VFD Earthing & EMC Study
Assessment of the earthing, bonding and screening arrangements around variable frequency drives. Fast switching produces high-frequency common-mode current that returns through whatever path is available — including motor bearings and instrumentation screens — unless a deliberate low-impedance path is provided.
What this study establishes.
Review of motor cable type, screen construction and screen termination at both ends.
Common-mode current measurement and the return path it is actually taking.
Bearing current risk assessment, including shaft voltage measurement where accessible.
High-frequency bonding assessment between drive, motor, and the structure.
Cable segregation review between drive output, control and instrumentation runs.
Mitigation recommendation — screen practice, dV/dt or sine filters, insulated bearings, shaft grounding.
What the work covers.
Assessment of the earthing, bonding and screening arrangements around variable frequency drives. Fast switching produces high-frequency common-mode current that returns through whatever path is available — including motor bearings and instrumentation screens — unless a deliberate low-impedance path is provided.
A 360-degree screen termination at both ends is what actually provides the high-frequency return path. Terminating the screen with a pigtail is common, looks acceptable, and defeats most of the screen's benefit at the frequencies that cause the trouble.
What lands in your inbox.
Review of motor cable type, screen construction
Review of motor cable type, screen construction and screen termination at both ends.
Common-mode current measurement and the return path
Common-mode current measurement and the return path it is actually taking.
Bearing current risk assessment
Bearing current risk assessment, including shaft voltage measurement where accessible.
High-frequency bonding assessment between drive, motor, and
High-frequency bonding assessment between drive, motor, and the structure.
Cable segregation review between drive output, control
Cable segregation review between drive output, control and instrumentation runs.
Mitigation recommendation
Mitigation recommendation — screen practice, dV/dt or sine filters, insulated bearings, shaft grounding.
How we run it.
Scope & data capture
We confirm the question the study must answer, agree the measurement or modelling points, and collect what the work depends on: drive and motor cable specification, lengths and routing; motor bearing type and any existing shaft grounding or insulation; earthing and bonding arrangement between the drive panel, motor and.
Measurement & modelling
Engineers carry out the measurement and modelling on site and in software, under operating conditions representative of the problem rather than a single convenient snapshot.
Analysis against standard
Results are assessed against IEC 61800-3, IEC 60034-25, IEC 61000-6-2 and IEC 61000-6-4, with the assessment basis and any measurement uncertainty stated rather than implied.
Report & recommendations
You receive a signed engineering report with findings ranked by consequence, the reasoning behind each conclusion, and mitigation options costed so they can be acted on or deferred deliberately.
Assessed against the published limits.
Common questions.
Typically in one of these situations: repeated motor bearing failures on drive-fed machines, especially fluting patterns; instrumentation or communications interference that follows drive operation; long motor cable runs, or drive retrofits onto motors not rated for converter supply. If none of these apply, the study is unlikely to be the right next step and we will say so.
To scope and run the work we need drive and motor cable specification, lengths and routing; motor bearing type and any existing shaft grounding or insulation; earthing and bonding arrangement between the drive panel, motor and structure. Where any of it is missing we can establish it on site, which changes the scope rather than blocking the work.
Primarily IEC 61800-3, IEC 60034-25, IEC 61000-6-2 and IEC 61000-6-4, IEC 62305-4. The applicable framework depends on your connection agreement and jurisdiction, so we confirm which applies before measurement rather than after.
Ready to start the engagement?
Tell us about your site and the problem you are seeing. We come back with a fixed scope, a fixed fee, and a named lead engineer.