Red Seal Electrician Practice
Signalling and communicationQuestion 127 of 1506

A 20 mA current loop is a digital network. What weakness does it have?

  1. A wiring break would fail the entire network
  2. Its high impedance makes it noisy in the plant
  3. It only works with fibre
  4. It needs 480 V
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Correct answer: A wiring break would fail the entire network

The low impedance gives good noise immunity.

Source: Lessons in Electric Circuits IV: Digital (Kuphaldt), 14.2: Networks and Busses

Practice signalling and communication

Questions last reviewed: 18 October 2026