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Roger
11-14-2003 23:32:15
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Re: Re: Re: Re: Emglo compressor qquestion in reply to steve b, 11-14-2003 15:11:52
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A magnetic motor starter is a heavy-duty switch. It has large contacts and is pulled shut very quickly by a magnetic coil, which reduces arcing when making and breaking the connection. These features allow it to withstand the high current loads common when starting motors. They also have overload protection built into them, usually in the form of "heaters" which are designed to trip out the switch when current draw becomes excessive (overloaded motor). The main leads come into the top of the starter, in your case, 220V. A lead from one of the mains is taken off and run through the pressure switch. It then comes back through the starter overloads, and into the coil which pulls the switch shut. When the pressure switch closes, current is allowed to flow from one of the main leads, through the pressure switch, and back to the starter, which then energizes the coil in the starter and pulls the connections shut. On most single phase 220V starters, the coil is 110V, hence, you use only one lead from one of the mains to run the coil. On larger starters running, say, 575V, 3phase, two leads are taken from two mains and run through a control voltage transformer, which knocks it down to 110V, which is then used to run the coil. You can get starters that have full voltage coils, however it is more common to use 110V, as this voltage is used to also run things like timers, safety shutdown switches, hour meters and the like. Your pressure switch can easily handle the current load required to operate the starter coil, but the small contacts in the pressure switch are nowhere near capable of handling the inrush current of a compressor motor. Any electrical supply shop should sell starters.
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