My cottage and the ajacent retail unit share a thatched roof but the electrical supplies are from two different street cables. As it happens the retail unit is TT
Gas bonding
- Thread starter SUNRAY
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My cottage and the ajacent retail unit share a thatched roof but the electrical supplies are from two different street cables. As it happens the retail unit is TT
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Giving that very little (certainly including loss of a network neutral) is impossible, the words I have emboldened above seem redundant.
You seem to be suggesting that 'metallic water mains that are extremely low impedance to ground' which enter a property must be eliminated - since, if they existed, the regulations would certainly require them to be bonded. However, since BS7671 says nothing about that, what are you suggesting requires your "should not"?
Kind Regards, John
I think that there are, in fact, some 'pros', as well as 'cons', of TN-C-S. For example, a 'lost neutral' with TN-C-S will normally be immediately apparent, whereas a lost or inadequate TN-S earth (much more common) can go unnoticed for a long time.
Kind Regards, John
What would make it "immediately apparent" ?
Loss of power maybe. Then exposed and bonded pipe work would at a potential much higher than"Ground" potential. Safe provided the perimeter of the equipotential zone was not bridged. Outside water taps could be lethal. Reading a gas meter would be hazardous
Reduced voltage maybe. Then exposed and bonded pipe work would at a potential much higher than"Ground" potential with significant, possibly hazardous, currents flowing to Ground by some sneak routes.
No apparent loss of power. Then current that would normally flow along the Neutral would be flowing along various low impedance sneak routes to Ground.
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Exactly. Unless it occurred at a time of extremely low demand, it is surely very unlikely that a return path through extraneous routes to earth would have a low enough impedance for many loads to function normally, if at all?
Don't forget that I was talking about 'pros' and 'cons', not absolutes. Even if you invoke the (not impossible) scenario of an extremely low impedance extraneous path to earth, that will be very rare, so in the majority of cases the problem will be 'immediately apparent'.
Kind Regards, John
Could have been worse - they might have misunderstood the entire "gas bonding" phrase.
We know all that, but it's a pretty unusual situation ***.
I was, needles to saying, talking about the usual situation of a single building which contains multiple flats/apartments/offices/whatever, and it would be very unusual for the electrical installations of those 'units' not to have 'earths' which were not all derived from the same source.
[ *** Interesting, for what it's worth, it seems that not all DNOs share the same concerns as yours. My infamous house is, in fact 'mid-terraced' (that's what the insurers call it!) since, in 1950, bits on either side (billiards room on one side and servants' quarters/nurseries/kitchen on the other side) were sold off as separate dwellings. All three are currently TT, and there are certainly metal pipes traversing all three. I have been offered TN-C-S (by a DNO man who was here for another reason). Knowing your experiences, I asked him if that would require electrical isolation of the pipework between dwellings etc., and he actually laughed, before saying something along the lines of "are you concerned about the possibility of being struck by lightning?"! ]
Kind Regards, John
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Is it a bit claustrophobic in that suit, Ban?
Nah - it's open from top to bottom at the back - wanna see?
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