Generator back-up system

[ricicle]

I don't agree with it only being suitable for one piece of current using equipment as long as additional precautions are taken into account i.e. earth free local eq. bonding.

I was generalising about using portable/handheld equipment from an un-earthed genny. Equipotential bonding would be difficult to achieve unless you could see the cpc in the appliance flexes as the bonding conductor. Would it be enough to stop a rise in potential between two exposed conductive parts if there was a fault on each to either side of the supply winding ? (before of course that the protective device operated as the exposed conductive parts are connected together via the cpcs so creating a short-circuit) Am I waffling

 

[Spark123]

In most instances the CPCs will be fine, however if you start looking at larger systems a smaller CPC may be too small. A lot of emphasis is placed on all polled fusing.
Never mind the waffling, this is much more interesting than Mr Burnedmywilly's thread.

 

[ricicle]

He's actually took his one man show over to the IET now

 

[JohnW2]

OK, I'm back, so will try to catch up .....

In an IT system you wouldn't have the N-E link in the generator, the source is left floating (or a big resistor linking N-E),

Yes, that's true, and the N-E link is present in my genny.

Are you suggesting that I disconnect the earth rod? - it would obviously only take a few seconds!

That wouldn't be a good idea without knowing exactly what you have, is the N-E link present in the generator?

Don't worry, I have no intention of removing the earthing; the question was rhetorical! As above, the N-E link is present.

I guess that everyone would be 'happy', and most scope for debate would vanish, if I simply moved the earth connection from the rod from the present (CU) end of the 'supply cable' to the genny end. It would then be indisputably a TN-S system (I could even stop using the explicit earth connection and make it TN-C-S if you really wanted!). However, I would argue that the effects of such a change would be fairly academic. In particular the path to earth from any CPC in the installation would be virtually the same (in fact, fractionally greater in resistance); the earth conductor of the supply cable ('CPC' if you wish to call it that) consists of about 5 metres of 2.5mm² core plus the SWA armour - I think about 10mm² copper-equivalent in total. Beyond removing the potential for discussion about the system in the future, can you think of any real benefit of making such a change?

If you haven't seen all of the discussion, you may wonder why this separate earth rod, rather than simply connection to the house's main MET and hence using the house's main (TT) earth electrode. That's really just a matter of convenience - the path to the house's MET would probably be best part of 20 metres, and not very easy to route.

Kind Regards, John

 

[Spark123]

Personally I wouldn't be that bothered if the rod is at one end of the cable or the other in your instance.

Maybe look to cross bond between the two rods as you are reliant on copper pipework to provide the link, if someone was to insert plastic pipe you'd have the potential for two different earth systems to be simultaneously accessible.

 

[JohnW2]

Personally I wouldn't be that bothered if the rod is at one end of the cable or the other in your instance.

As must be apparent from what I just wrote, I'm not bothered either. If it were done, it would only really to be stifle any agument about whether the system was, or was not, strictly TN-S at the moment!

Maybe look to cross bond between the two rods as you are reliant on copper pipework to provide the link, if someone was to insert plastic pipe you'd have the potential for two different earth systems to be simultaneously accessible.

That already effectively exists. Both the 'mains supply MET' and the 'generator supply MET' have MPBs attached to the incoming pipework in virtually the same place - no more than an inch or so of copper pipe between them (hardly enough room to get a pipe cutter between them, let alone to insert a piece of plastic pipe ). I reckon that's good enough for me.

Kind Regards, John