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Why use a contactor?
This may be a duplicate post
Lew --------------------------------------------------------------- "DaveC" wrote: A friend (in USA) with a 220v, 1-phase horizontal bandsaw in his home machine shop wants to replace the 1/4 hp motor with 1/2 hp and rewire with an auto-off switch (when the blade cuts through the metal). I always default to using a 3-wire control with contactor, but he asks the logical question: "Why?" -------------------------------------------------- What you are describing is known as under voltage protection. Safety pure and simple is the best reason for using it. --------------------------------------------------- Other than the "If the power fails while cutting" answer (which he says seems of limited additional value on a saw with auto-stop feature) I wasn't very convincing. ----------------------------------------------- What happens in the event you lose power and as a result you lose lighting as well as power to the saw? Without under voltage protection, when power is restored, the saw will restart automatically which can be disastrous, especially if the lights haven't restarted. Your insurance company will also like you. ------------------------------------------ What are the arguments for using a contactor as opposed to a simple on-off switch of equivalent rating? --------------------------------------------- See above. Lew |
#2
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Why use a contactor?
On 1/11/2014 10:44 PM, Lew Hodgett wrote:
This may be a duplicate post Lew --------------------------------------------------------------- "DaveC" wrote: A friend (in USA) with a 220v, 1-phase horizontal bandsaw in his home machine shop wants to replace the 1/4 hp motor with 1/2 hp and rewire with an auto-off switch (when the blade cuts through the metal). I always default to using a 3-wire control with contactor, but he asks the logical question: "Why?" -------------------------------------------------- What you are describing is known as under voltage protection. Safety pure and simple is the best reason for using it. --------------------------------------------------- Other than the "If the power fails while cutting" answer (which he says seems of limited additional value on a saw with auto-stop feature) I wasn't very convincing. ----------------------------------------------- What happens in the event you lose power and as a result you lose lighting as well as power to the saw? Without under voltage protection, when power is restored, the saw will restart automatically which can be disastrous, especially if the lights haven't restarted. Your insurance company will also like you. ------------------------------------------ What are the arguments for using a contactor as opposed to a simple on-off switch of equivalent rating? --------------------------------------------- See above. Lew I suspect that because most 220 volt machines are used more in an industrial setting, in the US, than in the typical home work shop. In an industrial setting there are numerous machines that are operating all the time. With a power outage all machines stop but do not come back on after workers leave. Imagine all of them powering back up with no one standing around to turn them off when the power is restored. With the lower voltage machines typically found mostly in home shops it is unlikely that more than one would come back on by itself nor a group of people that might be around when the power is restored, hence you don't often see a magnetic switch being used. I suspect the magnetic switch is more if an industrial safety measure that many of us enjoy the benefits from in our home shops. Having said that and IIRC my relatively new Delta 15 inch stationary planer does not have a magnetic switch although it is wired for and runs on 220. I suspect that particular model with its switch configuration is not available as an industrial unit. |
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