I said and why I believe it.It's true that each country may consider different criteria to define its own safety standards, but there is one rule that generally applies to all: common sense (the "least" common of the senses).

author: bostonman
author_rank: Super Contributor
timestamp: May 11, 2025, 11:10:42 pm
content: I'm sure you're correct and accurate.My point is really that if it's not code to combine DC and AC, then it shouldn't be promoted as such.We try to pass along accurate information on here, and passing on information that's not code is incorrect because it could result in an accident; regardless if your experience tells you otherwise.I get it, not all codes are for safety and some are ridiculous. An example would be (unless I'm wrong) in MA it's code to have an outlet accessible every 12" (or maybe 24") in a kitchen - this means something like a blender can have a plug 12" (or 24") to the left and right of it. Can we pass along advice on here that tells a user to install an outlet every 36" instead without risking injury, of course.Now, besides the issue I previously mentioned such as codes vary, someone may Google a similar subject and come across your reply. This person may not have a brick fireplace or whatever, read your post, and install DC and AC together behind a hundred-year-old wall that doesn't mix well with a box that gets warm.

author: Analog Kid
author_rank: Super Contributor
timestamp: May 11, 2025, 11:43:19 pm
content: Quote from: bostonman on May 11, 2025, 11:10:42 pmRight, except that that's a permissive part of the code ("may have"), not a restriction ("must not have").I treat code restrictions pretty much as gospel.

author: bostonman
author_rank: Super Contributor
timestamp: May 11, 2025, 11:50:53 pm
content: In MA an inspector wouldn't pass a newly wired house or a rewired house if the outlets aren't every 12" (or 24").

author: Analog Kid
author_rank: Super Contributor
timestamp: May 11, 2025, 11:56:59 pm
content: Quote from: bostonman on May 11, 2025, 11:50:53 pmOK, I misunderstood your post. When you said "it's code to have an outlet accessible every (12"/24")", I thought you meant that it was permissible--not required--to have outlets spaced this closely.That does seem a bit ridiculous. So maybe it could be ... quietly omitted from your plans when building/remodeling your kitchen (provided you don't get inspected) without compromising safety.

author: bostonman
author_rank: Super Contributor
timestamp: May 12, 2025, 01:44:08 am
content: My friend had their house rewired due to poor wiring throughout and the inspector didn't pass it due to a single additional outlet needed in the kitchen due to that 12/24 distance - maybe it was something that could have been "overlooked" and this inspector was nitpicking because it was only a "should" code, I don't know. This is where I learned about this MA (Massachusetts) code.When I had my house upgraded to 200A (I had this done as part of installing central AC because I needed a separate panel or just do a 200A upgrade for a few bucks more), the electrician had to install a light over the breaker panel (to provide light for future electricians to perform work), and, if I didn't already have one, an outlet outside should anyone need to service the outside compressor. The light over the breaker panel was silly because I already have lights near it. The lights provide plenty of light, and, ironically, the light over the panel causes too much glare.My point is that codes are important for safety but also for silly reasons, and maybe the code book is worded as 'required' or 'should', I'm really uncertain. Most likely someone who almost never did electrical work can wire a light "hot", not use junction boxes, etc... and never have a fire or get a shock. It doesn't mean that practice should be passed along as advice on here just because someone or many have "never seen a failure" when wired in such fashion.

author: Langdon
author_rank: Frequent Contributor
timestamp: May 12, 2025, 02:04:25 pm
content: 12 feet or 12 inches?12' = 12 feet. (144")12" = 12 inches (1')

author: Monkeh
author_rank: Super Contributor
timestamp: May 12, 2025, 05:01:28 pm
content: Code:Part III. Required Outlets210.50 Receptacle Outlets. Receptacle outlets shall beinstalled as specified in 210.52 through 210.65.210.52 Dwelling Unit Receptacle Outlets. This sectionprovides requirements for 125-volt, 15- and 20-ampere receptacle outlets.(C) Countertops and Work Surfaces. In kitchens, pantries,breakfast rooms, dining rooms, and similar areas of dwellingunits, receptacle outlets for countertop and work surfaces thatare 300 mm ( 12 in.) or wider shall be installed in accordancewith 210.52(C)(1) through (C)(3) and shall not be consideredas the receptacle outlets required by 210.52(A).(1) Wall Spaces. Receptacle outlets shall be installed so that nopoint along the wall line is more than 600 mm (24 in.) measuredhorizontally from a receptacle outlet in that space. Thelocation of the receptacles shall be in accordance with210.52(C)(3).Put simply it's required to actually provide useful outlets rather than throw a couple in at random and leave people trailing extension cords around their kitchen.

author: Analog Kid
author_rank: Super Contributor
timestamp: May 12, 2025, 06:45:43 pm
content: Quote from: Monkeh on May 12, 2025, 05:01:28 pmThat actually seems quite reasonable, given the number of countertop appliances a modren kitchen is likely to have.Outlets are cheap and easy to install, at least for new construction. (Remodels not so much.)You can use a GFCI receptacle as the "starter" and just chain the others on the load side of that one.

author: Langdon
author_rank: Frequent Contributor
timestamp: May 13, 2025, 08:51:54 pm
content: My in-floor heating had a 120VAC line for a 24V transformer and a 15VDC signal line in the same box.I'm not saying it's a good idea, but it worked fine for 15 years.

author: 5U4GB
author_rank: Super Contributor
timestamp: May 14, 2025, 08:24:41 pm
content: Quote from: Analog Kid on May 04, 2025, 08:27:20 pmWell, the ones sold at the local hardware store are. The ones from Aliexpress are unlikely to be...

author: 5U4GB
author_rank: Super Contributor
timestamp: May 14, 2025, 08:27:55 pm
content: Quote from: floobydust on May 04, 2025, 10:22:59 pmThey didn't mention anything about a junction box, and in any case Shelly's work that way so it's likely an ESP32 would too.

author: Terry Bites
author_rank: Super Contributor
timestamp: May 15, 2025, 04:59:37 pm
content: It depends on the voltage. If the low voltage directives or equivalent in your local standard are met, then yes. Typically this can be up to 600V.I think that they have to share a common grounding system though.I wouln't do it by choice though, I dont like induced hum on my DC.