---
title: "Grounding and shielding; inductive and capacitive shielding"
subject: "Instrumentation II"
chapter: 6
key: "semester_5/instrumentation_ii:grounding-shielding-inductive-capacitive"
source: https://www.bctengineer.com/q/semester_5/instrumentation_ii/grounding-shielding-inductive-capacitive
site: BCT Engineering
---

# Grounding and shielding; inductive and capacitive shielding

Instrumentation II · Chapter 6: Grounding And Shielding

- Asked in: 2079 Baisakh, 2+4 marks
- Video: [Cable Shielding & Capacitive Coupling Explained | EMC Design Fundamentals](https://www.youtube.com/watch?v=NfRm32dUenY) — Spectrum Speak
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/instrumentation_ii/grounding-shielding-inductive-capacitive
- Whole chapter: https://www.bctengineer.com/md/semester_5/instrumentation_ii/chapter-6

## Question

Define grounding and shielding. Explain inductive and capacitive shielding mechanisms.

## Short answer

Grounding provides a low-impedance reference for safety and noise; shielding blocks electromagnetic fields. Capacitive shielding uses a grounded conductive barrier to divert displacement currents. Inductive shielding uses high-permeability material at low frequency to divert magnetic flux, and conductive material at high frequency to create eddy currents that cancel the field.

## Answer

#### Grounding
**Grounding** is the provision of a low-impedance path to a reference point (earth/chassis) for return currents, fault currents and noise, giving a common reference potential and safety.

#### Shielding
**Shielding** is surrounding a circuit, cable or component by a conductive (or magnetic) material to block or reduce the transfer of electric, magnetic and EM fields between the source and the receiver.

#### Capacitive (electrostatic) shielding
- Noise passes through stray capacitance: I = C·dV/dt.
- A grounded conductive shield (foil, braid, metal box) between source and victim splits the stray capacitance. The noise current goes to ground through the shield and not into the victim.
- The shield must be properly **grounded** (to the reference of the receiver circuit) and cover the receiver conductor fully. Lower coupling capacitance results.

```text
 Source --C1--[shield]--C2-- Victim
                 |
                GND
```

#### Inductive (magnetic) shielding
- Noise voltage induced is V = M·dI/dt.
- At **low frequency** (below about 100 kHz), use a high-permeability material (mu-metal, steel) that provides a low-reluctance path to divert the flux around the victim. A thick shield is required, and grounding does not matter.
- At **high frequency**, a nonmagnetic conductor (copper, aluminium) works: eddy currents induced in the shield produce an opposing field, cancelling the incident field.
- Other ways: reduce loop area, twisted pair, increase distance, cross the wires at right angles.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is shielding?
   A. Providing a path to earth for fault current
   B. Tying all grounds to one point
   C. Surrounding a circuit or cable with conductive or magnetic material to reduce field transfer
   D. Increasing source dV/dt
   Answer: C. Shielding blocks or reduces electric, magnetic and EM fields between source and receiver. (Key point: Shielding definition)

2. What must be true of a capacitive shield?
   A. It must be of high-permeability steel
   B. It must be properly grounded and cover the receiver conductor fully
   C. It must be left floating
   D. It must be thin and unconnected
   Answer: B. Grounding diverts the noise current away from the victim. (Key point: Capacitive shield)

3. How does a magnetic shield work at low frequency?
   A. High-permeability material provides a low-reluctance path to divert flux around the victim
   B. Eddy currents cancel the field
   C. It forms a Faraday cage with ground
   D. It raises receiver impedance
   Answer: A. Mu-metal or steel guide the flux away; grounding does not matter. (Key point: Low-frequency magnetic shield)

4. How does copper or aluminium shield high-frequency magnetic fields?
   A. Flux is diverted by high permeability
   B. Charge is drained to ground
   C. It increases mutual inductance
   D. Induced eddy currents create an opposing field that cancels the incident field
   Answer: D. Eddy currents in a nonmagnetic conductor oppose the incident field. (Key point: High-frequency magnetic shield)

## Related in Instrumentation II

- [Inductive noise and capacitive coupling shielding](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ainductive-noise-capacitive-shield) — Instrumentation II, chapter 6
- [Grounding and shielding to reduce PCB noise](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Apcb-grounding-shielding-noise) — Instrumentation II, chapter 8

## Related in other subjects

- [Transformer at resistive, inductive, capacitive loads](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines%3Atransformer-loading-conditions-phasor) — Electrical Machines, chapter 2