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Campsite Circuit Breaker Tripping - An Annoyance that can be Avoided

Does this scenario sound familiar?

You arrive at your campsite, check in, pitch up and start to setup. You plug in the electrical hook-up cable and thecircuit breaker trips. It’s getting dark ! The circuit breaker is locked away in a box so you have to find the campsite warden who obliging flicks the switch back whilst muttering  “all American RVs seem to do this”. You ensure all appliances are turned off before hooking up again (a good practice anyway) but to no avail – the circuit breaker trips again. It’s even darker!! Once more you call out the warden and finally the hook-up is successful.

Why does this happen when I hook-up ?

A professional UK electrical conversion will incorporate a suitable continuously-rated step down transformer (not a yellow building site box) which will transform the 230v hook-up to 110v in order to power the roof A/C, microwave, fridge/freezer and other 110v appliances.

At the instant of switching on a transformer a large current will flow even when there is no load. This is caused by a phenomenon known as “Inrush Current”. This is because the transformer core is not fluxed and offers no impedance. This “Inrush Current” can be several times the normal full load current but is rapidly suppressed as the flux builds up and the transformer core becomes fully magnetized.

Let’s consider the case of a 5kVA transformer.

The full load current is 21.74 amps (Power = Volts x Amps, hence Amps = Power/Volts).

The peak “Inrush Current” could be as much as 5 - 10 times the full load current or > 100amps. The campsite may have a 16amp circuit breaker which will trip at 3 – 5 times its rated value or 48 to 80amps. Clearly there is potential for tripping the circuit breaker.

Campsites in Europe often only have 6amp hook-ups and hence the problem is even worse with the circuit breaker tripping at 18 to 30amps.

The amount of “Inrush Current” is also dependent on the VA rating of the transformer so a conversion that utilises a 4kVAtransformer will be less susceptible than one with a 5.5kVA transformer.

Why does the problem not occur every time I hook-up ?

Mains electricty is in the form of an alternating current or AC. This means the direction of current flow alternates from live to neutral and neutral to live. In the UK this change in current flow occurs 50 times per second or at a frequency of 50Hz.

The amount of “Inrush Current” is determined by a factor which is unfortunately outside of our control and largely down to good luck regarding the timing of connecting the hook-up.

The “Inrush Current” is least if the if switching takes place when the voltage wave is at its peak. If switching takes place when the voltage is zero then the peak current is greater as illustrated in the diagrams below.

Can this problem be avoided ?

The solution to this annoying problem is achieved by limiting the maximum current that can flow when the transformer is turned on by incorporating a "Soft Start Module" into the installation.

Here at Griffin American Motorhomes we have been very successful in avoiding this problem by ensuring that all UK electrical conversions performed by us incorporate a "Soft Start Module" hence eliminating this annoyance.

We have also found that it is possible to retro-fit a "Soft Start Module" to an existing installation on an RV at a relatively low cost.

Please contact Griffin American Motorhomes on 01761 300489 for more details.

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