![]() ![]() Pins 2-7 connect to the coil, with 1, 3, and 4 being the first set of contacts (common, N.O., and N.C. For these relays, the numbers 1-8 orbit the base. NEMA Octal BaseĪ slight variation occurs in the NEMA convention for the circular keyed base with 8 pins. From the preceding description, it is now clear to see what each number represents. ![]() Regarding the smallest relays, we should expect an SPDT relay to have only terminals listed 1 - 5 - 9 - 13 - 14. connection, the choice would be 1 and 9, or perhaps 4 and 12. You should expect to use terminals 5 and 9, or alternatively, 8 and 12.ĭPDT relay with dual NEMA and IEC numbersįor an N.C. Terminals 13 and 14 indicate the coil in the NEMA convention.Īs an example, suppose you needed to connect a circuit to an N.O. Finally, 9-12 are the common leg terminals to supply voltage on a dry contact. 5-8 indicate the normally open (N.O.) terminals. Since you are more likely to encounter a smaller one, the numbers for a smaller DPDT relay might look like this:ġ-5-9 for the first contact set, and 4-8-12 for the second contact set, then 13-14 for the coil.Ĭomparing these to the larger common double-pole relay, the 4PDT, we would also find all of the mysterious missing numbers in between those on the double-pole model.įor this relay with four contact sets, 1-4 indicate the normally closed (N.C.) terminals. Under the NEMA (National Electrical Manufacturers Association) standard, the terminal numbers are labeled 1-14 in the largest typical 4PDT relays. Industrial control relays are primarily produced under NEMA and IEC standards, which means that you might see relays with one or the other, but often both number conventions side-by-side. You might still have to look up those wiring diagrams, but perhaps we can remove some of that aggravation that stems from confusion. In this Info Byte, learn the purpose and reason behind the often-confusing terminal numbers. Add in the various sizes, single- vs double-pole configurations, and the best you can hope is that a drop-in replacement is readily available on the supply shelf. terminals, as well as the coil, is difficult to begin with. Determining the screw terminal locations of common, N.O, and N.C. At 150☏ the relay shuts off and the current stops.Wiring relays can be a difficult challenge even for experienced electricians. In this example, the relay will stay activated and let current flow through the light bulb until the temperature of the thermistor reaches 150☏. Common pin relay code#The CodeĪfter everything is connected, upload this code to the Arduino: #include See our article on Making an Arduino Temperature Sensor for more information. If you do use a 100K Ω thermistor, you’ll need to change line 7 in the code below to Temp = log(100000.0*((1024.0/RawADC-1))). If you use a 100K Ω thermistor, use a 100K Ω resistor. ![]() For example, I’m using a 10K Ω thermistor, so the resistor should be 10K Ω as well. The value of the resistor should be the same order of magnitude as the thermistor. The thermistor part of the circuit is set up as a voltage divider. It’s dangerous to put the relay on the neutral wire, since if the device fails current can still fault to ground when the relay is off. This way the relay is on the hot side, and current is switched before it reaches the light bulb. Connect the side leading to the light bulb to the NO terminal of the relay, and the side leading to the plug to the C terminal. Identify the hot power wire (red wire in the diagram above) in the cord leading to the light bulb and make a cut. ![]()
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