Twin ground rods is Fairly universal practice in North America.
Water pipes are No longer Metal so those are Not viable grounds.
Neither are Gas lines, Not in the least because these too, are of plastic.
However there are still a Very large percentage of Bldgs and houses that were built under previous generation code rules.
No need to mention that most Every homeowner 'dicks around' with his home armed with exuberance and no actual knowledge..
Water pipes are No longer Metal so those are Not viable grounds.
Neither are Gas lines, Not in the least because these too, are of plastic.
However there are still a Very large percentage of Bldgs and houses that were built under previous generation code rules.
No need to mention that most Every homeowner 'dicks around' with his home armed with exuberance and no actual knowledge..
AFAIK twin ground rods are only common practice in the U.S.A where soil conductivity is poor, this is the only house I've owned or lived in that has dual grounding rods. (In fact during the rewire the electrical inspector required our electrician to add the second rod and upgrade the existing bond to the cold water supply lines, he also made him install a bond across the water meter, and check that the gas line was not part of the grounding system. The electrician who was very experienced was surprised, but admitted he had never done a job in our city before. I live in a city adjoining Boston proper) Nowhere else I have ever lived in MA or NH had multiple grounding rods. It is a requirement of the community I live in, adjoining towns don't always require it.
Plastic and copper pipe also are not permitted for natural gas fittings in Massachusetts, (black iron only) and water lines from the street into homes are still commonly copper up to the meter and if pex is used for domestic hot and cold water a copper manifold is not too uncommon..
Have a look at the NEC, in the US it defines the minimum requirements, local requirements if more stringent override them.
Plastic and copper pipe also are not permitted for natural gas fittings in Massachusetts, (black iron only) and water lines from the street into homes are still commonly copper up to the meter and if pex is used for domestic hot and cold water a copper manifold is not too uncommon..
Have a look at the NEC, in the US it defines the minimum requirements, local requirements if more stringent override them.
our household ac power were all derived from 3 phase sources,
with lines A, B and C as "live" phases....
the dropwire to your house could be any one of
those phases plus a neutral return wire...
a neutral is supposed to be zero volts, but in reality it is not.
fusing the line side is mandatory, for safety reasons...
Here in the U.S. three phase power is not commonly distributed to single family residences. In my neighborhood specifically (I know this from our electrical inspector) the power is carried by a 3 phase delta distribution system at 22kV (!) and there are single phase transformers connected across any two phases of the delta, over the length of the neighborhood the load is fairly evenly distributed across the phases. Power delivered to the residence is 230V single phase with the center tap connected to neutral (and ground!). My mains vary over a range of about 234V - 242V (117V - 121V) during the course of a 24 hr period. Sadly the waveform is not recognizably sinusoidal during peak, a trapezoid is more like it, the pole pig apparently runs on the verge of saturation - which seems to be standard these days here.
I remember when the power company replaced the transformer on the pole outside my last home, I was somewhat friendly with the plant manager and called to comment on the crappy waveform, he laughed and told me that the new transformer was rated at twice the capacity of the old one, but weighed about 1/3 as much - we figured reduced core mass was the reason. It was also much smaller!
I remember when the power company replaced the transformer on the pole outside my last home, I was somewhat friendly with the plant manager and called to comment on the crappy waveform, he laughed and told me that the new transformer was rated at twice the capacity of the old one, but weighed about 1/3 as much - we figured reduced core mass was the reason. It was also much smaller!
Ahhhh there are Always the exceptions 
I'm familiar with the CDN codes and have worked with the Standard bldg code..some.
Twin Gnd rods is a standard requirement "here'', driven in semi close proximity to each other.
Gas is delivered in seamless Plastic piping, from mains feed to appliance proximity.
New Underground gas mains / supplies are plastic as well.
Plastic is allegedly more durable and doesn't crack.
Water pipes haven't been either Iron or Copper for close to 20 years.
Iron rusts out while Copper dissolves/perforates from the chlorine.
That said, ineptly joined plastic water pipes fail as well. And rats love to chew through them when thirsty
Transformer cans are 'spectacular' when they explode A fireball like an incendiary grenade.
Bldgs need to be armoured if within 20 feet of one (bldg code item)
One Should Not ! live near one, for a variety of reasons. Despite assurances.
I'm familiar with the CDN codes and have worked with the Standard bldg code..some.
Twin Gnd rods is a standard requirement "here'', driven in semi close proximity to each other.
Gas is delivered in seamless Plastic piping, from mains feed to appliance proximity.
New Underground gas mains / supplies are plastic as well.
Plastic is allegedly more durable and doesn't crack.
Water pipes haven't been either Iron or Copper for close to 20 years.
Iron rusts out while Copper dissolves/perforates from the chlorine.
That said, ineptly joined plastic water pipes fail as well. And rats love to chew through them when thirsty
Transformer cans are 'spectacular' when they explode A fireball like an incendiary grenade.
Bldgs need to be armoured if within 20 feet of one (bldg code item)
One Should Not ! live near one, for a variety of reasons. Despite assurances.
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Those rats are pretty smart.. lol
They got rid of chlorine around here almost a decade ago, and use ozone instead - not sure what effect that has on water pipes. (The water tastes a lot better now.) The copper pipes here seem to be in pretty good shape, but have to be at least 40yrs old. The water line that comes into the house is copper tubing, and I suspect is older still.. The water folk say it should last a century, and it is definitely not original to the house, so hopefully it is not something I will have to worry about.
New water mains around here seem to be some odd resin/fiberglass affair with plastic inner? Ours is still ancient, but I expect it will be replaced in a few years.
They got rid of chlorine around here almost a decade ago, and use ozone instead - not sure what effect that has on water pipes. (The water tastes a lot better now.) The copper pipes here seem to be in pretty good shape, but have to be at least 40yrs old. The water line that comes into the house is copper tubing, and I suspect is older still.. The water folk say it should last a century, and it is definitely not original to the house, so hopefully it is not something I will have to worry about.
New water mains around here seem to be some odd resin/fiberglass affair with plastic inner? Ours is still ancient, but I expect it will be replaced in a few years.
There tends to be a lot of rule of thumb that is followed these days by inspectors and electricians. Technically, NEC requires only one ground rod if the resistance to ground results in values less than 25 ohms. IF it's greater, supplementary grounding is required, which consists of a second ground rod. Since the electricians are not equipped with ground testers (you don't use a multimeter for this test) the general command is to put in the second rod and be done with it.
Also, it is required that ground rods be spaced apart AT LEAST as far as their length. Greater distances are more effective, so with a 8 foot ground rod 8 foot spacing is required, 12 feet is better.
So in industry the rule of thumb is two ground rods 8 feet apart. Neither of these are specifically stated as required, it's a rule of thumb that avoids any controversy.
Latest practice is also multiple bonds on the neutral: one at the pole (or pad if ground level) one at the meter and one at the panel. But the important point is once you reach the panel, no more bonds on the neutral.
Also, it is required that ground rods be spaced apart AT LEAST as far as their length. Greater distances are more effective, so with a 8 foot ground rod 8 foot spacing is required, 12 feet is better.
So in industry the rule of thumb is two ground rods 8 feet apart. Neither of these are specifically stated as required, it's a rule of thumb that avoids any controversy.
Latest practice is also multiple bonds on the neutral: one at the pole (or pad if ground level) one at the meter and one at the panel. But the important point is once you reach the panel, no more bonds on the neutral.
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