CTS Power, Grounding, and Electrical Safety

Question 1

What is the primary purpose of a technical ground (also called a 'clean ground' or 'audio ground') in an AV system rack?

Accepted Answer

To establish a low-impedance, low-noise reference point that reduces hum and interference in audio/video signals

Answer

A technical ground provides a stable, low-impedance common reference for all signal grounds in the system, minimizing voltage differences that cause hum (60 Hz noise) and other interference. It is separate from the safety ground whose job is fault current protection. Both are important but serve different purposes.

Question 2

A 'ground loop' in an AV system most commonly manifests as which symptom?

Accepted Answer

A 60 Hz (or 120 Hz) hum in audio and/or horizontal bars rolling through a video image

Answer

A ground loop occurs when two pieces of equipment are connected by a signal cable while also being grounded through different paths at different potentials. The difference in ground potential drives a current through the signal cable shield, inducing 60 Hz hum in audio and visible horizontal roll bars in analog video. The solution is to break the loop with an isolation transformer or ground lift.

Question 3

When calculating the load for a 20-ampere, 120-volt circuit in an AV rack, the NEC (National Electrical Code) recommends limiting continuous loads to what percentage of the circuit's rated capacity?

Accepted Answer

80%

Answer

The NEC requires that continuous loads (those running for 3 hours or more) not exceed 80% of the circuit's rated ampacity. On a 20 A circuit, this limits continuous draw to 16 A (1,920 W at 120 V). Exceeding this causes breakers to trip and wiring to overheat. This 80% rule is fundamental for safe rack power planning.

Question 4

What does a power conditioner provide that a basic surge protector does not?

Accepted Answer

Line conditioning including EMI/RFI filtering and voltage regulation to clean AC power

Answer

A power conditioner filters EMI (electromagnetic interference) and RFI (radio frequency interference) from the AC mains, and often includes automatic voltage regulation (AVR) to correct sags and swells. A basic surge protector only clamps transient voltage spikes. Clean, stable AC is essential for noise-free audio systems and stable digital equipment operation.

Question 5

What safety hazard does the 'one-hand rule' address when working on powered electrical equipment?

Accepted Answer

Preventing current from passing across the chest by keeping one hand away from grounded surfaces

Answer

The one-hand rule keeps one hand behind your back or in your pocket when probing live circuits. If both hands contact a circuit simultaneously, current can flow hand-to-hand across the chest, passing through the heart. This path is lethal at relatively low voltages. Current flowing hand-to-foot is less likely to affect the heart. This is a foundational electrical safety practice.

(CTS) Certified Technology Specialist Practice Test

(CTS) Certified Technology Specialist Practice Test

CTS Power, Grounding, and Electrical Safety