Join 3,366 readers in helping fund MetaFilter (Hide)


How do I safely implement this one-off home electr(on)ics project?
December 2, 2013 2:39 PM   Subscribe

How do I safely and (pretty) cheaply implement this one-off home electrics / electronics project? I have a low-wattage controller that will drive a high-wattage load having to do with the heating of water. I already have a GFCI extension cord that will stand between EVERYTHING and the wall outlet. The main complicating factor is that this is a single, custom-built thing so I need to use off the shelf pieces for a housing, etc.

I need to power a PID controller that draws about 5W at 120V, which will power a 1500W water heater, via a solid-state relay, also at 120. I am certain I will be plugging into a 20+ amp circuit and as mentioned above the fold, everything involved will run through a ground fault interrupter. I have a circuit diagram. Basically I am trying to figure out the mundane stuff, like how to cheaply and safely mount the components (PID controller, SSR, socket, plug) and wire them together. Like, can I put some galvanized steel screws into a wood board as terminals and connect heavy gauge, insulated wires between the various terminals, then securely mount that board in a tupperware box? Is there such a thing as a breadboard that can take 20A that I should be using instead? Thanks for any advice.

(The ultimate goal is to set up a RIMS wort heater and circulator for home brewing, if that helps picture things.)
posted by Joey Buttafoucault to Home & Garden (6 answers total) 1 user marked this as a favorite
 
I would head to the electrical section of the hardware store and get a subpanel box to put everything in. Got a tapped place to run in a ground screw. And then maybe put the 15A capable relay or switch on a socket in its own junction box, just to isolate things further.

For joining wire generally, use wire nuts. If you need more connections than wire nuts can handle there are various options. For instance, typing "15a terminal blocks" into Google gives me all sorts of ways to connect wires from screw terminal to screw terminal.

And you don't want to run any live power into wood or into connectors attached directly to wood. It does conduct, maybe not much, but it also breaks down over time if you run a current through it. My wooden boat friends spend hours tracing millivolt differences on metal parts to try to keep the current which could potentially run between those parts from eating away at the wood. Even if you don't have any immediate issues with wood as an insulator, you will over time. Better to stick with the established tools.
posted by straw at 4:06 PM on December 2, 2013


Without being able to even consider picturing how you'd think such a thing could possibly be acceptable (or even safe, since you're asking the question), I'll just point you to the Mouser page for "barrier terminal blocks". From there, you can graduate to searching for suitable housings…

And suggest you get someone who is at least familar with electrical wiring, if not someone licenced in your particular jurisdiction, to check your work before plugging it in or leaving it where out people might touch it.
posted by Pinback at 4:07 PM on December 2, 2013


The way I'd do this as an electrician is I'd mount everything to a steel back plane in a steel, PVC or fiberglass box (whatever was cheapest). A back plane box will come with either a screw on or hinged cover and if you get a weatherproof box it won't have any knock outs; only the holes you cut.

You can cut a round hole in the side of the box for a round single T-Slot receptacle. They make panel mount units but regular ones will work with a couple nuts and bolts and be cheaper.

Your cord would come in via a strain relief sized to your cord.

Anywhere I needed to connect to wires together I'd use a Din Terminal (feed through block) mounted on DIN Rail. You can probably get a DIN mounted relay that would work for you. Anything that needed to bin insulated can be mounted to the back plane on insulated standoffs.

If you didn't get too fancy with the box you could probably do it for under a hundred bucks.

However DIN rail and terminal are really cheap. At a minimum please use that rather than rolling your own with screws mounted to wood.

Really to do this safely you should use a listed box with cover. Sadly that's also the most expensive part unless you can squeeze every thing into standard outlet box (maybe a 2, 3 or 4 gang). If you don't want to go that route you could make a fold up metal project box of a few different designs. Make two boxes, one slightly larger than the other and slide it over the first for a lid. Or maybe repurpose an old Desktop PC case. Or you might be able to find an electronics project box large enough though they tend to be as expensive as electrical boxes.
posted by Mitheral at 4:24 PM on December 2, 2013 [1 favorite]


You might be able to find some tips from this SparkFun tutorial.

I know you're heavy into your design, but if you decide to punt I'd recommend the Dorkfood DSV Controller, ($99 on Amazon) which seems to do pretty much everything you need.

Personally I could sleep better with a premade, UL/CSA listed device taking care of things instead of something I put together myself.
posted by JoeZydeco at 4:56 PM on December 2, 2013


I have made something very similar with an old UPS case (which is very convenient because it comes with an outlet already installed). A visit to the thrift shop or recycling centre should yield plenty of electrical devices that you can remove the guts from and use for your project.
posted by ssg at 10:14 PM on December 2, 2013


Thank you for all the suggestions so far. I will at the very least be using terminal blocks and/or wire nuts as appropriate for each junction. I honestly don't remember which hat I pulled the "wood board" idea out of but I will certainly NOT be doing that.
posted by Joey Buttafoucault at 4:13 PM on December 4, 2013


« Older My partner infrequently takes ...   |  I'd like to get a nice bottle ... Newer »

You are not logged in, either login or create an account to post comments