I’ve just had a new house built in Atlantic Canada. This morning I noticed a bit of a tingle from my coffee machine when I touched it with wet hands. The machine has a grounded (3 pin) plug and I checked - it has 0V between the parts I touched (the entire metal outer case) and the ground socket in the outlet. So, I got curious and did some more measurements. It turns out there is 20V AC (and about 300mV DC) between the ground in my outlets and me when I’m standing on my floor (sealed concrete slab) with bare feet.
I assume this isn’t good?
I’ll be calling the electrician that wired the house in the morning, but I’d appreciate any insights you might have.
Canada has, I think, the same electrical grounding approach as the USA for modern construction-- TN-C-S if using IEC notation. So there should be a ground rod (or two) on the property which ties (aka bonds) the electrical ground with the building itself. This should result in the floors and walls being the same voltage as the ground pin at every receptacle, and thus the surfaces of every metal appliance.
It’s hard to imagine a missing bonding link to the ground rod for new construction, so the next possibility is that an appliance somewhere is miswired and is using the ground wire as a neutral. While it’s true that the TN-C-S grounding system does bond ground and neutral, the ground wire must not actually carry any current in regular service.
Problems from a ground wire being used as the return path include: 1) generating interference for sensitive circuits that expect the ground wire to be unused, 2) possibility of tripping GFCI circuits, and 3) most disturbingly of all, the ground wire voltage is raised above that of the building, creating a shock risk.
Most insidious of all is that a miswired appliance will “pollute” the ground wire for the entire house with this dangerous voltage. So troubleshooting would generally require either measuring for “objectionable current” on the ground wire of every branch circuit, or shutting off circuits until the ground wire voltage disappears. If every circuit is powered off and the voltage still appears, then it might actually be the missing bonding link mentioned earlier. A competent electrician will be able to diagnose either scenario, though either really shouldn’t be happening for new construction.
Oh brother, if you think new construction is good… Bless your heart. A missing or detached earthing is totally possible with the terrible quality of most new homes and the hit or miss nature of home inspections.
I have seen brand new luxury condos that practically need the entire structure rehabed because the builders were so bad. Then there are new detached homes that have envelopes so bad that you can check how many rafters are broken by looking in from the flashing.
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I was here for the build - I worked as a labourer for the main contractor. The electrical ground is bonded to ground with a pair of ground rods. But I am almost certain there is nothing bonding electrical ground to the slab. My slab sits on 2" of closed cell foam - so it is isolated from “actual” ground. As I re-read this before posting I’m remembering that there are bits of rebar puncturing the foam to (for example) anchor bits of plumbing during the concrete pour - so it’s not really isolated. I’m confused.
I should add that I might have a bit of a complex grounding situation. I’m sharing a well and internet connection with my old house which is about 200’ away on the same property. A brass fitting on the poly pipe bringing water into my new house is at the same potential as my slab - that is, 20V from electrical ground.
I’m using Cat6 copper to share the internet and am only getting 100Mbps on the link. I had tested the cable at 1Gbps before it was buried. I’ve been assuming the cable got damaged, but I’m now thinking it’s related to my ground issues.
Again, I know there are too many unknowns for anyone to “solve” this for me, but I do appreciate the input and guidance. I’ll be turning off and unplugging everything this morning to (hopefully) rule out a faulty appliance.
Normally, the bonding arrangement should also include a connection to the slab, by way of a piece of rebar poking up from the foundation. The point of bonding is to attach as many normally-grounded things together, and this usually happens around the service entrance, as a matter of convenience. Here in California, we might use an outlet box on the side of the house to reveal the rebar bonding link, but perhaps Canada puts it somewhere else due to the heat loss in winter.
That the new house is a subordinate structure has a small impact on how the bonding is set up. Since neutral and ground are already bonded at the service for the old house – and I’m assuming there are no transformers used over that 200 ft wire run – the new house must make sure to not bond ground and neutral. Indeed, after the bonding point in the old house, ground and neutral should never be intentionally bonded anywhere else. A mistaken bond can lead to the “objectionable currents” I mentioned earlier, but this is diagnosed the same way by turning stuff off to see if the voltage goes away.
But apart from this difference compared to the old house, all other things should be bonded to the new house’s ground: water fitting, shield wires (if present) on any telecom wires, gas pipe. Because of your substantial distance between the two structures, it’s possible that the grounding system would have been simpler if the electrical service was “derived” using a transformer, such that the new house would have a different service that would be bonded to its ground, just like a standard home. But that ship has sailed.
Once the source of your ground current is found and mitigated, you may also consider bonding this water fitting to ground, at both the old and new homes. That way, if a future issue arises with the ground, it won’t be using the water as a conductor and causing a shock risk. Even if you don’t find the source of ground current, this is still a good idea, since some ground currents are perfectly natural – especially over 200 ft – but the risks posed by them can be mitigated by forcing everything to be at the same voltage (thus no more shock risk).
Indeed, one way that electricians test for the magnitude of a ground fault is to set up a temporary bond and measure the current through it. If large residual currents start to flow, it might indicate that the proper bonding elsewhere is faulty. I think you correctly assessed your issue as definitely non-trivial and an electrician should investigate thoroughly.
Seeing as you’ve already buried the cable, my comments are a bit late. But ground issues for twisted-pair Ethernet cables between buildings is a known issue, with no real solutions other than using non-conductive fibre optic cables or wireless links to bridge between buildings. At my work, we somewhat regularly see issues with twisted-pair cables running between buildings on campus, with the typical result being the death of the switch port where the cable plugs into.
It’s true that Ethernet is supposed to use mini-transformers to isolate the grounds at either end of the cable, but that’s not the only issue: having 200 ft of conductor means that a distant lightning strike induces a sizable voltage on these wires, even when underground. Those mini-transformers behind each port might only tolerate 2000 volt spikes, so if they’ve already been damaged by induced voltages, degraded performance would permanently affect the switch port, although the cable might still be intact.
You may want to re-verify your Ethernet cable using different equipment at the ends, but it may only be a matter of time until future issues arise. At work, we solved most of our woes by changing to wireless APs (eg Ubiquiti) aimed using line-of-sight for existing buildings. Between new buildings, we run fibre cables and then use a converter to turn it back into standard twisted-pair Ethernet once inside the structure.
That makes sense, but I don’t have it. My son is an electrician in Australia and he thinks it’s a bit strange that I don’t have it too.
No - I’m only sharing water and internet between the buildings. They both have their own feed from the power company.
I do plan to add surge protectors to both ends. They’re so cheap I’d be silly not to.
I have tried a few different things, and I think it did connect at 1Gbps once, but didn’t stay that way. It did run at 1Gbps when I used it as a fly lead to test it before it was buried. So, unless it was damaged during the back fill, it should work if I can fix the ground issues. The ethernet isn’t a big issue for me - it was a bit of an afterthought - a trench was being dug for the water so I bought a cable and dropped it in the trench before it was back filled. I already have a pair of Ubiquiti GigaBeams that work amazingly well - if fixing the ground issues does not fix the ethernet, I’ll just keep using the GigaBeams.