sub main

[Chr!s]

Good question Ian. I've asked it before and not had a satisfactory answer.
The term "equipotential zone" does not appear in the definitions in BS7671 (unless I'm blind).
So, what is it and what defines its boundaries?

Agreed, its not mentioned as such, GN5 touches on it a little.

The way i look at it is a zone of equal potential under fault condition.The two main paths of current for electric shock are hand to foot and hand to hand.

Take a single room, Extraneous coper pipe, next to an exposed conductive part. Now if theres a fault on the exposed conductive part there will be a difference in potential between the two, so we bond the pipe, this reduces the touch voltage of hand to hand shock.But what if the floor introduces earth potential, then we must consider hand to foot shock.

When creating an equipotential zone we ensure that simultaneously accessible parts are either at the same potential or make them so they dont introduce potential. Most floors in houses dont introduce earth potential, so the risk considered is hand to hand.

Thats not to say some floors dont introduce earth potential, many tiled or concrete floors may.

So if we export the pme to an outbuilding can we create an equipotential zone?

Is the floor at earth potential?

Are there exposed and extraneous parts?

If we have a broken pen current may flow through the exposed and extraneous parts, now if the floor introduces no potential then theres no risk of hand to foot shock, the risk is hand to hand, but if we bond all exposed and extraneous back to the met then we will have similar potential between the two, so reducing the risk of hand to hand shock.


HTH

 

[Chr!s]

I dont forget, Potential isn't always necessarily earth potential,

 

[poheZ]

how about terminating it in a gland and connecting it to an mcb!

 

[malcolmsanford]

is this deja vu

 

[IQ Electrical]

Hi guys im doing a job that needs a sub main to a outbuilding was going to use 16swa but not sure what to do at origin with conecting in to a consumer unit size wise any ways round it or will it fitt ok

You might want to look at the consumer unit size and construction first, is it metal clad or pvc?

Is the 16mm cable size to allow for a large load or volt drop on a long run?

Check the rating of the consumer unit and indeed, the supply itself before adding large loads.

 

[ElectricIANJ]

no massive load only a bedsit thing 2rings 2 lighting thats about it will go10mm now ive slept on it ,gland off in to a box on outside keep inner sheath on till hit consumer unit i think