Extra-Low Voltage Switching and Power Over Ethernet

Flashcards covering extra-low voltage switching system components, three-wire and two-wire relay operations, and Power Over Ethernet (PoE) standards and infrastructure.

What are the voltage limits for extra-low voltage according to Section 0 of the Canadian Electrical Code (CE Code)?

Any voltage not exceeding $30\,V\,ac$ or $60\,V\,dc$.

What is the primary function of a relay in an extra-low voltage switching system?

It allows a lower voltage control circuit to switch a higher voltage power circuit.

According to Rule 12-3030, why must a barrier be installed in an extra-low voltage switching cabinet?

To provide separation between the line voltage circuits and the extra-low voltage control circuits when they are in the same enclosure.

How does the momentary activation of extra-low voltage relays differ from standard relay operation?

The coils are only energized briefly to change contact position and then power is removed, as they are held in place by a mechanical latch.

What are the power loss advantages of extra-low voltage switching?

There are fewer power losses ($I^2R$ losses) in the control circuit because the load current only flows in the power circuit.

How does an extra-low voltage switching system simplify configurations requiring multiple switching locations?

Several extra-low voltage switches can operate a single relay in parallel, eliminating the need for three-way and four-way switches.

In a three-wire extra-low voltage relay system, what is the function of the rectifying diode?

It allows pulses of current to flow to the coil in one direction (changing ac to dc) to protect the relay coils, which are not rated for continuous operation.

How many wires are required for a switch and a relay in a three-wire system that includes a pilot light?

A four-wire switch and a five-wire relay (which includes an extra set of pilot contacts).

How does a two-wire relay system control the direction of the armature movement?

Two diodes control the direction of dc current through the coil, which changes the polarity of the magnetic field to be attracted to a permanent magnet in either the on or off position.

What are the three basic components of a Power Over Ethernet (PoE) system?

The power sourcing equipment (PSE), Ethernet cabling, and a powered device (PD).

What is the functional difference between an endspan and a midspan in PoE infrastructure?

Endspans (PoE switches) contain all circuitry for data and power transmission for new systems, while midspans (PoE injectors) add PoE capability to existing non-PoE systems.

What is the maximum output rating for a Type 4 Power Sourcing Equipment (PSE)?

$100\,W$.

According to Rule 16-000 1) e) of the CE Code, how are PoE systems classified?

As Class 2 power and data communication circuits.

According to Rule 16-320, what are the output limits for PSES in a PoE system?

A maximum of $100\,VA$ and $60\,V\,dc$.

What six factors affect the conductor ampacity of Ethernet cables in PoE systems according to Rule 16-330?

The type of cable, conductor size, temperature rating of cables and equipment, number of cables bundled together, ambient temperature, and current rating of connectors and components.