Difference between dead short and short circuit

[Scifen]

Hi looking for some help about faults and symptoms and difference between short circuit, dead short, and overcurrent to know which fault you have.

Is short circuit line and and neutral fault
dead short zero resistance and a tripped breaker
And overcurrent to much current in circuit causing fires. Any help much appreciated thanks

 

[davesparks]

A short circuit is a fault of low or negligible resistance between two conductors which are at different potentials, so it could be a fault between L and N, L and E, L1 and L2 etc.

A dead short is a slang term used to describe the same thing.

Overcurrent means any situation where more current flows than the circuit is intended/designed for, this can be an overload or the current which flows as the result of a fault such as a short circuit.

 

[pc1966]

And overcurrent to much current in circuit causing fires.

Fires are started by too much heat (along with a fuel & oxygen of course, but for now think about the heat as the source of ignition).

Too much heat can arise from several causes:

• Overload - when a circuit is subject to a larger current than the cable(s) are rated for. For example if multiple high current loads are put on sockets fed from the one source. This should not be possible if properly designed as the OCPD (over current protective device - a fuse or breaker normally) ought to disconnect power before the cable will reach a temperature when it can be damaged.
• Short circuit - basically the same as an overload but a much higher current due to a direct contact between line & neutral (or line-line on 3-phase, etc). Again, this should not cause any damage if properly designed as the OCPD should disconnect very fast such that the let-through energy (referred to as "I2t" but really is current-squared-time) is below the damage threshold of the cable.
• Bad connection or conductor damage. This has nothing to do with good design as such but is down to poor installation, or the effects of corrosion, or from vibration / thermal cycling causing screw terminals to release slightly, or from a conductor being nicked or strands broken by flexing. Here you get a local hot-spot at the bad connection and almost always gets worse with time.

 

[Cookie]

Typically we refer to a zero ohms short circuit as a "bolted" fault.

 

[telectrix]

Typically we refer to a zero ohms short circuit as a "bolted" fault.

we refer to it as "Oh, Sh*t"

 

[Cookie]

we refer to it as "Oh, Sh*t"

Along with new tools.

 

[Dustydazzler]

Dead short - short circuit are the same thing...

a dead short to earth can be referred to as an earth fault