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Richard Burns

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• Nov 19, 2017

• #21

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

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• Nov 19, 2017

• #22

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

 

cprfenom

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• Nov 19, 2017

• #23

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

 

Wilko

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• Nov 19, 2017

• #24

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

 

cprfenom

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• Nov 19, 2017

• #25

I knew it would be obvious when pointed out.

Thank you

 

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mrloy99

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• Nov 19, 2017

• #26

Andy-1960 said:

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

Click to expand...

One or the other...manual changeover.

Richard Burns said:

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

Click to expand...

Thank you...

 

Richard Burns

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• Nov 19, 2017

• #27

mrloy99 said:

One or the other...manual changeover.

Thank you...

Click to expand...

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.

 

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mrloy99

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• Nov 19, 2017

• #28

Richard Burns said:

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.

Click to expand...

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

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• Nov 19, 2017

• #29

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

 

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mrloy99

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• Nov 19, 2017

• #30

PEG said:

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

Click to expand...

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..

 

PEG

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• Nov 19, 2017

• #31

Hi,it may be beneficial,to find the spec on the supply characteristics,which should be available to yourself.

Maybe not in this case,but some installations can have dual intakes,TN-S and PME,and there are very specific requirements,regarding separation distances,bonding,removable links,etc.

 

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mrloy99

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• Nov 19, 2017

• #32

PEG said:

Hi,it may be beneficial,to find the spec on the supply characteristics,which should be available to yourself.

Maybe not in this case,but some installations can have dual intakes,TN-S and PME,and there are very specific requirements,regarding separation distances,bonding,removable links,etc.

Click to expand...

Ok thanks..Substations arn't really my game.,but I'll try and get more info