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What are the basics of an electrical system?

Mar. 07, 2024

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Electrical Circuit Basics

Overview

Electricity is a fundamental part of the workings of most vehicles and this section aims to explain the basic principles of electrical circuits. Hopefully this will give you an understanding and allow you to carry out some simple calculations for specifying the electrics in your auto or marine wiring projects.

The fundamentals of an electrical circuit

In its most simple form, an electrical circuit consists of three fundamental parts:

A power source to drive electrical current around the circuit (a battery)
A conductor to carry the current around the circuit (some cable)
A load that has resistance (a bulb, a heating element, a motor etc.) and converts the electrical energy into another form (light, heat, kinetic etc.)

The conductor is used to connect the positive side of the power source to the load which is then connected back to the negative side of the power source to complete the circuit. A current will then flow through the load, converting stored energy in the battery to another form.

A circuit often includes other components such as switches, resistors, diodes, capacitors, fuses, relays etc. but these three fundamental parts will always be present in every electrical circuit.

Describing the workings of an electrical circuit

These terms are commonly used when describing electrical circuits:

Volts (V) - A measure of electrical potential difference between two points in a circuit. In most modern passenger cars, light commercial vehicles and small craft this is 12V, however larger commercial vehicles, agricultural equipment and large boats may use 24V. Additionally some older cars and motorbikes may use 6V.
Amperes (A) - A measure of the amount of electric current flowing past a point in a circuit in a given amount of time (commonly abbreviated to 'Amps')
Ohms (R) - A measure of electrical resistance to the flow of current in a circuit.
Watts (P) - Power, which is a measure of the rate at which an electrical circuit converts electrical energy into another form

It's often helpful to understand these concepts by using the analogy of a plumbing system:

Volts
is equivalent to the
water pressure
in the plumbing system
Amps
is analogous to the
flow rate
of water through the pipes
Ohms
in analogous to the
size
of the pipes

Watts is a universal measurement of energy conversion (or 'work done') so it applies equally to water systems as it does to electrical systems. A garden sprinkler will have 'power' due to the rate at which it converts the energy in the water into energy to rotate, just as a bulb will have a power as it converts electrical energy into light and heat.

This analogy can also be continued when we think about changing these values:

If you increase water pressure then more water will flow in a given amount of time. Similarly, if you increase voltage then more current will flow in a given amount of time.
If you reduce the size of the pipes then less water will flow in a given amount of time. Similarly, if you increase resistance then less current will flow in a given amount of time.

Current and current flow

The type of current utilised in the running of vehicle electrical systems is Direct Current (DC) where the flow of charge is in one direction and the voltage level is constant. Alternating Current (AC), as used in households where the flow of charge is in both directions and the voltage changes with time, is produced by the vehicle's alternator but is converted by a set of diodes (the rectifier) into DC which is then used to charge the battery.

The conventional way of thinking about current flow in a circuit is that it flows from the positive terminal of the battery to the negative terminal (or ground). Current flow is the movement of free electrons within the conductor and since electrons are negatively charged they actually migrate towards the +ve terminal of the battery when subject to a voltage difference, so current flow is from -ve to +ve.

This concept is fairly counter-intuitive for most people and so the convention of current flow being from +ve to -ve has stuck, and it makes little practical difference.

The relationship between Volts, Amps, Ohms & Watts

The relationship between these various terms is described in two very simple equations, allowing you to calculate any unknown value as long as you know the 2 other values.

Ohm's Law - states
the relation ship of Voltage to Current & Resistance:

Watt's Law -
states the relationship of Power to Voltage, Current & Resistance

For a given power requirement, a higher voltage will require fewer amps and vice versa. This is the reason that circuits operating at 12V DC can produce much higher currents than would be experienced in household AC circuits that operate at 240V AC.

The following diagram is a handy visual reference showing all of the possible arrangements of the above equations that you might need to work out the unknown value:

One of the most common uses of the above equations is for calculating the current drawn by a load (bulb, heating element, motor etc.) so you can select a suitable size cable for a circuit. It can be seen from the above that this arrangement is:

So for example, if we wanted to wire up a light that we know has a power rating of 50W, then the current draw would be 50W/12V = 4.17A. This tells you that you could use a cable with a rating of 4.17A or above, however it is good practice not to design a circuit operating at the upper end of the cable's rating and so you should select a cable with some additional capacity. In this case 0.5mm² (11A) cable would be appropriate.

This specific re-arrangement of Watt's Law is worth remembering as it comes in useful again and again when determining an appropriate size cable to use.

Ground

In order for an electrical circuit to be complete the positive terminal of the battery must be connected through the loads and back to the negative terminal, otherwise current cannot flow. In automotive vehicles the negative terminal of the battery is very often connected to the metal chassis which is a good conductor and effectively makes the entire chassis (and body of the vehicle, if metallic) a common ground point. The chassis can then be thought of as a large extension of the negative battery terminal and proves very convenient for grounding different parts of the electrical system, as there is normally a suitable chassis (or body) location close by to complete the circuit. This is only possible because of the use of rubber tyres which virtually insulate the vehicle from earth, preventing current leakage. In fact tyres do conduct slightly due to the carbon content in the rubber which helps remove static build-up, but the resistance is relatively high and so the effect on the electrical system very small.

In marine craft the hull is more often than not of a fibre glass (GRP) or wooden construction, materials which are not electrically conductive and so not suitable as a common ground point. Even if they were conductive (e.g. some boats have steel hulls) this is still not suitable as the hull would have a connection with the seawater surrounding it (an excellent conductor) which would provide a current leakage path to earth. So in marine craft all circuits must return to the negative battery terminal to complete the circuit. In practice this is achieved by having busbars (common ground connections) at various locations in the craft to provide conveniently sited ground return points to consolidate many individual circuits.

Negative and Positive Ground

In older vehicles it was common for the chassis to be connected to the +ve terminal of the battery (known as a positive ground), however this was superseded by the negative ground we are familiar with today. This does not affect simple devices such as bulbs and fuses which are not sensitive to polarity, but can be a problem for some equipment such as gauges, senders and electronics, so many people restoring classic cars opt to have their electrical system converted to negative ground for convenience.

Disclaimer - The information contained in these articles is provided in good faith and we do our best to ensure that it is accurate and up to date, however, we cannot be held responsible for any damage or loss arising from the use or mis-use of this information or from any errors or omissions. The installer is ultimately responsible for the safety of the system so if you are in any doubt, please consult a qualified electrician.

Summary

You depend upon electricity in your home. But how much do you know about how electricity works in your home? Do you understand how electricity enters your home, how it’s distributed, and the devices that control it and provide you access? In this beginner’s guide to electrical work, we’ll get you up to speed on the basics of your home’s electrical system.

Why Understanding Your System is Important

Your power company takes care of getting power to your home, but once it enters your home, everything related to your home’s electrical system — wiring, switches, outlets, fixtures — is your responsibility. As a homeowner, it’s important to know enough about the basic components of your system to make smart decisions about safety, maintenance, and upgrades.

Safety. Over 6% of home fires are caused by electrical issues. That’s a significant number. Knowing the basics of how electricity works in your home may prevent an unnecessary electrical fire.
Maintenance. An electrical problem in your home may not be quite as obvious as a leaky faucet. Regular evaluation and maintenance of your home’s electrical basics may prevent problems from developing.
Upgrades. Do you want to add more outlets, new switches, or smart features to your home’s electrical system? How about adding a standby generator or other device? Understanding your home’s electrical basics can help you make informed decisions.

System Connection and the Electric Meter

Unless you’re partly or wholly off the grid, your electricity comes to you via your electric company’s mains. The mains can be above-ground or buried underground. But before you can use the electricity in your home, the power company needs to know how much power you’re using. That’s the job of the electric meter, which is located between the mains and your home and measures the amount of power that your home consumes. There are three types of electrical meters.

Electromechanical - If your electric meter has a series of dials and a spinning disc behind a glass cover, you’ve got an electromechanical meter. While the technology for these is pretty old school, they are still fairly common. Usually, a power company employee must manually read the meter so they know how much power your home has used.
Smart meters - These electronic meters can communicate directly with the power company, allowing more accurate tracking of when and how much power you’re using. These units have digital displays and can be read remotely.
Bi-directional meters - Most electric meters only measure the power you consume. If you produce your own power, via solar panels or some other source, you may be able to sell the excess power you produce back to the power company. Bi-directional meters measure both the power coming in, and the power you’re sending out.

It’s important to know that you don’t own the electric meter. It’s the responsibility of the utility to install and maintain the meter. If you ever have questions or concerns about your meter, contact your electricity provider.

Disconnect Switch

Your home may have a disconnect switch located near the electric meter. Throwing this switch will cut off all power to your home. That’s useful in the event of an emergency or if major work is being done on the electrical system. If your home doesn’t have this switch, don’t worry. You can still cut off all the power at the main service panel.

Breaker Panel

Once past the electric meter, electricity must be distributed throughout your home to the switches, outlets, appliances, and other devices that need power. Your breaker panel is where the process begins. The service panel is known by many names: breaker panel, breaker box, service panel, and distribution panel are some of the common ones. If you have an older home you may have a fuse box that performs the same function.

Main circuit breaker
The power line entering your home first passes through the main circuit breaker. This switch controls the flow of power to the branch circuit breakers also located in the service panel. By flipping this switch to OFF, you can cut all power to your home.

Branch circuit breakers
Power is routed from the main circuit breaker to branch circuit breakers. Each of these switches controls the flow of power to a portion of your home, and if they detect too much current flowing through them they’ll shut off, or “trip.” For example, one branch circuit breaker may control power flowing to your kitchen outlets and lighting, while another controls power to an electric range. Branch circuit breakers are “single-pole” or “double-pole.” Single-pole breakers control the flow of 125-volt current used by wall outlets, lights, and so on, while double-pole breakers control the flow of 250-volt current used by dryers, electric ranges, electric-vehicle chargers, and other appliances. Circuit breakers are rated by amperage. A higher number means that the circuit can handle a higher electric load. Most household 125-volt circuits are rated at around 30 amps.

Sub-panels
Some homes will have sub-panels connected to the main breaker panel. These are smaller service panels containing fewer breakers. They’re often used when an addition or outbuilding has been added to the home, or when a backup generator is wired into the home’s electrical system.

Interested in learning more about your home’s circuit breaker panel? Check out this guide.

Wiring

Wiring is the unseen component of your home’s electrical system. Depending upon where the wiring is located and what the applicable building codes are, the wiring in your home may be composed of non-metallic cables, metallic cables, or wiring in metal or plastic conduits. The exact types that should be used will be specified in local building codes and industry standards. It’s important to make sure that the cable you’re using is up to the task, so if you’re taking on a home improvement or expansion that involves electrical wiring, consult with a qualified electrician before beginning the job.

If your home was built between 1956 and 1972, you should be aware that it may contain aluminum wiring. This wiring is much more likely to present a fire hazard than copper wire, and it should be replaced or repaired. Team Enoch is fully qualified to handle this safety concern, so contact us for an assessment of your risk.

At Team Enoch, we’re ready to handle any wiring job, from big to small. Contact us if you have any questions about the wiring needs for your home.

Electrical Devices and Circuits

Electrical devices include all of the items in your home that use electricity. Some are hard-wired into your home’s electrical system, like overhead light fixtures and electric outlets in the walls. Some devices, like your toaster, use power provided by an electric outlet. Power travels through your home’s wiring via one of two different types of circuits.

Multiple device circuits power several outlets, switches, and fixtures. If you’ve ever had to reset a circuit breaker after all of the lights and outlets in a room have gone out, you’ve seen an example of this.
Dedicated circuits only power one device. Common examples of dedicated circuits are those that power appliances like water heaters, dryers, electric ranges, furnaces, and so on. By using dedicated circuits, these devices can be installed or serviced without shutting off power to other areas of the home, while the risk of circuit overloading is reduced as well.

Switches

You’ve got switches all over your home. They’re used to control the flow of power throughout your home, so you can turn on light fixtures or control the flow of power to outlets, ceiling fans, and other devices. Depending on the electrical circuit they’re installed in, you’ll find different types of switches.

Single-pole switches control one device or outlet. They’re probably very common in your home.
Three-way switches are used in pairs so you can control a single device, like an overhead light fixture, from two different spots. You’ll find them in spots like the ends of staircases or at the different entrances to a room, like a living room.
Dimmers let you adjust the intensity of lights. Adding a dimmer switch to overhead lights is a fairly easy home improvement.
Motion-sensor switches turn the power on to your lights when they detect motion. Adding motion-sensor switches can help you save power or make areas like stairways safer.
Smart switches let you use your home’s Wi-Fi system to control the lighting in the rooms of your home through dedicated apps.

Outlets

Outlets are all the same, right? Not so fast — there are different types of outlets that are best suited for different applications throughout your home. Let’s take a look at the most common electrical outlets you’ll find in your home.

15A 125-volt outlets are most likely the most common outlets you’ll find in your home. There are two versions, ungrounded and grounded. You can tell the difference by the addition of an opening for the plug’s ground pin below the two vertical slots. These outlets are good for general usage, but it may be wise to upgrade these outlets for improved safety, particularly if they’re located in your kitchen or bathroom.
20A 125-volt outlets are designed to handle heavier loads, so they’re a good choice for using power tools or large appliances. You can identify these outlets by the addition of a small horizontal slot connected to one of the vertical slots.
250-volt outlets are special outlets that are used for connecting to electric ranges, clothes driers, and other appliances and devices that require this higher voltage.
AFCI (Arc Fault Circuit Interrupter) outlets prevent arcing — sparks jumping between loose wires — that can result from overheating or faults in your wiring. They can provide an extra level of safety in your home.
GFCI (Ground Fault Circuit Interrupter) outlets shut off automatically when they detect a sudden surge of power that can occur when water contacts the outlet. They’re a must for bathrooms, kitchens, and outdoor outlets, and a smart choice for garages and any other locations where there’s a danger of contact with water.
Switched outlets are tied to specific outlets in your home. With a switched outlet, you can turn on or off lights or other items plugged into the outlet when you enter or leave a room.
Smart outlets can communicate with remote controls or apps. You can program them or control them remotely to turn the power on and off automatically. With the use of apps like Google Home and others, you can even employ voice control.
USB outlets are a smart upgrade if you have devices that you need to charge regularly. They’re convenient and more attractive than plug-in “wall warts.”

Stepping Outside the Grid

While the vast majority of Americans get their power from power company mains, self-generation of power for emergency backup, money-saving, and environmental responsibility is becoming more common.

Solar panels and other alternative power sources offer the prospect of saving money and generating power in a responsible way. Consulting with an electrical or solar contractor to determine the best way to tie into your existing system is a good first step.
Whole-home backup generators are an increasingly common option for homeowners who want a reliable source of energy available in the event of storms or power outages. Generators powered by natural gas or propane are an excellent option. Learn more about whole-home standby generators in this bl

Playing Smart With Your Electrical System

Maintaining or working on your electrical system is serious business. Follow these four guidelines:

Safety first! If you choose to do any electrical work in your home, always remember to shut off the power to the circuit you’re working on at the breaker panel. If you’re not confident or sure about what you’re doing, hire an electrician.
Inspect and replace. Check out your electrical system regularly. Cracked outlets, faulty switches, and frayed wiring should always be replaced right away.
Use high-quality components. Buying cheap replacement parts like switches or outlets, or cheap components, like extension cords or surge protectors, is a false economy that may cause big problems later on.
Don’t overload circuits. If you regularly trip a circuit breaker, you’re overloading the circuit. Move appliances or other items to other circuits and consult with an electrician on how you can upgrade your system to handle the load.

Upgrade and Repair With Team Enoch

At Team Enoch, we’ve got the knowledge and skills to repair or upgrade your electrical systems. Whether it’s as simple as a new wall switch, or a bigger job like a standby generator, EV charger, or new breaker panel, we’re ready to help you evaluate what you need and get the job done right.

If you're in the Dallas Fort Worth area Contact us today and we’ll be happy to talk with you about your electrical needs. Remember, estimates are always free!