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  • Thread starter TheFullHitSpark
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Discuss Running PME (TNCS) outdoors? in the Electrical Forum area at ElectriciansForums.net

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TheFullHitSpark

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Alright guys, ime racking my brains and books trying to find out why my boss told me that you are not supposed to run PME outdoors to say out feeding a garage or a shed of some sort, i know about potential differences.... also i know some about special locations but i just cant understand why your not allowed PME, surely if the cable is protected by an RCD, the same as it would be if you was using an earth steak for TT what is the difference?? can someone elaberate on this for me please. if this is the case you would have to have an earth steak which would be a seperate means of earthing than provided from your source, but obvioulsly your (PME) earth would still have to provide protection for the cable feeding the (sub main).

Thinking outloud abit.. :p



If someone could show me the light i would be mostly appreciative.




Cheers guys, also as you all probably know this forum is the dogs go-nads...
 
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heathelect

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  • #2
hiya mate its something to do with pme not being a true earth, therefore if you run a pme earth to a metal framed external building a difference in potential may occur in the event of an earh fault,so you should not use the pme earth, you have to create your own earth with a rod. (i think), perhaps someone can explain it better, regards dave.
 
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Spudnik

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  • #3
Do you REALLY REALLY want to know?:D
 
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heathelect

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  • #4
jason, come on explain all
 
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Spudnik

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  • #5
ok.

Houses usually (although not always) have insulating floors etc which mean that main bonding can establish a reasonably equipotential zone, so even if the electrical system's earth is at some higher voltage (e.g. PME with a broken CNE) it would be difficult to get a shock while inside the house. Go outside, or in an outbuilding with a damp concrete floor (no damp proof membrane) and voltage differences can rocket!
 
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DYCHE4230

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  • #6
There appears only to be a problem if there are extraneous conductive parts in the outbuilding...

The impression I get is that the presence of extraneous conductive parts does not preclude the use of an exported TNC-S earth, it mearly means that they have to be bonded back to the submain MET with the same size cable as is appropiate for doing the same in the main building, and that the same sized or bigger earthing cable is used to provide the earth to the submain board, and as this is not always practical, a way of avoiding having to install bigger cables is to convert the remote installation to TT, and bond extraneous bits back to this

I think!!!!!!
 
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sivoodoo

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  • #7
This is interesting, could some of you seasoned sparks provide a diagram?

It would be very useful and informative.

Thanks

Si.
 
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TheFullHitSpark

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  • #8
If the floor was a big steel grid and all extraneous conductive parts were bonded to it in the out building, you would be able to use the PME?
 

hasel5

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Arms
In my view wire as a normal circuit provide the right type of protection for the circuit IE 30MA RCD/RCBO at correct rating for cable ETC and thats it 35 years exp and all the certs you can think of plus a degree in logic
 
G

GAZHUDDS

  • Thread Starter Thread Starter
  • #10
Alright guys, ime racking my brains and books trying to find out why my boss told me that you are not supposed to run PME outdoors to say out feeding a garage or a shed of some sort, i know about potential differences.... also i know some about special locations but i just cant understand why your not allowed PME, surely if the cable is protected by an RCD, the same as it would be if you was using an earth steak for TT what is the difference?? can someone elaberate on this for me please. if this is the case you would have to have an earth steak which would be a seperate means of earthing than provided from your source, but obvioulsly your (PME) earth would still have to provide protection for the cable feeding the (sub main).

Thinking outloud abit.. :p



How do you have your Earth steak, Me? Medium rare!
 
B

beaver74

  • Thread Starter Thread Starter
  • #11
In my view wire as a normal circuit provide the right type of protection for the circuit IE 30MA RCD/RCBO at correct rating for cable ETC and thats it 35 years exp and all the certs you can think of plus a degree in logic
yes but the reasone that the pme becomes a prob lem ifs if the neutral conductor fail/broke (yes 1000/1 chance)earth conductor could raise in voltage
as stated in a house all pipe work ect would raise so no shock risk
the use of a r,c,d will not save you in this senario as the earth which will raise in voltage even when r,c,d trips will stay at a dangerous voltage
 
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TheFullHitSpark

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  • #12
are you even a spark beaver? you wouldnt be using the neutral as a means of earth feeding the sub, it would be a seperate conductor. You dont make any sense!
 
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jimes

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  • #13
what he mesans is the neutral is the earth in pme supply
 
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beaver74

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  • #14
are you even a spark beaver? you wouldnt be using the neutral as a means of earth feeding the sub, it would be a seperate conductor. You dont make any sense!
it pme neutral is conected to the earth
make sense now???
 
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Seselectrical

  • Thread Starter Thread Starter
  • #15
If there is no extraneous conductive parts in the outbuilding u can export tncs.
 

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