# Series and Parallel Circuits

All hams should have at least a limited understanding of basic circuits, and this means being able to differentiate between series and parallel components.

Besides numerous license exam questions (dozens below in green boxes; knowing helps you pass the exams), some technical discussions in ham radio will throw the terms around so let’s explore the matter here.  In addition to our own presentation, some excellent web references are given at the end for further (and often more interesting) information.

Before jumping into circuits, let’s discuss series and parallel connections.  Visualizing this will help us understand series and parallel circuits.

As the name suggests, series connections are lined up end-to-end.

We’re demonstrating with resistors but the principle applies to any two-terminal component: capacitors,  inductors, diodes, cells/batteries, and light bulbs can all be wired in series with two or more of each (or a mix of different parts).  Lining them up terminal to terminal makes a series connection.

Schematically, 3 parts in series looks like this:

From this simple schematic we intuitively see that the current flowing through a series string has to be the same though the chain; there is nowhere else for electrons to flow (current).

Equal current is one way of defining a series circuit.

Also as the term suggests, parallel connections are side-by-side.

Again, demonstrating with resistors and again, the principle applies to any two terminal component.  Arranging components across each other makes a parallel connection.

Schematically, 3 parts in parallel looks like this:

From this simple schematic we intuitively see that the voltage across parallel components must be the same.

Equal voltage is one way of defining a parallel circuit.

We just learned that current is the same through components in series, and voltage is the same across components in parallel.  What about  the voltage across series components, and current through parallel components? Continue reading

# 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.

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.

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.

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.

While fuses and circuit breakers do not directly provide shock protection, they may do so Continue reading