VSD keeps tripping the RCD / safety switch
The upstream RCD drops out when a drive is powered up or ramped — the drive itself shows no fault. Drives leak to earth by design (EMC filters and long screened cables), and standard RCDs don't always get along with them.
Safety first
Drives store lethal charge in their DC bus — isolate and WAIT the manufacturer's stated discharge time before touching terminals, and prove dead. Never solve this by removing the RCD from a circuit that needs it; the fix is correct protection selection, not less protection.
Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.
Apprentice mode
Full walk-through — the why, what readings mean, mistakes & safety.
Likely causes
Ranked from most to least likely.
- 1
Normal EMC-filter earth leakage
Most likelyThe drive's built-in EMC filter deliberately couples the phases to earth through capacitors — a continuous standing leakage. On a 30 mA RCD there may simply be no headroom left, especially at switch-on.
- 2
Wrong RCD type for a drive load
#2Drive leakage isn't clean 50 Hz — it's high-frequency with DC components a Type AC (or sometimes even Type A) device can't judge properly. Most drive manuals call for a Type B (or specified Type F) RCD; the wrong type either nuisance-trips or, worse, goes blind.
- 3
Long or screened motor cable capacitance
#3Every metre of screened motor cable adds capacitance to earth, and leakage rises with it (and with switching frequency). A cable-length change or a re-route often 'causes' the new tripping.
- 4
A genuine insulation fault in motor or cable
#4Don't let 'drives always leak' hide a real fault — a wet or cooked motor leaks for real, and the RCD is telling the truth.
- 5
Switching frequency set high
Least likelyHigher carrier frequency = more capacitive leakage current. A drive re-commissioned for quiet running can suddenly out-leak the RCD.
Reports are saved on this device to reflect what you actually find.
Testing sequence
Work through one test at a time. Expected reading and what each result means.
On the tools? Job Mode shows one test at a time with thumb-sized buttons — your place and readings carry straight over.
Enter Job ModePin the moment: does the RCD trip at drive power-up (before any run command), at the run command, or only at speed?
Power-up trips point at the EMC filter inrush; run/speed trips point at motor-side leakage (cable + motor, rising with output).
The timing tells you which side to measure first.
Random trips under way: treat as marginal standing leakage — measure it properly next.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
RCD trips with a VSD on the circuit
→ step 2 - 2decision
Does the motor + cable IR test clean (disconnected from the drive)?
Yes→ step 3No→ step 4 - 3decision
Is the measured standing leakage a big share of the RCD's rating?
Yes→ step 5No→ step 6 - 4result
Genuine insulation fault — repair/replace motor or cable. The RCD was right.
- 5result
Characteristic leakage too high for the device — address cable length, switching frequency, and the protection arrangement per manual + rules.
- 6decision
Is the RCD the TYPE the drive manual specifies (commonly Type B)?
Yes→ step 7No→ step 8 - 7result
Everything measures fine? Verify the RCD itself, then review the circuit design.
- 8result
Fit the specified RCD type/rating — wrong type can't read drive leakage properly.
Common mistakes apprentices make
- Removing or bridging the RCD to 'fix' the tripping — protection removed from exactly the kind of circuit that leaks.
- IR-testing into the drive's output terminals and killing the drive.
- Swapping RCD brands but never the TYPE, when the manual plainly calls for Type B.
- Forgetting that a cable re-route or carrier-frequency change is a leakage change.
When to stop & escalate
RCD type/rating selection for drive circuits must land inside the wiring rules and the drive manual together — when they seem to conflict, that's a design review, not a field improvisation. Persistent high leakage with healthy insulation may need the supply arrangement reconsidered (dedicated circuit, different protection philosophy) by whoever owns the installation's design.
If you're past your competence, authorisation, or the safe limits of the job — stop and hand it on. There's no fault worth getting hurt over.
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Related faults
VSD trips on earth/ground fault
The drive trips with an earth/ground-fault code — typically the instant it outputs — indicating leakage to earth on the motor or output cabling.
RCD / RCBO keeps tripping
An RCD or RCBO trips repeatedly — immediately on reset, randomly during the day, or only when certain equipment runs. The earth-leakage protection is doing its job; something is leaking.
Motor with low insulation resistance to earth
An insulation resistance test on the motor reads low to earth — a sign the winding insulation is degraded, damp, or contaminated, risking trips and failure.
RCD nuisance tripping with lots of electronics
An RCD trips intermittently with no single faulty appliance — typically where many electronic devices (with filters/SMPS) share one RCD, each adding a little standing leakage.