Fagor alarm E304: Power bus voltage too high (with E215 hard-trip and E306 software variants)
DDS drive display code (seven-segment; PS/XPS/RPS power supplies) · Fagor PS/XPS/RPS
What it means
DC bus exceeded limit because regenerated braking energy has nowhere to go - ballast circuit open or undersized. XPS/PS front-panel LED table (red steady) covers the same failures on older units without numeric display.
Likely causes
- external ballast resistor ER+TH burnt open (thermostat tripped permanently)
- internal ballast connection bridge missing after module swap
- crowbar/braking IGBT in PS/XPS failed short-open
- vertical-axis decel energy exceeding ballast capacity
Triage note: Check thermostat continuity in ER+TH - a tripped stat reads open and mimics a burnt resistor. Verify bus-bar torque while inside; arcing bus joints produce the same trip.
Replacement parts
We supply the following units for this alarm — tested, warranty-backed:
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ER+TH-18/+FAN
External ballast resistor (with thermostat + fan) · Primary suspect
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XPS-25 / PS-25B4
Regenerative/non-regenerative power supply module · Common cause
Need the part urgently?
Send us alarm E304 with your machine details — typical RFQ turnaround is 24–48h.