The Wanderer
This, and a few further Tech Notes, addresses common member queries. As many are similar, the Tech Notes on the CMCA website enable answers to be readily found (but not necessarily relevant years later). This one relates to supply cables. It is included because their choice and usage is dangerously prejudiced by ongoing postings on web forums from those unaware their understanding of electrical safety technique is no longer valid.
Q: SEVERAL OF YOUR RECENT ARTICLES REFER TO MAJOR CHANGES IN WIRING RULES. WHAT ARE THESE CHANGES?
A: They relate mostly to protection against electric shock. A healthy heart can withstand surprisingly high current for a fraction of a second. If current is halted within 0.4 second, the chances of survival are high, but the heart cannot cope with even minor current (typically above 30 milliamps) for much longer than that.
Electrocution commonly occurs when electrically live metal is accidentally contacted. Current may then flow through the body to earth. The original protection was to ensure all touchable metal was connected to earth. This provided some protection but even a tiny amount still flowing through the body can kill.
The next step was circuit breakers designed to cut excess current flow within 0.4 second (those in hospitals, etc. operate faster) but only assist if the total current then exceeds the circuit breakers’ current rating. They protect cabling far more than people.
The major breakthrough in electrical safety is residual current detection. It works like this:
A typical electric circuit has two main conductors. Current flows through one conductor, then through the appliance and back to the power source through the other conductor. A residual current detector (RCD) compares these two currents. As long as they are equal, all is well. If their current flow is unequal – some can only be flowing to earth. The route can be via a fault within an appliance, a child using a knife to clear bread stuck in a live toaster, cutting a power lead when using a saw, dropping the hair dryer into the wash basin, etc. In most such circumstances the RCD cuts off power within 0.25-0.4 second.
An RCD is not a 100 percent safeguard. Whilst less likely, if both conductors are touched at the same time: e.g. by the (now late) Uncle Jack trying to remove a still live broken light globe, current is likely to flow from one conductor to the other via Uncle Jack. Little or none may necessarily flow to earth. In effect, Uncle Jack becomes the electric load. The circuit breaker may open – but not in time to save life. Despite this, however, since the changes in electrical protection in Australia (in power circuits since 1991, and lighting since 2000) deaths through electrocution have roughly halved – to about 50 a year.
It is vital to understand, or at least accept, that electrical safety protection necessitates tight control over (the now obligatory compliant) supply cables. If their length or current capacity is exceeded (e.g. by co-joining cables or using a 10 amp cable to carry a 15 amp load), it increases the critical time to save life before power is cut off.
Q: A CARAVAN PARK REFUSED TO ALLOW ME TO USE MY OWN SUPPLY CABLE. THEY CLAIMED IT WAS NOT ELECTRICALLY COMPLIANT. WHAT IS REQUIRED?
A: Supply cable requirements are detailed in Table 5.1 of AS/NZS 3001:2008 as amended 2012. Those for caravan park use must be at least 10 metres. Length must not exceed that shown for the specified conductor area. Current must not exceed that shown for it to be cut off within that critical 0.4 second. Co-joining them, or using a 10 amp cable to carry 15 amps, substantially extends the time before current flow is broken.
Q: MANY CARAVAN PARKS INSIST ON SUPPLY CABLES BEING INSPECTED AND TAGGED ‘FOR SAFETY’. CAN THEY INSIST ON THIS TAGGING?
A: Yes. Occupational Health and Safety Acts oblige employers to ensure their workplace is safe. This includes possible hazards associated with electrical equipment, assessing risks and eliminating or controlling those risks.
Caravan park managers (and RV rally organisers) are well aware that many supply cables are unsafe. Many have completed a course enabling them to do so and can legally insist on inspecting such cables.
They check conductor size and length, that active and neutral conductors are connected to the correct pins, that the earthing conductor is secure, that moisture cannot enter, that the compressive fastenings hold the cable securely within the plug and socket and if the earth pin has been filed down. Any of the above will result in your cable rightly being rejected.
All supply cables are checked at CMCA rallies. Some 20%-25% are typically found to be faulty. At one (2014) Australian Caravan Club Muster, of the 212 cables checked, 84 (40%) were faulty: five had broken earth wires, and 24 had active and neutral reversed.
Q: ALL CARAVAN SUPPLY OUTLETS (AND SUPPLY CABLES) SEEM TO BE 15 AMPS. I NEED TO PLUG MY RV INTO A 10 AMP SOCKET AT HOME BUT THE EARTH PIN IS TOO BIG. CAN I HAVE SOMEONE MAKE UP A 10 AMP TO 15 AMP ADAPTOR CABLE OR FIT A 10 AMP PLUG TO MY EXISTING 30 METRE 15 AMP CABLE? OR (AS IS OFTEN SUGGESTED ON FORUMS) FILE DOWN THAT EARTH PIN TO FIT?
A: Australian-compliant RVs have 15 amp socket inlets, and 15/16 amp circuit breakers that enable 15 amps to be drawn via the supply cable. If that cable and its connectors are rated for 10 amps they would be grossly overladen at 15 amps.
There is thus no safe or legal way an RV capable of pulling 15 amps can be used with a 10 amp cable. Its draw must be automatically limited to 10 amps.
All of the suggested ‘fixes’ are illegal and potentially dangerous. If the need is only at home, have a licensed electrician install a 15 amp outlet socket.
If, however, a 10-amp plug, cable or socket is used, you must limit the RV’s draw to that 10 amps by having its circuit breaker/s replaced by 10 amp units (some RVs have combined RCD/ circuit breakers). The inlet socket plug too must be replaced by a 10 amp inlet. No known direct replacement meets AS/NZS standards 60320.1 or 3123, or IEC 60309) nor the obligatory IP24 protection. The Clipsal 56 A1310 surface mounting 10 amp inlet socket meets all requirements but is bulky and costly.
A legal alternative (subject to waterproof storage and physical cable restraint etc) is to have the supply cable permanently fixed at the RV end. (Section 3.2.3 of AS/NZS 3001:2008 refers). Cable length/size restrictions, etc. are as Table 5.1.
Most owners settle for an Amp-Fibian adaptor. This is a short (1.8 m) lead with a 10-amp plug and a hard-wired 10-amp circuit breaker/RCD in a waterproof enclosure that accepts any standard approved 15-amp cable up to 12 mm diameter. Be aware that from 20/12/2013 – 06/02/2014 these units were accidentally supplied with 15/16 amp circuit breakers (identified by the clear marking ‘C16’). There was a recall but a few may still be around.
Table 5.1 (AS/NZS 3001:2008 as Amended 2012). Maximum lengths of RV supply cables
Disclaimer: I have an extensive working background in electrical engineering but I am not a licensed electrician.
All you need to know about the electrical system in caravans and motor homes is in Collyn Rivers’ Caravan & Motorhome Electrics. That and his other books – including his brand-new Caravan & Motorhome Book is available from CMCA NHQ or directly from the publisher at caravanandmotorhomebooks.com
Category: Technology
Written: Tue 01 Mar 2016
Printed: March, 2016
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