300kW Cummins Phase Loss Fault

Application

Prime power for a rock crushing operation producing material for golf course construction. There’s no adequate utility service at the pad, so the generator carries the crusher directly rather than sitting as backup. Any fault that takes the unit offline takes production with it, along with the crew that’s already on the clock.

Unit and Site Capability

300kW Cummins on a 24-volt starting system, two batteries at 1050 CCA each, replaced within the last twelve months. The customer keeps a mechanic on staff and handles their own oil and filter service, so the site is capable of routine work and equipped to execute a repair with the right direction. That shaped how we approached this from the first call.

Reported Fault

Phase loss alternating between phase one and phase two. The crew had found that cycling the main breaker roughly ten times would clear the fault and let the unit pick load back up, but it kept returning with no identified cause.

Phase loss protection exists to keep the unit from single-phasing. Repeatedly clearing the alarm to force it back online puts the three-phase motor loads on the crusher and the alternator itself in the position the protection was installed to prevent. Every restart was a gamble, and the failure it was risking would have been considerably more expensive than the fault itself.

The alternating pattern is the useful detail. A fault that moves between phases points toward something intermittent on the sensing or connection side rather than a hard failure in one leg, and the fact that breaker cycling clears it narrows the candidates further. Breaker contacts, terminations, sensing leads, and the control board are all live possibilities at this stage.

Remote Diagnostic

The alarm history wasn’t accessible to the site crew, so we walked their mechanic through the control panel over video to pull the log. That’s where the alternating phase one to phase two pattern was identified — it hadn’t come through in the verbal description at all. Unit configuration, battery age, and CCA on both batteries were confirmed on the same call, ruling out the starting system as a contributor before anyone drove anywhere. No charge for any of it.

Scope Quoted

Two-hour on-site diagnostic written against the identified fault. Because the remote work had already narrowed the field and cleared the batteries, the scope reflects the actual work in front of us instead of hedging against every possibility

Resolution

The alarm logged immediately prior to the phase loss, confirmed root cause, whether the repair was performed by our tech or by the customer’s mechanic with our parts and direction, actual cost against quoted, and downtime avoided. Request a customer quote once the unit is back in service.