The top left terminals are 13 and 14, and if we look at the breakdown of the terminals in the previous section, 3 and 4 indicate an N.O. In the case of this 6PST relay shown below, the first number clearly indicates the contact set - 1 through 6. or N.C.ĦPST Relay with integrated terminal blocks showing IEC numbers Many single throw relays have more than 4 poles, but each pole is limited to only either N.O. The coil terminals are unique, as they are designated A1 and A2 - not often a cause for confusion. For the large 4PDT model, the numbers would end with the final set being 41, 42, and 44. If there was a second contact set, the ordered numbers would be 21, 22, and 24. would read 14 (“one four”, okay, I’ll stop now). Therefore, for the first contact set, the common would read 11 (or as I would say, “one one”), the N.C would read 12 (or “one two”), and the N.O. If the relay is a double-throw, where the common terminal connects to both sets of contacts, simply omit #3 from the list of functions - there's only one common. The second digit identifies the purpose of the terminal: The first digit identifies the set of contacts (or ‘poles’), starting with 1, but these relays can be more than just 4 poles. Terminals are always 2-digit numbers, and both digits should be interpreted separately. The International Electrotechnical Commission (IEC) numbers can be used in a wider variety of ways without losing meaning. in that order) and the second set being 8, 6, and 5 (common, N.O., and N.C. 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. Wiring relays can be a difficult challenge even for experienced electricians.
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