Home installations and efficiency

Explain what the main distribution board (consumer unit) of a home is, where it is usually located and what two functions it performs (distributing electricity and providing protection).

Circuit breakers (MCBs) and residual current devices (RCDs) are located in the consumer unit. Explain what each one protects: one protects the installation and appliances, and the other protects people.

When plugging in a faulty appliance, the RCD trips and the whole house loses power. Explain what the RCD detected, what steps you would take to safely reset the installation, and why this switch must never be bypassed.

The electrical installation is divided into circuits (lighting, sockets, kitchen...). Explain what a circuit inside a home is and give two advantages of keeping them separate.

A circuit breaker trips when more current flows through its circuit than permitted; an RCD trips when it detects a current leak. Provide a specific scenario for each trip and explain what each one protects.

In the electrical panel shown in the figure, a user notices that the $25\ \text{A}$ miniature circuit breaker (MCB) for the kitchen trips frequently when preparing food while the washing machine is running. A neighbour advises: "Replace that breaker with a $32\ \text{A}$ or $40\ \text{A}$ one; that way it won't trip again and you'll be able to turn on all three appliances at the same time".

1. a) Verify quantitatively whether the $25\ \text{A}$ breaker will trip when the oven ($3.000\ \text{W}$), the washing machine ($2.200\ \text{W}$), and the microwave ($800\ \text{W}$) are running simultaneously at a voltage of $230\ \text{V}$ ($P = V \cdot I$).
2. b) Technically refute the neighbour's advice: predict what will happen in the electrical installation's conductors if the MCB is replaced with one of a higher rating without changing the cable cross-section, justifying it using Joule heating and the risk of fire according to the REBT.
3. c) Propose a standard technical solution (circuit distribution according to the REBT) and a rational usage guideline that prevents tripping without the need for construction work.

The figure shows a domestic consumer unit through which electricity enters and flows out to the home's circuits, with an element marked with ?. State what this element is, explain when it trips, and what or whom it protects.

The diagram shows the floor plan of a house with the circuits running from the consumer unit to the rooms, with a circuit marked with ?. Identify which circuit each line corresponds to and reason why the kitchen usually has its own dedicated circuit.

Design the home automation control system for HVAC (reversible heat pump) and motorized blinds in a penthouse in Madrid with a large south-facing window, subject to a time-of-use electricity tariff (cheap off-peak hours from 00:00 to 08:00; expensive peak hours from 10:00 to 14:00 and from 18:00 to 22:00).

1. a) Write the logic control rules table for winter and for summer, indicating in each case: input sensors (indoor temperature, outdoor solar radiation, tariff schedule), the logical condition, and the actuators' action (raise/lower blind, HVAC mode and setpoint temperature).
2. b) Justify how your design takes advantage of the building's thermal inertia and passive solar gains to minimize consumption during peak hours without compromising the occupants' comfort.

Describe the path of water inside a house from the mains supply (the main inlet) to a hot water tap, naming the main stopcock and the water heater or boiler.

A family installs a programmable thermostat, occupancy sensors in the hallway, and timer control on the water heater. Explain how each of these three smart home measures saves energy.

During the renovation of an old home that lacks a residual current device (RCD) and earthing in the sockets, an amateur installer claims: "If we install new, properly rated $16\ \text{A}$ miniature circuit breakers on each circuit, people will be fully protected against any electrical contact with the metal casing of a faulty washing machine".

1. a) Technically refute this claim: if the phase wire comes into direct contact with the metal casing and a barefoot person touches it (approximate body resistance $R = 1.500\ \Omega$ at $230\ \text{V}$), calculate the current that will flow through their body. Compare this value with the ventricular fibrillation threshold ($30\ \text{mA}$) and with the minimum current that trips the $16\ \text{A}$ circuit breaker.
2. b) Explain the physical operating principle of the residual current device (RCD) and justify why it is the only device capable of protecting life in this scenario, whether earthing is present or not.