Square D Class 9999 Auxiliary Contact for Definite Purpose Contactors, 20 to 90 Amp

Square D Class 9999 Type D auxiliary contacts, the field-installed add-on contact blocks for Square D definite purpose contactors and starters rated 20 through 90 amps. These are the contactors fitted inside most packaged air compressors, dryers and pump panels.

An auxiliary contact is how the rest of the panel finds out what the contactor is doing. It is a spare set of contacts that moves with the main poles, so it gives you a dry contact that follows the motor exactly. That is what you wire a run light, an hour meter, a sequencing interlock between a lead and lag compressor, or a run signal to a dryer or a building management system. Without one you are left guessing, or stealing a signal off a load conductor, which is neither safe nor reliable.

Part reference

• AUX-10: Square D 9999D10, one normally open contact
• AUX-01: Square D 9999D01, one normally closed contact
• AUX-11: Square D 9999D11, one normally open and one normally closed contact
• AUX-20: Square D 9999D20, two normally open contacts

Key specifications

• Class 9999, Type D auxiliary contact block
• Rating: 3 A at 120 VAC; NEMA B600 contact rating, 600 VAC maximum
• Mounts on Class 8910 DPA definite purpose contactors and Class 8911 DPS starters, 20 A through 90 A
• Also fits Class 8965 DPR reversing and hoist contactors
• Field installed, snaps onto the side of the contactor

Picking the right arrangement

Normally open is what you want for a run indicator, an hour meter or a run-permissive signal to downstream equipment, because it closes only while the contactor is energised. Normally closed is for the reverse logic, such as an idle or standby indication, or an interlock that must open when the motor starts. The 9999D11 gives you one of each on a single block, which is the usual choice for a lead and lag pair where one contact signals the panel and the other interlocks the other machine. The 9999D20 gives you two independent normally open contacts when you need to drive two separate circuits.

Check the contactor size before ordering

These blocks fit the 20 A to 90 A definite purpose frames. They do not fit Square D NEMA Type S starters, which take the Class 9999 Type SX contacts instead. If your starter carries a NEMA size rating rather than an amp rating on the nameplate, you need the SX series, which the Warthog Air Compressor Store also stocks.

Square D Class 9999 auxiliary contacts for definite purpose contactors, part numbers 9999D01, 9999D10, 9999D11 and 9999D20, supplied by AirComParts through the Warthog Air Compressor Store alongside starter coils, overload relays and pressure switches for compressor control panels.