Proper contactor

[GENERALCOOL]

Dear Friends,

Suppose that we have a compressor that gets 10 amp current form each phase at full load condition.
What is your opinion about choosing proper contactor for this compressor ?
1.25 * 10 amp is enough (%25 over) ? or 2.25 * 10 Amp (%225 over) ? or twice bigger ?

What is your opinion for choosing proper contactor for this compressor ?

Thanks.

http://www.generalcooltrade.com

[Tayters]

Go bigger, not much difference in price. Don't forget start up current will be a lot higher momentarily also.

Cheers,
Andy.

[frank]

A contactor is just an electrically operated switch. As Tayters says, go bigger. I would select one around 25A.
The overload should protect the compressor motor and the MCB/Fuses should protect the cable.

[Tycho]

Pick one that is slightly larger.
Contactor should be chosen for the operating current +10-15%, peak current is in the specs for the contactor

Make sure it is AC-3 rated for starting a motor.
https://en.wikipedia.org/wiki/Contactor

[narkom]

https://electrical-engineering-portal.com/sizing-the-dol-motor-starter-parts-contactor-fuse-cb-thermal-overload-relay

[chemi-cool]

Allen-Bradley. best contactors ever made.
No other make can compete with them.

[Glenn Moore]

Contactors are rated for full load amps and have nominal ratings typically 6, 10, 12,’16 ,20, 25,32 amp etc . They have a Locked Rotor rating of 1.6 times their nominal rating ie a 10 amp contactor will have a locked rotor rating of 60 amp for start up purposes. This will cover reciprocating compressors without problems, but typically Scroll compressors have a higher Locked rotor current for the same sized recip motor. So for a Recip compressor with full load amps say 10 amps a 12 amp contactor would suffice but if it’s a Scroll compressor with 10 amps FLC then a 16 amp contactor would be required to withstand the higher LRA of the scroll
Using an undersized contactor will reduce its useful working lifetime dramatically , and could cause irreparable damage to the motor “burnout” or welded in contacts etc .oversizing contactors give little benefit but incur a cost penalty
A good quality overload will give both overload and single phaseing protection
Measuring the motors current draw while setting the Hp control will give a good indication of where the overload should be set to to prevent nuisance trips but to give maximum protection to the motor

[Topher Co]

My experience is that using anything that is "just enough" or slightly undersized opens you up to voltage drop, which increases amps, which causes heat. Like everyone said, (https://www.beaconsaves.com) go for the slightly larger rated contactor.

[nike123]

Compressor contactor should be sized according to LRA rating and operating voltage of compresor and not FLA, and we should choose contactor with LRA rating same, or better, one size above that.
15493

In this way we dont need to worry if AC3 rating matches starting carateristic of our compresor type!

On the other hand, compressor contactor thermal protection should be set exactly at compressor FLA rating and not "slightly" above that, because triping treshold of 1,14x is already incorporated in setting dial.
Also, there are 4 classes of thermal overload.
https://www.se.com/in/en/faqs/FA22893/

Class 10 should be used for refrigeration compressors.

What I prefer to use, if there is place in switchboard, aditionaly motor circuit protector.
https://thegrid.rexel.com/en-us/knowledge/product-faqs/w/wiki/885/motor-protection-circuit-breakers-mpcb-and-motor-circuit-protector-mcp#