Service neutral protection

[dala]

I too am having a hard time visualizing and believing this. Where did this happen? Do you have a link to news accounts of these events?

This happened in Ocean Beach on Fire Island, New York. I only found 1 link but it had not mentioned the cause.

Fire Island is a barrier beach on the South coast of Long Island surrounded by the Atlantic Ocean and The Great South Bay. This is a harsh environment for any home. I'd say less than 5% of the homes on the island as a whole are occupied all year. The others are occupied June through September.

Probably the real problem is that Fire Island isn't as high a priority for the POCO being that there are so few yearly residents. A break in the bonding between the primary and secondary neutral is highly possible. I don't think so but if there was a small corroded break in the bonding wire, would that be detectable by any other means than a visual detection? My goal here is to create a way to protect a house should a breakdown (like the incident of my original post) of the POCO's equipment occur. A homeowner would be responsible for their own secondary protection installed at their house. This would also be easier to maintain because that equipment would be at ground level, easily visible by all. In other words, a break in a wire would more likely get replaced if it wasn't at the top of a telephone pole - barely visible by someone looking for it.

I got a phone number of the Ocean Beach F.D. and will give them a call today to find out the "official" cause of the fire.

 

[kwired]

This happened in Ocean Beach on Fire Island, New York. I only found 1 link but it had not mentioned the cause.

Fire Island is a barrier beach on the South coast of Long Island surrounded by the Atlantic Ocean and The Great South Bay. This is a harsh environment for any home. I'd say less than 5% of the homes on the island as a whole are occupied all year. The others are occupied June through September.

Probably the real problem is that Fire Island isn't as high a priority for the POCO being that there are so few yearly residents. A break in the bonding between the primary and secondary neutral is highly possible. I don't think so but if there was a small corroded break in the bonding wire, would that be detectable by any other means than a visual detection? My goal here is to create a way to protect a house should a breakdown (like the incident of my original post) of the POCO's equipment occur. A homeowner would be responsible for their own secondary protection installed at their house. This would also be easier to maintain because that equipment would be at ground level, easily visible by all. In other words, a break in a wire would more likely get replaced if it wasn't at the top of a telephone pole - barely visible by someone looking for it.

I got a phone number of the Ocean Beach F.D. and will give them a call today to find out the "official" cause of the fire.

A loss of bonding between primary and secondary neutral would not be a problem unless the primary phase had contacted the secondary side only. Now that we know this is an isolated area there is a good chance the primary neutral was open on the main supply to the island, when the phase to ground fault happened it found paths through these homes that was low enough resistance for a substantial amount of current to flow, yet was not enough to operate overcurrent protection.

It is also possible that overcurrent protetion could have been a lower setting, seen that before - transformer bank was melting down because primary fuses were larger than needed and never opened.

Too large of a fuse is not the main cause of the problem but may complicate what happens when it is called on to provide protection

 

[LISHAJI]

This would not necessarily cause an hazardous overvoltage, as long as the distribution transformer remains in the circuit. But, if the transformer fuse operates to separate the transformer from the circuit, before the upstream line fuse, the secondary voltage rises to the primary voltage. Normally this happens, when transformer is too tightly fused; smaller, fast transformer fuses are more likely to clear before an upstream device. or when the upstream device is not a fuse, rather a breaker or recloser with time delay trip! Take it up with the utility!!

See attached, secondary voltage rise in p.u.

 

[dala]

See attached, secondary voltage rise in p.u.
View attachment 6306

I appreciate your diagram and explanation but the point here is that there was a breakdown somewhere on the primary side or at least i should say of the POCO's equipment. Current was flowing (through the internal circuits of at least 3 houses that burnt down as a result) where it shouldn't have been. These homes were shut down for the season. The water was drained and the main breaker was turned off. Electrical voltage and current found it's way into these homes through the direct connection of the utility neutral. There is nothing in place to prevent this. A homeowner needs to be able to protect their home if there is a breakdown in the POCO's equipment. I'm looking for a product or procedure like a sensor or something that would completely disconnect all circuit wiring inside the house when a situation like this occurs. Something that is acceptable by the NEC and POCO. Does anyone know of such a product?

 

[LISHAJI]

main breaker was turned off. Electrical voltage and current found it's way into these homes through the direct connection of the utility neutral.

As a consumer, we always finds helpless, if the POCO responsible for power quality is not doing their job well. I doubt neutral has anything to do with it. Its the hot cables. The secondary main breaker's contact clearance may be rated for less than 6kV. So if higher than right voltage is impressed, it would spark over and weld or form a conducting path. An since this is a high impedance fault there is no fault clearing. If the neutral was involved the current would not have made up through the residences as you mentioned.

Surge protective devices may be of some help, but very limited. Its has to be POCO solution. See attached the effectiveness of SPD, it fails in 1 second.

 

[bigsky]

This is what "grounding" is supposed to do, that is provide and hold a common reference point, which if properly done will limit any damaging potential rise. It would be much more damaging if the phase conductors were affected. If, for example, a 7200V primary conductor came in contact with a 240V secondary phase conductor, you would have, at least momentarily, a very damaging condition. Very likely, most if not all utilization equipment would be destroyed before protection could isolate. If this same conductor came in contact with a properly grounded secondary neutral, ther might be some very high current trying to return to it's source, but other than voltage drop associated with any distributed return path, the localized ground potential should be relatively close to zero (again, assuming properly grounded).

 

[kwired]

This is what "grounding" is supposed to do, that is provide and hold a common reference point, which if properly done will limit any damaging potential rise. It would be much more damaging if the phase conductors were affected. If, for example, a 7200V primary conductor came in contact with a 240V secondary phase conductor, you would have, at least momentarily, a very damaging condition. Very likely, most if not all utilization equipment would be destroyed before protection could isolate. If this same conductor came in contact with a properly grounded secondary neutral, ther might be some very high current trying to return to it's source, but other than voltage drop associated with any distributed return path, the localized ground potential should be relatively close to zero (again, assuming properly grounded).

Common reference point - yes.

Bring all metallic objects connected to the equipment grounding system to same potential as ground - yes.

Provide a low resistance path through the equipment grounding system to allow a high level of current to flow during a ground fault condition so that overcurrent protection will respond quickly - yes.

Provide a low resistance path via grounding electrode(s) and through earth to allow a high level of current to flow during a ground fault condition so that overcurrent protection will respond quickly - NO

The higher the voltage the more current the earth will carry, but there is still resistance there. There is a big difference between pushing 120 volts through earth vs, 7200 or higher, and how much current will flow.

 

[wirenut1980]

As a consumer, we always finds helpless, if the POCO responsible for power quality is not doing their job well. I doubt neutral has anything to do with it. Its the hot cables. The secondary main breaker's contact clearance may be rated for less than 6kV. So if higher than right voltage is impressed, it would spark over and weld or form a conducting path. An since this is a high impedance fault there is no fault clearing. If the neutral was involved the current would not have made up through the residences as you mentioned.

Surge protective devices may be of some help, but very limited. Its has to be POCO solution. See attached the effectiveness of SPD, it fails in 1 second.
View attachment 6315

Great post. Definitely more information is needed from the utility about what exactly happened before the original poster's question about a solution should even be asked. As others have stated, the 20 minute time frame is troubling for sure. Were all the damaged/burnt houses fed from the same distribution transformer? If so, then it sounds like a medium voltage ungrounded conductor did contact something common to all the houses, could have been service grounded or ungrounded conductor. If not, then the damage sounds like a transmission wire (69 KV or higher) came into contact with a medium voltage circuit underbuilt possibly. Just guessing now without more information.

For protection against high voltage, surge suppression or some sort of over-voltage relay possibly. But I've never seen that used on a residence, so I am not even sure it is possible.

 

[hbiss]

I've read through this whole thread and from what I can see it sounds like a primary to secondary cross or a transmission line to medium voltage line cross. I've seen the former situation myself and there is a video on the web of the devastating effects of the latter. No electro-mechanical device will be fast enough and a solid state surge suppressor is going to self distruct probably before doing any good also. The voltage will arc across an open main breaker as was said. Pulling the meter will give a much larger air gap. Dropping the service when vacant is the only protection and pray that nothing happens while the house is occupied.

-Hal

 

[LISHAJI]

-Hal

OH MY GOD!! THAT WAS UNBELIEVABLE!!

 

[gadfly56]

I've read through this whole thread and from what I can see it sounds like a primary to secondary cross or a transmission line to medium voltage line cross. I've seen the former situation myself and there is a video on the web of the devastating effects of the latter. No electro-mechanical device will be fast enough and a solid state surge suppressor is going to self distruct probably before doing any good also. The voltage will arc across an open main breaker as was said. Pulling the meter will give a much larger air gap. Dropping the service when vacant is the only protection and pray that nothing happens while the house is occupied.

-Hal

So we're assuming in the OP's case that EVEN WITH THE MAIN BREAKERS ALREADY OPEN, the potential was high enough that it created an arc from one or both phases inside the breaker case to push current back to the transformer? And current flow would be from the secondary neutral through the EGC to the bonded connection in the panel, up the neutral conductor, spark across anything that can't resist the 7,200 volts, back down the normally hot conductor, arc across the open breaker, and back to the transformer? Do I have this right?

 

[hbiss]

Don't forget the insulation on the wiring that gets destroyed also. The main breaker and panel will originally arc but quickly be turned into conductive carbon. This is about as predictable as lightning.


-Hal

 

[T.M.Haja Sahib]

The higher the voltage the more current the earth will carry, but there is still resistance there. There is a big difference between pushing 120 volts through earth vs, 7200 or higher, and how much current will flow.

See post #43.Even for fault of 4.8 Kv to 34.5kv,the voltage rise on the secondary is limited.This can happen only when the secondary fuse of the transformer is intact and ground resistance providing return path to fault current back to source is low enough.

 

[Dennis Alwon]

Are we talking about a loose neutral that will increase voltages on phase. We had this happen 5 miles from here. The neutral was broken underground and the house caught fire. The specifics I do not know but the inspector in that area called me about it. I have no other info.