Isolating transformer

Depends a bit on how you intend to energise, and what load is connected. If you want things like RCDs to work on the load side, then one side of the secondary will need to be earthed, and that will be your test board neutral. This does however largely defeat the safety aspect of an isolating transformer, except that it will not trip a primary side RCD.

Another aspect to consider is how realistic you want the faults on the test board to be - clearly re-creating a full10KA fault is not prudent, but  perhaps creating a supply that cannot blow a 13A fuse is not that realistic either . Problem is if you make it too good, it will blow the supply side breakers, which I presume is the sort of thing you are hoping to avoid.

I'm assuming that the idea is to test folks ability to wire things up, and to show common errors and their consequences ?

Also is something like a key switch and or a stop button a good idea?

Ben22:

I’m looking to create a training board for apprentices and trying to come up with a way to allow energisation but keeping any faults created separate from the installation, 


im thinking of using an isolating transformer. Unless anyone can suggest another method? 

surely the object of the exercise is for them to find and rectify any and all faults before anyone gets near to energising - ie dead testing and fault finding with instruments and the Mark I eyeball are a key part of the skill set being taught.


I'm pretty sure you aren't actually advocating "bang" testing via a safety source


Regards


OMS

Doubt if it helps but a training board for testing RCD  test meters should be feasable by creating secondary side TNS ie your E & N on one terminal and L on the other terminal of the output side. But not much to merit it.


If you are just using it to show working examples of lighting etc then a 12v SELV transformer and little LEDs could be a safe option

When I was an apprentice before the old Queen died in the Post Office trading school in each bay was. 24V transformer you connected your installation to on completion of your model of installation excellence. 


The test rigs you you did your fault finding on at a later course were 110V. The axe hanging over your head was if you blew a fuse you got back coursed to do it again. One of the faults on my last test was a coin behind a lamp plus a few other bear traps. 


In the PO training centres and the PO technical college you could not expose students to dangerous situations in training by putting on simulated faults on installations, machines, lifts, gas, conveyors etc. that could kill or injur. The same at the college I taught at. 

I'll show my different history here, but thinking back to the electrical engineering dept labs at Kings In London (basement of the strand palace), when things like transformers and AC motors and so forth were being taught, there was in effect un-isolated mains in  use on the bench with no special precautions, and in at least one  experiment  mains was present on 4mm screw terminals on a variac. I do recall a case in that experiment where one student got a bad shock, when the neutral "banana plug"  had come unplugged from his experiment. After that there was earnest debate about if the lab supplies needed to be fed via an RCD. In the end it was decided they did not, but isolator switches were fitted so the lab supervisors could then kill all the power to the students from a single point. That took place around 1990, so was well after the HASWA and so forth had got going. I was a postgrad at the time, and I was party to the discussions about what if anything needed changing, as like many others I augmented my income by demonstrating in the practical labs from time to time.  In many ways the labs and their equipment were a throwback to  decades previous, having had very little investment since the 1970s, but at the time you do not realise it unless you have been somewhere else as well to compare.

This forum feels like a specialist club, since I was once Head of the Electrical Department of the CEGB Training Centre in Leeds "Whitehall Road".?

When I was responsible for completely refurbishing this in the late 80s, the main electrical safety precautions were a main contactor with residual current protection (separate CT), widely distributed emergency stop buttons, locking off for isolation, good discipline and supervision.  Reduced voltages were in use as appropriate. I’m stretching my memory, but I don’t remember a situation where , supplying at reduced voltage such as 25v centre tapped (standard for portable lighting) or 12V  DC wasn’t sufficient.  We ran some large motors and MG sets, three phase and DC, but with everything “boxed up” and the greater danger being heavy rotating machinery. Our HV switchgear didn’t use any HV except for a 5kv megger. We had some derogations from the CEGB safety rules to reflect the reduced risk designed in, but this was a former Power Station and I had to issue permits etc under the rules for some circumstances.


Sadly I don’t have a record now for posterity, although the facility which trained me and where I later became a trainer, before moving up to Leeds is here. http://www.cegbmidreg.co.uk/ptc/ptcmenu.htm


PS Mike, I have found many of your contributions excellent and informative , as I have said in another forum my capability is more “ex” than “expert”  ?