question from electrical releative simpleton re: ground

Please forgive me if this is too advanced of a group to post such a
general / layman question. I thought I understood the safety issue
behind grounding electrical devices--that in a non-grounded device, if
a live wire in said device makes contact with a conducting surface
(like the metal surface of a washing machine), that touching said
surface would be equivalent to sticking your finger in a plug of
voltage equal to that of the wire resulting in a high likelihood of
electrocution.
I recently read a report of a local city boarding up a person's
home and denying the owner entry. It is suspected that that the city
wants the prime location land that the house is on though one of the
reasons given by a city councilman is that the house's "electricity is
not grounded" and that this is a fire hazard. If "the electricity" of a
house is "not grounded" how is this conceptually different from an
appliance not being grounded? And is either actually a fire hazard or
an electrocution hazard only?
Reply to
chimpanzo
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(I know this a simplified explanation that leaves out may details)
You have power ground and you have safety ground.
Put simply, you need safety grounding because the power company grounds one side of the AC supply. This is done at the substation. They hammer a copper stake in the ground and connect the neutral conductor to it. This is called the 'neutral' conductor. It is sometimes referred to as the power ground. That means that if you touched the other wire, called the 'hot' or 'live' wire, current can flow from the hot wire through your body to the earth. Depending on how good your contact is with the earth, how moist the soil is, etc, a current could flow through your body & kill or injure you.
If the live or hot wire comes loose, or insulation breaks down inside an item of electrical equipment with an ungrounded metal case or exposed metal parts, touching that metal would be dangerous therefore.
So the law requires every house to have its own ground connection also. This could be a copper stake hammered into the soil, or sometimes it is permitted to use a clamped connection to a buried water pipe. It has to as near as possible to where the power company's wires enter the house. This is called the safety ground.
So what we do is to run a separate grounded conductor from our safety ground stake to the outlet, in addition to the hot and neutral, and using a three pin plug, we connect the casing, metal parts, etc, to that "safety ground" conductor.
That means that if a loose wire or deteriorated insulation or bad wiring of the plug or cord led to contact between the live or 'hot' conductor and the metal casing or parts, the effect would be of a live-to-neutral short, and a heavy current would flow, blowing a fuse or tripping a circuit breaker, thus alerting the householder to the problem and removing the danger. Also, because the metal casing is grounded, It is at the same potential as the ground (the one that people stand on), and persons touching it will not get a shock while that is going on. Hopefully.
In the olden days, the safety ground removed the problem by blowing a fuse with a bang. Sometimes, say if you were using an electric lawnmower or hedge trimmer on a damp lawn with a long extension cord, you might still get enough juice to kill you by stopping your heart, without the fuse blowing. So nowadays you can get sensitive circuit breakers which sense even a tiny leakage and trip very rapidly and hopefully reduce the risk of fatal shock.
If the house's wiring does not have, or has lost, a proper ground connection right slap bang where the power company's wires come in the house, near the switchboard, then anyone using electrical equipment in that house could get electrocuted or insulation could deteriorate and enough current could flow, to heat up wall or floor material and ignite it.
It is usually a simple matter to put grounding problems right, although employing a trained and certified electrician is a good idea, and may well be required by law and/or insurance companies.
Reply to
mike.j.harvey
(I know this a simplified explanation that leaves out may details)
You have power ground and you have safety ground.
Put simply, you need safety grounding because the power company grounds one side of the AC supply. This is done at the substation. They hammer a copper stake in the ground and connect the neutral conductor to it. This is called the 'neutral' conductor. It is sometimes referred to as the power ground. That means that if you touched the other wire, called the 'hot' or 'live' wire, current can flow from the hot wire through your body to the earth. Depending on how good your contact is with the earth, how moist the soil is, etc, a current could flow through your body & kill or injure you.
If the live or hot wire comes loose, or insulation breaks down inside an item of electrical equipment with an ungrounded metal case or exposed metal parts, touching that metal would be dangerous therefore.
So the law requires every house to have its own ground connection also. This could be a copper stake hammered into the soil, or sometimes it is permitted to use a clamped connection to a buried water pipe. It has to as near as possible to where the power company's wires enter the house. This is called the safety ground.
So what we do is to run a separate grounded conductor from our safety ground stake to the outlet, in addition to the hot and neutral, and using a three pin plug, we connect the casing, metal parts, etc, to that "safety ground" conductor.
That means that if a loose wire or deteriorated insulation or bad wiring of the plug or cord led to contact between the live or 'hot' conductor and the metal casing or parts, the effect would be of a live-to-neutral short, and a heavy current would flow, blowing a fuse or tripping a circuit breaker, thus alerting the householder to the problem and removing the danger. Also, because the metal casing is grounded, It is at the same potential as the ground (the one that people stand on), and persons touching it will not get a shock while that is going on. Hopefully.
In the olden days, the safety ground removed the problem by blowing a fuse with a bang. Sometimes, say if you were using an electric lawnmower or hedge trimmer on a damp lawn with a long extension cord, you might still get enough juice to kill you by stopping your heart, without the fuse blowing. So nowadays you can get sensitive circuit breakers which sense even a tiny leakage and trip very rapidly and hopefully reduce the risk of fatal shock.
If the house's wiring does not have, or has lost, a proper ground connection right slap bang where the power company's wires come in the house, near the switchboard, then anyone using electrical equipment in that house could get electrocuted or insulation could deteriorate and enough current could flow, to heat up wall or floor material and ignite it.
It is usually a simple matter to put grounding problems right, although employing a trained and certified electrician is a good idea, and may well be required by law and/or insurance companies.
Reply to
mike.j.harvey
Niether term is defined in NFPA70. What you actually have is a"grounded" conductor and a "grounding" conductor.
The power company also grounds the system at the transformer near your house or building.
The system equipment grounding conductors do not simply connect to the grounding electrode. The grounding electrode conductor, the grounded supply conductor, the grounded conductors (white wires) and the equipment grounding conductors (green wires) are all bonded (connected together) in the main service panel. The return path from all of them is throught the copper service conductor back to the source. Take a look at the first diagram at
formatting link
There is the possibility of an elevated touch potential between earth and grounded objects in the event of a fault, which does raise the electric shock hazard a bit. However, everything is still bonded in the main panel. All exposed metal is still connected solidly to the grounded side of the system, and a fault anywhere in the system will still trip the protective device.
Grounding the entire system primarily serves another purpose. It stabilizes the voltage with respect to earth and prevents possible elevated potentials, flashover of insulation, etc. in the event of voltage transients such as lightning. It also allows the utility protective devices to function more effectively. In that sense, the statement about fire hazard is correct. Remember, however, that the system is still grounded a bit further away, at the utility transformer, so you still have some of this functionality.
I don't see the need for eviction, as any electrical contractor could easily install the necessary grounding electrode system.
Ben Miller
Reply to
Ben Miller

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