Mains wiring, to code
Which of the following is covered by the National Electrical Code?
Electrical safety of the station.
The NEC is not FCC material, and it is enforceable where you live. It governs the wiring; Part 97 governs the transmitting.
According to the National Electrical Code, what is the minimum wire size that may be used safely for wiring with a 20-ampere circuit breaker?
AWG number 12
Which size of fuse or circuit breaker would be appropriate to use with a circuit that uses AWG number 14 wiring?
15 amperes.
The pairing to remember: 14 gauge with a 15 A breaker; 12 gauge with a 20 A breaker. The breaker protects the wire, so it must be sized to what the wire can carry — never larger. A 20 A breaker on 14 gauge wire is the classic dangerous mistake, because the wire overheats before the breaker trips.
Which wire or wires in a four-conductor 240 VAC circuit should be attached to fuses or circuit breakers?
Only the hot wires.
Never the neutral, never the ground. A fuse in the neutral can open while the equipment stays connected to the hot side — live, with no indication.
GFCI
Which of the following conditions will cause a ground fault circuit interrupter (GFCI) to disconnect AC power?
Current flowing from one or more of the hot wires directly to ground
A GFCI compares current going out with current coming back. Equal means all the current is returning through the neutral as it should. A difference means some is returning by another route — through a person, most importantly — and it trips in milliseconds.
Note what it does not do: it does not protect against overload, and it does not protect you from contacting hot and neutral simultaneously. It detects current going where it should not.
Interlocks
What is the purpose of a power supply interlock?
To ensure that dangerous voltages are removed if the cabinet is opened.
A switch that removes power when the cover comes off. In high-voltage amplifier supplies it is the difference between a mistake and a fatality, and defeating it “just for a moment” is how people die.
The stored-charge warning from the foundations safety module still applies: an interlock removes the supply, not the charge in the filter capacitors. Wait, then verify with a meter.
Lightning protection
Where should the station’s lightning protection ground system be located?
Outside the building.
Outside. The entire point is to divert surge energy to earth before it enters the building.
Where should lightning arrestors be located?
Where the feed lines enter the building.
At the entry point, on a grounded panel, with every feed line and control cable passing through it.
Which of the following is required for lightning protection ground rods?
They must be bonded together with all other grounds.
All of them, together, including the electrical service ground. Two unbonded grounds are more dangerous than one — the reason is in the foundations safety lesson, and it is worth re-reading before installing anything.
And from that same lesson: no soldered joints in a lightning ground. The surge destroys them.
Towers
Which of these choices should be observed when climbing a tower using a safety harness?
Confirm that the harness is rated for the weight of the climber and that it is within its allowable service life
Rated for you plus everything you are carrying. A harness rated for 130 kg with a 90 kg climber carrying 20 kg of tools and a rotator has less margin than the number suggests.
What should be done before climbing a tower that supports electrically powered devices?
Make sure all circuits that supply power to the tower are locked out and tagged.
Lock out and tag out. Not “switched off” — physically locked, with a tag saying who locked it and why. Rotators, tower lights, and antenna relays all carry mains voltage, and somebody helpfully restoring power while you are up there is a foreseeable event that this procedure exists to prevent.
The Technician tower rules still apply: never climb alone, harness clipped before releasing your grip, crank-up towers retracted or blocked.
Generators
Which of the following is true of an emergency generator installation?
The generator should be operated in a well-ventilated area.
Carbon monoxide. Every year people die running a generator in a garage with the door open, which is not ventilation. Outdoors, well away from windows and doors, with the exhaust pointed away from the building.
Solder
Which of the following is a danger from lead-tin solder?
Lead can contaminate food if hands are not washed carefully after handling the solder.
Not the fumes — those are flux, an irritant rather than a lead hazard, though ventilation is still sensible. The lead risk is ingestion by hand-to-mouth transfer. Wash your hands after soldering, and do not eat at the bench.
Check yourself
- You are wiring a new 20 A circuit for the station. Minimum wire gauge?
- Your amplifier’s cabinet interlock is inconvenient during testing. May you defeat it briefly?
- What must happen before you climb a tower with a rotator on it?
Answers
- AWG 12. (AWG 14 pairs with a 15 A breaker.)
- Do not. The interlock removes dangerous voltages when the cabinet is opened, and it is the last thing between a lapse and an electrocution. And even with it working, wait and verify the filter capacitors have discharged.
- Lock out and tag out every circuit that supplies power to the tower — and have a helper, an inspected harness rated for your weight plus tools, and a retracted or blocked tower if it is a crank-up.