Magnetic starter + overload service
Inspect and set NEMA / IEC starters and thermal overload relays.
This guide is general field reference for trained, qualified service technicians. It is not a substitute for the original equipment manufacturer's service manual, applicable codes (NEC, OSHA, ASME, local), or the judgment of a licensed professional. Procedures, torque values, pressures, refrigerants, and safety requirements vary by make, model, jurisdiction, and revision. Always verify against current OEM documentation and follow your employer's safety program. Working on compressed-air, electrical, pressure-vessel, and refrigerant systems can cause serious injury or death. By using this guide you accept all risk; AirCompDX and its authors disclaim all warranties and are not liable for any damage, injury, loss, or code violation arising from its use.
Verify zero voltage on L1/L2/L3 to ground and between phases before touching contacts. Capacitor-start motors can hold a charge in the panel.
- Multimeter
- Megger
- Contact-tip burnishing tool
- Torque screwdriver for lug screws
- Contact kit (movable + stationary set)
- Overload relay matched to motor FLA × SF
- Coil if pull-in is weak or chatters
- 1LOTO and verify
Open disconnect, LOTO, verify zero volts L1-L2-L3-G with a meter known to be working.
- 2Inspect contacts
Pull the contact cartridge. Mild pitting and silver-oxide bloom are normal — burnish lightly. Copper-colored craters or welded tips = replace the contact kit.
- 3Coil check
Measure coil resistance against OEM spec (typically 30–300 Ω). Audible chatter under load with good voltage = mechanical bind or weak coil.
- 4Set overload
Set the OL dial to motor FLA × SF (or × 0.58 for line legs on a wye-delta starter). Confirm Class 10/20/30 trip class matches the start time of the load.
- 5Tighten lugs
Torque all line and load lugs to nameplate ft-lb. Loose lugs cause heating that mimics OL trips.
- 6Live test
Restore power. Record voltage on all three phases, amp draw at no-load and full-load. Imbalance >2% voltage or >10% current = utility or motor problem, not the starter.