UL 508 – Standard of Safety for Industrial Control Equipment
Intended for control and accessory devices for starting, stopping, regulating, controlling or protecting electric motors.
Requirements for construction, electrical clearances, insulation, grounding, marking, wiring.
Overload, endurance, dielectric withstand, short circuit, over &under voltage and temperature are important tests.
IEC 60947 (part 4 for contactors)-similar to UL508 with exception of IEC ratings
ARI 780/790-97 – inactive standard intended for Definite Purpose contactors (used in air conditioning equipment). OEM’s request testing to the requirements of this standard – the electrical and mechanical life test minimums and temperature rise requirements are more stringent than UL 508.
Other standards as applicable to specific product.
ARMATURE MAGNET A SMALL GAP IS LEFT TO BREAK THE MAGNETIC FIELD AND ALLOW ARMATURE TO DROP AWAY FREELY AFTER COIL IS DE-ENERGIZED SHADING COIL Magnetic Flux in Contactor Magnets
Low voltage – produces low currents and low magnetic pull. When the voltage is greater than the pick up voltage and less than the seal voltage the contactor may pick up but will not seal. As the coil is not designed to carry the greater current continuously, it will get hot and will either be damaged or burn out. The armature will chatter – creating noise and wearing magnetic pole faces.
High voltage – Drawing higher than rated current will cause damage and possible failure. The excessive force of the armature closing will wear the pole faces prematurely.
AC Hum – due to changing magnetic field, inducing mechanical vibration. Excessive noise can be caused by: broken shading coil, low voltage to coil, wrong coil, misalignment between magnet and armature.
Precision wound – turns are laid side by side & wire traverses
from one end of the bobbin to the other and back again during winding. Reduces voltage gradient with the coils and prevent accidental shorts. Winding thickness consistent
Random wound – Wire traverses back and forth across the bobbin but consecutive turns are not always adjacent. Winding thickness varies. Packs more copper in smaller space due to tighter nesting. Less costly because of higher winding speed.