Yaskawa A1000 rH Fault Code — What It Means
The rH fault on a Yaskawa A1000 VFD stands for braking resistor overheat. Yaskawa documentation identifies this as “Braking resistor protection was triggered,” and the fault is enabled when parameter L8-01 is set to 1. In practical terms, the drive is seeing too much regenerative energy during deceleration, so the braking circuit is being overworked and shutting down to prevent damage.
This fault typically appears when a motor is slowing down a high-inertia load too quickly, sending energy back into the drive faster than the braking resistor can safely dissipate it. The drive trips to protect both the braking resistor and the internal braking transistor from thermal failure.
Before You Replace Anything
Technicians often replace the braking resistor first without checking the drive parameters. Before swapping hardware, verify deceleration time settings and measure actual load inertia against the resistor duty cycle rating.
Common Causes
- Deceleration time too short (~40%) The drive is trying to stop the motor too quickly, generating more regenerative energy than the braking circuit can handle.
- Load inertia too high (~25%) The mechanical load has more stored rotational energy than the braking resistor was sized for, overloading the circuit during normal decel.
- Braking resistor undersized or mismatched (~20%) The installed resistor does not meet the wattage or duty-cycle requirements for the drive model and application.
- Braking resistor wiring or connection fault (~10%) Loose, damaged, or incorrect wiring at the braking terminals increases resistance and heat, or prevents the resistor from functioning at all.
- Failed braking resistor or internal braking circuit (~5%) The resistor itself has failed open or the drive’s internal braking transistor assembly is damaged, preventing proper energy dissipation.
Quick Diagnosis
Answer these to narrow it down fast.
Is the drive decelerating a heavy or high-speed load when the fault appears?
No: The fault may be caused by incorrect wiring, a failed resistor, or a drive internal fault. Inspect braking terminals and measure resistor continuity.
Does the braking resistor show correct resistance (ohms) and no visible damage or burn marks?
No: Replace the braking resistor with the correct Yaskawa-approved model for your A1000 frame size and application duty cycle.
Does the fault clear after increasing decel time by 50 percent and resetting the drive?
No: The braking resistor or internal braking circuit is likely damaged. Replace the resistor and escalate to Yaskawa if the fault persists.
Step-by-Step Fix
- Stop the machine and lock out/tag out the VFD and motor circuit before any diagnostics or parameter changes.
- Record the operating condition that triggered the fault, including decel time, load type, and whether the fault occurs on every stop or only certain cycles.
- Check parameter settings for deceleration time (often in the A1 or C1 group) and increase the decel ramp by 50-100 percent if it is very short for the load inertia.
- Inspect the braking resistor for physical damage, burn marks, or loose terminals, and measure resistance with a multimeter to confirm it matches the nameplate value.
- Verify braking wiring at the drive’s +1 and PR terminals (or B1/B2 on some frames) and at the resistor junction box for tight, clean connections and correct polarity.
- Cycle power and clear the fault, then test the drive under controlled conditions with the longer decel time to see if the fault returns.
- Replace the braking resistor if it tests open, shows damage, or if the fault persists after correcting decel time and wiring, using the Yaskawa-approved resistor model for your exact A1000 frame and power rating.
Parts Often Needed
| Part | Notes |
|---|---|
| Yaskawa braking resistor | Amazon | Must match your A1000 frame size (e.g. CDBR-4xxxB series for larger frames). Consult the A1000 technical manual or nameplate for the exact part number and wattage rating. |
| Braking resistor terminal hardware | Amazon | High-temperature ring terminals and hardware rated for the resistor current, if existing terminals show arcing or corrosion. |
When to Call a Pro
Call a qualified VFD technician or Yaskawa-authorized service provider if you are not trained in variable-frequency drive programming and high-voltage DC circuits. The braking circuit operates at DC bus voltage (often 400-800 VDC depending on input), which remains present even after AC input is removed and can be lethal. A technician should also be called if the fault persists after you have corrected decel time, verified wiring, and replaced the braking resistor, since the issue may involve the drive’s internal braking transistor, control board, or a complex mismatch between drive capacity and mechanical load that requires inertia calculation and resistor duty-cycle analysis.
Rough cost: A pro service call runs about $200-800 parts and service, depending on resistor size and labor.