Square D B6-90 Circuit Breaker

The Square D B6-90 thermal overload unit (melting-alloy overload relay) provides 600 V AC motor protection in Square D motor-control circuits. This Type B device trips on overload with a full-load current rating of 4.35–4.89 A and a 20‑trip class, making it suitable for guarding small- to mid-size motors in industrial control panels. The B6-90 is designed for plug-in mounting in compatible Square D overload assemblies and measures about 4.9 in long, 3.4 in wide, and 0.8 in high. In practice, it is used in motor starter circuits alongside Square D contactors and protective-relay kits to prevent overheating, rather than as a standalone circuit breaker.