B737 NG - Electricals

[owl-attack]

Hello

FCOM - "During a Flight Director or Autopilot ILS approach at glideslope capture. This isolates DC Busses during approach to prevent a single failure from affecting both navigation receivers and flight control computers"

Can some one please explain what single failure to which system are they talking about and how will this affect navigation receivers and FCC is the cross bus tie relay is not open (DC Busses Isolated) during glide slope capture

Thanks
Regards

[NSEU]

Can some one please explain what single failure to which system

I assume they are talking about an electrical short on one of the DC Busses which affects the DC voltage across the whole ship (with the busses tied). Unstable voltages from a faulty TRU might also cause equipment problems.

[EEngr]

electrical short on one of the DC Busses

This, exactly. Until the protection (circuit breaker) opens, the short will pull the bus voltage down to or near zero. With the buses tied, all DC loads will 'see' the low voltage caused by this single fault.

[Raptor71]

Another question on ELECTRICAL.

On the schematics, the iDG is directly connected to its transfer bus. ( unlike the APU or GPU).
Does that mean that if an IDG fails, its transfer bus is powered by the opposite IDG through its transfer bus?

Thanks

[RVF750]

What does the FCOM say, or your CBT? What do the lights on the ELECTRIC panel say when there is a source off? The hint is directly above it in amber.....

[NSEU]

What do you mean by ''directly connected''? All power sources have to go through some kind of breaker/s to get to the transfer busses (e.g. a GCB for the IDGs)

Your schematics may not be detailed enough. The functioning IDG provides power to the opposite (unpowered) tranfer bus via the powered onside transfer bus and two Bus Tie Breakers.