HELP! calculating ze

[Ste69]

Is it possible to calculate Ze?

I am in the middle of an assignment, and have this question to answer.

When confirming automatic disconnection of the supply it is necessary to determine the external earth fault loop impedance(Ze) of the system. State three methods by which this can be achieved.

i have 2, inquiry and measurement (my answer is a little more in depth lol)

to my problem, i want to say calculation and the tutor has said this is correct BUT when i look into it i can not find the calculation! i can work out (Zs) i.e Zs = Ze + (R1 + R2)

so am i right in thinking the question is wrong? or am i being an idiot and missing something here?

sorry for the long winded question.

 

[Plonker 3]

If Zs=Ze+(R1+R2) , then Ze=Zs-(R1+R2)

 

[Ste69]

If Zs=Ze+(R1+R2) , then Ze=Zs-(R1+R2)

cheers Dillb

is there any way i can confirm this for myself by looking in any books? i have GN 3, onsit guide, 17th edition. cheers

 

[Plonker 3]

No, but arithmetic is always correct as long as you know how to adjust it accordingly.

 

[Geordie Spark]

No, but arithmetic is always correct as long as you know how to adjust it accordingly.

Smart ar$e. :wink_smile:

 

[Silly Sausage]

I'd refer to it as algebra myself!

 

[Ste69]

so using transposition of formula....

it just seems odd to me. i mean when would you ever need to use this calcualtion?

anyway thanks for your help mate, much appreciated.

 

[Plonker 3]

I'd refer to it as algebra myself!

I refer you to #5

Smart ar$e. :wink_smile:

 

[ImpededLoop]

The only problem with calculation is that the Zs would have been measured with parallel earths connected which will give you a lower than actual value for Ze. Ze is tested with the earthing conductor disconnected from the installation to eliminate parallel paths.

Having said that, I can't think of any other way to give you a third method unless its ok to use any previous test results are available or the Ze is provided by a consultant/designer etc.

 

[Geordie Spark]

I'd refer to it as algebra myself!

I could never get my head around algebra.

Thick Geordie.

 

[Guest55]

Yes , that very formula is in the back of the OSG somewhere

fixed that for ya
;-)

 

[ipf]

I'd refer to it as algebra myself!

What's Angela's bra got to do with it ? :confused5:

 

[Corpy76]

What if you knew the PFC? And the voltage?

 

[Plonker 3]

fixed that for ya
;-)

Do you want one of these too?

Smart ar$e. :wink_smile:

 

[ImpededLoop]

What if you knew the PFC? And the voltage?

The problem would still be a lower than actual value as PEFC is measured with all earthing and bonding connected to provide the highest (worst case) value.