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How to provide power to a house using a portable generator

Published: January 2024

In this article we show you how to power your home using a portable diesel, petrol or LPG generator. We look at changeover switches, the importance of earthing and ensuring that MCBs and RCDs continue to function when the electrical supply is from a generator.

We discuss generator loadings and how to isolate non essential loads. We ask where to locate the generator when it's in operation, how best to safely isolate the mains supply and switch to a generator supply, including the procedures involved in generator start up.

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How to power a house with a portable generator

Even if you never need it in an emergency or you only ever use it for camping, to turn the engine or just for fun; having a generator on hand that you know can be relied upon to power essential loads, whatever the weather or the time of day, is great for peace of mind.

The fundamental concepts involved with switching a property's grid supply to a generator supply and how to operate the generator, once explained are easy to remember.

The purpose of this article is to show as clearly as we can how any householder can safely provide backup power to essential loads within a residential property using a portable or a small home diesel, petrol or LPG generator.

Essential Loads

Freezer, lights/lamps, router, laptop, mobile phone. Make a list of the important equipment, note it's power usage in watts and how to turn it on and off from the consumer unit and start with the bare essentials. At the end of the day the less self generated power that's used, the longer the fuel will last.

When seen and used only as a temporary power supply for essential loads only, generators do not to be large or expensive and they don't always need to run for long. Many portable generators that you might already own, when interfaced correctly with the property's electrical system, can generate enough power to keep food and medications in fridges and freezers cold, laptops and phones charged, alarm systems and security lights in operation, whatever might be needed in terms of a backup power supply that will take the edge off of losing a mains supply from the grid.

Changeover switch for a portable generator

Manual Changeover / Transfer Switches

Installing changeover / transfer switches is a service that we offer. Where we help is to make sure that when the supply is switched from a mains to a generator supply that anything required for the earthing systems to function, switches with it, ensuring that safety devices protecting the circuits such as MCBs and RCDs continue to work.

Essentially the changeover/ transfer switch safely isolates the mains electrical supply and allows the loads to be energised by the generator without the potential for grid back-feeding. When installed at the source of the incoming mains supply the transfer switch can then potentially switch any load from a mains supply to a generator supply without any changes needed to the internal wiring.

Generator Overload!

Generator outputs are rated in Watts, their continuous output and peak output ratings both need to be above the essential load calculations in watts, if the load is higher than the generation, the generator will conk out and stop. Inductive loads with motors such as power tools, pumps and fridges draw more current at startup than they use once running, the generator needs to be sized to provide for this.

When electrical loads are understood and under control, a diesel, petrol or LPG generator rated from 2-3kW (8.7-13A), although small compared to what's available, could be enough to supply the essential loads for a house.

Controlling the loads

When a mains power supply is unavailable, before starting the generator, the first thing to do is to switch off everything that hasn't already been identified as an essential load at the equipment, as well as isolating/switching off as many circuits as you can directly at the consumer unit(s).

With all non essential loads off, before turning off the essential loads, note where they are, what they are and in which order you will turn them on when the generator is warmed up and running.

Something that might be useful to do ahead of time, would be to mark the circuits at the consumer unit that will supply essential loads when they are running off the generator. This will help avoid non essential loads being turned on by mistake later, which might overload the generator, a well organised and labelled consumer unit, will also help to be able to supply generator power to different equipment and circuits as needed.

For example an unopened freezer will retain it's internal temperature for quite a while, keeping food frozen without power. Laptops and phones once charged, depending on usage can also last for quite a while on battery power. Providing generator power for an hour or two to these loads might be enough to take care of fridges, freezers and charging batteries for the following 24 hours.

Mains Isolation and Generator Startup

The transfer / changeover switch only allows the mains or the generator power through the switch and onto the loads. The switch also prevents the generator feeding the mains and visa versa. Once all the loads are off and the transfer switch has been switched to generator, it is safe to start up the generator.

Once the generator is running smoothly, introduce the loads one at a time, starting with the inductive loads, you'll likely hear the generator's engine adjust to the loads as they are introduced, wait for the engine to smooth out before introducing the next, until everything you need is drawing power from the generator.

You will then be able to turn the essential loads on and off in the normal way or at the consumer unit and start and stop the generator as needed.

When you want to reintroduce the mains supply, turn off the loads, turn off the generator, switch the transfer / changeover switch to accept the mains supply / isolate the generator supply and reintroduce the loads.

Where to put the generator

One of the good things about portable generators is that when not in use, you can leave them tucked away neatly somewhere and only roll them out when needed. The shorter the distance from the generators usual position to where it will be when in use the better.

Generator fuels include diesel, petrol and LPG which need to be stored safely and away from the generator when it's in operation. You can find guides online for how to maintain and store these different fuels safely.

When the generator is in use you should locate it outside and as far away from buildings as is practicle.

Generator engines are loud so take this into account when you decide where to locate it.

The generator will need to connect to the electrical network somewhere, this can be done using a weatherproofed cable specifically designed for one end to be plugged into a fixed outlet at the house, the other end being plugged into the generator.

Changeover Switch (for portable / home generators) Installation

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We are located in Wanborough, very close to Swindon in Wiltshire, Southern England, UK. From here we service clients within a 90 minute driving radius including the towns, cities and regions below:

Swindon: Abingdon, Aldbourne, Andover, Banbury, Basingstoke, Bath, Berkshire, Bicester, Blunsdon, Box, Bracknell, Bradford on Avon, Bristol, Burford, Calne, Camberley, Carterton, Cheltenham, Chippenham, Chipping Norton, Chipping Sodbury, Cirencester, Corsham, Cricklade, Devizes, Didcot, Evesham, Faringdon, Fleet, Gloucester, Gloucestershire, Hampshire, Henley-on-Thames, Highclere, Highworth, Hook, Hungerford, Keynsham, Kingsclere, Lambourn, Lechlade, Lyneham, Maidenhead, Malmesbury, Marlborough, Marshfield, Melksham, Minety, Newbury, Oxford, Oxfordshire, Pewsey, Purton, Ramsbury, Reading, Royal Wootton Bassett, Salisbury, Shalbourne, Slough, Stow, Swindon, Tewkesbury, Thatcham, Trowbridge, Wanborough, Wantage, Warminster, Wiltshire, Winchester, Windsor, Witney, Wokingham, Worcester, Wroughton and Yate.

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