Yaskawa GA700 semiconductor input fuses
Match voltage class, amp rating, fuse class, and the GA700 manual before replacing a blown input fuse tied to UV1.
$20-$160
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Yaskawa GA700 Fault UV1 — What It Means
UV1 on a Yaskawa GA700 drive (GA700 = Yaskawa’s heavy-duty industrial drive platform, successor to the A1000) indicates Main Circuit Undervoltage — the DC bus voltage has dropped below the minimum operating level. The GA700 monitors the DC bus continuously and trips UV1 when the bus falls below approximately 190 VDC on 200 V class drives or 380 VDC on 400 V class drives. UV1 is a protective fault; running the drive on an undervoltage bus would cause output waveform distortion, increased motor heating, and possible damage to the drive’s capacitors and power devices.
Common Causes
- Low or missing input supply voltage — Supply voltage below the GA700’s rated minimum (−15% of nominal on 200 V class, −10% on 400 V class) will pull the DC bus below the UV1 trip threshold. This is the single most common root cause across GA700 installs, especially on long feeder runs or facilities with heavy inductive loads sharing the same transformer.
- Input phase loss — A blown fuse or failed contactor on one input phase reduces the rectified DC bus voltage by roughly 30%, immediately triggering UV1. A drive can sometimes still power up and display normally with one phase missing, which is why measuring all three legs directly at the drive terminals matters more than trusting the upstream breaker’s indicator light.
- Momentary power interruption — A utility voltage sag or brief outage trips UV1. Check parameter E2-05 (UV Detection Time) — a very short setting causes false UV1 trips during normal supply transients that the connected motor and load would otherwise ride through without issue.
- Soft-charge circuit issue — If the inrush current limiting circuit (pre-charge relay or NTC thermistor) fails to close after capacitor pre-charge, the bus stays at a reduced voltage and UV1 trips at startup. This shows up as a repeatable trip every time the drive is powered up cold, rather than an intermittent trip under load.
- Capacitor bank degradation — Aged DC capacitors on older GA700 drives hold less charge during momentary voltage dips, causing UV1 trips that did not occur when the drive was new. Capacitor aging is gradual and heat-accelerated, so a drive mounted in a hot, poorly ventilated cabinet will show this failure mode years earlier than an identical drive in a well-cooled enclosure.
- Loose or corroded power terminal connections — A high-resistance connection at the input terminal block drops voltage under load even when the upstream supply and fuses test fine at no load. Thermal scanning during a maintenance window catches this before it becomes an intermittent UV1 trip that is hard to reproduce on demand.
- Undersized or shared transformer — If the GA700 shares a transformer with other large inductive loads (welders, other motor starts) that cause voltage dips when they start, an oversized load elsewhere on the same supply can be the actual cause even though the fault only ever appears on the drive.
Why UV1 Is a Protective Fault, Not a Nuisance Trip
The DC bus feeds the IGBT power stage that generates the drive’s output waveform. Running that power stage on a starved bus produces a distorted output waveform, increases motor heating at a given speed and load, and stresses the power devices themselves. UV1 exists specifically to stop the drive before that damage accumulates. Resist the temptation to defeat the fault by lengthening the UV detection time far beyond what a momentary supply sag would require, since doing so trades a nuisance trip for real risk to the power stage and capacitor bank.
Tools You’ll Need
- True RMS digital multimeter rated for the drive’s voltage class, with test leads rated for the working voltage
- Appropriate PPE: insulated gloves, safety glasses, and arc-flash rated clothing per your facility’s electrical safety program
- GA700 technical manual or quick reference for parameter access (U3 fault history, E2-05 timing) and terminal layout
- Infrared thermal camera or spot thermometer for terminal and cabinet scanning
- Insulation resistance tester (megohmmeter) if motor or cable insulation is suspected
- Correct-spec semiconductor input fuses on hand before condemning the existing ones
- Lockout/tagout kit for the drive’s disconnect and any upstream breaker
Safety: Lockout/Tagout and Stored Energy in the DC Bus
VFDs store dangerous energy in their DC bus capacitors well after input power is removed. This is the single most important safety fact to carry into any GA700 fault diagnosis.
- Never assume the drive is de-energized just because input power is off. The DC bus capacitors can hold a lethal charge for several minutes after disconnect, and discharge time varies by drive frame size and capacitor condition.
- Follow the GA700 manual’s specified wait time before opening the drive or touching bus terminals, and then verify zero voltage yourself with a meter rated for the bus voltage. Do not rely on a fixed wait time alone if the manual specifies a voltage check.
- Lock out and tag the input disconnect before any work inside the drive enclosure, and confirm no one else can re-energize the circuit while you are inside it.
- Treat every UV1 diagnosis as live-circuit work until proven otherwise. Measuring input voltage at R, S, T terminals means working near an energized circuit; use properly rated meters, leads, and PPE, and follow your facility’s arc-flash and electrical safety program.
- Do not defeat the soft-charge circuit or bypass the pre-charge relay to force a drive to start. The soft-charge circuit exists to limit inrush current into the capacitor bank; bypassing it risks catastrophic capacitor or fuse failure at power-up.
Step-by-Step Fix
- Review fault history first, before opening any panel. Access Fault History (U3-01 through U3-10) on the GA700 operator panel. If UV1 is logged with short duration, a momentary supply sag is likely. If it is logged with long duration, the supply is chronically low. This step needs no de-energization and often narrows the search significantly before you touch anything electrical.
- Lock out and tag the drive’s input disconnect if the next steps require opening the enclosure. See Safety above.
- Measure input voltage at R, S, T — With appropriate PPE, measure all three L-L voltages at the drive’s input terminals. The GA700 requires supply voltage within ±10–15% of the nameplate rating. Record all three readings, not just one, since a single missing or low phase is easy to miss if you stop after the first good reading.
- Check input fuses and circuit breaker — Inspect all three poles of the upstream protective device. Replace any blown fuses with the correct semiconductor-type fuses specified in the GA700 installation manual. Never substitute a standard fast-blow fuse for the semiconductor type the drive requires.
- Check parameter E2-05 (UV Detection Time) — If the setting is very short (< 0.5 sec), the drive may trip on normal utility transients. Increase to 2.0 seconds to filter out brief sags if the application allows, but do not use this as a substitute for fixing a genuinely low or unstable supply.
- Thermal-scan the input terminal connections if voltage and fuses check out fine at no load, since a loose or corroded terminal can drop voltage specifically under running load and test fine when idle.
- Inspect the soft-charge circuit — If UV1 trips every time at startup but clears after a power cycle wait, the pre-charge relay or inrush thermistor may be failing. This typically requires board-level or drive swap and is best handled by a qualified drive technician given the stored-energy risk in this area of the drive.
- Consider upstream shared loads — If the trip correlates with another large motor or welder starting elsewhere on the same transformer, the fix may be upstream (larger transformer, dedicated feeder, soft-starter on the other load) rather than anything inside the GA700 itself.
- Reset the fault — Press the RESET key on the operator panel or send a fault reset command via fieldbus after correcting the root cause, and observe the drive through a full startup and load cycle before leaving it unattended.
- Document the fix and the fault-history timestamps in your maintenance log so a recurring trip pattern is visible to the next technician who works on this drive.
Parts Often Needed
| Part | Notes |
|---|---|
| Input fuses (semiconductor) | Use Yaskawa-specified fuse type for GA700 ampere rating |
| Soft-charge relay or thermistor | GA700 frame-size specific; order from Yaskawa |
Technician Tips
When diagnosing VFD faults, always check the drive’s fault history before resetting. Modern drives store the last 5-10 faults with the drive state at the time (running, accelerating, decelerating, stopped). An overcurrent fault that occurs only during acceleration points to incorrect motor data or mechanical binding. The same fault during deceleration suggests regeneration issues. A ground fault that clears after disconnecting the motor and returns when reconnected means the motor or cable insulation has failed.
Prevention: Schedule annual infrared scanning of drive cabinets. Loose power connections and failing capacitors produce heat long before they cause faults. A 5-minute scan can prevent hours of unplanned downtime.
Need Replacement Parts?
Before ordering, match the drive part to the model number, voltage class, amp rating, and confirmed input-power fault. Check current prices on Amazon - prices and availability change frequently.
When to Call a Pro
UV1 on a GA700 driving a large motor (over 30 kW) should be investigated by a qualified drive technician. Incorrect supply voltage or a failing capacitor bank on a large drive can cause dangerous fault-trip energy releases during reset attempts.