ECN Forum Forums General Topics of the Trade General Discussion Area Class stumped?

Hi all,

I just got home from my journeyman class and we were given a practice test that the whole class checked together. One question had an answer that kinda half stumped the class, including the teacher.

Here it is:

Which are the three basic electrical faults?

a) Ground fault, partial ground fault, and open circuit.

b) short circuit, open circuit, and change in electrical value.

c) open circuit, incomplete circuit, and ground fault.

d)short circuit , ground fault, and partial ground fault.

The test writing program the teacher uses said the answer is (D), but what is a partial ground fault? Even our teacher has never heard of one!

Sam

[This message has been edited by wv-wire-wrangler (edited 10-04-2005).]

A partial ground fault would be a fault to ground not at full potential, such as in a motor winding.

Could it be where there is an accident? Some one stepped into a hole in the ground. Would that be a partial ground fault? I mean if the ground didn’t have the hole then the accident would not have happened.

Of course it will be hard to find a lawyer that will try to sue the ground no matter how much it was at fault.

Hey JW,

GOod one. Had me laughing for a good 5 minutes!!!

A partial ground fault is one that trips a GFCI but not the O/C device.
That may be the hardest one to find.

I like JW's explanation. However on what grounds(partial grounds?)are you basing that explanation.

Seems like an strange question, since a ground and partial ground fault are both types of short circuits.
A partial ground would probably be a high impedance ground, often one that doesn't pull enough current to activate a protective device (like gfretwell said).
A good example would be high voltage line falling on dry sand. The sand (basically glass) is such a high impedance that the line never trips. That's why you never see a lineman touch a downed wire without grounding it.

If it were are fill in the blank question, I would have answered 3 phase fault, line-ground fault and 3 phase arcing fault (high impedance fault)

Other flavors would be line-line fault, line-line arcing fault and line-ground arcing fault.

So maybe according to that author, a partial fault is an arcing fault.

I don't like the question either, BUT....

A partial ground fault is one most often on a high line (distribution or transmission levels) where you have an arc to ground, way to small to cause an interruption current.

What is does cause is RFI, TVI, etc. In Other Words, a ground fault NOT at interruption levels that uses power, and causes customer problems.

I disagree with this question entirely. There are only 2 basic types of faults, shorts and opens.

You can then get more specific and subdivide both of those categories, such as ground faults, line to line faults, etc.

But "partial ground faults?" That is very vague and confusing in my opinion.

Peter