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.


In message .com,
writes
Recently came across this from Franklin Electric.
http://www.franklin-electric.com/aid/vol15no6.htm " 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


--
Neil J. Harris