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Pop Quiz

Test Your Knowledge Of Building Power

TRUE OR FALSE

1. Electrical power only runs in the direction of the cables that carry it.

2. Inter-system ground noise is the noise that exists between the power grounding wires of different pieces of equipment.

3. GFCI stands for Ground Fault Current Interface.

4. Waveform distribution noise, which can result in system halts and data loss, can be caused by (radio) transmitters, faulty equipment, ineffective grounding, and proximity to an EMI/RFI source.


ANSWERS

1. FALSE. Electrical power is conveyed from source to load in the form of both electric and magnetic fields. The path is defined by the two conductors that normally run parallel. As long as the conductors are parallel and close, the loop area formed by the conductors is minimized, and the electric and magnetic field energy is confined to a small region between and around the conductors. But when the loop area of a power circuit is made large, the field energy will spread out to envelop everything both within and outside the loop, resulting in electromagnetic interference (EMI) that can affect AV systems.

2. TRUE. Inter-system ground noise is sometimes referred to as “ground loops.”

3. FALSE. A Ground Fault Circuit Interrupter (GFCI or GFI) protects against electrical shock due to excessive leakage currents or other faults. People are most vulnerable if their bodies are grounded because that provides a path for leakage current from faulty equipment. The National Electrical Code (NEC) requires the use of a GFCI to protect receptacles at certain locations where people are most likely to be in contact with ground — for example, around plumbing and at most outdoor locations.

4. TRUE. Possible ways to eliminate system noise include removing transmitters, reconfiguring grounding, moving away from EMI/RFI sources, increasing shielding, using filters, and using isolation transformers.

Sources: Jensen Transformers, Neil Muncy

 


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