Hi Budgie
Your two attached articles answer why we're using lightbulb overload devices. They were recommended by a friend who is installing them on his large DCC layout (he uses ZTC/Taunton Controls kit)
Remember that this is an exhibition layout; that means that I want minimum disruption to operation, hence the up/down DCC supply split. The theory is that we could experience a minor and brief short which, with the lightbulbs, will result in the bulb glowing/lighting momentarily (electrically absorbing the short) but preventing the Command Station/Booster from tripping (stopping everything in that direction). Obviously if we get a dead short, then the bulb will light and the DCC kit will overload. The bulbs are intended to create smoother and more reliable operation. If you look at your attached articles, one of them recommends Digitrax PM42 units (we did consider these) - these are in effect the same as the bulb, but in the form of a breaker - i.e on or off and you are simply subdividing your layout as you would your house. What the bulb does is to smooth current peaks because of the time taken to heat the filament. All electrical systems have a degree of tolerance; because our electrical load (the train) is moving, shorts can occur very briefly and sometimes having an overload system that is too sensitive (too quick) to shut down is a blessed nuisance as the wiring/motor etc can cope with the small spike in current. Where a short is more serious, both the bulb and the system overload, saving the chip and other delicate electronickary
Just in case you were wondering, the bulb holders are car light bulb holders with 21W low voltage bulbs - if you want to know a more technical description and source, I'll post that if it'd be helpful?
So that's the theory; the proof will be in the pudding! And if you have checked messrs Bachmann and Hornby back-to-back tolerances recently, you'll know that they are erratic; that's where I expect to get our problems/shorts from!
All the best