Cold Blooded Eye Candy

Thermostat Dos and Don'ts

Kassandra and Jason both share their experiences with thermostats over the years. There’s a wealth of information contained, from setting up your entire room to a tutorial for wiring two Rancos together - double protection for your herps!

Hot Wires 380

In the wide world of keeping reptiles, there are very few things that are constants from species to species and keeper to keeper, and supplemental heating is one of those uniting factors. Most species require at least a basking area for optimum health. The heat element can vary from heat tape to a space heater to a basking lamp, but they share one common feature - all require the addition of a thermostat if you want to provide the correct temperature - and avoid burning your house down.

Unfortunately, one thing we’ve learned over the years is this: thermostats and everything associated with them do fail. We've seen it happen so many times, including in our own collection. In our case, we were lucky and only lost some eggs in an incubator. We’ve witnessed many keepers fall victim to a runaway thermostat failure - losing part or all of their collection, and sadly sometimes their entire home.

First and foremost.....DO NOT SKIMP ON YOUR PURCHASE! While we do realize that money can be a factor when making caging and supply purchases, this is arguably the most important area when it comes to taking care of your animals, as a vital element of proper caging.

This cannot be overstated. The cost of lost animals and equipment due to a malfunction or a fire always outweighs the initial cost of your thermostat setup. Don't wait until a fire or overheated thermostat kills off animals to upgrade your setup. Do it right the first time! Please understand, this isn't to ruffle anyone's feathers. We say this from experience. We've seen too many fires and too many thermostat failures cook other people's animals. Don't be one of those stories!

The first thing to consider when planning your heating setup is your residential power. In the United States, most household outlets are wired to 15amp circuit breakers that supply 115 volts of single-phase AC power. You’ve probably noticed that power receptacles seldom appear solo. What most people are familiar with are pairs of receptacles spaced around a room for convenience.


Each set of plugs is called a “gang.” Some people will have double gangs in their homes, which house four receptacles in one. Take a minute to determine what kind of outlets you have. Those with two holes are ungrounded and should not be used for heating reptile cages. Most people will have plug receptacles with three holes each - the half-round hole is the ground and offers a degree of safety to the system. The best of the best is the GFCI outlet. “Ground Fault Circuit Interrupters” have a built in circuit breaker that will cut power to the outlet if anything plugged into it becomes grounded. You’ve probably seen these in your bathroom and kitchen - they are required in wet locations by building code. For an extra level of protection, consider replacing the outlet you plan to use for your heating set up with a GFCI version.


It is common for all the outlets on an entire wall, or even
an entire room to be on the same circuit. You must know how many circuits you have to work with, to ensure you don’t overload your household circuit and end up with no heat at all! This is particularly important if you are heating many cages, if you are using high-wattage heating elements/bulbs, or if you also have other appliances that draw considerable power in the room. You don’t want to end up tripping your circuit breaker every time you run the vacuum, for example, or lose power to your racks every time a fridge compressor kicks on.

Fluke 117a

If you do not have access to a multi-meter (example above), you can figure out which of your outlets are on the same circuit by plugging in a radio or lamp into each gang and turning the circuit breaker off. Once you have determined how many circuits you have servicing the room you keep your reptiles in, you can plan your heating set up.

There are four components to a heating set-up: The individual heating elements, the thermostats, the power strip/surge protector, and the cabling that connects them.

The first step is to identify what kind of heat source you are using and determine how much power it can draw. It is perfectly fine to run multiple heating elements on the same thermostat set-up, but
NEVER mix heating element types. Four-inch heat tape heats up much differently than eleven-inch heat tape, or heat rope, or ceramic heat emitters. In the same vein, do not run back, belly and/or indirect heating systems together. To clarify - it’s okay to run five 10-slot racks with belly heat rope on the same thermostat set, but it is NOT okay to run one 10 slot rack with belly heat rope and a stack of boa cages with ultratherm mats on the same thermostat.

Most heat tape and rope is “low wattage” - check with the manufacturer to see how much each of your cages or racks will pull. Heat emitters and basking bulbs have the wattage marked on them (or their packaging) and are usually much high power-consumers than heat tape, rope or mats. Now, add up the power draw of all the elements you want plugged into the same thermostat set up.


For the purposes of this tutorial, we are going to refer to the RANCO ETC 111000 Digital Temperature Control (as seen above). This is our thermostat of choice. They cost under $50/each on and can handle a 1500 watt load. There are many other thermostat options - if you choose to use a different thermostat, make sure you buy one that can handle the power draw your set up requires. Remember - no matter how fancy your thermostat set up, if you’re using high-wattage heaters, you’re never going to get more than 1800 watts from a standard 15 amp circuit - you will need to upgrade to a 20 amp circuit, or better yet - spread your system over multiple circuits.

Now here is the key to a truly safe thermostat set-up - dual redundancy. That’s right - we have a thermostat for our thermostat. For each set-up, we purchase two RANCO ETC controllers. They are wired together and each has a probe reading temperature in the caging system. In this manner, we remove all most all risk of runaway thermostat failures. A tutorial for this setup is illustrated later in this post.

The next element of your set-up is the power strip/surge protector. It’s not mandatory to use one, of course, but doing so offers yet another fail-safe (surge protectors also have safety mechanisms built-in) and a lot of flexibility when it comes to rearranging your caging. Don’t be a cheapskate and buy the cheapest one you see. Purchase a high quality strip with a surge protector - the kind that offers the $50k electronics replacement guarantee. Those tend to be of higher quality, with “guts” that will weather the test of time. Once again - make sure it’s rated to handle at least 15 amps of current! We also prefer surge protectors with the on/off button that actually lights up, so it’s easy to tell when power is being provided to the strip. Don’t forget to select a surge protector that has enough spaces for all the heating elements you need to plug into it!

The final element of your set-up is the wiring you use to connect your system together. The simplest way to go about this is to purchase an appropriate extension cord - it has the all the wires you need, a tough cable jacket, and handy plug ends you can put to good use. When selecting your cord, use the same parameters as you used for your surge protector. Be sure to purchase cords that are of good quality and rated to handle the absolute maximum amperage your setup might draw. Example: you plan on wiring up a couple of Ranco ETCs to an oil heater for an incubator (rated at 1500 watts, of course), but you buy a cord that's only rated for 8 amps, you’re going to have a bad time.

By bad time, we mean that the power requirement of the oil heater (1500 watts) will exceed what your 8 amp cord can provide. To figure that out, while not exact*, you can use this simple ratio:

1 amp = 100 watts.

So in the case of the cord rated for 8 amps, you would figure out it’s power rating in this way:

If 1 amp = 100 watts, then 8 amps = 800 watts

That doesn't cut it! The oil heater is rated at 1500 watts! Move those eyes down the aisle a bit and find the cords that are rated for at least 15 amps. If you elect to use that 8 amp extension cord, you risk overheating it. When this happens, the cord will melt, catch fire, and could burn your house down. Don't be "that guy"! It’s always better to err on the side of caution!

* What we mean by “not exact”, if you were to figure the exact amperage draw using Ohm’s Law (E=I/R) and (P=I*E), you would actually come up with, in the case of the 1500 watt/115 VAC setup, 13.043 amps, not 15. For math in one’s head....the ratio above requires no calculator Happy.

We’ll break down how we wire up our Ranco ETCs below. While we are both experienced aircraft electricians, the concepts below aren’t that difficult. If you’re not comfortable, by all means, don’t attempt to wire these. These guidelines are meant to be just that: guidelines. We’re not responsible for mistakes made on your part.

With that out of the way......

Here’s a short list of parts you’ll need. Because we are wiring thermostats that handle 1500 watts of power, we’ll assume we’re going to wire everything up with parts rated for 15 amps.

2 Ranco ETC 11000s
1 Power Strip/surge protector (15 amp rated)
1 Extension Cord (15 amp rated). We usually use either a 15 foot or 25 foot cord, depending on our needs.
2 Cable Clamps, 3/8” (they’ll hold the wires in place at the bottom of each Ranco)
2 Wire Nuts (for your green or “ground” wires)

For tools, you’ll simply need:
1 #2 Phillips screwdriver
1 small common (flat head) screwdriver, about 1/8” width on the tip
1 set of wire strippers
1 set of large diagonal cutters
1 utility knife (or razor blade, if you prefer)


Let’s begin. Notice the two different wire colors? Let’s start there, just to give you an overview of this particular setup. The orange wire on the left Ranco is coming directly from a wall outlet (your power source). That’s why you see the words “Power In” on that Ranco. The two units are connected by a jumper wire with the second unit labeled “Power Out”. You should then notice the black wire coming out of that Ranco. That’s where we wire a high quality power strip/surge protector, or a single, heavy duty plug (usually for a single, high power heat source, such as an oil heater). Just imagine the electricity as if it were water – it flows in the direction from the wall outlet to first Ranco, then the second, and finally to your heat source. Keep that in mind when we crack these open and look inside.

You’re going to do some chopping! Start with your extension cord. You want to remove the “female” end first, only the plug. Now cut off two more pieces: one at about 4 inches, the other at about 14 inches. Those are your jumpers. You’ll use those later. After that, cut the male end off of your power strip/surge protector (just the plug!) and you’re ready to strip. You’ll want to remove about 2 1/2 inches of the outer most insulator on your long cord, both ends of your 14 inch jumper, and also the end of your power strip. This is where your utility knife or razor blade will come in handy. Take care to only cut the outer jacket, though. If you cut too deep you risk damaging the insulation for the individual wires inside!

Use the 4 inch piece to make your jumpers that you’ll see below. They’re outlined in the diagram and the picture. To terminate (terminate simply means to connect), you’ll need to strip about 1/2” off of each wire so that you have bare copper making contact inside of the terminal blocks. Those green wires? They simply get twisted together with a wire nut inside of each Ranco. Too easy! BEFORE YOU TERMINATE, install your wire clamps into the Rancos, THEN run the wires through the wire clamps. Trust me on that one. You can’t do it after you terminate the wires. Don’t worry, we’ll remind you again later.

Trust us, it’s not as complicated as it looks. We’re going to refer back to the below picture quite a bit, but before we do, remember - think of electricity as if it were simply water flowing through pipes. If you follow the’s very simple to understand this picture. Ignore the green wires (safety grounds) for a moment and concentrate on the “black” and the “white”. Those are the pipes, and their color tells us which way the water is going. The water needs to make a complete circle starting at the wall, through all of the wires (pipes), then back to the wall. Black? That’s the “hot” wire. As far as our water is concerned, think of that black pipe as the pipe COMING FROM the wall outlet. Follow the numbers below, 1 through 10....and follow the flow!

Hot Wires

Don’t worry, #1 is hiding under the other two wires. It’s there! Next, you’ll notice that those are little 4 inch “jumper” wires that go from 2 to 3 in the first Ranco as well as 7 to 8 in the second. The terminals where the 2 and 7 are just termination points, just make sure that you terminate them where it says, “120 VAC”. The real action happens at the 3 to 4 and the 8 to 9. That’s your relay, where the thermostat shuts on and off the “water flow”. Remember, 1 is coming from the wall outlet and 10 is going to your power strip/heat source, also known as your “load”. Have a look at the actual wire diagram from Ranco for a single ETC.

Ranco Wire Diagram

This diagram will come with your Ranco, but we’ve added some numbers and wire labels to clarify. This is the wiring diagram for only one Ranco, not two, but it should help clarify what you may not see in our picture above. For starters, the 4 inch “jumper” we mentioned above is clearly labeled here, from #2 to #3. Next, notice the White Wire, known as your “common” or “neutral” wire. That’s how your “water” gets back to the wall after it goes through all that black pipe! Where do you think the word “circuit” comes from? It’s just a big circle! It starts at the wall and ends at the wall: black to white, or hot to common/neutral. One difference you’ll notice between the diagram and our picture is where the white wires terminate, #7 on our diagram. You basically put both white wires in the terminal block (notice our picture!), just like you do for the black on #2 of the diagram. Electrically it all works the same, but they drew it a bit differently on the diagram. A blue #8 may have helped out if it was placed next to the “120 VAC” on the diagram, but it should make sense without it. The “water” makes it back to the wall there.

About that “Load” thing again. A “load” in electricity is basically whatever is drawing power from the plug - it could be a light, a hair dryer, a heater....whatever. In the case of our diagram, it’s actually two things: first, since you’re wiring two Rancos together, the first “load” is your second Ranco. In the case of the second Ranco, it’s your power strip/heat source. You’re basically repeating the above diagram for two Rancos, connected by the 14 inches of extension cord you cut in the beginning.

Ranco closeup

This is where a video would be handy. One of these days. This is the inside of a different Ranco. It’s a single Ranco wired up, but it’s a much closer pic. One difference: the ORANGE wire is still plugged into the wall, it just happens to be on the right in this picture. The first Ranco unit in the above picture (the one on the left) has the orange wire on the left. No matter, they still connect the same inside the unit. The Yellow wire in this picture is actually a power strip/surge protector, instead of a second Ranco. Again, no all terminates the same! Very simple - Remove the cover of your Ranco with that #2 Phillips screwdriver. DON’T FORGET YOUR WIRE CLAMPS! Install those next before you run your wires through. You’ll want to tighten them down on your wires after you run them through the clamps. Next, connect your two commons/neutrals together in the “COM” terminal using the small common (flat head) screwdriver. Install one end of that 4 inch jumper, along with your “wall side” hot/black wire into the “120” terminal. The other end of the 4 inch jumper goes to the “C” terminal on the other block. The final hot/black wire goes to the “NO” terminal. Lastly? Connect your two green (ground) wires together with that wire nut. I used an automotive splice in the last pic, but a wire nut is soooo much easier to use. Remember, you’ve got two Rancos to wire! They’re basically copies of each other. Once they’re both wired, put your covers back in place and you’re ready for the next step.

Now, how do you USE it, once you have it wired? Well, plug that male end into the wall and let’s get started. DO NOT plug in any heat sources until you’ve tested it out. This setup will tell you if all that mumbo jumbo above actually worked. It’s easy enough to follow the instructions that come with the unit, but we’ll outline it below and apply it to the double thermostat setup.

You’ll want to set each one up individually, starting with the one plugged directly into the wall. Once it’s plugged in, you should see the digital readout come on. You have 4 settings you’ll need to adjust. First, you’ll press the “set” button. Your first setting choice will be F or C for Fahrenheit or Celsius. Press Up or Down to choose “F”. Press “set” again. Next, you’ll set your actual temperature. This will need to be adjusted as you tweak your cages/racks/incubator, but choose a number to start with. Let’s say 85 degrees. Press up or down to select 85. Press “set” once again. The next setting is the differential temperature. This is how many degrees it’ll fluctuate from your setting of 85 before turning off and on. We choose 1 degree. Toggle up or down until you get to “1”. This keeps our temperatures “tight”, or as close to the 85 degrees we set as possible. Press “set” again. Lastly, you’ll have C1/H1. This is heating/cooling mode. Since we’re using a heat source, we’re heating. Select “H1”. Press “set” one last time, and the settings are complete. Now for the second unit....

Setting up the second unit is the exact same as above, except the temperature setting. We usually set the second one up about a degree warmer than the first, or in this case, 86 degrees. In the event the first unit ever gets stuck in the “ON” position, the second unit will still be able to shut on and off at the 86 degree mark, protecting whatever it’s controlling from overheating!

When the time does come to plug your heat sources into your new thermostat setup, remember, make sure you put those probes directly on the heat source (if you can). With the double thermostat setup, you’ve got two to contend with. We recommend putting them in the same location so that they’re both accurately measuring the same thing. If you spread them out, you could get two wildly different temperatures! Give your cages and racks some time to heat up and even out awhile before you put animals in them. Use your temp gun to check temps periodically. If the temps are too hot or too cold, go back through the 4 settings outlined above and adjust accordingly.

You can also periodically check to see if your units are functioning properly by adjusting the primary unit up a few degrees to see if it’s indeed heating and shutting itself off properly. Once you notice it’s functioning properly, you can always readjust down to the original temperatures. Periodically checking any thermostat is a good practice. Keep that temp gun handy!

One day, we promise, we’ll do a video on the double method. Until then, we hope you got something out of this LONG tutorial. Happy Here’s a shot of our incubator when it was in it’s “test phase”. You’ll find a double Ranco setup running a single 1500 watt oil heater inside. It’s been solid for us for a couple of years now.


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