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Spehro Pefhany

On Mon, 29 Aug 2011 08:58:55 +0000 (UTC), the renowned
(Andrew Gabriel) wrote:

In article ,
DaveC writes:
I may be able to obtain a very small 2-pole 240 vac contactor I need rated
for 50 Hz only.

If I install it in N. America, what's the implication? Is the hold-in
magnetism less than if it were 60 Hz? Just noisy?

Yes, the hold-in force will be proportionally less. If the
coil impedance was due entirely to the inductance, it would
be 50/60ths of the force. However, part of the current limiting
is done by the coil resistance, and that won't change so the
reduction in hold-in force will actually be less than this.

The pull-in force before the magnetic core is closed also
depend on the impedance and resistance, but the impedance
will be lower, and thus the pull-in force will be reduced by
even less.

The pull-in force usually has to overcome a faily weak return
spring. The hold-in force has to overcome a stronger contact
pressure spring. Providing both these conditions are still met,
you should be OK. Ideally, you should check that you have a
reasonable working margin by testing the coil at lower
voltage. If you don't, then the contactor might fail to
close properly on minimum supply conditions which could cause
it to burn out.

snip

A side effect of reduced holding force can be that it is more
sensitive to opening due to external vibration in the wrong axis (and
especially so when the input voltage is on the low side). That could
cause malfunction of whatever it's connected to and premature failure
of the contactor. This might not be so easy to test without a shaker
table etc., but it should be considered if the operating conditions
involve vibration (including vibration from another nearby contactor).

Best regards,
Spehro Pefhany
--
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