Switch contact ratings for motor?

[Nutz]

I'm sure this is a straight forward question for someone here...Is there a
rule of thumb for switch ratings when switching inductive loads?

I have a timer switch with contacts rated as 16A resistive. With a 240V
single phase supply what what is the maximum power (HP or kW) motor the
switch will operate.

cheers

 

[Tzortzakakis Dimitrios]

I'm sure this is a straight forward question for someone here...Is there a
rule of thumb for switch ratings when switching inductive loads?

I have a timer switch with contacts rated as 16A resistive. With a 240V
single phase supply what what is the maximum power (HP or kW) motor the
switch will operate.

Yeah, usually they are called AC 3 and AC 4, IIRC. What's right for your
case, is AC 3, for induction (squirrel cage) motors. Although the spec for
your timer says 16 A, it would be a good idea to use your timer to operate a
relay (magnetic contactor) and choose a single phase, two contact relay.
This will move the (electrical)stress of opening and closing the contacts
from the timer to the relay . I usually use those transparent single phase
relays, which here are called valve type, because they are trasparent and
look like old fashioned valves. They come with a base, that can be installed
on a rail (panel) or with screws, and when the relay is toast, you just plug
in a new one, instead of trashing the whole timer. BTW, the specs for AC 3
are: printed on any relay, and you can ask the vendor (where you buy it)

 

[Kirk Johnson]

I'm sure this is a straight forward question for someone here...Is there a
rule of thumb for switch ratings when switching inductive loads?

I have a timer switch with contacts rated as 16A resistive. With a 240V
single phase supply what what is the maximum power (HP or kW) motor the
switch will operate.

cheers

I'm an anal wrenching specialist!

Kirk Johnson

 

[Tzortzakakis Dimitrios]

If a switch is motor rated it will generally have an HP rating on it.
You can usually get away with using small fractional HP motors on a
switch rated at 16a resistive but I would not use more than 1/3 to
1/2HP on one.
I believe what T.D is talking about is a "solid state relay" in the US
and that will handle whatever the relay is rated for on a very small
operating contact

No, it's a normal electromagnetic relay, but I know how its called only in
greek. (Rele lychnias). See here, for example:
http://www.alifragis.com.gr/view_cat.php?cat_id=520
They just have a transparent cover, and usually are single-phase, rated
contacts for 16 A.