11/12/2017
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Caravan Electrics: Avoid Tripping Out

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We've all overloaded our mains supply at some time. Here's how to make sure you keep within your pitch's limit, how to calculate how much current you are using and begin to master caravan electrics

Our technical writer Terry Owen, a chartered engineer, is a year-round caravanner with a detailed knowledge of all aspects of caravanning, including caravan electrics

The caravanner who says he's never tripped out his mains electricity supply is a bit like the beekeeper who says he's never been stung. He's either brand-new to the hobby, or he's got a short memory!

There is no doubt that mains hook-up can add much to our caravanning comfort but the site's supply can deliver only a fraction of the power we use in our houses. If we use too much — CLICK — off it goes, and we're left to sort out the mess.

Tripping the supply can make you unpopular on a site, especially if you have to go and get a member of the site's staff to put the supply back on again. Worse still, you may even have tripped the supply to neighbouring pitches.

Caravan electrics: Overload and Earth Fault

There are two ways in which you might trip the supply. The first, and most common, is through overload. In other words taking more power than the supply can handle. The second is through an earth fault, which may be caused by a faulty appliance or cable. Earth fault trips often take out a whole bollard or section of the site, whereas overload trips generally just affect one hook-up. In this article we'll look at both and what you can do to avoid falling victim.

The typical supply to a modern house is rated at 80 or 100 amps but the best you'll see on a campsite is just 16 amps. Older campsites, and many continental ones, may have only 10 amps or even six.

With limited power to play with, we need to think carefully before switching something on. We need to have some idea how much power it will consume. As a rule, items that produce heat use a lot more power than those that don't.

Power Hungry Appliances

For example, a hair dryer rated at 1600 watts will consume 70 times the power of an 18.5" LED TV rated at 23 watts.

Microwave in a caravan
Above: Microwaves can be power hungry


Microwave ovens can use more power than you might think, too. The reason is their rated power is an indication of what goes into the food rather than what is taken from the mains, which can be nearly twice as much.

Kettle in a caravan
Above: A caravan kettle like this uses only about one third of the power of a domestic one


With all these things to bear in mind it can be difficult to know just how much current you may be drawing at any one time. A rough guide: 1000 watts equates to just over four amps at 230 volts.

The following table shows the typical power used by some common items

Appliance Watts Amps Appliance Watts Amps
Truma space heater (high/low) 2000/1000 8.7/4.3 Truma Ultrastore water heater 860 3.6
Truma Combi heater (high/low) 1800/900 7.8/3.9 Whale Rapid Heat water heater 1500/750 6.5/3.3
Alde boiler 3150/2100 13.7/9.1 Whale 2000/1000 8.7/4.2
Thetford cooker hotplate 800 3.5 Small Microwave 900 3.9
Domestic fan heater high/low 2000/1000 8.7/4.2 Sandwich Toaster 750 3.1
Domestic Kettle 2400 10.5 Hair Dryer 1600 7.0
Travel Kettle 750 3.3 Curling tongs 50 0.2
Fridge 120 0.5 Fridge freezer 220 1.0
Small 2 Slice Toaster 1000 4.3 Avtex 18.5" LCD TV 23 0.1
Power supply unit 700 max 3.0 max Laptop computer 50 0.2

Controlling overloads

Overload trips are controlled by miniature circuit breakers or MCBs for short. These are the modern day replacement for fuses. Just like a fuse, they will tolerate a small overload for a short period but will trip immediately with a large overload, including what may occur with a short.

Trip switches - caravan electrics
Above: Three MCBs and an RCD on a Bailey caravan


By and large every caravan has three MCBs, each feeding its own circuits. Unless an individual circuit is overloaded, they are unlikely to trip. The most common scenario is when the combined current of the caravan's MCBs exceeds the rating of the MCB in the supply stanchion, causing it to trip.

Overload trips may take a minute or more to activate depending on how much overload. This means that, if you accidentally switch something on, you may have time to switch it off again before power is lost.

Load-monitoring devices

It is possible to buy load-monitoring devices that measure the current at the supply point and relay the information by wireless to a small display panel. Primarily designed for home-use to tell you the cost of electricity being drawn, you can also set them to show you the loading in kilowatts (KW).

Current is measured using a sensor that clamps around one of the supply wires next to the meter. This is not as easy to arrange in a caravan so you may need an electrician to install the sensor for you.

wireless energy monitor
Above: A wireless energy monitor


Once fitted, you can easily see how much power your caravan is using and adjust it to stay within your limit. The only thing to bear in mind is there may be a short delay in the information being displayed. This is because, to save battery life, transmissions are not continuous but made every few seconds.

The Owl monitor we tried transmitted every six seconds but could be set to transmit every 60 seconds. It also had an auto power save mode that ensured it transmitted every six seconds only if the power changed, otherwise it transmitted every 60 seconds.

Load controlling devices

Alde load monitor

A good device to help master your caravan electric for those with Alde heating can invest in Alde's load monitor device (part number 3010-246). This consists of a sensing coil threaded through the live wire feeding the caravan. Installation should be by a qualified electrician.

Alde's load sensing coil
Above: Alde's load sensing coil


It senses the current and sends the reading down a wire to the digital control panel where you can see it. You can then select the current rating of your supply in the range five to 17 amps. If the set level is exceeded, the boiler is powered down in stages to prevent tripping of the supply.

Of course, it's still perfectly possible to overload and trip the supply but the Alde boiler will not be to blame.

Alde's current display screens
Alde's selection screen
Above: Alde's current display and selection screens


Swift Command system

For the 2016 model year Swift has introduced a comprehensive power control system on its Elegance, Continental, Conqueror and Elite models. It includes a 230-volt current monitoring system that works similarly to Alde's load monitor in that it switches off heating elements if a user defined current level is breached. You can also see the mains hook up current in amps.

Swift Command
Above: Swift's new Command panel can show the hook up current and control it. Here the panel is displaying the current from a solar panel


Earth fault trips

Earth fault trips are instantaneous. They have to be, because an earth fault could result in electrocution. In normal operation the current in the live and neutral wires should be identical. All the current that flows down one wire should return via the other having done its job in powering the kettle, the heater or other appliance.

When an earth fault occurs, some of that current leaks away to earth and creates an imbalance. It's that imbalance sensed by something called a Residual Current Device (RCD), which then trips the supply.

The amount of imbalance needed for a trip is small, just 30 thousandths of an amp (or ampere, to quote the full name). This is designed to prevent death through electrocution as might otherwise happen if you touched something that had become live.

RCD button - caravan electrics
Above: It's a good idea to operate the test button on your RCD each time you hook up
Neon tester - caravan electrics
Above: A neon tester will also help ensure your safety


All caravans with a mains installation have to have an RCD by law. The campsite supply also must have such a device but it may be shared by more than one hook-up point so, if you trip it, your neighbours could be affected too.

The most common cause of earth faults on a caravan is electric kettles. If your supply RCD trips the instant you switch the kettle on, the chances are the kettle is faulty and should be replaced.

If you can't positively identify and isolate the cause of an earth fault, do not continue to try to use the caravan's hook-up. Get your caravan electrics looked at by a qualified electrician.

Caravan Electrics - Top tips

  1. If you have a TV make sure it will run off 12 volts and power it that way. Then, if the mains trips during your favourite soap, you can carry on watching by courtesy of the leisure battery.
  2. If your supply is just 6 amps, never switch on more than one item at once; if 10 amps, two items and, if 16 amps, three items. It won't prevent all trips but it will help.

Caravan towing electrics explained

7-pin caravan electrics
7-pin caravan electrics

 

Everyone knows that hooking up the caravan towbar electrics lead is a vital part of the hitching process, but what does the connection actually help with on the road?

There are two types of sockets that you'll find on caravans when it comes to towing electrics. Tourers manufactured before the 2009 model year were fitted with two seven-pin plugs – one black 12N plug and a grey 12S. Modern caravans, however, have the electrics consolidated into a more convenient 13-pin plug.

If you do have a tourer with the old seven-pin plugs then fear not as there are plenty of adapters available to convert between the old and new. Our advice if you get the option, plump for the contemporary 13-pin option every time.

What are they for?

Caravan towbar 13-pin electrics

Caravan 13-pin electrics (post 2009)

Pin number Function Wire size Wire colour
1 Left indicator 1.5mm Yellow
2 Rear fog lamp 1.5mm Blue
3 Earth 2.5mm White
4 Right indicator 1.5mm Green
5 Right tail lamp 1.5mm Brown
6 Brake lamp 1.5mm Red
7 Left tail lamp 1.5mm Black
8 Reverse lamp 1.5mm Pink
9 Permanent 2.5mm Orange
10 Switched supply (fridge) 2.5mm Grey
11 Earth pin for 10 2.5mm White/black
12 No current allocation
13 Earth pin for 9 2.5mm White/red

 

Caravan towbar 7-pin electrics


Caravan 12N 7-pin electrics (pre 2009)

Pin number Function Wire size Wire colour
1 Left indicator 1.5mm Yellow
2 Rear fog lamp 1.5mm Blue
3 Earth 2.5mm White
4 Right indicator 1.5mm Green
5 Right tail lamp 1.5mm Brown
6 Brake lamp 1.5mm Red
7 Left tail lamp 1.5mm Black

 

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