Ze and zs?

[kevinlondon]

Just a quick question, but what does Ze and Zs mean in relation to earthing? Is it to do with calculations?

Thanks for your help

 

[kai]

ZE is the earth loop reading at the intake position (fusebox etc).
ZS is the earth loop reading at the furthest point on a given circuit - example being the switch drop on a lighting circuit.

 

[RF Lighting]

Ze is the external earth fault loop impedence
Zs is the earth fault loop impedence at the furthest point on a final circuit

They are used to ensure that automatic disconnection will be achieved in the desired time in the event of an earth fault.

 

[kevinlondon]

Thanks for your help, I was reading an electrical book today and couldn;t quite grasp it! Also L1 and and L2, what exactly are they? I leanred a bit at the earthign systems TT, TNS and TNCS

 

[Spark123]

L1 and L2 in which respect?
These definitions are used all over the place i.e. on light switches and labelling of phases which are two different things.

 

[RF Lighting]

Do you mean R1 and R2? These are used in relation to testing earthing on an installation.

 

[kevinlondon]

sorry i meant R1 and R2

 

[kevinlondon]

I'm trying to learn about electrics from a few books I have but some of it seems hard to grasp on my own. I can understand swtiching, lighting circuits, 2 and 3 way switching, ring ircuits etc but reading and learning about testing and inspections seems a bit tricky on my own!

 

[ricicle]

R1 = resistance of Line conductor from protective device to measured point on circuit.

R2 = resistance of circuit protective conductor from earth terminal to measured point on circuit.

Both usually measured together at extremity of circuit by linking L to E at consumer unit and testing across L to E on circuit.

The R1 + R2 can be added to Ze to calculate Zs.