Had a small electrical fire in the flooring of an unoccupied rental house. Happened about a week after the plumber cut a galvanized water pipe under the house. Upon inspection after the fire dept. removed the flooring in the area, I noticed there is a single cloth type #12 wire connected to a loose grounding clamp onto a galvanized pipe under the floor. A forensic PE investigator told me that if this wire is a neutral, or grounding conductor it could have a current running through it only, but no voltage after it passes through the load ??? I thought the two were always together :? I am going to trace this wire to it's origin, and terminate, and run a proper wire pair back to the panel bus, and also bond the galvanized pipe with a jumper, and clamps. Point to this post, can the neutral or ground carry current only with no voltage ?
House with potential fire issue
- Thread starter dronai
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K8MHZ
Senior Member
- Occupation
- Electrician
Current can be measured from one point. Voltage has to be measured from two points, as voltage is a difference in potential. In order for current to flow through the conductor in question, there must be a voltage present when measured from one end of the conductor to the other.
The old conductor you see may likely be an added ground for a receptacle or a circuit in order to change from two wire to three. It used to be legal to get a ground from the nearest grounded metal so you didn't have to go back to the panel. It is not a neutral, that much I am sure of. It may be able to be (illegally) used as one, though.
This statement is 100% fact ? That is the message I first received from the PE engineer, that it is a ground. I am concerned as to why the ground was carrying enough current to start a fire, that's why I thought it was a neutral wire in the loop (circuit).
SparkyHC
Member
- Location
- Southern New Jersey
Was it actually reported that this wire started the fire? Or is this your assumption?
The fire department was called, they shut the main off, and took up the flooring in the burned area, and exposed the wire, and the clamp to the pipe. Yes it has been determined by the Fire department inspection, the insurance companies PE Forensic fire investigator, and myself that this was the cause.
SparkyHC
Member
- Location
- Southern New Jersey
and this was an "arcing" fault, or a short circuit, or an overheated conductor?
How did this wire ignite the surrounding material? The fact that is had current flowing through
it is incomplete as all electrical wiring conducts current and most of the time never ignites...
How did this wire ignite the surrounding material? The fact that is had current flowing through
it is incomplete as all electrical wiring conducts current and most of the time never ignites...
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
First, any bad neutral connection will be in series with the connected load. That makes a voltage divider. The low side of a load does not magically become zero volts. It has to be connected through a (hopefully very small) resistance to the utility neutral to pull the voltage down.
There are two possibilities here:
1. The wire is a ground wire, but was incorrectly bonded to the neutral at an outlet or plugged-in device. Then a secondary failure caused the official neutral to open, sending the normal load current through the ground wire.
2. The wire is a ground wire only and is not paralleling the neutral, but a line-to-ground fault in a connected load caused some current to flow through the ground. As long as the current was too low to trip the circuit OCPD, the load might even continue to appear to work correctly. But there would be a high current in the poorly connected ground wire.
As for the relationship to the plumber cutting a pipe, that could have altered the ground connection path through the plumbing, but that alone should not have had any effect on current flowing where none had been before. It is more likely that the vibration either loosened an existing ground connection, causing it to heat up, or caused a completely open ground connection to start carrying current from a pre-existing wiring fault.
The ground clamp was loose on the galvanized pipe in the burned area. ....Fact one- A week earlier, the plumber had cut a galvanized plumbing pipe, Fact two, a week later two trades were using the same circuit (Hence the large load) about an hour later the owner walked in with the plumber working alone under the house, and saw all the smoke, and called the fire department. To answer your question, "the expert" Forensic PE, said it was caused by arcing at the loose clamp.
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SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
One possibility is that if the house shares underground metallic piping with the rest of the neighborhood & someone has lost their neutral, it is now being supplied by the piping system through the Grounding Electrode Conductor. The lost neutral could be at the house that caught fire or one of the neighbors.
It should be possible to measure current on the pipe & GEC. This situation also presents an electrocution hazard in addition to the fire hazard. Be careful if you decide to open the GEC attached to the pipe. If current is present with the main OFF then one of the neighbors has a bad neutral. If the current is only present with the main ON, then this house has a bad neutral.
It should be possible to measure current on the pipe & GEC. This situation also presents an electrocution hazard in addition to the fire hazard. Be careful if you decide to open the GEC attached to the pipe. If current is present with the main OFF then one of the neighbors has a bad neutral. If the current is only present with the main ON, then this house has a bad neutral.
The part in bold appears to be the cause according to the PE. The loose clamp with a large load is what caused the fire. IMO, If you remove part of the galvanized plumbing system which is the best ground path for a short circuit, that would leave the ground rod as the next best thing to remove a short circuit. The house system would function without any grounding at all, it just wouldn't be safe if there was a short circuit. So why would the suspected wire have current at all ? maybe a short ?, or a bootleg neutral ? This is what confuses me as to the exact cause.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
See items 1 and 2 in my post.....
First thing I did, was to call the poco and test for an open neutral on their side. Utility side was good. Your right though, It could be one of the neighbors using this houses neutral.
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Item 1: Yes, your right, in that if the two wires, ground, and neutral were incorrectly bonded at the device, the path of least resistance could be that plumbing system Item 2: is a possibility as well.
Can you draw out the point of the service entrance, how the service entrance is grounded, at what point the neutral is bonded to the ground, at what point the galvanized water comes into the picture to establish why there Han been current flowing at that point. If you don't sort out the relationships of the neutral and the ground you're just chasing your tail. It is of my opinion that there shouldn't have been current of ant degree flowing at the point in question. This is a symptom of another problem.
SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
The Grounding Electrode System has little to do with clearing ground faults or short circuits. Please watch this link, slides 10 -68 are critical. http://www.tirebiter.net/downloads/ludecke.html
I can't open your links, but the GES if bonded correctly at the main service with the neutral bus, should clear ground faults.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Oh no my friend, a GES will not clear ground faults in many or really most cases.
Tis not the function of the GES to clear faults. Reread 250.4.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
The download link marked Zip file is actually just a Stuffit archive renamed to .zip extension. Most utilities for zip files cannot unpack it. The large PPT file does open in PowerPoint or a PowerPoint viewer.
Still can't open it, but I know the function was designed for lightning strikes. When my computer savvy wife gets home, I will have her open the file.
I will get you more info tomorrow when I go back.
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