Stumped by ground/neutral voltage

[gpedens]

stumped by neutral ground voltage

stumped by neutral ground voltage

Wayne just a comment on one of your earlier replies about disconnecting neutrals and/or grounds or even water pipes for that matter. You hit the nail on the head and drove it home. As you said you can get the primary voltage by lifting enough neutrals and grounds. This is one thing that a lot of folks forget.

One thing I always recommend is doing current measurements before disconnecting a neutral or an ECG or anything remotely resembling one, including water pipes and rebar in cement. Even steel columns in large manufacturing plants. If the metal or earth area is large enough even 100's or 1000's of amps will only give a fraction of a volt drop. We in the good ole USA operate with primary and secondary neutrals tied together at the transformer. We also tie our ecg and neutrals to our water pipes, building steel, etc in some form or fashion.

Over the years several copper thieves have toasted themselves stealing safe to touch bare low or no voltage ground wires. City workers replacing old iron or metal pipes have ended up with some pretty good sparks or hefty welding rods. Age and corrosion tend to make grounds ineffective or move current to other areas.

Please always measure current with some sort of clamp meter in the ground, neutral, ECG, etc before you disconnect it. Where I work I always insist on putting a jumper around any bare wire found in the ground before cutting it, even if it reads zero current. Just in case a load gets switched while I'm cutting. Then put a clamp meter on the jumper before I remove one end. You can survive the voltage but the current will make you a crispy critter. Make certain primary neutral and ground are good in the area. Check pole ground wires and anchor wires for current 1 to 3 poles away from the area of the problem. Low or no current in these indicates the neutral is carrying most of the current and you are safe to kill power to the home and lift some load neutrals provided you check for current or open the breaker first before lifting the neutral.

The main thing to remember is that lifting a neutral under load will kill you just as quick as grabbing the hot leg. The only thing that might save you is the resistance of the load limiting the current. And that would be about a 7 to 15 watt light bulb. And I dont recommend you try it.

 

[PhaseShift]

From the ground rod at the pole where the transformer is located to a wire/screwdriver/rod driven into the ground a few feet away. The same voltage was running throughout the system ground to earth.

So since the neutral was bad in the first place the current was traveling through ground system and its resistance and thus causing a voltage between the ground system and earth?

Wayne just a comment on one of your earlier replies about disconnecting neutrals and/or grounds or even water pipes for that matter. You hit the nail on the head and drove it home. As you said you can get the primary voltage by lifting enough neutrals and grounds. This is one thing that a lot of folks forget.

One thing I always recommend is doing current measurements before disconnecting a neutral or an ECG or anything remotely resembling one, including water pipes and rebar in cement. Even steel columns in large manufacturing plants. If the metal or earth area is large enough even 100's or 1000's of amps will only give a fraction of a volt drop. We in the good ole USA operate with primary and secondary neutrals tied together at the transformer. We also tie our ecg and neutrals to our water pipes, building steel, etc in some form or fashion.

Over the years several copper thieves have toasted themselves stealing safe to touch bare low or no voltage ground wires. City workers replacing old iron or metal pipes have ended up with some pretty good sparks or hefty welding rods. Age and corrosion tend to make grounds ineffective or move current to other areas.

Please always measure current with some sort of clamp meter in the ground, neutral, ECG, etc before you disconnect it. Where I work I always insist on putting a jumper around any bare wire found in the ground before cutting it, even if it reads zero current. Just in case a load gets switched while I'm cutting. Then put a clamp meter on the jumper before I remove one end. You can survive the voltage but the current will make you a crispy critter. Make certain primary neutral and ground are good in the area. Check pole ground wires and anchor wires for current 1 to 3 poles away from the area of the problem. Low or no current in these indicates the neutral is carrying most of the current and you are safe to kill power to the home and lift some load neutrals provided you check for current or open the breaker first before lifting the neutral.

The main thing to remember is that lifting a neutral under load will kill you just as quick as grabbing the hot leg. The only thing that might save you is the resistance of the load limiting the current. And that would be about a 7 to 15 watt light bulb. And I dont recommend you try it.

In this case would the situation be that since neutral was broken the connection back to the transformer source was on the ground system. With the ground system intact it would present a low resistance and therefore most of the primary voltage would drop across the primary of the transformer. However if someone were to lift this system ground somewhere it could create a larger impedance compared to the transformer primary and thus put a large voltage at the location where the ground is lifted. Is this correct?

 

[hurk27]

So since the neutral was bad in the first place the current was traveling through ground system and its resistance and thus causing a voltage between the ground system and earth?

yes the resistance of the grounding system is just like any resistor in a circuit, a current placed across it will cause a voltage drop across the resistor, this voltage drop will be in the form of voltage from one end to the other,
in this case from the service neutral/ground bond/grounding electrodes to Earth.

In this case would the situation be that since neutral was broken the connection back to the transformer source was on the ground system. With the ground system intact it would present a low resistance and therefore most of the primary voltage would drop across the primary of the transformer.

I wouldn't say that the impedance of the grounding was low, but it was low enough to keep the high voltage in check being in series with the transformer primary. if the transformer was of a larger type and more load was on it, this voltage would have been much higher.

However if someone were to lift this system ground somewhere it could create a larger impedance compared to the transformer primary and thus put a large voltage at the location where the ground is lifted. Is this correct?

yes just like if you open a neutral with a load on it, the voltage on this neutral towards the load will have the full voltage on it, only limited by the resistance of the load, which since there is no current across this load because the neutral is open, then it will be the full 120 volts, in the case of a transformer, and there is no other grounding then it would be the full voltage of the primary.