WEBVTT NOTE Mains Wiring, Towers, and Generators 1 00:00:00.000 --> 00:00:02.760 Mains wiring, to code. 2 00:00:02.760 --> 00:00:08.339 Question. Which of the following is covered by the National Electrical Code? 3 00:00:09.239 --> 00:00:13.359 Answer. Electrical safety of the station. 4 00:00:13.959 --> 00:00:27.368 The NEC is not FCC material, and it is enforceable where you live. It governs the wiring; Part 97 governs the transmitting. 5 00:00:27.368 --> 00:00:38.453 Question. 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? 6 00:00:39.353 --> 00:00:44.930 Answer. AWG number 12. 7 00:00:45.530 --> 00:00:56.205 Question. Which size of fuse or circuit breaker would be appropriate to use with a circuit that uses AWG number 14 wiring? 8 00:00:57.105 --> 00:01:00.305 Answer. 15 amperes. 9 00:01:00.905 --> 00:01:17.993 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. 10 00:01:17.993 --> 00:01:29.385 A 20 A breaker on 14 gauge wire is the classic dangerous mistake, because the wire overheats before the breaker trips. 11 00:01:29.385 --> 00:01:40.600 Question. Which wire or wires in a four-conductor 240 VAC circuit should be attached to fuses or circuit breakers? 12 00:01:41.500 --> 00:01:44.842 Answer. Only the hot wires. 13 00:01:45.442 --> 00:02:00.293 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. 14 00:02:00.293 --> 00:02:11.025 Question. Which of the following conditions will cause a ground fault circuit interrupter (GFCI) to disconnect AC power? 15 00:02:11.925 --> 00:02:19.134 Answer. Current flowing from one or more of the hot wires directly to ground. 16 00:02:19.734 --> 00:02:29.680 A GFCI compares current going out with current coming back. Equal means all the current is returning through the neutral as it should. 17 00:02:29.680 --> 00:02:38.587 A difference means some is returning by another route, through a person, most importantly, and it trips in milliseconds. 18 00:02:38.587 --> 00:02:53.210 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. 19 00:02:53.210 --> 00:02:58.730 Question. What is the purpose of a power supply interlock? 20 00:02:59.630 --> 00:03:05.800 Answer. To ensure that dangerous voltages are removed if the cabinet is opened. 21 00:03:06.400 --> 00:03:21.627 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. 22 00:03:21.627 --> 00:03:37.160 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. 23 00:03:37.160 --> 00:03:43.280 Question. Where should the station's lightning protection ground system be located? 24 00:03:44.180 --> 00:03:46.884 Answer. Outside the building. 25 00:03:47.484 --> 00:03:55.373 Outside. The entire point is to divert surge energy to earth before it enters the building. 26 00:03:55.373 --> 00:03:59.900 Question. Where should lightning arrestors be located? 27 00:04:00.800 --> 00:04:04.975 Answer. Where the feed lines enter the building. 28 00:04:05.575 --> 00:04:13.455 At the entry point, on a grounded panel, with every feed line and control cable passing through it. 29 00:04:13.455 --> 00:04:20.015 Question. Which of the following is required for lightning protection ground rods? 30 00:04:20.915 --> 00:04:26.315 Answer. They must be bonded together with all other grounds. 31 00:04:26.915 --> 00:04:44.985 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. 32 00:04:44.985 --> 00:04:53.435 And from that same lesson: no soldered joints in a lightning ground. The surge destroys them. Towers. 33 00:04:53.435 --> 00:05:01.395 Question. Which of these choices should be observed when climbing a tower using a safety harness? 34 00:05:02.295 --> 00:05:11.199 Answer. Confirm that the harness is rated for the weight of the climber and that it is within its allowable service life. 35 00:05:11.799 --> 00:05:29.439 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. 36 00:05:29.439 --> 00:05:36.787 Question. What should be done before climbing a tower that supports electrically powered devices? 37 00:05:37.687 --> 00:05:44.796 Answer. Make sure all circuits that supply power to the tower are locked out and tagged. 38 00:05:45.396 --> 00:05:53.928 Lock out and tag out. Not "switched off", physically locked, with a tag saying who locked it and why. 39 00:05:53.928 --> 00:06:10.063 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. 40 00:06:10.063 --> 00:06:22.904 The Technician tower rules still apply: never climb alone, harness clipped before releasing your grip, crank-up towers retracted or blocked. Generators. 41 00:06:22.904 --> 00:06:29.885 Question. Which of the following is true of an emergency generator installation? 42 00:06:30.785 --> 00:06:36.785 Answer. The generator should be operated in a well-ventilated area. 43 00:06:37.385 --> 00:06:55.425 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. 44 00:06:55.425 --> 00:07:00.843 Question. Which of the following is a danger from lead-tin solder? 45 00:07:01.743 --> 00:07:09.536 Answer. Lead can contaminate food if hands are not washed carefully after handling the solder. 46 00:07:10.136 --> 00:07:23.500 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. 47 00:07:23.500 --> 00:07:41.346 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. 48 00:07:41.346 --> 00:07:48.816 May you defeat it briefly? What must happen before you climb a tower with a rotator on it? 49 00:07:54.816 --> 00:08:10.592 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. 50 00:08:10.592 --> 00:08:17.451 And even with it working, wait and verify the filter capacitors have discharged. 51 00:08:17.451 --> 00:08:34.256 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.