Storm scare....I need some thoughts/opinions

[SPIKER]

The SAND and Lightning can make glass art underground where the sand is melted by the lightning strike. I forget what they call it but remember hearing about it a long time ago..

Sister was at home when their place had the mains blown up and same with the 3 surrounding homes one ended up burning to the ground as couple were in FL at time it hit. close to 15K of damage to her home where a good bit of wiring as well as most every thing that was plugged in was toasted.


Mark

 

[Ken45101]

The induced charge in the ductwork and beams could be just from the airborne lightning strike, not from something in the ground. I hear my ham radio antennas start to arc long before I actually hear any thunder here. I have some big (6") knife switches to ground a couple of the antenna feedlines and I will sometimes leave them almost grounded but with a quarter inch gap to the ground post and then enjoy listening to the charge picked up by the antenna arcing to the ground contact.

 

[General Lee]

The induced charge in the ductwork and beams could be just from the airborne lightning strike, not from something in the ground. I hear my ham radio antennas start to arc long before I actually hear any thunder here. I have some big (6") knife switches to ground a couple of the antenna feedlines and I will sometimes leave them almost grounded but with a quarter inch gap to the ground post and then enjoy listening to the charge picked up by the antenna arcing to the ground contact.

Interesting. Makes me nervous, and wonder if something is wrong with the house and if if I need to make corrections somewhere to avoid it happening in the future.

 

[TCJatko]

You're welcome. The general contractor wanted so badly for me to declare lightning as the cause- and the insurance company would have bought it since Orlando really gets hammered by it, but I try to be honest. A backhoe operator had hit the main power feed for the complex, but only cut the neutral. Thus 240v was sent to the phone system, computers, TV's, and even the radio clocks in all the rooms.

Sorry to divert this thread, but help me out here. If the backhoe severed only the neutral leg, then how would 240 v get to 120 v appliances? Aren't those appliances powered by one leg of the 240, and the return is the neutral? So you might have 120 v on one side of your outlet, but the other half would be dead and nothing works. Correct?

 

[Fawken]

Sorry to divert this thread, but help me out here. If the backhoe severed only the neutral leg, then how would 240 v get to 120 v appliances? Aren't those appliances powered by one leg of the 240, and the return is the neutral? So you might have 120 v on one side of your outlet, but the other half would be dead and nothing works. Correct?

Here is how it works- and it can happen in your home as well: You are correct that we get our 120v by center tapping a 240v source. What happens is there are two, separate legs of 120. Separate being the operative word. The air conditioners in the rooms straddle both legs but also have some inherent leakage to ground. The 240 v is trying to find a pathway to complete it's circuit and the shortest distance to complete the path is through the plugged in AND turned on appliances.

 

[CobyRupert]

The rebar doesn't do much for you. Here's an interesting case I worked for the Illinois Teacher's Retirement Fund in 1999: Orlando, Florida. Lightning capital of the world. The Retirement Fund was the majority shareholder in the Wyndham Orlando Resort Hotel & Convention Center. After tracing a transient surge that did $169,000 damage back to a backhoe accident, I was asked to verify all building ground rods with a Megger. This resort is a campus with 28 separate buildings originally constructed in the early 70's as an apartment complex. Turns out virtually all of the original ground rods were bad due to being encased in glass. Lightning had entered the circuit and turned the silicon based sandy soil to glass.

If the rebar is tied into all the other rebar in the slab, then you essentially have a ground rod (ground electrode system) with a surface area that is many many many times more effective than a single ground rod. This is why tying in the rebar system, like a water pipe, into the ground system, when available, is part of the code.

 

[Fawken]

If the rebar is tied into all the other rebar in the slab, then you essentially have a ground rod (ground electrode system) with a surface area that is many many many times more effective than a single ground rod. This is why tying in the rebar system, like a water pipe, into the ground system, when available, is part of the code.

Rebar rusts very quickly. In dry areas, rebar in a slab doesn't reach anywhere near deep enough to hit "moist earth." I helped write NEC article 250 and contributed to NFPA sub code on grounding and bonding. Do not rely on rebar for a ground.

 

[Fawken]

Sorry to divert this thread, but help me out here. If the backhoe severed only the neutral leg, then how would 240 v get to 120 v appliances? Aren't those appliances powered by one leg of the 240, and the return is the neutral? So you might have 120 v on one side of your outlet, but the other half would be dead and nothing works. Correct?

And I found this diagram which may help clear it up:

 

[Mace Canute]

The rebar doesn't do much for you.........

What about NEC Article 250.52(A)(3)?

 

[Mace Canute]

Sorry to divert this thread, but help me out here. If the backhoe severed only the neutral leg, then how would 240 v get to 120 v appliances? Aren't those appliances powered by one leg of the 240, and the return is the neutral? So you might have 120 v on one side of your outlet, but the other half would be dead and nothing works. Correct?

I posted this a few years back about what happens when a neutral goes "open". Hopefully this diagram will help people visualize what goes on.

For purposes of clarification, we'll leave the earth ground out of the picture. Once the neutral opens, the first load when turned on won't work and every load on that same hot leg will also not work. As soon as a load on the other hot leg is turned on, you have created and completed a series circuit. As you turn on more and more individual loads, you create a complex series and parallel load situation so again for purposes of clarification lets consider just two loads, one on each hot leg. The thing is, with a series connection, the current flowing through every load is exactly the same. Has to be.

As you see in the example, with a load on each hotleg, the open neutral suddenly places those two loads in series. What we want to calculate is the voltage potential (voltage drop) across each load. Another given is, the total of all the voltage drops across all the loads adds up to the total applied voltage. Has to be. In an open neutral situation, that would be 240 volts.

Volts (voltage drop) equals amps times resistance. Again, for purposes of clarification lets assume the resistance of each load remains the same with respect to what it was in a normal situation, (in real life it may or may not but for our purposes here, it doesn't matter) Going back to our power equation, you can calculate the voltage drop across each load. In a normal situation, each load sees only that current flow allowed by the resistance of the individual loads, and the voltage remains constant. In an open neutral situation, the current flow through every load is the same and the individual voltage drops across each load are what fluctuates.

As you can see, the loads with the higher resistance are the ones that see the higher voltage drop across them and vice versa. This also means that if both loads have exactly the same resistance, everything will appear to be normal. It also means that as more and more loads with different resistances are turned on, the voltage drop across every one of them will change, but the total of all of them must still add up to the applied voltage - 240 volts - but each individual load sees a different voltage drop across it.