A la ITC-BT-9 diu que en el cas que s'utilitzin interruptors diferencials al quadre de protecció i control s'haurà de tenir molta cura amb la seva tria i hauran de ser de tipus selectiu (S). Per quin motiu?

At an open or uncontrolled intersection, yield if a. your road is paved and the crossroad is not b. the cross road is paved and yours is not c. you have two or more passengers in your vehicle d. you did not yield in the last intersection

The forerunner to cell phones, pdas, and smartphones was

How do we use the sumif formula (when dealing with different formats) ?