> Because the alarm wire carried current only during a fault, an open 25-inch strap produced the same electrical state at the receiving end as a healthy power plant.
I’m a building automation and controls tech in Manhattan, and for this exact reason digital feedback points and alarms are always normally-closed, and analog points are 4-20mA. This allows differentiation between nominal zero values and a fault in the loop.
Disasters like this are what our best practices are borne from.
> Because the alarm wire carried current only during a fault, an open 25-inch strap produced the same electrical state at the receiving end as a healthy power plant.
I’m a building automation and controls tech in Manhattan, and for this exact reason digital feedback points and alarms are always normally-closed, and analog points are 4-20mA. This allows differentiation between nominal zero values and a fault in the loop.
Disasters like this are what our best practices are borne from.
This is an awesomely clear and methodical explanation of system failure.
The overall site has a cozy feel to it. Well done