Circuits within a caravan

Does anywhere in Part 6 state "except caravans"?

new section 721 is explicitly for caravans...

Just noticed that the example usage notice that is shown  says testing should be every 3 years....

Given that they may be plugged in at many different locations with different supply characteristics

how can you possibly test this???/

A section specifically for caravans is not new, (edit) and as Geoff has already said section six still applies to the whole of the regs

You can certainly carry out your inspection and the dead tests.

Thank you gentlemen....

You can certainly carry out your inspection and the dead tests.

And some live tests too - e.g. RCD operation. If the caravan circuits are well designed they should be safe for a very wide range of supply characteristics. Remember that testing is less about verifying that the installation complies with the regs directly, as verifying that it complies with the design and is free (AFARP) from installation defects. Readings should be considered within the context of the supply in use at the time - e.g. getting a Zs reading of 100Ω when connected to a TT supply with a 'Ze' of 99.9Ω is probably acceptable, while getting a 5Ω reading with a TN-S supply with 'Ze' of say 0.5Ω probably indicates some serious problem.

  - Andy.

Mobile travelling caravans are subject to much bumping up and down and vibration so need thorough regular testing. Flexible cables are best rather than sold conductors for these, and double pole M.C.B.s. 721.43.1.

I do work in static caravans on sites where the caravans  never move. They have, or had, wheels but really are a small home. Any external cables can be damaged by mice, rats or squirrels and can be dangerous. The supply R.C.D. and internal R.C.D. should be carefully tested as the caravans are to be TT earthed and rely upon the R.C.D.s

Recently I inspected a static caravan prior to doing some work. The supply was from a small brick built supply building. It supplied three static caravans. The three were protected initially by a single 300mA S type R.C.D. Then the three  caravans each had 30mA R.C.D.s and a B40 M.C.B. for each hook up point. When I took the cover off the consumer unit inside the caravan it was supplied in 1.5 3 core flex which ran down to a blue 16 Amp caravan plug under the caravan. As the heating and cooking are mainly by gas there have so far been no overloading problems, but new electric heaters will require the upgrading of the supply cable from the 1.5mm2 3 core flex. Incidentally the consumer unit contained a B32 M.C.B. for the ring final circuit.  But most sites restrict the supply to 16 Amps. maximum for each caravan. (708.55.1.5.) but B.S. 7671 states this as being a bare minimum rating.

The site supply has not been maintained or tested for many years, and some metal enclosures in the supply building have rusted so much that a finger can be poked inside them. So they may be 20 years or more old.

I doubt that the brick building R.C.D.s have been tested at all in many years.

721.411.3.1.2 requires structural conductive parts which are accessible from within the caravan or motor home to be bonded to the caravan's main earthing terminal. I take issue with this, especially where motor homes are used and may be supplied by a P.M.E. supply at anytime, such as on a house drive etc.

Z.

AJJewsbury said:

And some live tests too - e.g. RCD operation.

The 9th Edition (2022) of IET Guidance Note 3 Inspection and Testing illustrates (Figure 2.37) a test method for testing 30 mA RCDs in caravans, which avoids unwanted tripping of an RCD protecting the socket-outlet to which the caravan connects.

If it's the illustration i think it is it's also handy for testing cascading rcd's as well.( i know not fully compliant) e.g i had a supply to a garage the other day on an EICR where there was an rcd in the house protecting the supply cable and an rcd in the garage board. 

Gary

aligarjon said:

If it's the illustration i think it is it's also handy for testing cascading rcd's as well.( i know not fully compliant)

There are illustrations for the general installation case, as there are other occasions where sending residual current back down the protective conductor might cause erroneous readings etc. (e.g. with small generators, say 5 kVA or less, or where protective conductor currents might affect the test).

However, I can see that some configurations of domestic prosumer's electrical installations (PEIs) may need cascaded RCDs.

The 'not fully compliant' statement (presumably regarding selectivity?) is potentially a moot point, because it is, of course, mandated by BS 7671 in certain circumstances - caravan connection socket-outlet and within the caravan itself being a good example.

Yes i was referring to selectivity, and in this particular case not an issue, or likely to. 

Gary