This post is the conclusion to the Thermostat series. In the last post we looked at a few different Thermostat types and chose a Bi-Metal style for our Wood Shop installation.
I’ll get into the specifics of each part shortly, but let’s take a quick look at the parts for this project.
Sometimes I’m in the hardware store looking for a particular piece for a project and feel like I’m wearing a blindfold. I’m sure that what I need is here… sigh… somewhere…… I just can’t see it.
Some days I will walk away with nothing, because they just “don’t have” what I need. Other times I will pick up a few parts and see what I can do. I enjoy experimenting with new pieces of hardware because the more I learn about each piece the more the blindfold begins to fall away.
Looking at row upon row of hardware pieces is both bewildering and inspiring. With experience, you can start making connections between which pieces work together.
This can turn into a real treasure hunt when you begin combining things from different isles throughout the store. Perhaps a quick trip to the plumbing department will turn up a piece can contribute to an electrical project.(foreshadowing)
This 3-Hole box will be the focus of our build instructions. It has a hole on each end, and one in the bottom.
At the end of the post, I’ll show you a 5-Hole box alternative that might work better for your shop.
Enclosure Ratings and Standards
While we are on the subject of enclosures, let’s take a second to look at the standards available that we can use to rate our project.
Electronics enclosures are rated by a couple of different standards organizations.
For a bit of standard related humor, check out this clever and all too true XKCD web comic.
The National Electrical Manufacturers Association (NEMA) is the most common in the US. I feel that their numbering system is less that ideal. An alternative European setup by IEC is called the IP rating system.
The nice thing about IP ratings is the two digit number system. The first number is determined by solid object protection and ingress, the second is for protection from liquids. This make it easy to spec out a rating for your application based on where it will be used.
This webpage has a great deal more information on the subject and includes a handy cross reference.
Good circuit design means ensuring all parts of your device are properly specified. We don’t want any weak links. The thermostat we are using can switch up to 22 Amps, so we will match our wire size to that.
The particular cable type we will use is called “12-3 Service Cord”. This is a good choice for a liquid fuel heater because the Seoprene jacket is solvent resistant and flame retardant.
To connect this round cable to our box, we will use a cable connector. We previewed three different connector styles in the Switched Outlet project, but those were for flat Romex cables and will not work for the round service cord.
The cable connectors I chose is a three-piece construction. Be sure to pick a connector that will fit the diameter of your cable. If you look closely, the text on the top of the plastic bag lists the cable diameter range as 0.260″ to 0.375″.
From left to right, you can see the Box Fitting, the Rubber Gripper and the Compression Nut.
Here is the King Thermostat we selected in the last post.
Choosing to use 12-3 service cord also affects our choice of input and output plugs. Be sure the terminals will accept 12 AWG wire.
Let’s get started
I gathered the parts listed above and did a preliminary fit, this is when I first noticed a problem. Here you can see how the Thermostat Switch Bracket interferes with the large mounting flanges in our box.
No worries though, a quick trip to the shop and a little Dremel action took care of that problem.
With the box “edited”, we can get back to work. I decided to buck the trend here and read the manufacturer’s instructions. You know, that piece of paper that usually goes straight to the trash along with the packing material. It included this handy schematic diagram.
We can see from the image above that we will be switching the HOT wire. This single pole Thermostat works well for 120VAC applications. For 240VAC, where there are two hot wires, we would need a double pole Thermostat.
The Thermostat has two wires coming from its switch. A RED wire and a BLACK wire. Per the instructions we are to connect the LINE, that is the voltage coming from the wall, to the RED wire. The LOAD, which is our heater, is connected to the Black thermostat wire.
The White neutral will pass straight through with no connection to the Thermostat.
The Green ground conductor will pass through as well, after being tied to the Thermostat case.
Step by Step
First cut two pieces of service cord, also referred to as cable, about 12″ long. Feel free to use longer lengths if you prefer.
Removing the Cable Jacket
First, we will prepare one of each cable to go into the box. Strip 4-5″ of jacket off each cable.
Does this next picture worry you? I know most people would think it is OK.
No matter how careful I try to be, I always nick the insulation of the wires when I try to remove the cable jacket this way. This is a problem because any damage to the insulation could lead to DANGER down the road.
So I’ve switched to a head-on approach for getting the cable jacket off. Start your side cutters at the end of the cable, with the point in the gap between two of the wires.
Snip your way down the cable then turn the side cutters 90 degrees and cut along the perimeter of the cable.
This method removes the cable jacket without cutting into the wire insulation.
After the cable jacket is gone, strip about 3/4″ off each wire in the cable. This is about the right amount for wire nut connections.
Attaching the Plugs
Now prepare the other end for the plug. Again begin by stripping 1″ of cable jacket off the plug end.
The female plug has a strip gauge on the inside, so use that to expose the correct length of bare copper on each wire, for both cables.
Although the other end of the cable is still un-terminated, it is good to get into the habit of sliding the hood on first.
Attach the Black wire to the Gold colored screw, the White wire to the silver screw and the Green wire to the Green screw.
Once both plugs are assembled, it is time to put the cables into the box.
First, spin the box fitting into the box.
Then slide the compression nut on the cable.
Only after the nut is on the cable, install the rubber gripper. Position it about 1.5″ beyond the stripped jacket.
Slide the prepared cable into the box and hand tighten the compression nut.
Double check to be sure that the jacket is protecting the wires all the way into the box. If not, loosen the nut and pull a bit more cable in. Tighten the compression nut once you have the cable properly positioned.
Wire Nut Connections
For connecting the wires in the box, we will use wire nuts.
Yellow wire nuts are rated for one to three 12 AWG wires. This will work well for the Red, Black and White wires.
Connect the BLACK wire from the MALE plug to the Thermostat’s RED, LINE wire.
Connect the BLACK wire from the FEMALE receptacle to the Thermostat’s BLACK, LOAD wire.
Then connect the White neutral wires from each plug’s cord together with the final Yellow wire nut.
The last wire nut is not like the others. It is bigger and it is RED. Here’s why:
Choosing parts based on their maximum capacity is like holding your foot to the floorboards while driving down the interstate. Besides being illegal, it is hard on your vehicle to run at 100% for a long time. This is why I try to give my parts a little breathing room when considering them for a task. Maximum values are typically determined by tests in ideal conditions. Gunning your car down a hot desert highway would be even less advisable, so remember to keep ambient conditions in mind when selecting parts.
This bigger wire nut can easily manage the two 12AWG wires from the cables along with the 14 AWG pigtail.
Connect the pigtail wire to the screw on the inside of the Thermostat cover and the connections are DONE!
Close it Up
Man, that sure look like a lot of stuff to fit into such a little box. The key to getting it to fit easily is to tuck the wire nuts into the corners of the box.The middle area must be kept clear to allow room for the Thermostat switch.
Two screws hold the Thermostat to the box. Then you can snap on the cover.
Enclosure Rating Example
If we install our Thermostat into the 3-Hole box without plugging the unused hole, you could accidentally slip your finger into this hole and be exposed to 120VAC. Our box would get a NEMA 1 rating and an IP 21 rating at best.
Just by installing the plug, we’ve sealed the enclosure from debris and stray fingers. Our box is now in the NEMA 4 and IP 44 range, pending certification of course.
Here is an alternative Thermostat mounting method using that 5-Hole box.
All the wiring is the same, with the exception that we will put both cable connectors in at one end of the box. This prevents unnecessary bend strain on the cable.
With a bit of 1/2″ pipe, you can mount this box to a floor flange as shown below.
The right angle connector was the hardest to find in the plumbing isle. It is called a “Street” connector, so if you are looking for one, find a helpful associate and ask for it. If you can’t find a helpful sale associate, you’re shopping in the wrong stores :).
All that is left now is to go out to the shop and plug it into the heater!
If you have questions about any of the products or procedures in this project, let me know. You can get in touch with me through the Contact page, or by leaving a comment below.
I’m open to ideas for future projects here at The Lumber Lab. Please leave a comment below if you have a suggestion.
If you want to pick up a few of the parts I’ve listed here in this post, visit Lumber Lab aStore.
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