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Syllabus Sections:- Safety Electricity This section is given for information only and your safety is your own concern and these notes cannot protect you for doing stupid things even if accidental.This web site is made available on the understanding that any information is given in good faith and the BRATS cannot be held responsible for any misuse or misunderstanding. Particularly in this section where any doubt exists a suitably qualified electrical contractor shall be consulted.for more information refer to this pdf file. http://rsgb.org/main/files/2019/12/UK-Earthing-Systems-And-RF-Earthing_Rev1.4.pdf 8A1 50 Recall that lethal voltage can exist in equipment and that live circuits may be exposed as soon as the equipment case is removed. The syllabus text says it all !!! Lethal voltage can exist in equipment and that live circuits may be exposed as soon as the equipment case is removed. There is a saying "It is the volts that jolt but the mills (Milliamps) that kill". It is considered that any voltage above say 40 volts can under circumstances be considered lethal when more that 10 mills of current flow. RCD can trip at >>>>>>>> ??????Of course if you are opening up a valve RF amplifer, for instance, you may have 1000's of volts on the valve that is a very lethal voltage at such low milliamps current. If you have to replace filters or components inside a transceiver then it MUST be turned off, if not you may not only cause you damage but quite possibly the same will happen to the electronic components of the device you are working on. If you have to work on a live system then only use 1 hand out and the other in your pocket, so as to avoid a direct line to your heart in the worst case scenario Also do not ware headphones while working on equipment as a sudden noise may cause you to grab the radio and complete a lethal circuit. There are usually protection devices in equipment which turn off the mains supply when the case is opened but not always so err on the safe side and when opening a case unless the mains power is not only turned off but the mains plug removed that you are entering a very serious situation where death could be the result if you receive an electric shock. ------------------------------------------------------------------------------- 8A2 50 Recall
that in PME systems the main earth terminal is
connected to the neutral of the electricity service at
the consumers' premises TNC-S stands for Terra Neutral Combined Separate, in principle this means the supply to your house comes on a cable that has a combined neutral and earth function, know in the trade as a PEN cable, Phase, Earthed Neutral, PME is a form of TNC-S where the combined neutral/earth is earthed multiple times between the substation and you, PME means Protective Multiple Earth. However PME is not the only form of TNC-S, TNC-S can also be supplied as PNB, Protective Neutral Bonding. This is either a single point connection from a Pole mounted transformer, often rural overhead, or a new supply taken from a existing TNS service, where they join the neutral/earth together. PNB services only have 1 point of earthing, either at the joint or at the consumer service fuse. So in essence the mains earth of your house is bonded or joined as it enters your house to the neutral conductor, which under normal operations for your house all will be fine BUT using faulty Ham radio equipment can cause some additional problems ...see below Any Bonding work MUST be done by a qualified electrician after an inspection by the qualified electrician. It is an offence to do it yourself and not have the work inspected. Take a look at the photos below ................................. The photo in the middle above shows the new connection to the earth block of the earth cable from the internal consumer unit and note the new yellow notice below the earth block which now makes the installation TT. The TT system is where the customer’s installations are connected to earth via a separate electrode ( earthing rod ) which is independent of the supply. The photo on the right above shows the new earth connection to an earth rod and the lead to the meter box in conduit. This was all carried out under a "Minor Electrical Installation Works Certificate" by a qualified electrician.
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8A2
50 continued Recall
that under severe fault conditions PME systems have
the potential to cause fatal electric shocks and/or
fires in amateur radio stations. --------------------------------------------------------------------- 8A2
50 continued Recall
that the RF earth in an amateur Station should be
connected to the PME bonding point in accordance with
the District Network Operator's requirements or the
IET Wiring Regulations to maintain safety under fault
conditions. In all electrical mains work if you are not qualified then you must use in somebody who is electrically qualified !!!! ------------------------------------------------------------------------- 8A6
50 Understand
that no work should be undertaken on live equipment
unless it is not practicable to do otherwise. As
soon as the covers are taken off a piece of electrical
equipment connected to the mains supply there is a danger of
electric shock. The source of a potential shock may not be
easily apparent as the live terminals may be shrouded but
what if a transformer's terminals are not covered ? --------------------------------------------------------------------------------------------------------------------------------
8A6 50 continued Understand
that suitable precautions must be taken to avoid
electric shock.Suitable precautions that can be taken to avoid electric shock if you have to work on "live" mains equipment are :- • consider where potential dangers lay ( in other words do a risk assessment ) • don't just poke about in the equipment if you do not know what you are trying to resolve • use only one hand on the equipment to avoid a path across your heart by touching the equipment with two hands • use only properly insulated tools such as screw drivers where only the tip is exposed • when all else fails stop and put the case back on AFTER having first turned the power OFF
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