The measured value of loop Impedance for a circuit is 2.4 Ohms

[Rather be Fishing]

Is it fault for fire protection and basic protection, protection against electric shock

 

[westward10]

Fault protection in this case is where such protection (ADS) may not be achieved by a protective device alone.

 

[Rather be Fishing]

Continuity of a ring final circuit has been tested as part of an initial verification of a new primary school. All the sockets outlets are connected directly to the ring.

The circuit loop length is 58m long wired in 4mm2 live and 1.5mm cod flat profile cable.

The circuit is protected by a 32 A BS EN 60898 type b circuit breaker

The installation has a measured ze of 0.29 ohms

What is the expected as for this circuit?

A. 0 24 ohms
B.0 28 ohms
C.0.53 ohms
D. 0.58 ohms

I've done some calculations but I'm not getting any of those answers which means im doing it wrong.

This is what I have done

Zs = ze + R1 + R2

16.71 x 58 /1000 = 0.96 ohms


O.29ohms + 0.96 ohms

Zs = 1.25 ohms

Obviously that is not right

 

[westward10]

You have done it as a radial circuit not a ring final.

 

[Rather be Fishing]

You have done it as a radial circuit not a ring final.

You have done it as a radial circuit not a ring final.

Other then divide it by 2 I've no idea what I need to do

 

[Lister1987]

Have a look through, compare against yours and see where you may have gone wrong. Come back and tell us once you've figured it out (where you went wrong, not the answer)

 

[westward10]

Remember when the ring final is connected your resistance is halved due to double csa but the distance is effectively halved.

 

[Rather be Fishing]

Nice one @Lister1987

Pen and pad is the way foward for sure

I have to get to bed really as im up early and Ive had a long day with college thrown back into the mix but I'll be cracking straight back on with this tommorow.

Cheers for going to the trouble of writing that out

And also to @westward10 for much the same reasons

 

[Lister1987]

Nice one @Lister1987

Pen and pad is the way foward for sure

I have to get to bed really as im up early and Ive had a long day with college thrown back into the mix but I'll be cracking straight back on with this tommorow.

Cheers for going to the trouble of writing that out

And also to @westward10 for much the same reasons

Just remember to be methodical, helps to give sources too; Table G1 for R1+R2 values, Table G2 for the multiplier etc, it helps it get enground in the mind.

 

[Rather be Fishing]

I'll be cracking straight on with this after work and something to eat.


My plan was to spend all day sat and sun on revision as well as the remainder of this week but I've just been put on call for my new Job starting Friday. You couldn't write it. I bet it's one of them weekends.

 

[telectrix]

Other then divide it by 2 I've no idea what I need to do

divide by 4: (R1+R2)= (r1+ r2)/4 for a ring.

 

[westward10]

divide by 4: (R1+R2)= (r1+ r2)/4 for a ring.

He is supposed to be trying to work it out?

 

[Rather be Fishing]

Thanks for all the help guys can't quite believe it.

 

[Rather be Fishing]

Here we go

 

[Rather be Fishing]

Here's another one