Relationship ze and pfc

[Kyle_Trainee]

So I’m currently studying Ze and pfc etc kind of understanding it.
main question really is about the relationship between them both I understand that the lower the Ze the higher the fault current but why is this? Is it just simply to do with ohms law? And I’m just over thinking and confusing myself

Any responses would be appreciated

 

[Mike Johnson]

I think it buried in the Multiverse with Jean Luc Picard. ? If anyone is confused it's a joke.

I find my sense of humour is directly proportional to the amount of wine I have drunk, I'm a giggler not a fighter. ?

 

[Deleted account]

It's a long time since I was at school, but isn't I = V/R the same as V = IR something like transposing one of the divisors to the other side of the resultant make it a multiplicand rather than a divisor?

No it’s totally different.

 

[Mike Johnson]

Is this the full ten minute argument or just a disagreement, I did pay for the full ten minutes. ?

 

[Julie.]

It's a long time since I was at school, but isn't I = V/R the same as V = IR something like transposing one of the divisors to the other side of the resultant make it a multiplicand rather than a divisor?

Err yeah

 

[Julie.]

Is this the full ten minute argument or just a disagreement, I did pay for the full ten minutes. ?

No You didn't

 

[pc1966]

When I was at school it was simply I=V/R ? it just seems as though its change for change sake. ?

Started to charge by the letter, make more money the new way

 

[pc1966]

Incidentally, why is this thread under "Electrical News"?

 

[DPG]

Incidentally, why is this thread under "Electrical News"?

Didn't even realise it was.

 

[Vortigern]

No You didn't

Yes he did.

 

[Vortigern]

The less the resistance the easier a current is able to flow. The better the flow the bigger the bang. Of course practically a higher resistance can lead to a current flow that is too low to cause the OCPD to operate within the times required by BS7671. So the measuring of Ze/Zs has a number of ramifications to it both ways, i.e. is it too high or too low, each has their own problems.

 

[Soi disant]

The IET's "Electrical Installation Design Guide" has some examples of the slightly more tricky cases on pages 76-81

Great little book, BTW - I can strongly recommend that anyone who wants to understand more should get a copy.

Also Paul Cook's Commentary on IET Wiring Regulations. Unfortunately the most recent one is for the 17th Edition (dunno what's going on there), but as the laws of physics dinnae change, it's still a useful book. Maybe, given it's now out of date, try to get a s/h copy on eBay - they are around.

​

 

[Soi disant]

It's the bloody EU I expect.

Nah - if it was it would be done in reverse à la française, so

I/V = 1/R

 

[Soi disant]

The better the flow the bigger the bang.

Here's an interesting exercise for y'all. Look up the amount of energy in a stick of dynamite, and compare it to how long a supply cable fault upstream of a cutout has to last to release the same amount.

 

[pc1966]

Here's an interesting exercise for y'all. Look up the amount of energy in a stick of dynamite, and compare it to how long a supply cable fault upstream of a cutout has to last to release the same amount.

Or watch the video:

Admittedly that is a lot more PFC that a domestic system will see, but still impressive what it does.

 

[Les Macaulay]

It's most certainly changed then, when I was at school it was V = IR

Looks like they have changed it all around.

Have to watch carefully, I have no doubt that they will change it again in the future to R = V/I or something.

Julie, have you heard of transposition?