Electric Motor Overload Protection?

Recently came across this from Franklin Electric.

" In order to properly protect a three-phase submersible motor, ambient-compensated, quick-trip overload protection must be used. This can be either a fixed heater or adjustable overload relay, as long as it is ambient-compensated and quick-trip." Also "should select the relay based on the set and maximum amperage ratings of the motor as shown in the heater tables and footnotes on pages 16 & 17. Optimum motor protection may be obtained by setting adjustable overload relays at 5% above actual motor amperage, especially when motors are lightly loaded."

Am wondering if this information for 3 phase submersible motors is also relevant to single phase motors?

Am interested in any comments.

Ken

Yes. In the UK any motor over 1/2 HP single or three phase is supposed to have a "starter" this usually includes the overload relay. European and UK overloads are calibrated such that you set the overload to match the motor nameplate full load current, you don't have to add the extra

5%. Older UK overloads were marked with the "trip" current as is US practice. The ones with separately selectable heater elements usually came with several self adhesive labels to fit to the adjustment dial with both types of marking. Single phase motors often have thermal trips in the motor and don't need an external overload relay. The overload will protect the motor from damage if it is stalled, such as debris jamming your pump. Small motors are used for things like fans, where an overload is not likely to occur, if the bearings were to seize through lack of lubrication you would throw it away, you wouldn't care if the windings burnt out.

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Neil J. Harris