Please Help Diagnosing Electrical Fault - Page 1
Forum section: electronics / projects

author: HeZ
author_rank: Newbie
timestamp: December 22, 2016, 12:07:46 pm
content: Hi all,I have a serious electrical fault at my house and I am hoping to have have a discussion and do some diagnostics here. Any licensed electrician, or anyone with half a brain for that matter, will shut off the power here so fast that they will leave back to the future style skid marks all the way to the main breaker (Yes I have half a brain, it is off). So I am hoping to understand the possible causes as best I can to assist the tech and expedite getting my power back. I have a degree in Electronic Engineering and in Mechanical Engineering, but my knowledge of house wiring/standards/high power stuff is pretty lacking.The problem is that my house Earth (faucets, earth pin of wall socket) is floating above the real Earth (drains, etc). The amount that it floats depends on how many inductive loads I have connected. With everything on it is at 96V! This is everything from PC monitors, microwave, 3D printers, etc.. Every single inductive load affects it. The only resistive load that I have is a 2000W heater and that does not seem to affect the voltage at all.Things I know:EARTH to NEUTRAL (from wall socket) = BADFaucet to shower drain = BADFaucet to EARTH of wall socket = 0VA new water heater had just been installed before I moved in, this was my original suspicion as a plastic fitting could potentially break the earth link to the faucets. But I don't think that would explain the potential I see between E and N at the wall. So maybe a bad MEN in my SSB?I live in a block of units, so I am inclined to think that this is more on the house side than on the street side as I think one of them would have noticed by now if they were affected. It is quite a nasty shock.Thanks,ChrisP.S. Unless it is really constructive, you do not need to waste your time giving me safety tips. When it comes to this high power stuff, I DON'T know what I am doing - and I am smart enough to know that. Well how do I know E-N at the wall? No I did not stick my multimeter into the socket, I stuck my multimeter into a disconnected IEC-C13, then several meters away I plugged that cable into the wall.P.P.S. Is this likely to compromise the performance of my RCD? Obviously this is irrelevant in this case as nothing is going to be energized again until this is fixed, I am just curious.

author: flynwill
author_rank: Regular Contributor
timestamp: December 22, 2016, 02:41:24 pm
content: I would start by locating and inspecting the service entrance for the building.I'm afraid I don't know what the Australian code requirements would be but here in the US there will generally be both a "ground rod" (copper or copper-plated steel rod) driven in to the ground near the service entrance and a connection to a cold water pipe. Both connections are typically bare #4 wire inside steel spiral conduit (like "BX" cable). Both the neutral and the safety ground should be tied to these at the service entrance.From you symptoms it does indeed sound like the service entrance is tied to the cold water pipes, but they in turn have an insulating fitting somewhere between the building and the city water supply, and the earth ground either doesn't exist or is faulty.How old is the building? Was two-wire (no safety ground) wiring ever used in Oz? Here it is quite common to find 3-prong outlets retro-fitted to old 2-wire wiring with the safety ground left floating.

author: SeanB
author_rank: Super Contributor
timestamp: December 22, 2016, 03:29:36 pm
content: As above, you have a broken PE bond in the system, and this causes anything with significant capacitance between line and ground ( which is why the heater has no effect, it has low capacitance, try again with something like an electric iron, which has a close coupled element) which is raising the potential on the ground wire above the real ground. As you will have a bond between neutral and PE in the meter box and this should bond to the water piping, there is likely a broken ground on the supply, a broken link in the meter box or an open earth at the meter box or connecting the meter box to the consumer unit earth bonding strip. your RCD will still trip when pressing test, as this simply induces a differential current inside the device, and it will trip, and it likely will trip with a faulty load, but you will still get a possibly lethal shock from the earthed metalwork of any appliances.If the water heater was recently replaced, likely either they forgot to reconnect an earth bond between heater and the pipes, did not connect the bonding across the heater input and output, or replaced the piping along with the supply earth connection with plastic piping. In all cases call the supply authority that owns the meter, and report the fault, and they will come out and inspect the meter side, and check that the ground bond is still good. If the supply side, or the meter box, they will likely replace it FOC, or at least confirm thier side is fine, and the fault lies downstream of the meter terminals, and that you need an electrician to do repairs, either attach the ground wire inside the consumer unit box again, or replace the failed ground wire in the system.Quick test, that is reasonably safe and easy to do, is to take a steel rod around 2m long, unpainted, and hammer it into the ground at least 1m outside, and water it with a hose till the ground is wet, to make a good ground connection. A cup of table salt before the water will also help temporarily. then bolt a wire to the rod ( make sure to get a nice connection to shiny metal) and lead inside. Then check voltage between your CEE socket and this rod, line rod, neutral rod, PE and rod, along with line neutral line PE and neutral PE. Then these will tell which likely fault is present. and the likely cause of it.