By TEBAOFLEX Jyen. Originally published on June 9, 2026.
Why a shield can carry unwanted current
Two cabinets can have different potentials because of load currents, fault conditions and the impedance of their bonding network. Connecting a screen at both ends can create another current path. Its current depends on the whole circuit, not just the DC resistance of the shield.
A cable screen is intended to control electromagnetic coupling. It must not become an unintended substitute for the protective conductor or a remedy for missing equipotential bonding. Diagnose the source of the potential difference before changing connections.
Single-end and both-end bonding are application choices
A single-end screen connection can be appropriate for some low-frequency instrumentation circuits where the equipment instructions require it. It avoids a direct low-frequency conductive loop through that screen, but does not provide a universal solution at every frequency.
High-frequency EMC often benefits from low-impedance connections at both ends and circumferential shield contact at enclosure entries. A long pigtail adds inductance and can weaken performance even when its DC resistance is low. ABB drive guidance illustrates why short, broad and 360-degree connections matter.
No single frequency threshold dictates the correct arrangement for every analogue, digital and drive installation. Cable length, shield type, common-mode current, equipment isolation and the bonding network all influence the result.
Never remove safety bonding to cure noise
Follow the equipment documentation for PE, cable armour, screens and signal reference. Where potential differences are excessive, the solution may involve improving bonding, changing routing or using a specified galvanically isolated interface. It is not permission to disconnect the protective earth.
Bonding conductor size and installation must meet the applicable safety and EMC design. A generic 16 mm² instruction is not a substitute for fault-current, protective-device and installation assessment. Work on energized equipment requires the appropriate competent personnel and procedures.
Capacitive connections need an approved design
A capacitor provides frequency-dependent impedance, but it is not an automatic safe compromise between single-end and both-end bonding. It must be suitable for the circuit voltage, transients, leakage, failure modes and any hazardous-area restrictions.
For illustration, an ideal 10 nF capacitor has reactance about 318 kΩ at 50 Hz and 1.59 Ω at 10 MHz. At 5 V and 50 Hz, its ideal current is approximately 15.7 microamps. Real leads and components add inductance and other limitations; the calculation is not an installation recommendation.
Commissioning evidence
Record the intended shield connection at each end, verify continuity and enclosure contact, and inspect conductor segregation and cable entry details. Compare noise or communication performance under representative drive switching and load conditions.
If a change improves one symptom, also verify that safety, surge protection and other interfaces remain compliant. A successful bench reading does not prove that an improvised shield connection is acceptable in service.
Primary references and specification evidence
The references explain the cited technology or manufacturer example. They are not TEBAOFLEX product approvals or evidence that a supplied batch has passed the tests. Request the exact product drawing, specification edition, acceptance criteria and traceable records.
Discuss your application
Discuss the duty, installation and required documentary evidence with TEBAOFLEX. WhatsApp: +86 185 9591 3361. Product suitability and test obligations must be confirmed for the specific order.