Electrical Hazards

Safety is an important topic in ham radio.  There are 11 questions on electrical hazards in the USA Technician class license exam pool, 13 questions on tower safety and associated grounding, and 13 questions on radio frequency (RF) hazards.

Several of these have been used by us previously but in retrospect we should have given the safety topic more airtime, pun intended.  New hams are unlikely to have antenna towers so we don’t plan to discuss tower safety much.  That leaves electrical and RF hazards to cover.

This post will address general electrical hazards and related safety; a future post will focus on RF hazards.

Radios and accessories are electrical devices so let’s start with the most obvious hazard: electric shock, which is caused by current flowing through a human body.  Current is useful in electronics but harmful when flowing through a person.  Current can disrupt heart and lung function at even low levels.  It can also cause unwanted muscle movement, or prevent it (can’t let go).  At higher levels, electric current will damage skin and internal organs.

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There are many factors in electric shock and there are other electrical hazards.  But this is a big one and you should avoid touching live circuits.

Fire is another electrical hazard.  When too much current flows in conductors, the wires can get very hot and ignite combustible material.  In fact, the US National Electrical Code is actually a document of the National Fire Protection Association (NFPA), not a government agency.

To limit the risk of fire and other damage, every power circuit needs some form of  protection.  Fuses are quite common; their internal metal melts at a pre-determined current to disconnect power.

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Also, a smaller (amp rating) fuse can safely be inserted in a protective circuit but one should never put in a larger one.  A fuse is sized to the circuit requirements and wiring  is sized to the fuse.  So a higher-ampacity fuse will not properly protect the wires or the circuit and serious overheating may occur in both AC and DC power circuits.

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In addition to one-time use fuses, circuit breakers are another popular form of circuit protection; these may be reset and are often used as an on/off switch.

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While fuses and circuit breakers do not directly provide shock protection, they may do so indirectly.  Should a fault develop internally to an electrical device, hazardous voltage could appear on the surface a metal-clad appliance.  By grounding metal enclosures, an internal fault should blow a fuse or trip a circuit breaker, thus interrupting a shock hazard.  This is why most AC power cords have a third wire which is grounded, and it should connect to the metal chassis.  In the USA this is a green wire; universally (and internationally), green with yellow stripe.

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In addition to circuit protection (fuse, breaker) and grounding, shock protection is further enhanced by using ground fault protection.   Ground fault circuit interrupters (GFCIs) work by monitoring supply and return current levels.  Any imbalance indicates some current leakage to ground (earth).  The assumption is that this current is passing through a human body and triggers a circuit shut-off at a specified level (5mA in USA).   By plugging radio and test equipment into a GFCI outlet or GFCI accessory, the shock hazard is minimized.

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Not all electrical hazards are from household AC line voltage.  Most modern radio gear operates on 12VDC power. Circuit protection still applies; fuses are needed at 12VDC.

12VDC is the nominal voltage of a vehicle battery for mobile use.  Portable operation is a popular ham activity.  Along with the growing use of solar power cells, 12V batteries are used as a power source or for backup.

Many of these batteries have tremendous energy capacity; car batteries have enough juice to make huge sparks and melt metal tools.  Even smaller lead acid and lithium batteries pack a huge punch.  When working with any kind of battery, avoid shorting it out with wires or other metal.  Also charge batteries properly.

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One last general shock hazard is not so obvious.  Aluminum electrolytic capacitors are frequently used in power supply circuits of radios and other electronics.  These can store hazardous voltage for some time after power is switched off.  Be aware when working in or on equipment with large capacitors.

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To reinforce the importance of the safety topic,  the USA General class license exam pool has 15 questions on electrical hazards and tower safety and 12 questions on radio frequency (RF) hazards.  The Extra class exam pool has 11 mixed-category hazard and safety questions.

So have fun with ham radio but keep all this in mind and do it safely!

A little supplement on high-power electrical systems which hams may encounter:

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