Tuesday, 3 April 2012

FAILED - A pair of controllers

If there is one sure-fire way to fall out with all your mates, it is to tell them that their electrical equipment has failed a Portable Appliance Test (PAT). Being a gluten for punishment I offered to do just this. The first thing to understand is that portable appliance testing is there to check that the appliance will remain safe under fault conditions. It is not about testing to see if the appliance is working properly. The usual retort, when the owner of a piece of equipment is on the receiving end of a red FAILED sticker is to state that it has been used for years and it works perfectly. Once the concept is explained, most owners are only too pleased to know there is a problem and will have the appliance repaired. This can be as simple as replacing a missing screw or fitting a complaint fuse. Sometimes it can be a bit more involved or even bizarre as the following will show...

Oh dear, failed stickers!
Last Saturday I was carrying out some PAT testing at my local Meccano club. Most of the equipment that passed the visual check passed with flying colours. There were a few dodgy looking extension leads that ended up being condemned for having damaged cables, socket and plugs or non-compliant plugs. Some had all four!

It was a lump of cardboard!
On the whole, the most common reason for failure was either non compliant-plugs or bad cable restraints. All of which are easily rectified. There were three items that I could not pass on the day one was a 110v American power supply that I had to bring back here to test - it passed - the other two were a different matter. 

One is an Orbit controller of relatively modern vintage. This looked good from the outside no problem there, all the case fixings were sound and there was no visible damage. The unit was fitted with an IEC lead connector so no issues with the cable. The problem was that something inside was loose. All modern transformer cases have to be user unserviceable, in other words riveted together. This meant I could not open the case on-site. There is a limit to how many tools I want to take out to a 'favour' job and as I didn't have the van with me, there was no backup outside!  So the unit came back to the workshop for further inspection. It could have been anything. there was no way I was going to even test this unit until I knew what was loose inside. After removing the pop rivets that held the case closed, I was amazed to find a piece of cardboard wrapped around the mains transformer.

The case is closed and fixed with pop rivets
What on earth it was supposed to be doing is beyond me. It did not need to be there as the high voltage terminals are all solder connections to parts that are fixed in position, therefore insulation is prided by 'air' (a physical separation held in place by mechanical means). The cardboard was removed and the screws that hold the transformer were sealed and marked not to be removed. This unit and its ICE lead can now be tested.

Old colours and this knot is the cable
restraint. That will have to go!
New cable and a cable tie used as a cable restraint will
need trimming before the case is closed
The other controller was an ancient Triang unit similar to one I had in my first train set over 50 years ago! This one was in a bit of a state. Screws missing, non-complaint plug and fuse, bad cable restraint and suspect, non-harmonised (wrong colour insulation) cable. On the bench, the case was opened and a new cable and restraint fitted. After a good blow out with the airline the case was reassembled using pop rivets. This unit too is now ready for testing.


It seems that we modellers hang on to transformers and controllers for years. Apart from obvious damage to cases and the power cable, plugs are the most frequent reason for failing the visual check. A modern, compliant plug has insulated live an neutral pins and is moulded with all the relevant approval logos and numbers as can be seen here on the left. The plug below, on the right is the old type without the insulated pins, secure fixing screw etc.  

Tomorrow we will see if the controllers pass the electrical tests and get nice green stickers!


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