General > General Technical Chat

The US electrical system

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richard.cs:

--- Quote from: tom66 on June 29, 2020, 03:12:11 pm ---Frankly given all of this I'm shocked (no pun intended) that "granny chargers" (i.e. portable EVSE) are still permitted and sold with cars, despite the well known fire hazards.

--- End quote ---

The risk approaches for cars and electrical installations are so fundamentally different. All EVs could come supplied with a pair of yellow rubber washing up gloves and be connected to the mains with permanently-live M10 wingnuts and the majority of deaths would still come from allowing minimally-trained persons to manoeuvre tonnes of metal at high speed in public places rather than electrical shock.

It's very hard to argue that car manufacturer's should spend anything on electrical safety when they would save more lives spending that same money on improved brakes/seatbelts/airbags/etc., let alone that they should worry about TNC-S touch voltages.

themadhippy:
IF were ripping out the  network and starting from a clean sheet we should spent a few quid on  distributing the neutral from the source to the point of use,would make things lot safer.

--- Quote ---The risk is that if PEN fails due to cable damage, corrosion, poor maintenance etc
--- End quote ---
In the uk the biggest cause of failure of the bond from neutral to earth at substations was the same cause of train signalling failures, being tied to the towbar of a 4x4 or transit and driven off down the road at  high speed

--- Quote ---as far as I am aware there are only two ways to solve the problem:
- Earth rods until.
--- End quote ---
Its a "problem" thats well document and covered in sevral parts of the uk wiring regs,put simply if your taking power outside the house dont take the earth,source it locally.

IanB:
I'm a bit puzzled about the discussion of potential hazards from unexpected earth potentials.

Isn't it an important requirement that earth is bonded to all exposed metalwork (water pipes, gas pipes) in an installation?

If I could get a shock from touching my charging EV, couldn't I also get a shock from touching a garden tap for a hosepipe?

What is the difference between these cases?

helius:

--- Quote from: IanB on June 29, 2020, 03:34:11 pm ---If I could get a shock from touching my charging EV, couldn't I also get a shock from touching a garden tap for a hosepipe?

What is the difference between these cases?

--- End quote ---
Conceptually they are the same: the metal object is bonded to the equipotential zone of the building, but you are standing on a section of earth that is outside and can be at a different potential in case of significant earth leakage, or if the building's link to earth is broken because of poor maintenance. People can and do get shocked by touching outside faucets, and worse problems are found around boats.

tom66:

--- Quote from: IanB on June 29, 2020, 03:34:11 pm ---If I could get a shock from touching my charging EV, couldn't I also get a shock from touching a garden tap for a hosepipe?
--- End quote ---

Yes you could, but you don't tend to find two-tonne water garden taps parked on driveways accessible to the public, postman and neighborhood cat.

More seriously I think this is the reason plumbing tends to be grounded.

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