AirComParts Replacement Starter Coil for Square D NEMA Motor Starters and Contactors, Sizes 1 to 5

Replacement magnetic coils for Square D Class 8536 and Class 8502 NEMA motor starters and contactors in sizes 1 through 5, the starters fitted to most industrial reciprocating and rotary screw air compressor packages.

A burned coil is the single most common reason a three-phase compressor stops starting. The symptom is unmistakable once you have seen it: the control circuit is live, the overload has not tripped, but the contactor will not pull in, or it buzzes and chatters instead of seating. Sometimes you can smell it before you open the enclosure. Coils fail from sustained low control voltage, from a contactor whose armature faces are dirty or misaligned so the coil never fully seats, and from simple age in a hot compressor room. Replacing the coil is a ten-minute job and costs a fraction of a new starter.

Part reference

• COIL-N1: Square D 31041-400, NEMA size 00, 0 and 1 starters and contactors
• COIL-N2: Square D 31063-409, NEMA size 2 starters and contactors
• COIL-N3: Square D 31074-400, NEMA size 3 starters and contactors
• COIL-N4: Square D 31091-400, NEMA size 4 starters and contactors
• COIL-N5: Square D 31096-400, NEMA size 5 starters and contactors

Specify your coil voltage when you order

Square D coil part numbers carry a two-digit voltage suffix that is not shown above, because each size is stocked across the full voltage range at one price. Size 1 through 4 use codes such as -42 for 110/120V, -48 for 208V, -47 or -51 for 240V and -57 for 440/480V; the size 5 family uses a different scheme, with -09 for 120V, -15 for 208V, -18 for 220/240V and -24 for 440/480V. Read the voltage off the coil you are replacing, or off the starter's wiring diagram, and tell us at checkout. If you are not sure, send us a photo of the old coil and we will decode it for you.

Starter compatibility

• Size 00, 0, 1: Class 8536 Type SA, SB and SC starters, Class 8502 Type SA, SB and SC contactors, Class 8903 Type SM lighting contactors
• Size 2: Class 8536 Type SD starters, Class 8502 Type SD contactors, Class 8903 Type SP lighting contactors
• Size 3: Class 8536 Type SE starters, Class 8502 Type SE contactors, Class 8903 Type SQ lighting contactors
• Size 4: Class 8536 Type SF starters, Class 8502 Type SF contactors, Class 8903 Type SV lighting contactors
• Size 5: Class 8536 Type SG starters, Class 8502 Type SG contactors, Class 8903 Type SX and SY lighting contactors

Fix the cause, not just the coil

If a coil has failed early, replacing it alone will get you running but will not keep you running. Check the control transformer voltage under load rather than at rest, since a starter that drops out on inrush is a coil killer. Clean or replace pitted main contacts and check that the armature pole faces close flat and square. On a compressor that short-cycles, fit a pressure switch with a wider differential or a proper unloader setup, because every start is a fresh inrush through that coil.

AirComParts replacement magnetic coils for Square D NEMA size 1, 2, 3, 4 and 5 motor starters and contactors, cross-referencing Square D 31041-400, 31063-409, 31074-400, 31091-400 and 31096-400. The Warthog Air Compressor Store also stocks auxiliary contacts, overload relays and pressure switches for compressor starter panels.