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ISO DC bus off light


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Hi, All

Normally when the battery is turned on you will get 4 AC and 3 DC bus off light, tie the DC bus then all three DC buses will be powered.

On tail # 74-4704 the ISO bus off light will extinguish when the battery is turned on, with out DC bus tie SW tied? The ISO off light will not press to test at this time. When the DC bus tie is tied the ESS and Main DC lights extinguish and the ISO will Press to Test. I guess this was the original operation, but was changed by a TCTO to the normal way listed above.

Does anyone know what the TCTO is that changed this or why it changed?


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The TCTO that was for the modification for the isolated DC circuitry was 1C-130-941. The result of this modification will alert aircrew of this condition so that battery

power conservation measures may be initiated to limit power usage to essential requirements. As far I know this TCTO should not have affected the press to test function. All the lights are jumpered together for the press to test. Where is this aircraft from? When the Battery is turned on, the Isolated bus is always powered. This is what bus the lights are powered off of.

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