Final answer:
All the options provided are classified as Extra-Low-Voltage circuits since their voltage ratings are under the ELV threshold. The power ratings (VA) do not determine ELV status; only voltage does. However, option (d) with a lower power rating aligns more closely with typical ELV usage.
Step-by-step explanation:
In the context of electrical systems, an Extra-Low-Voltage (ELV) power circuit is generally defined as one that has a voltage that is not exceeding 50V AC or 120V DC. Therefore, analyzing the options given:
- (a) A 28V circuit with a 1500VA rating.
- (b) A 30V circuit with a 500VA rating.
- (c) A 32V circuit with a 500VA rating.
- (d) A 28V circuit with a 50VA rating.
Each of these options has a voltage lower than 50V AC, therefore they all can be considered as Extra-Low-Voltage circuits. However, it is likely that the question seeks the circuit that is typically of a voltage and power range more commonly associated with ELV usage. If we look at the VA (Volt-Ampere) ratings, the power demand may also play a role in classifying a circuit as ELV, especially concerning safety regulations and design norms. Nevertheless, power ratings alone are not the determining factors for ELV classification; voltage is the primary criterion. Therefore, the correct answer would be all of the provided options, as they all have voltage ratings under the ELV threshold, but option (d) with both low voltage and low power rating is the most indicative of typical ELV applications such as small electronic devices.