Portable Generators - Guide to Selection and Connection

Our interest in generators started back in 2012 when we were renovating our home and wanted install a back-up system. What at first seemed a simple idea became rather complicated to understand. We've developed this page to try and provide a definitive easy to follow resource for anyone looking to buy or connect up a portable generator. It does not cover larger commercial or fixed generator installations.

What type of generator should I chose?

Portable Generator

A portable generator uses a combustion engine to directly turn an alternator, which generates AC electricity.
Typically the most cost effective type of generator per kWh output, they are great for inductive loads like power tools which need a lot of current to get started.
A governor controls the engine’s speed to maintain an output which has a steady voltage and frequency. The process is not entirely precise and can be affected by the load on the generator. Such variation is generally fine when supplying many lights and power tools.
However, sensitive electronic items such as computers, home automation systems and microwaves are critically dependant on a smooth pure sine wave output with a very stable voltage and frequency. Using a standard portable generator may damage sensitive electronic equipment.

Inverter Generator

An inverter generator uses a combustion engine to turn an alternator, which produces high frequency AC electricity. Unlike a standard portable generator this is then converted into DC, before an inverter converts it back to AC. Whilst it sounds a little complicated, these additional steps essentially ensure that the output is not so dependent on the running speed of the engine and is unaffected by the load placed on the generator.
Inverter generators provide a very stable pure sine wave output, with a consistent voltage and frequency which is as good as that from any mains supply.
The increased stability makes them the ideal choice for powering sensitive electronic equipment. For this reason, they are recommended for home back up supplies and motor homes.
They are more expensive per kWh output, but are generally more compact and light weight. They are easily identified in pictures by their outer plastic casing.

What size of generator do I need?

In order to establish what generator power output you require, we've developed a simple Excel spreadsheet that does the hard work for you. Download the file here and follow the instructions below. Note that the spreadsheet will not work in 'read only mode' either click on the option to edit or download it.

Step 1

Find the rating of all of the appliances which will be connected to the generator at any one time, by checking the appliance rating plate/label. If that fails, Google the operating manual.

If the rating is only stated in Kilowatts (kW) or Amps (A), the spreadsheet has a handy converter to change them to Watts (W):

Step 2

Enter the name and rating in Watts (W) of each appliance. These must be recorded in either the resistive OR inductive load column.

Resistive loads are items which do not contain a motor. They require a steady amount of current; the start up and operating current are the same. Examples include:

Lights
Computers
TV
Entertainment systems
Kettles

Inductive loads are items which contain a motor. When an inductive load is first powered up, it draws a much larger start up current, typically 2.5-3 times its normal operating current. For example a 500w drill may briefly draw 1250-1500w when it starts up. The appliance will generally only state the power that it normally consumes, not the start up power required on the label. Examples include:

Power tools such as drill, saws, planers and sanders.
Refrigerators
Microwaves
Electric deep fryers
Coffee machines
Hair dryers
Pumps

Step 3

The spreadsheet will automatically calculate the continual power and peak power that you require from a generator. Choose a generator which has a continual AND peak rating which is equal or greater to those calculated

Example Calculation

In this example, the generator is being used to provide emergency back-up power to a home. The total resistive load is 450W, and the total inductive load 500W.

The generator required in the example would therefore need to have a continual rating of at least 950W AND a peak power rating of at least 1950W.

Is run time Important?

Think about the scenarios in which you will use the generator to determine the required approximate continuous run time. This is the maximum length of time that the generator will need to run for without being turned off. Ensure that you choose a generator with a continual run time which meets or exceeds your requirement.

How do I connect up the generator?

Direct Connection

The most common method is for the appliances being powered to be plugged in either directly to sockets on the generator or via an extension lead. Ensure that you choose the appropriate sockets on the generator to enable this. If the generator doesn't have the socket you need, one of our adaptors may help (see guide at the bottom of this page).

Hook-up

The generator is connected to a mobile unit such as a caravan, motorhome or catering trailer. Appliances are connected via sockets within these structures, as opposed to directly to the generator. Any installation must be installed and tested in accordance with the IET Wiring Regulation (BS7671).

The most common connection for a generator hook up is a lead with a:

CEE 16A (IEC 60309/commando) plug connected to a socket on the generator. If the generator only has a 13A socket, then a short 13A plug to 16A socket adaptor is used.
CEE 16A (IEC 60309/commando) socket which connects to an inlet on the mobile unit.

We provide a range of hook-up leads and adaptors on our generator page. In contrast to 99% of leads available online, ours are constructed from robust black or orange rubber, not cheap blue artic cable.

Home Emergency Power Back-up

The simplest way to use a generator to provide power in a home during a power cut is to use an extension lead to power appliances directly (direct connection). We offer a range of extension leads for this purpose, including a double extension lead with USB sockets. As you’ll want to keep the heat inside your home when using a generator in the winter and not leave a door open, our letterbox connector provides an ideal solution. Already popular with Electric Vehicle owners, the slim line connector allows an extension lead to pass through a letterbox, as UK 13A plugs will not fit through most.

Whilst it is possible to connect a generator to the supply side of a home consumer unit to enable all circuits to be powered (subject to the generator rating), this is a complex situation which must be installed by a qualified electrician. A special changeover switch must be fitted to ensure that the home can only ever be powered by either the mains supply or generator at any time, and earthing arrangements need to be carefully considered. Below is a picture of the set up in our own home.

Under no circumstances connect a generator to your home using a lead with a 13A plug on both ends. This is incredibly dangerous; there is a reason that such a lead is often referred to as a ‘widow maker’!

Does the generator need an earth rod and do RCDs work?

Portable generators are normally operated without the use of an earth electrode, as it would be impractical to install one in the ground each time. In this 'floating' system, the earth and neutral are also not connected together. Plug in RCDs and extension leads with RCDs will not operate with a floating system - for this reason, all of our generator extension leads are supplied without an RCD.

When used for a hard wired home back up systems, an electrician will install a suitable earthing arrangement and fit a link between the neutral and earth.

Further technical guidance on both arrangements can be found in these useful articles from NICEIC and the IET.

How do I decide what connections I need on the generator?

The connections you’ll need on a generator will depend both on how you plan to connect it and what load you need to power.

230v 13A socket

Commonly provided on UK generators and enable direct connection of UK appliances. 13A extensions leads can also be used for direct connection and home back up applications. 13A sockets have a number of limitations:

The total current that can be drawn is 13A (2990w). To find the total current of the load, divide the total continual power required in Watts that you calculated by 230.
Whilst 13A plugs can withstand almost 13A over short periods e.g. boiling a kettle, they do become warm when more than 10A is drawn continually.
Unlike IEC 60309 commando connections they are not splash proof and may let in water during adverse weather.
A 13A plug to 16A IEC 60309 socket adaptor is required to connect to a hook-up.

43mm diameter

230v 16A Blue Sockets (IEC 60309)

Commonly found on UK generators and provide a number of advantages over 13A sockets:

Total load of 16A (3,680W) can be provided, enabling the connection of higher power appliances.
Connections are IP44 rated splashproof.
Hook-up cables can be connected directly.

The disadvantage is that if a 13A socket is not also provided, an adapter is required to directly connect UK appliances.

57mm diameter

230v 32A Blue Sockets (IEC 60309)

Provided on larger generators. They are great for commercial higher power applications.
For domestic use, you can use one of our adaptors to convert it to 2x 13A UK or 2x 16A commando sockets.

16A - 56mm diameter

32A - 63mm diameter

415v 16A and 32A Red Sockets (IEC 60309)

Provided on larger generators. They are great for commercial higher power applications where three phase power is required.
For domestic use, you can use one of our adaptors to convert it to 2x 13A UK or 2x 16A single phase commando sockets.

Normally black or blue

mm diameter

230v 16A Schuko (often called a European 2 pin) socket

The Schuko socket is easily confused with the 230v 16A CEE socket. However it is actually easy to tell apart, as it only has 2 receptacles (holes).

Commonly found on generators imported from Europe.
One of the most common questions that generator owners contact us about is how to use them in the UK. Our range of adaptors can safely convert them to either UK 13A or 230v 16A IEC commando sockets.
As a connector, they have the same maximum load (16A 3,680W) and IP44 splashproof rating as a commando socket.

What if the sockets on the generator don't perfectly match the plugs on the appliances I need to power?

Worry not! Tough Leads manufacture the widest range of heavy duty adaptors to enable appliances with a variety of plugs, to be connected to a wide range of sockets found on generators across the UK and Europe.

Given the number of different appliance plugs and generator sockets, it can be confusing to know which adaptor you need. We've developed the handy table below to make it easier. Simply find the plug that the appliance has across the top and the generator socket you need to connect it to down the side. Click on the picture of the adaptor where they both meet and you'll be taken to the appropriate page. Each adaptor page contains an illustration of a typical application, to provide further guidance. We're always happy to provide advice if you'd like to contact us.

	Appliance	Plug
Generator Socket	230v 3A UK	230v 16A CEE	230v 32A CEE	415v 16A CEE	415v 16A CEE
230v 16A CEE		Direct fit	Not technically possible	Not technically possible	Not technically possible
230v 32A CEE			Direct fit	Not technically possible	Not technically possible
415v 16A CEE			Not technically possible	Direct fit	Not technically possible
415v 32A CEE					Direct fit
230v 16A Schuko			Not technically possible	Not technically possible	Not technically possible