Many amateur transceivers use a Molex like 6 pin power connector in a 3 x 2 array of pins. These connectors are used on many Icom, Kenwood, and Alinco radios, and possibly some other brands.
At least some proprietary AC power supplies for these transceivers use pins 3 and 6 of the connector for control of the AC power supply and they may have AC line voltage present on one of those pins even when the power supply's power switch is off. An example is the Kenwood PS-30, where pin 3 is connected to unswitched AC line voltage.
Though these power connectors are polarised, the scheme used does not effectively prevent incorrect engagement of plug and socket. It is quite easy to incorrectly engage one row of pins of the plug and socket when the plug is rotated 180 degrees from the correct alignment. If this is done, the AC line voltage is applied to the +12VDC line of the transceiver, whilst the power supply -12VDC lead is applied to the transceiver ground even if the power supply's switch is OFF.
Note that excessive force is not required to mate the plug and socket in this way, there is less physical resistance to this connection than when mating the connector up properly.
The results of such a connection are high voltage and fault current, which are likely to be catastrophic to the transceiver, but of more importance, could result in a transceiver chassis that is at AC line potential if the ground connection is not made or fails before a protective device operates, giving rise to a serious risk of personal injury or death.
All amateurs should review their use of AC power supplies with these transceivers to determine if this hazard exists in their station, and if it does, to take action to prevent accidents. The work around is to never insert the DC power plug from an AC power supply into one of these transceivers unless the AC line cord is removed from the mains power outlet.
In my own case, I modify the power supplies to disconnect the AC control wires from the transceiver cable. Of course, you should only attempt modification of equipment if you are competent to do so, and such modifications may void any warranty. If you are not competent, you should seek the assistance of a competent person.
Use this information entirely at your own risk.
Note in the picture above, that pins 3 and 6 are those on the right hand side, and have no contacts fitted to this modified power supply.
© Copyright: Owen Duffy 1995, 2021. All rights reserved. Disclaimer.