Westinghouse DB and DHP Series Circuit Breaker Rebuild

The Westinghouse DB and DHP series are drawout air magnetic circuit breakers manufactured by Westinghouse Electric — a name that passed to Eaton when Westinghouse exited the switchgear business. These breakers were installed in Southeast utility substations from the 1950s through the 1980s and remain in service throughout the region. Southern Switch rebuilds DB and DHP breakers at our Palm Harbor shop, serving utilities and contractors who need these breakers back in service without a full switchgear changeout.

DB vs. DHP: What They Are

The DB is Westinghouse's distribution class drawout air breaker — used in low and medium voltage switchgear for bus protection, tie breaker, and feeder applications. The DHP is the Drawout High Power variant, designed for 5kV primary service in metal-clad switchgear. DHP breakers handle higher fault interrupting duty than the DB line and use correspondingly heavier contact assemblies and arc chute stacks. The DHP-250 and DHP-500 designations refer to the interrupting capacity in MVA at the rated voltage — not current rating. Both types use the same fundamental air-magnetic arc interruption mechanism but are sized and rated for different duties.

Contact Assembly

Westinghouse DB and DHP contacts use silver-faced copper for the main current-carrying surfaces. The moving contact assembly consists of a contact arm with spring-loaded fingers that engage stationary contacts in the closed position. Arc runners guide the arc from the main contact parting point into the arc chute above. The contact wipe — the distance the moving contact assembly travels against the stationary contact before the contacts fully separate — determines the contact pressure and affects contact resistance in the closed position.

During rebuild, SSC measures contact gap (the distance between open contacts) and contact wipe (the compression distance when closing) against Westinghouse service specifications for the breaker type. Silver-face contacts with pitting deeper than 1/32 inch or silver overlay worn through to the copper base are replaced. Spring finger pressure is measured with a calibrated gauge — low finger pressure increases contact resistance and produces heating at the contact interface under load current.

Arc Chutes and Arc Runners

The Westinghouse DHP arc chute uses a stack of ceramic splitter plates with fiber side cheeks. Arc runners — the conducting rails on either side of the arc chute entry — guide the arc from the contact parting zone upward into the splitter plate stack. Arc runners accumulate erosion at the arc impingement zone over repeated operations; heavily eroded arc runners allow the arc to dwell in the lower chute zone longer than intended, accelerating splitter plate erosion at the base of the stack.

SSC inspects arc chute ceramic plates for cracking and erosion and the fiber side cheeks for carbonization and delamination. Plates with hairline cracks in the body of the plate — not surface crazing from heat — are replaced. Heavily carbonized fiber cheeks are replaced as a set with the ceramic stack. Arc runners with more than 1/4 inch erosion at the arc impingement zone are replaced; worn runners are among the most commonly overlooked components in a DHP rebuild.

Operating Mechanism

The DHP uses an air-gap trip latch mechanism: a spring-powered close mechanism drives the contacts closed, and a trip latch holds the mechanism in the latched position until a trip signal releases it. The manual reset feature on DHP breakers requires the operator to manually reset the mechanism after a trip before the breaker can close again — this is intentional and not a fault condition. The slow-close hazard on DHP breakers is real: manually closing a DHP without the mechanism fully charged and latched produces a slow close that generates excessive arcing at the contact faces.

Mechanism service includes disassembly and cleaning of old dried grease from all pivot points, inspection of close and trip springs for set (permanent deformation reducing spring force), latch inspection for wear on the latch face, and full relubrication with appropriate grease. SSC tests close and trip coil pickup voltages and verifies that the trip coil operates reliably down to 70% of rated control voltage.

Insulation Inspection

Phase barriers and bus bar insulation in DB and DHP breakers are phenolic or similar thermosetting resin. Surface tracking — visible as dark carbon traces running across an insulator surface — indicates that leakage current has repeatedly carbonized the surface along a path between two conductors. Tracking that is limited to the surface can sometimes be sanded to remove the carbon path; tracking that has penetrated to the bulk insulator material requires replacement. SSC measures insulation resistance phase-to-phase and phase-to-ground at 1000V DC and flags values below 100 MΩ for further evaluation.

Test Protocol

Rebuilt DHP breakers are tested for contact resistance (microohm measurement across each phase), close and trip timing, high-potential, and insulation resistance. DHP-specific: after arc chute reassembly, SSC verifies arc chute alignment — the chute must seat correctly over the arc runner entry zone for the arc guidance to function as designed. A chute that is seated forward or rearward of the specified position will produce erratic interrupting performance. SSC issues a written test report for each rebuilt breaker documenting as-found and as-left test values.