Diverted Neutral Current.

Well son, in some places they use the same wire for both neutral and earth, in the suppliers equipment, these being separated in the consumers installation.

Since water pipes should be bonded to the earth wire, some of the neutral current returns via the neutral wire, and some via the water pipes. Note that neutral current from neighbours may return via your water pipes. Such current therefore still flows when your installation is isolated.

60 amps sounds an awful lot though. I would be most reluctant to disconnect any earthing or bonding connection that was carrying 60 amps. A dangerous voltage could result, even with the main fuse removed. 60 amps is also a fire risk if it passes through any small conductors or any imperfect connections.

Well a high current in the pipework might suggests that the main neutral path is not so great - but recall that the current will split in the ratio of the inverse resistances of the two paths, and the resistance of plumbing can be very low indeed.

Even a 15mm copper water pipe has a conductor cross-section of nearly 35mm2 of copper, - being 0.7mm(wall thickness) * 47mm (circumference). So in parallel connection between a typical house supply cable of 35mm wavecon plus a meter and  some 25mm tails, versus a 15mm copper water pipe, the resistances will be similar and, when you allow for water pipes being cooler than street mains cables it should not be a surprise if the current split between similar lengths of 35mm feeder cable and 15mm water pipe could approach  50/50.  The water pipes running up in streets not yet converted to plastic  are quite a lot larger in cross-section. It is quite possible that in such cases the lower resistance path taking the bulk of the main neutral current may well be the plumbing, with the armour of the wavecon reduced to the minor role of taking current around electrical gaps in the plumbing network. 

Indeed the bonding can be good enough to mask problems in the supply network, and while rare, there have been a few reported incidents of shocks and even the odd tragic electrocution while installing water meters and replacing stop taps.

Mike.

Made me smile when someone says to the guy OK? And he says yes I think a more appropriate reply mite have been are you having a laugh? This things bloody well live