Brats FLC Safety

Bredhurst Receiving and Transmitting Society

7. Safety
Now most people think that safety is something that is an annoying inconvenience but it is not that at all - its one of the most important subjects in the hobby. It may be a bit of a pain but it does need to be learned. In the whole of this section think about preservation of life - now that you have entered the hobby we want you to continue to enjoy it and think of safety all the time. Safety 9a Sources of danger: mains, power supplies and high current batteries. 9a.1 Recall that high voltages carry a risk of electrocution and high currents carry a risk of overheating and fire. Mains When you were young your parents will probably have told you to never play with electronic things. However, did you ever understand why ? Well the reasons were :- Many mains operated electronic items have high voltages flowing through the cables and in some of the circuitry. These high voltages with an associated flow of current would almost certainly be enough to ELECTROCUTE you. If you are wearing any sort of jewellery i.e. rings, wrist watches etc. these must not be allowed to touch the circuitry as they could make contact with say a "live" wire which would complete the circuit, through you, and lead to your ELECTROCUTION. High current batteries But dangers also lie in wait for your with the humble nicad cell and car battery. Both of these types of battery can deliver high current even though it is a low voltage. Elsewhere you will have learned (will learn) that :- power = voltage times current so a 1.2 volt nicad delivering 20 amps for a short time is actually delivering 24 watts of power, which is about the same as the average soldering iron. The heat generated could easily burn you. Even greater power can occur with a 12 v battery which could deliver for a short while 100 amps which is 1200 watts more than a small electric fire!! Thus there is danger in high voltage from electrocution and high current from heat (burns) Power supplies A power supply converts the Mains 230 Volts down to 13.8v to run amateur radio equipment and hence the Power Supply in a common piece of equipment in the amateur radio shack combine both the Mains and High Current and so both the dangers listed above apply to power supples. 9a.2 Recall why mains powered equipment should have a safety earth. Recall that special care is needed with earthing arrangements if your house has PME. Recall that details of PME earthing can be obtained from the local electricity supply company and are covered in a separate leaflet. Have you ever heard about a topic called Earthing? Well it gives an extra way of protecting you should your electronic / electrical equipment develop a fault. Imagine that a stray wire inside a piece of equipment has come loose. If this happens to be the "live wire" and it touched the case and there was no "earthing" ( or earth) then the case also would become live and we would have a possibility of electrocution should you touch the case. To greatly reduce this risk equipment should have all casing "earthed" - that is a lead attached to the case (internally) and then the lead connects to the fused plug via the normal mains lead. Now if that "live wire" came loose and touched the case it would ,what is called, "short" to EARTH and by doing so blow the fuse and thus shut off the electrical supply to the equipment and make it safe. However, if your house has PME you will need to take more care. If in common with most people entering this hobby you have no idea what PME stands for then at least you know it must be something technical and that basic (not in detail) information needs to be know:- Learn that you can find out information about PME earthing from your local electricity supplier. That there are dangers associated with operating an amateur radio station if RF earthing is also provided Oh yes what does PME stand for ?? PME stands for Protective Multiple Earthing 9a.3 Recall that a correct fuse must be fitted to all electrical equipment. and that this is in the live wire of mains-powered equipment and according to the manufacturer's instructions in low powered equipment. What is a fuse ? A fuse is a special part of a mains plug or other circuit which has a very relatively thin wire running through it. A fuse is said to "blow" if too much current flows which makes the wire disintegrate or even vaporise. Thus the purpose of the fuse is to blow if there is a fault condition in a piece of equipment, or in its connecting cable, which is causing too much current to be drawn. The purpose of the fuse is shut down the supply thereby protecting the supply and the resultant action also has a secondary effect to try to reduce damage to the equipment and supply cable and especially to try to prevent a fire. You should always think of the fuse as the last defence against disaster !!! If it blows then sort out the problem, or get someone else to do so before re-using the equipment. 9a.4 Recall to work only inside equipment which is disconnected from the mains. At this stage of the hobby taking off the covers and having a poke about inside is likely to do more damage than good. Modern equipment is so complex that even with circuit diagrams and pictorials of the circuit boards it is still not easy to see where a fault lies. But I want to see what is inside - spoil sport !!! However if you must risk doing more damage to your non-functioning piece of equipment there are several major safety rules:- Switch off the main supply at the socket Remove the plug from the socket before opening up the equipment. Do not touch the circuitry with your hands - capacitors can remain charged at mains voltage even after the equipment is turned off !! 9a.5 Recall the correct way to wire a 3-pin mains plug. This is how to FIT a 13AMP PLUG Three-core flexible mains lead is normally round, in shape, with an outer plastic covering. You need to take off about 40 - 50 mm of the outer plastic coating of the cable with a pair of wire stripers or knife. Take off the front case of the plug, Undo the wire grip and place the cable in through the grip and then screw back down tightly. Put the blue (neutral) wire in its grove and cut the wire so it goes fully into the socket then remove 5mm of the covering on it. Do the same with the yellow and green (earth) and brown (live) wires. Make sure there are no frays or whiskers on any of the wires so twist all the strands of each wire together. Push each wire to the its correct terminal and screw each down tightly. When you are satisfied that all are properly in place and each wire going to the correct terminal put the cover back on and screw down tightly. Which wire went where ?? Yellow Green to EARTH, Brown to LIVE, Blue to NEUTRAL. Look carefully at the picture above and identify three things that are wrong. See the bottom of the page for the answer. 9a.6 Understand the need for a clearly marked switch to turn off all station equipment in case of emergency. With most if not all the equipment in the radio shack being connected in some way to the mains it should be common sense that there should be a clearly marked switch to turn ALL the electrical supply, to all equipment, in the shack clearly marked. Then in the event of an emergency where the accident is likely to have been caused by electricity the switch can be readily turned off. 9b Actions to be taken and avoided in the event of an accident. 9b.1 Recall that, in the event of an accident involving electricity, the first action is to switch off the power. Recall that the casualty must not be touched unless the power has been switched off. In the case of an accident that involves electricity, which hopefully will not happen to you. Do not touch a person until you know definitely that the power is switched off. It is important to take the following steps. Turn off the power at the main switch. This should shut down all close electrical installations, but if you are unsure switch off everything at the main electricity switch and have a torch handy as all the light will go out !!! When you know for sure the electrical supply has been cut off, move any cable or portable plug socket or what ever appears to be in contact with the person. Then very carefully, ideally with a wooden broom handle move the person clear of all electrical contacts. Place the person in the recovery position and see what ever other help you can give. If necessary get someone else to call 999 for emergency help Switch off the power THEN attend to the injured person 9c Station layout and tidiness 9c.1 Understand the reasons for not having wires trailing across the floor: trip hazard and the risk of frayed insulation. Trailing wire and cables are trip hazard and risk of fraying!!! You must always keep your radio shack neat & tidy. There must not be any loose wires trailing across the floor as this could be a electrical hazard as you could trip over or pull wires out of sockets and hurt yourself. Also cables that are walked over time and time again as well as being a trip- hazard could fray or damage. So even without cables all over the place it is a good idea to regularly check all leads are in good condition and to replace as necessary. 9c.2 Recall that elevated wires and antennas must be suitably located and secured. When you put up wires, feeders etc, outside think of the location and how they are fixed. Is the location suitable or could it be knocked by say a window cleaners ladder? If it were knocked would the fixing be secure enough to keep the cable in place? 9c.3 Recall that antennas and feeders should not be sited close to overhead power cables. Extra care should be taken when putting up antennas. Antennas must never be placed near overhead power cables as these carry high voltages and are not necessarily insulated. Thus there are two dangers:- Touching the cable whilst putting up you antenna The ladder you are standing on touching the cable Both could result in death from electrocution of if not that then being thrown from the ladder, and the fall to the ground might kill you. 9c.4 Recall that antenna erection is potentially hazardous and that it is advisable to have someone to help you. Understand the need for at least one adult should be present. You must be very careful when putting up your antennas. If using a ladder make sure you have at least one adult with you :- so they can hold the bottom of they ladder in case the ladder moves so they are there and can obtain medical assistance quickly should it be needed they can warn anybody getting to close to the ladder that you are working overhead What if I drop something whilst up the ladder ? Let's hope you don't but ALWAYS have the person at the bottom of the ladder wearing a hard hat, in case you do drop something and it is a good idea to wear a hard hat yourself whilst up the ladder. 9c.5 Recall that antenna elements should not be touched whilst transmitting and should be mounted to avoid accidental contact. Note: this does not apply to low powered devices such as hand-held equipment. What are antenna elements ? These are the wires or other metal parts that make up the antenna. When you are transmitting the sole aim of the antenna is to radiate your signal efficiently. To do this the RF signal will at times be at high voltage and other high current along the antenna. There is thus a danger of RF burns even at relatively low levels of operating power. Don't touch an antenna when it is being used to transmit a signal 9c.6 Recall that particularly high antennas may need special protection against lightning. The saying goes "put your antenna as high as possible". This is a good idea but when a storm is about then the static in the air will arrive at your antenna and be conducted down to the shack. So as to reduce damage to equipment disconnect antennas and wall sockets during a storm and preferably earth the aerials. Antennas, and particularly high antennas, need special protection against lighting. At this level of the hobby that is all you need to know, as good lightning protection is difficult to achieve. 9d Safe use of headphones 9d.1 Recall that excessive volume when wearing headphones can cause damage to hearing. You must take care when using headphones that the volume control is set to a relatively low volume. Cracks and pops that are heard from time to time increase the volume and this could cause damage to your hearing is the levels reach excessive levels. Answers to the plug picture question 1 There is the bare wire end of the Live wire sticking out through the end of the connector 2. There is the bare wire of the Neutral no far enough into the Neutral connector 3. The cable through the cable clamp is not in far enough to prevent it being pulled out in the event that someone tripped over the cable. Did you spot all three ... it is subtle difference like this you need to look out for in the exam.