An overview of our safe working practices
Now I would like to refer you to the image above which lists a very clear step-by-step procedure that we want you to follow at every job you visit without fail. Throughout the course, we will keep going back to this until it is routine for everyone.
The first step is to visually inspect the plug, socket, and mains cable for any damage which could include any bad previous repairs, severe safety concerns, signs of overheating, and electrical supply issues.
The damage to the wall socket above is a good example of a customer trying to draw too much current through a standard socket, this is quite common when they try to run appliances like tumble dryers via an extension lead connected to the socket, but it could also indicate the electrical connections in the socket are not tight enough which would cause arcing and then generate too much heat. The same fault could also be caused by the electrical connections in the plug not being tight enough.
The image above is a good example of a possible rodent infestation such as mice or rats. These little fellas love chewing cables!
The image above is a good example of the connections in a terminal block not being tight enough which causes the supply to arc and then generate too much heat. It could also be caused by the supply cable and fuse not being rated correctly for the power consumption of the appliance.
The image above is a good example of a dangerous repair, as you can see the fuse has probably gone and somebody has decided to wrap it in tinfoil, it also looks like they have used 6mm twin and earth cable which is designed for hard-wired appliances that need to draw more current than a standard 13a plug can provide. There is a good chance the cable and the appliance being overrated for the plug is what will have caused the fuse to go. Because this is something you might encounter it would be good practice to always remove the fuse from a plug to inspect it.
If the customer reported a power fault with their appliance, then just by visually inspecting it you will have already located the problem but this doesn’t necessarily mean that it is the root of the problem and further investigation would be required.
Once the visual inspection has been carried out and you are satisfied everything is ok then it is time to do the Earth Loop Impedance Test from the wall socket the appliance is plugged into (freestanding machine) or the terminal block if it’s a hard-wired machine. We will discuss this step in more detail in the module to follow (see Earth Loop Impedance module) but put simply we do this to prove the socket the appliance is using is safe for the customer.
If you are satisfied with the results from steps 1 & 2 then the next thing to do is an Earth Continuity test. Just like step 2, we will go into more detail about how we do this in the module to follow (see Insulation Resistance and earth continuity module) but put simply this test is to prove the appliance has a satisfactory earth connection to any exposed metal parts of the cabinet that the customer can touch.
Following after steps 1 – 3 is the Insulation Resistance Test, again we will go into more detail in the modules to come (see Insulation Resistance and earth continuity module) but put simply this is a form of stress test to make sure there are no components leaking to earth which would cause the appliance to trip the MCB/RCD in the consumer unit or in a worst-case scenario cause an electrical fire.
This is a functional test to try and confirm the fault that has been reported. Some machines will have a built-in service mode for engineers that will allow them to test certain functions or read fault codes, but some won’t and you might have to put the appliance on a short program to observe what it’s doing or not doing. It is also worth mentioning that sometimes the fault will be obvious and, in that instance, a functional test at this stage may not be required.
This step is all about diagnosing the fault and then either repairing the faulty component or replacing the faulty part. How effective this step is, is all about you as an engineer.
Before you can perform a function test to see if the repair is successful you will need to repeat steps 3 & 4, firstly to make sure the appliance is safe to connect back to a power supply, and to make sure you haven’t created any other electrical faults during your repair. For this step to work, you must have done the Earth Continuity Test and the Insulation Test before the repair so you have some readings to compare to your final set of tests to.
Now you have proven the appliance is safe to reconnect to a power supply it is time to do a function test. This test is to prove to yourself and the customer that the reported fault is no longer present and that the machine is now functioning correctly within the manufacturer’s specification.
As we mentioned earlier on in this lesson, these steps must be followed on every visit almost religiously and I can promise you if you follow these steps and make it part of your routine then it will enable you to do the best job possible to the highest standards possible.