TNS

[westward10]

Have you carried out a Ze at the boards.

 

[mrloy99]

Have you carried out a Ze at the boards.

A couple of months ago yes when it was first powered up..As far as I remember it was around 0.07..(quite big job over a hundred DBs so not sure)

 

[mrloy99]

What is the nature,of the fault?

No continuity on an accessory fault traced to defective modular kit.faulty circuit disconnected (I think)unless labled wrongly.not confirmed yet.
Bed time for me.Maybe I'll have another look tpmorrow

 

[Andy-1960]

Are both A & B supplies used at the same time or is it a duty / standby situation?

 

[Wilko]

Assuming 70mm conductor size for both N, at 20C the resistance for 30m is about 0.024Ohms. And a 37m run would be 0.03Ohms. Unless I've made a no-coffee-yet mistake.

 

[Richard Burns]

For the Neutral Earth loop on the installation you describe the 0.03Ω sounds about right (as Wilko has just said!)
So the A installation sounds correct but the B does not.

 

[Wilko]

Great diag RB, and kind as always.
I'd made a slip but by luck ended up still in the ballpark

 

[cprfenom]

Can i ask how you calculated the 0.024? At risk of looking dumb

 

[Wilko]

Hi - RB diagram in post #21 - 30m of the 2 cables added up

 

[cprfenom]

I knew it would be obvious when pointed out.

Thank you

 

[mrloy99]

Are both A & B supplies used at the same time or is it a duty / standby situation?

One or the other...manual changeover.

For the Neutral Earth loop on the installation you describe the 0.03Ω sounds about right (as Wilko has just said!)
So the A installation sounds correct but the B does not.

View attachment 39394

Thank you...

 

[Richard Burns]

One or the other...manual changeover.

Thank you...

Therefore the neutral of the non operational supply (B) is probably not connected to your live supply as this would mix the two systems of the supply transformers.

 

[mrloy99]

Therefore the neutral of the non operational supply (B) is probably not connected to your live supply as this would mix the two systems of the supply transformers.

Both supplies are operational..voltage to earth is 240 on both systems..There is some info about earthing neutrals through impedences(fig 44.1)and section 442 .not too clear to me..
Incidently when I measure on megohm scale I am showing 0.00

 

[PEG]

Hi,what is the set-up,regarding the two supply transformers,and what is feeding them?

 

[mrloy99]

Hi,what is the set-up,regarding the two supply transformers,and what is feeding them?

Hi.I cant really comment.I will need to investigate further.The complex has 5 sets of HV/LV Transformer rooms(Subs) (Times 2 :A+B) I believe there are two independant 11,000volt ring mains.They wont let us doe_heads in to the substations.
So I could still be looking at either a neutral earth fault or a missing earth link on neutral...I've been trying to read up but it appears the HV earth &LV earthed neutral can either be separate or common or through an impedence..