Project Tips From Doug

My favorite part of posting a project is the questions I get afterwards. A lot of times, I kind of forget that everybody has a different way of doing things and different reasons for their choices. Since I'm wiring up a project (Pro EM-50 metering a water heater, with contactor control), I think it is a good time to show a few thing about how - and why - I build my projects the way I do, so I'll share a few of the regular questions I get and their answers, plus several tips i have to make life easier for you.

Why din rail?

Because it's there? I use din rail for my projects at home because that's what I use for projects at work. I'm familiar with it, it's a standardized mounting form factor, and Shelly's Pro product line are all din rail products. It's also a lot cleaner, making it easy to look at and understand what I've done. Since I use a lot of my own DIY projects to illustrate concepts for Shelly customers, that's very important to me.

Why polycarbonate?

Because - SCIENCE!

Not really. Actually, a few years ago, just before the launch of our Pro line, I needed to identify din rail enclosures I felt comfortable recommending to customers. In Europe, everybody's load center is din rail - must be a breeze buying breakers over there. Here, you have industrial electrical firms and panel shops. that use a lot of din rail, but usually metal enclosures. While Shelly Pro products have Ethernet, it's still important to showcase some of the RF features - Wi-Fi range extender, Bluetooth gateway, etc. - but, also, isolating low voltage cabling in an enclosure with line voltage can be a headache. In my testing, I found polycarbonate to have the best performance compared to fiberglass, PVC, and other plastics. So I stuck with it.

Will other enclosures work?

100% - you don't need to use a din rail enclosure, a poly carbonate enclosure, or use the same brand terminal blocks. As long as your setup is electrically safe, meets code, and the end result realizes your goals for the project, you've done it the right way.

Tips:

Planning:

My very first step when building an enclosure is to sketch it on the whiteboard, so I know how many terminal blocks I need. My second step is to lay out the terminal blocks, so i make sure there's enough room, I have them centered on the din rail, and I know where to drill for my strain reliefs. However, I don't screw down the din rail until I'm ready to start wiring - if I have to take the bar off, the mounting holes will strip out.

Ferrules:

Whenever you use stranded wire, you should crimp a ferrule on. When you lock down a terminal onto stranded wire, the strands spread out, possibly even pushing strands outside of the connection, which can shock someone. Even if there's no danger to anyone, it reduces the capacity of the wire to carry current. It's an extra step but makes a better mechanical connection.

One quick note - while testing my fittings, I realized that this is aluminum wire, so I need to step up from 10 awg to 8 awg. I was already waiting for ferrules, since this one is too small to sit over the insulation, so not an impact to my timeframe on this project.

Drilling:

Tape the area where you're going to drill. This will limit the spread of dust (or plastic) and prevent cracking. I use painter's tape so that I don't have to clean off glue.

Strain Reliefs:

Strain reliefs do what the name suggests - they relieve strain on the wire and hold in place - preventing someone from stepping on a cable and popping a live wire out of the enclosure.

Terminal block covers:

You should always use a cover on exposed end blocks - this prevents the possibility of someone grazing a finger across a live electrical connection.