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What is a triac? 
Proportional thermostats have a component called a triac that is used to regulate the power to the heating device. Triacs are also widely used in most household dimmers and other appliances. They basically perform the function of a fast triggering solid state switch. 

What can cause a triac to fail? 
While typically robust they are susceptible to damage and failure under certain circumstances just like any other electrical component. Most often this occurs during electrical spikes from the power company, short circuit scenarios, overheating/overloading, or the occasional manufacturer defect. 

What happens when a triac fails? 
Triacs typically fail by no longer passing any power through them or fail by passing full power through them. Once a triac has been damaged the control circuitry no longer has control of the triac's output power. While failing in either state is undesirable failing in the ON state can pose a serious safety/fire risk. 

What about relay based thermostats? 
A relay is a mechanical switch that is operated magnetically and makes a click noise every time it engages or disengages. Inside the relay are contacts that the power flows through. While relays typically are immune to voltage spikes passing through them they do still have potential for failure. Each time a relay activates or deactivates under load there is often an arc inside the relay. Over time the spark wears at the contact points and can cause higher resistance generating lower output voltage, heat, and relay failure. This arc also can weld the contacts together creating a uncontrolled full ON state. 

Are there other options? 
Spyder Robotics LLC has been leading the way in thermostat performance and safety. We now offer hybrid technology in many models of the Herpstat product line. These models use high quality triacs (rated at more than double the maximum wattage ratings on our thermostats) to provide proportional control over the power. We then back the triacs up with a safety relay that can cut power to the entire output circuit should a triac fail. This setting is based off the user adjustable high/low alarms and can be enabled by the user. By using both technologies together you gain an extra layer of safety from a runaway scenario. While we do still produce models without the safety relay for those on a budget we still recommend one with the safety as a first choice. 

What steps can be taken to help increase safety? 
1. Surge suppressors can be an important step to protect your equipment from failure. However, purchasing a low end suppressor not only may provide little to no protection they can actually cause interference causing a thermostat to stay in a ON state. Look for surge suppressors rated for large flat panel TVs and computer equipment. Keep in mind that surge suppressors wear out over time and require replacement. 

2. Look for quality name brand heating devices that were originally manufactured for heating pet enclosures. Often heating devices not originally intended for animal care are assembled by individuals and resold. It is recommended that these devices should be assembled and inspected by a qualified electrician. It is very important that you inspect your heating devices routinely for cleanliness, damages, and function. 

3. If your heating device left in a unregulated ON state has the possibility of extreme overheating or fire risk then a secondary inline backup thermostat or a thermostat with a built in safety relay should be used to provide redundancy. 

4. Double and triple check your cords anytime you setup an environment for the first time or move/clean your setup. A common mistake people make with multi-output thermostats is connecting a temperature probe and inserting it into an environment and then connecting that environment's heating device to the wrong outlet on the thermostat. For instance #1 probe and #2 outlet going to a cage and #2 probe and #1 outlet going to the other. This typically causes the environment with the probe to not reach the set temperature and the other environment to overheat as its uncontrolled. 

5. Do not overload the thermostat. Never exceed the manufactures maximum rated wattage on a thermostat. This can cause overheating and result in thermostat failure. You can check with the manufacturer of your enclosure for its power rating. When in doubt you can check the total wattage easily by plugging the enclosure into a power meter and plugging the power meter into the wall. The most common product for this is named Kill-A-Watt and is usually available locally at home improvement stores and electronic stores. We do not recommend having the thermostat inline for the wattage test. We recommend testing without animals in the enclosure. 

6. Running multiple racks/enclosures using a single thermostat output and probe does carry risk. The environment that does not have a temperature probe runs unmonitored and is susceptible to overheating. 

7. Fire prevention steps are important. There should always be a smoke alarm in the animal room and its battery and function should be routinely tested. A fire extinguisher rated for electrical should also be installed in a easily accessible location. Teach your family members how to use it. For some facilities an electrical fire prevention sprinkler system may be recommended. 

8. Evaluate your locations wiring. The most common electrical source to rooms have a breaker rated at 15 amps. This is equal to a maximum of 1800 watts. This power may be shared between all devices in the room and possibly the room lights as well. It can be very easy to overload your locations wiring which could result in a electrical wall fire. Simply installing a larger breaker can violate code as well as cause the failure if the wire gauge running to the room is insufficient. When in doubt get a professional electrician to look at your installation. 

9. When setting up a new environment be sure to monitor it closely for the first day of use. While we pretest every unit that we build and select components from name brand companies expecting reliability it is still an important step. The typical saying is that electrical components with manufacturing defects fail within the first 24 hours of use. 

10. Keep electronics and water separated. Do not place water dishes on top of or beside thermostats. 

11. Recheck and monitor all equipment after a power outage or storm in case damage has occurred. If you live in an area that often experiences brown out or black out power conditions we recommend installing a power conditioner that supports boosting and pure sine wave operation. 

12. Backup generators may affect the operation of thermostats. Many of them do not output clean enough power for proportional thermostats to turn on/off the outputs properly. We have tested with common portable generators and our results indicate that they typically do not allow proportional thermostats to work properly. We have tested with Honda inverter based generators and found they produce clean power and allow proportional thermostats to work properly. Computer uninterruptible supplies are not recommended as they typically produce modified sine waves that will not allow the thermostat to work properly. Standard 12Vdc to 120Vac inverters also are not recommended for proportional thermostats as they typically produce modified sine waves that will not allow the thermostat to work properly. When using any backup power supply we recommend a secondary inline backup thermostat or thermostat equipped with a built in safety relay. 

Why are you telling me all of this? 
Here at Spyder Robotics LLC we care about our customers, friends, family, and the animals they keep. We feel that our products are designed to be full featured, economic, and reliable. We intend to provide as much information that we can to selecting the right thermostat product and to prevent property damage, injury, or death. Whether you purchase a Herpstat thermostat or one of our competitor's product we ask that you keep safety first. 

Should you feel this information needs refinement or have additional information we should add send your ideas to Join us in helping to keep the reptile community safe. 

The information in the article is to be used at your own risk. Spyder Robotics LLC assumes no responsibility or liability for the use or accuracy of this information. Last Edited 2/21/2012