Safety

Question File Number 10



Exam Page | Introduction | Control Panel | Booklist | Order Form | Questions | Study Notes

Amplifier | Mixer  | R Circuit | Resistors | Signals

Abbre  | Certificate | CW  | CW-Test  | Exam  | IARU  | ITU  | NZART  | Internet  | Syllabus

01 | 02 | 03 | 04 | 05 | 06 | 07 | 08 | 09 | 10 | 11 | 12 | 13 | 14 | 15
16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30


Station Safety

Equipment used in an amateur radio station may contain very high voltages. There may be voltages high enough and the the current may be enough to kill you. This is serious business. Be very careful.

Until You Know What You Are Doing - KEEP OUT

Keep your fingers and other conducting material away from the insides of power supplies, amplifiers and transceivers.

Electricity can, and does, kill. It takes between 100 and 200 mA to kill you, 10 mA to frighten you, and you can feel 2 mA. An ungrammatical expression sums it up - It's the volts what jolts but the mils that kills. Your skin resistance controls the strength of the current. Head to toe, it can be a dry 500 000 ohm or a wet 1000 ohm. A typical figure for hand to foot, the usual path of the current, is 500 ohms. Between the ears the resistance is about 100 ohm.

Common-sense precautions are very necessary. Work on live gear only when absolutely necessary, and, even then, keep one hand in your pocket. Even after switching off, earth all high voltage points to discharge capacitors, as some of these retain lethal charges. Ensure that equipment is well earthed. Stand on an insulated floor and avoid working in damp conditions.

Display a mouth-to-mouth resuscitation chart on the shack wall. Do not be lulled into a sense of false security about low voltages. Death by electrocution has occurred at 42 volt.

tick 

Don't Play With Anything - Unless You Know What You Are Doing

THINK OF YOUR OWN SAFETY. Should you come across someone who has been electrocuted, ensure that all live circuits have been turned off before attempting a rescue.

An RF Earth

Your station must have an RF earth. All modern equipment has an earthing terminal on the back panel and this should be connected to a good earth. Drive a length of water pipe into the ground - a couple of metres long. A thick copper cable should be connected from the back of the radio to the earth pipe.

Connecting to The Mains

Other Regulations that are not a part of the radio world but which affect you are New Zealand's electrical regulations. These apply up to the primary winding of any transformer and cover the AC side of any mains power supply. There are published circuits, particularly from American sources, which do not comply with the New Zealand requirements.

In New Zealand the MEN (Multiple Earthed Neutral) system of mains wiring is used. The neutral wire is normally connected to earth at the transformer or, in a domestic installation, at the switchboard. Thereafter, it should be completely isolated from earth. A separate earth wire is run to all equipment, and used to securely bond any exposed metal to earth at the switchboard. If a live wire now contacts the metal, a short-circuit to earth is caused and the fuse or circuit breaker will operate. If this was not done, the metal could remain live and be a real hazard.

Regulatory Requirements That Must be Observed

1. It is illegal to switch the neutral wire only. If this is done, any capacitive or resistive leakage will raise the potential of the chassis to 230 V, the full-phase voltage. While a lethal shock under these conditions is unlikely, a non-lethal shock may be very unpleasant. The danger is when two chassis, livened to different phases or one to phase, one to neutral, should come into contact. Similarly, if a fault should occur on a chassis, then there is no way of finding out until an accident occurs. It is permissible to switch both phase and neutral, and if you are operating your equipment off a long extension cord it would probably be safest to do this.

2. It is illegal to insert a fuse in a neutral line, even if the phase is also fused. There is no guarantee that two fuses of nominally the same rating will fail at the same time. If the neutral one goes first, a similar situation as when switching the neutral only could arise.

3. For your own protection you should check that all the equipment you buy or construct complies with New Zealand's electrical regulations.

4. A lot of imported Amateur Radio equipment designed for other wiring systems should be modified to comply with the New Zealand requirements.

tick 

Flexible Cords

Wiring

This diagram shows the colour-coding in use with flexible mains cords. The more modern equipment use the colour code: brown, blue, green/yellow.

Rescue Breathing

While on the subject of safety, it is a good idea for both you and someone in your household to be able to carry out rescue breathing or some other form of resuscitation if required. Classes are usually available in most communities.

If you find someone who has suffered an electric shock, be sure to switch off the supply before attempting to make a rescue. Avoid further tragedy.

tick 

Safety Devices

The importance of having a good earth lead from an appliance cannot be over-emphasised. Check your appliances and equipment regularly.

If you are going to work on a mains power supply unit which is transformer-less, or which has an unusual transformer arrangement, it is advisable to use an isolating transformer between that power supply unit and the mains.

An isolating transformer is a double-wound transformer - it has identical primary and secondary windings. The secondary floats rather than having one side connected to earth. This is unlike the mains which has the neutral lead connected to earth at the switchboard.

Both wires from the transformer are hot with respect to each other but not hot with respect to earth. Should a fault develop in an attached appliance such as a leakage to a metal case, that case will not be hot (and dangerous) with respect to earth.

An earth-leakage circuit breaker or residual current device is another safety device that you may find in some installations. It consists of a relay arranged so that if the mains phase and neutral currents become unequal, as could happen with a fault in an appliance causing a current in the earth wire, the supply is very quickly switched off.



tick 

Further details about NZART can be obtained from the web at  NZART. There are several categories of NZART membership which include Transmitting and Non-Transmitting. Anyone interested in radio can join. E-mail enquiries to  nzart@nzart.org.nz will bring details about NZART Membership. On-line details about  Joining NZART - Membership has advantages.
Contact Webmaster at e-mail  webmaster@nzart.org.nz
Compiled Mon Nov 29 2010 at 8:11:49pm


01 |  02 |  03 |  04 |  05 |  06 |  07 |  08 |  09 |  10 |  11 |  12 |  13 |  14 |  15
16 |  17 |  18 |  19 |  20 |  21 |  22 |  23 |  24 |  25 |  26 |  27 |  28 |  29 |  30

Introduction |  Control Panel |  Booklist |  Order Form |  Questions |  Study Notes