Electrical Wiring

Circuit damage, overheating, fire or explosion, if no overcurrent protective devices are in place.

Short circuit - Wikipedia, the free encyclopedia

Big spark, metal melting and if your electrician did their job correctly, a circuit breaker or fuse set will safely interrupt the current flow.

Look up "Arc Flash"

"Don't cross the phases, crossing the phases is bad."

"How bad Egon?"

BANG!!

If done correctly - time travel, if done incorrectly - death.

Seriously, you say you are an electronics and instrumentation engineer AND you appear to be working on mains voltage compressors and contactors and you are asking questions like this!

Try first to connect or short phase "R" and "Y" then you will conclude what will happen then...probably a " BIG BANG",

Definition:

Short circuit, abnormal connection of low resistance between two points of a circuit that usually causes a high, potentially damaging current to flow. To protect against damage, devices such as afuse or a circuit breaker are used. They sense the excess current and break the circuit so that no current can flow. They must be replaced or reset manually once the cause of the short circuit is removed

A short circuit is an extremely hazardous phenomenon; the current in the circuit usually increases abruptly. As a result, strong mechanical forces are created in electrical apparatus, and the temperature of the conductors is increased substantially, which may cause damage. An electric arc frequently develops at the point of the short circuit, causing a breakdown. In an electrical system the voltage to consumers is decreased during a short circuit; for single-phase, two-phase, and two-phase-to-ground short circuits the voltages become asymmetric, thus partially or completely disrupting the normal power supply. A short circuit can disturb the dynamic stability of an electrical system and, as a result, cause serious system damage.

When the conductors of power lines are short-circuited to ground, a strong electromagnetic field is produced in the surrounding space, inducing electromotive forces in nearby communications lines that are hazardous for both service personnel and apparatus. When current is flowing from the point of a short circuit along the surface of the earth, a potential difference (a voltage hazardous to a walking person across the distance of one pace) that is dangerous to life may occur. To provide protection from the effects of short-circuit currents and to ease the requirements for mechanical and thermal stability of electrical equipment, measures are taken to reduce the magnitude of the currents (current-limiting reactors, sectionalization of electric networks, and so on) and to automatically and rapidly disconnect the faulty parts of the network (fuses and automatic circuit breakers, as well as relaying devices and automatic apparatus).

After the event, around 2/3 of the single phase appliances and all of the 3-phase equipment downstream will cease to function as the circuit protective devices will have operated. Depending on the nature of the building, the outcome will be in a range varying from moaning and/or personal abuse, through to divorce proceedings at one apex, to being sued for loss of electrical service at another apex, to invoking career limitations and/or summary dismissal at another apex, assuming the Fire Brigade has put any fire out and that no loss of life has occurred. Also, one might reasonably assume that insurance premiums on the building will increase as the full story of the circumstances surrounding this stupidity becomes apparent.