Security issues power switch wiring

[yunger]

A fun thing happens if the neutral going back to the distribution trannie gets high resistance or open. The voltage at any one socket is then determined by the balance of loading between the two hots and the in-house neutral. A heavy current user on one side of the incoming 240Vac pulls its side down and the other side's voltage rises until the currents balance since the current in the neutral which balances these things can't eat the difference. So if you have a high-resistance neutral at the distribution box, the voltage on any wall socket can drop precipitously if it's on the same side of the 240 as, say, a refrigerator, toaster, or hair dryer. A wall socket on the other side can shoot up to dramatically high voltages as the two sides of the two hot lines must add to 240.

funny, i recently experienced this. i replaced galvanized water pipes with pex...noticed an arc when i disconnected the metal pipes. i figured it was a grounding issue even though i had driven a couple copper rods for safety ground.
i noticed that when i turned on a space heater or used power tools lights would get brighter. i ended up rewiring the house, new breaker box, new meter box, new wire up to the drop. problem still there.
i called the power company and they found that the nuetral was disconnected at the transformer. who knows how long it had been that way. 100 year old house. apparently the metal water pipes were acting as nuetral connecting to my neighbors.
good thing it was fixed before it started to fry things in my house.

[soundguruman]

funny, i recently experienced this. i replaced galvanized water pipes with pex...noticed an arc when i disconnected the metal pipes. i figured it was a grounding issue even though i had driven a couple copper rods for safety ground.
i noticed that when i turned on a space heater or used power tools lights would get brighter. i ended up rewiring the house, new breaker box, new meter box, new wire up to the drop. problem still there.
i called the power company and they found that the nuetral was disconnected at the transformer. who knows how long it had been that way. 100 year old house. apparently the metal water pipes were acting as nuetral connecting to my neighbors.
good thing it was fixed before it started to fry things in my house.

The #1 problem with commercial power is open/ corroded/ intermittent neutral.
This can blow the crap out of your house. I have seen this type of defect melt the circuit panel buss bars.
Depends on how the pole transformer is configured, but causes major power surges.

It is possible under certain circumstances for 17,000 volts to enter your house, when the neutral is open.
The worst possible scenario.

[g1]

It is possible under certain circumstances for 17,000 volts to enter your house, when the neutral is open.

Care to explain how this could possibly happen, without involving lightning strikes?

[pdf64]

Maybe if the secondary completely lost its ground reference (which I guess is what the neutral is), then the secondary may float to a high voltage above ground.
But the power deliver would be limited to the secondary phase voltage/s.
The actual voltage it could float to would likely be limited by the insulation leakage resistance on the secondary, which would act to provide a loose ground reference?
Pete

[soundguruman]

Maybe if the secondary completely lost its ground reference (which I guess is what the neutral is), then the secondary may float to a high voltage above ground.
But the power deliver would be limited to the secondary phase voltage/s.
The actual voltage it could float to would likely be limited by the insulation leakage resistance on the secondary, which would act to provide a loose ground reference?
Pete

yes it is possible when the neutral between the power plant and the distribution transformer fails.
depending on how the power company wires the distro, the high voltage can come right down into the panel, thru the neutral wire.
This actually happened in a 3 phase service on Kauai. The power was for a radio station transmitter building.
It caused 12,000 volt coupling caps to explode and melt..etc. inside the transmitters. Very similar to lightning strikes.
The power company had installed chart recorders, and it blew the pens right off the paper charts.

I finally installed a Liebert regeneration system. It was $22,000 plus air freight. I fixed up a zig zag neutral for the single phase devices.
By disconnecting the secondary distro neutral, and creating our own neutral, we were able to stop the explosions and stabilize the power.
I also grounded the building away from the power company ground (separated them).
I drove three 12 foot rods 8 foot apart in a triangle shape, and welded 1 ought wire between them, then to my zig zag.

Now, that's what I call a power surge. Holy sheep crap.
In Hawaii, the electricians call this "wild three phase." Oh, it's wild.

[Steve Conner]

I can see how this could happen, if the power company connected the neutral wires for the high and low sides together, and the neutral got open on the high side and poorly grounded on the low side, and the load got unbalanced. The unbalance current on the high side would try to get to ground/neutral through your low voltage installation.

On our medium and high voltage distribution systems, we just use three phase wires, there is no neutral. The neutral on the low voltage side comes from the star point of the distribution transformer secondary, and is connected to ground at the substation.

To get 11kV coming from your outlets on this system, you'd need to lose the connection between neutral and ground at the substation, and have a breakdown between high and low voltage sides in the distribution transformer. I guess that is theoretically possible too

[soundguruman]

I can see how this could happen, if the power company connected the neutral wires for the high and low sides together, and the neutral got open on the high side and poorly grounded on the low side, and the load got unbalanced. The unbalance current on the high side would try to get to ground/neutral through your low voltage installation.

On our medium and high voltage distribution systems, we just use three phase wires, there is no neutral. The neutral on the low voltage side comes from the star point of the distribution transformer secondary, and is connected to ground at the substation.

To get 11kV coming from your outlets on this system, you'd need to lose the connection between neutral and ground at the substation, and have a breakdown between high and low voltage sides in the distribution transformer. I guess that is theoretically possible too

It can definitely happen. I was there to see it.
The poor radio station was flamed over and over for years.
Fortunately, I was not responsible for wiring the commercial power...but I ran the transmitters off a 50KW Marine Corps diesel generator for months to avoid the power company.
The transmitters were miles down a dirt road in a cane field, and there was nothing I could do to get the power company to fix the defects.
I remember the sound of that high voltage on the poles arching, you could hear it for miles away..KA BLAM! Scary I tell you. All you can do is stand back and cover your ears.

[bob p]

I remember when someone here linked to a youtube video of a power station switch opening with high voltage on it. The arcs and noise were impressive.