Fault Level

Because of the greater voltage, line-line faults can produce greater fault current. However, line-neutral or line-ground faults are probably more common. Either type can produce excessive fault current.

But, in an effcetively grounded system, line-to-ground current can be much higher than line-to-line fault current.

Provided the circuit protection devices operate when one occurs, neither is more dangerous than the other, and neither will have excess fault current for very long. So for a correct installation, the question is abstruse.

how about learning power system stability?

That's a different issue.

please defiend dangerus Do Not Post Email Addresses -Admin

<sigh> This looks like homework.

Please provide MUCH more information as it depends on a number of factors (is this a power grid transmission system, distribution system, inside a factory, inside a piece of equipment, dangerous to what - people, the equipment, what protection equipment is employed, what earthing system is employed, etc, etc, etc).

It is subjective and there is no single answer.

Please provide more information.

The most dangerous fault is the one not protected for in the power distribution circuitry. Since most circuits do not have ground fault interrupt protection a hot to ungrounded shell to victim to ground is much more dangerous than either fault presented.

Yeah, I know that a GFI can become a pain because these devices safely fail more often than they save a life. But they do save lives. I'm one of the saved lives, but that's another story.

I believe you suffer a deeper death when electrocuted by a line-to-ground fault than if electrocuted by a line-to-line fault. That is why one side of an electric chair circuit is connected to ground, they want you deader.

You mean the wiring to a chair doesn't have a 30mA RCCB? Someone may get hurt, dammit! - Surely that's illegal.

The RCCB should be 10 mA, because they made the head wet with water.

Good point.

The fault is considered dangerous not in terms of the level of fault current, rather it is considered dangerous in terms of the severity of the personnel, equipment and operational damage that may be caused by the fault.

In this sense, the most dangerous fault is the arching fault (a fault having short air gap in the fault path). Arcing fault releases enormous amount of energy to the air media and causes 'Arc flash' which produces very high temperature (greater than 5000 degree F). So, arcing fault is more dangerous (see http://cr4.globalspec.com/comment/518549) types of fault.

Any other fault also results in dangerous situation if it exists longer period due to the protection system not work properly.

Faults are always bad and harmful but unfortunately they are not avoidable. However, if the system is properly designed with appropriate protection, coordination and equipment rating, faults are not dangerous even though it causes power outage in the faulty area.

- MS

But... it's not my fault!

jt.