An electrical puzzle.

Yes, I should have been clear I was taking a historical perspective. Power systems did not start in the well organised form they are today, it happened in steps starting about 1880. Back then, there were a multitude of supply options, where pretty much every local authority and insurance company had their own ideas, mostly incompatible. In 1900, an electrician had to make sure the switchboard was made of an acceptable material, usually either Marble or Slate. Only problem was, Slate was unacceptable to Marble loving authorities, and Marble unacceptable in the next town. More disagreements about paper, rubber, asbestos, and other types of insulation, and some insisted on Lead sheathed cables whilst others banned it outright. DC was initially universal, with domestic systems available in odd steps between 30V and 500V, maybe more. When AC arrived, early systems also delivered individualistic voltages, and alternated from as low as 15Hz to as high as 120Hz, not necessarily accurately. For several years 30Hz was the most common system in the UK.

It was a mess, typical of new technology, where Tom, Dick and Harry competed laissez faire for work, and it wasn't clear which system was best. Lots of electrocutions and fires, and enormous fun with tram systems before earthing was introduced. Very dangerous by today's standards! In the end, government intervened, set up the National Grid, standardised on 50Hz, and either absorbed compliant generators or shut them down. 60Hz was thought to be too racy for British generators at that time and 50Hz puts less strain on the mechanicals. Others realised technology was improving and reliable 60Hz was achievable and more efficient.

UK Domestic supply started as a nominal 250V, then dropped to a nominal 240V, I think to save energy during WW2, then was made a nominal 230V on paper for compliance with Europe, though the system didn't change. Actual UK voltage seems to vary by time and location - anything between 216V and 253V is within tolerance, and it's not unknown for local bits of the network to run outside those limits. I've never seen 230Vac in the real world, usually higher where I live, 237V as I type this.

Frequency varies too: the grid originally maintained a strictly accurate 50Hz, but at some point it was realised peak loads can be managed by altering frequency slightly. Now if the system starts to overload, cuts can often be avoided by dropping frequency a little so less energy per second is delivered to consumers. TVs carry on as normal, but kettles take longer to boil.

So the mains probably isn't 230V at 50Hz, and 13 Amp fuses don't blow at 13A. But it all works reasonably well.

Dave

i believe all European countries use "time correction" these days, meaning the average frequency will be constant. This keeps watches with synchronous motors correct with no manual correction needed.

Do should I earthe my water/gas pipes?

Hi Duncan

After reading this thread .

There is only one answer to your question ,get the advice of a qualified electrician.

Maurice

Indeed not - they will go more or less for ever at 15 A, but will go pretty promptly at 20 A.

We have been told that the water pipe is plastic to the stop cock, so there is nothing to bond.

However, we haven't been told about the gas supply. If it is yellow plastic, there is also nothing to bond; but if it is metal (cast iron) then it should be bonded.

If the installation is reasonably modern and has been certified, then it should be all right. If not, get an EICR -,an electrical installation condition report.

If required any bonding is on the consumer side of the gas meter, not to the supply pipe.
Same applies to the water supply, bonding is on the installation sfter the stopcock if needed.

Emgee

Where the bonding is attached was not the point. After all, if the supply is plastic, it would be pretty pointless to put a cable clamp around such a pipe. However, Emgee is correct per 544.1.2.

Dave (SOD) said:
" Frequency varies too: the grid originally maintained a strictly accurate 50Hz, but at some point it was realised peak loads can be managed by altering frequency slightly. Now if the system starts to overload, cuts can often be avoided by dropping frequency a little so less energy per second is delivered to consumers. TVs carry on as normal, but kettles take longer to boil. "

Not quire correct. The average frequency is held accuratly to 50Hz. Changing frequency does not change the power consumed by resistive loads like kettles or electronic equipment. Induction motors will change power with frequency but only if the change in speed alters the power consumed mechanically.

That said, the power stations DO vary the frequency of their indiividual generators slightly to control power. This is to control the power supplied to the grid by that particular generator. It may be easier to think about the resulting phase shift controlling the power.

Robert.

Many thanks to those who clarified my earlier misunderstandings. Very educational, this forum.

In my home, the rising water-main is plastic, connected through a brass stop-cock to the usual copper pipes inside the building. When the house was heated electrically with hot-air, the water pipe wasn't earthed. However, when I switched to gas central heating, the whole system was. Now a thick copper wire runs from just above the stop-cock back to the consumer unit. Also, in the bathroom, the radiator is wired back to earth. The gas-piping is earthed on the consumer side of the meter. The gas supply pipe is plastic.

Reading the regulations the bonding is optional, but I think it's been done to address two different risks, They arise because copper pipes are poorly insulated:

• To prevent electrocution inside the house should Live accidentally connect to a pipe anywhere in the building. This is particularly important in the bathroom.
• Wherever the uninsulated copper pipes touch the wall and floor they are partially earthed. Thus there's a risk of a fault starting a fire. Badly earthed pipes become a hazard if there's anything in the electrical installation that could connect to them. They allow current to flow without blowing the fuse.

In my home, both risks were geographically impossible when I had hot-air heating, but both became possible as a result of fitting copper connected central-heating radiators in every room. Both risk are avoided by bonding.

A third risk doesn't apply. In my home, the supply pipes are both plastic, so there isn't any risk of a large fault current damaging the gas or water system by earthing through them.

Dave

Hi, as the frequency of the mains is concerned, measuring mine it fluctuates quite randomly between about 49.9 to 50.9, but it is mostly just either side of 50, this is over a period of about 15 minuets.

Regards Nick.

There is no need at all for that main equipotential bonding - the plastic pipes cannot introduce a potential into the building and its electrical installation.

My house was wired to 15th Edition and has a van's worth of supplementary equipotential bonding. Both pairs of hot and cold water pipes are joined under the double stainless steel sink and even the sink is bonded to them. This is all despite electrical continuity of the copper pipes, brass taps, and steel sink. It is mad!

Bonding is not the same as earthing even though green and yellow cables are used for both. If there is a fault within a boiler or fan-assisted radiator (where else could one occur?), the fact that the appliances are earthed will ensure ADS: the fault circuit is along the circuit protective conductor and not the pipes and bonding.

Seeking to rely upon bonding for ADS would not be safe - the copper pipes could be replaced by plastic ones or insulating joints could be installed.