Just sent a letter to the QST Editor with respect to incorrect advice given in a recent issue (The Doctor is In, August 2014, Page 55): I read with interest the column with respect to powering an amateur radio amplifier from a residential 240V, 1 phase, 3 wire power source. The column editor stated that two (2) breakers should be installed in the home electrical panel to feed each ungrounded, current-carrying conductor from the amplifier. From an electrical safety standpoint and the provisions of the National Electric Code, NFPA 70, this advice is dangerous. Reference NFPA 70, Article 250.15. To summarize; an overcurrent condition shall open all ungrounded conductors via the overcurrent protection device (circuit breaker). Two (2) single pole breakers can be used but a connecting bar SHALL be installed that connects both handles so that a fault will cause both breaker handles to activate. The danger is that faults will often only trip on one leg of the circuit corresponding to the portion of the waveform at that time. If a ham installs two single pole breakers that are not connected, then only one side may trip, leaving one leg energized. This presents a definite electrocution hazard as the ham will assume that all parts of the 240V circuit are deenergized. Solution: Install a two (2) pole breaker of the appropriate amperage and AIC rating.
Posted on: Wed, 23 Jul 2014 12:58:27 +0000
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