Site Electrics Explained Things have come a long way since the days of gas lights in caravans and central to the process of change has been our use of electricity. Virtually all new caravans now come with mains wiring as well as a 12 volt battery operated system. In response to this more and more sites are installing mains hook ups. But how do we use them safely and how do we avoid the embarrassment of tripping them out?

Plugs and Sockets

If using a site in the UK then the site owner is required by law to ensure that the electrical system complies with the latest edition of the IEE regulations. It will also need to be inspected annually by a competent person and a certificate issued. Outlets are normally found on posts or walls and should comply to European standard EN 60309-2.

Connection is via a suitable lead with a plug to match. Normally this will have been supplied with your van but, if not, you can get one from any local dealer. For general use the connecting lead should be at least 25m long (any less and it might not reach) and be made of good quality 3 core flex with each core having a minimum conductor size of 2.5 sq mm.  There are occasionally circumstances where one lead is not long enough and a second is required. The two leads should be joined with the EN 60309-2 plug and socket. Do not use taped joints or the household 13 amp plugs and sockets. These are unsuitable for outdoor use. Ensure that the joint is off the ground and away from puddles etc. For extra protection you can buy purpose-made 'seed pod' covers which clamp round the plug and socket. Where a lead is coiled up such as the one in the picture on the right it should be completely unwound before use. This is to prevent any build up of heat.

Unwind fully before use!

Once pitched make sure that the isolating switch in the caravan is in the 'off' position. This avoids the possibility of any arcing which might arise if you connect with a load attached. First plug one end of the lead into your caravan and then the other into the site socket. Some site sockets are switched on by an adjacent switch, others by (sometimes pushing and) turning them once the plug is in. Look for any nearby instructions or diagrams. You can now return to your van and close the isolating switch. You should now be ready to use your appliances but, as an extra precaution, I always recommend the use of a mains testing plug. These cost around a tenner and consist of a 13 amp plug with 3 neon lights set inside. You simply plug it in and switch on. If all 3 neons light then all is well. If not the instructions will tell you what is wrong. You may need to consult the site owner or a qualified electrician to fix the problem.

3 neons lit - all OK

Connecting Abroad The big advantage of European standards is that more and more European sites are adopting them. Most sites are now equipped with EN 60309-2 sockets so UK sourced leads will fit. There are however a few that have yet to make the change so it is wise to invest in a continental adapter. Most caravan accessory shops sell them. The adapter simply consists of continental two plug connected to an EN 60309-2 socket as shown in this picture on the right

The other thing to be aware of is that continental sites sometimes have no convention about wiring the live and neutral conductors. This means it is quite possible to experience something called revere se polarity.This become an issue when the switch feeding an appliance only switches one of the conductors, as is the case with most UK kit. In the UK this is not normally a problem as the wiring convention such that it is always the live conductor that is switched. If the polarity is reversed then this means that only the neutral conductor is switched so the appliance remains live even though switched off..This could become dangerous if the appliance was faulty The simple way to check for reverse polarity is to use the 3 neon plug mentioned above Some older Swift caravans were fitted with reverse polarity indicators which will light when they detect this situation.

LH neon only - reverse polarity!

One way to deal with reverse polarity is to have a second continental adapter wired such that the live and neutral are transposed.

Staying Switched On

In order to avoid tripping your supply (and possibly your neighbour's) you need to know how the various protection systems work. On any supply there are normally three types of protection. 

Earth Leakage Protection - instant trip

The first is known as earth leakage protection. This is the protection which helps to avoid you receiving a lethal electric shock if you touch something live. It works by detecting the currents which flow in the live and neutral supply wires. Normally these should be absolutely identical. However if you touch a live component then some current may flow through you to earth. This results in a small imbalance in the live and neutral currents and causes the supply to trip very quickly. You may receive a shock but it should not kill you. 

This earth leakage protection can also help protect you from shock if you have a faulty appliance e.g. electric kettle. If the appliance has an earth fault it will trip the supply the moment you plug it in or switch it on. If this happens then either get it checked by a qualified electrician or throw it out!

As well as there being an earth leakage protection device (often known as an RCD or Residual Current Device) on the site supply there should also be one inside the caravan. You can recognise it by the test button alongside. Pressing this button simulates an earth fault and should cause the switch to trip. The power must be on on for it to work. It's worth getting into the habit of testing the trip regularly. I test mine each time I plug the caravan in just to be on the safe side. If it fails to trip call in a qualified electrician.

Site earth leakage breakers often control more than one outlet and are usually out of reach of caravanners. If yours trips you will probably have to see the site owner or manager.

Fault Protection - instant trip
The second type of protection is fault protection. This operates when there is a short circuit on the system (e.g. live and neutral wires touching). Years ago wire or cartridge fuses were used almost exclusively for this job. These days Miniature Circuit Breakers (MCB's) have taken over for consumer duties. MCB's have the advantage that they are easy and quick to reset and that no fuse wire or spare components are needed. If a short circuit develops the MCB will trip instantaneously. 

This picture clearly shows the miniature circuit breakers in a modern caravan. The one on the left is the main isolator and contains an inbuilt earth leakage detector. The blue button is the test button to check that it works. The breakers to the right are for the various circuits within the caravan. These will trip in the event of overload or fault.

Overload Protection - slower trip
The third type of protection is overload protection. This is also handled by the MCB. Whereas with a fault an MCB will trip instantaneously, with an overload it may take some minutes—just as is the case with a conventional fuse. So if rated at 10 amps then the supply MCB should provide 10 amps indefinitely. If you draw 11 amps the supply will not trip immediately but may take several minutes. Overload trips are characterised by the trip occurring a minute or two after you switched the last appliance on (or it came on automatically via its thermostat). Most sites have individual MCB trip switches for each outlet so if you do trip on overload then only your van, or a small group of vans, should be affected. The problem is that you may have to get the site owner or manger to reset it if it's locked away.

Caravans are also fitted with MCB’s for individual circuits. If any trip then you have too much load on that circuit or possibly a fault.

Before switching on too much load it's a good idea to find out what rating the hook up is. Modern Uk sites tend to be 16 amps but older ones may be 10 amps or even less. The higher the rating the more load you can switch on before the supply trips.

There's no easy way to be certain just how much current you may be drawing at any one time. As a rough guide 1000 watts = 4 amps at 230 volts. The following table gives a  guide for some common items. Allow an amp on top for any standing loads such as the fridge and battery charger.

* Microwaves are normally rated by their output power but the power drawn from the mains can be up to twice as much

Special Precautions For Rallies
When site electrical systems are being designed an average load factor (or diversity factor) is used to calculate the required rating of the incoming supply. For example if a site had 10 outlets each rated at 10 amps the designer will assume that the average demand on any one outlet at any one time will be no more than say 5 amps. This means that the incoming supply needs to be rated at 50 amps. Normally this will be more than sufficient because whilst some may have space heating switched on (high load) others may be empty

Rallies can present special problems because of the organised way in which rally-goers tend to behave at certain times. Imagine a freezing cold day when ralliers return to their vans, following an event, and do so all at the same time to escape the cold. So many space heaters, kettles and water heaters get switched on within a few minutes that the site supply becomes overloaded and the whole site trips. Marshals running rallies during cold weather should bear this in mind and advise everyone to use gas to get the van warm before switching over to electricity for space heating.

Another problem ralliers can occasionally face (especially on the continent) is that of low voltage. On poorly designed site systems the effect of a high load can sometimes be to reduce considerably the voltage fed to each caravan. Mains lights may be dim or mains powered TV's may not work properly. Worse than this some battery chargers (switch mode type) can actually be damaged if operated from relatively low voltages much below 200 volts. The answer is to reduce the site load.

Top Tips

• Always switch one appliance off before switching another on

• Operate TV's from 12 volts where possible so that if the mains supply trips you can continue watching your favourite programme

• For continental travel have a second mains adapter made up with the live and neutral reversed. Use this as a quick fix for reverse polarity

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