The consensus is that ~30mA is the threshold for a fatal shock under
ordinary circumstances:
https://en.wikipedia.org/wiki/Electrical_injury
and
https://www.asc.ohio-state.edu/physics/p616/safety/fatal_current.html
Thus, most countries pick 30 mA as the trip for GFCI (RCD). Picking a
greater current increases the risk of fatalities, while picking a lower
current increases the risk/frequency of nuisance tripping. 30 mA is the
smart place to set the standard trip.
Nuisance tripping due to the lower 5 mA threshold actually reduces
safety, if you think about it for a bit. Whole house GFCI protection is
totally impractical at 5mA, while it is completely acceptable and the
normal practice at 30 mA. Unprotected circuits in the household raise
the safety risk, obviously. Bedroom outlets are a prime example of
non-GFCI protected areas under the NEC. (They have arc fault protection,
but that is a different animal entirely.)
Nuisance tripping will cause folks to defeat the GFCI protection by
simply using an extension cord to an unprotected outlet (like one in a
hallway) when they are in an area that requires a GFCI, like outdoors,
or in the kitchen.
Keep in mind that 30 mA GFCI protection is required over the entire
household, you can, but you aren't required, to use a single device to
accomplish that coverage. I have several separate GFCI breakers, each
covering different portions of my house. I have a separate GFCI breaker
for the lighting. I have a separate GFCI breaker for the front outlets
and one for the rear outlets. I have two separate GFCI circuits for
outdoor outlets. They aren't terribly expensive, and having separate
ones helps isolate any problems that may occur.
On 3/12/2024 8:42 AM, Lee Hart via EV wrote:
Cor van de Water wrote:
my garage has a GFCI circuit. As a consequence, I cannot use
my garage to do any development work, because as soon as
I plug in one of my HP power supplies, even before I turn it on,
the heavy capacitive filtering on the AC line will trip the GFCI
because it indeed creates a current to ground.
The easy answer is a big isolation transformer. I have some big 1KW ones that I
use. (If anyone needs one, I have many, holding down the basement floor).
If I am not mistaken, the NEC has a class of GFCI (and I used to have
a breaker) that trips at 50mA, I believe there is even a 500mA limit.
The original idea for a GFCI was safety; to keep people from being electrocuted
(i.e. junior sticks a fork in the toaster with one hand to get his bread out,
while the other hand is resting on the grounded sink. The 5mA limit was chosen
as the maximum current that a normal healthy person would survive, since they
can let go and jump away from the source of the shock. In medical settings, an
even lower limit of 0.5mA was required, on the basis that hospital patients may
well not be able to remove themselves from the source of the shock.
But these limits proved to be hard to design for. So manufacturers have lobbied
for higher limits of 50mA. That's more than enough to kill a person. Yet the
last I knew, our EVs are being designed to allow up to 50mA of ground leakage
before their GFCI trips.
500mA for a GFCI limit? Gah! That would not only kill someone, but *cook* them
as well!
--
Excellence does not require perfection. -- Henry James
--
Lee A. Hart https://www.sunrise-ev.com
If I am not mistaken, the NEC has a class of GFCI (and I used to have
a breaker) that trips at 50mA, I believe there is even a 500mA limit.
This is only used in industrial settings where a lower limit will
indeed trip guaranteed.
On Mon, Mar 11, 2024 at 10:50 AM (-Phil-) via EV wrote:
Keep in mind that excepting North America, only (part of) Japan uses a
lower voltage. In the US (residential) system, no conductor is ever over
about 160v peak-to-peak with respect to ground, whereas in NZ/EU you are
getting over 300v P-P, which is arguably 4 times more lethal. I'd
definitely want everything protected by GFCI/RCD if I had those voltages
everywhere.
On Mon, Mar 11, 2024 at 10:25 AM EV List Lackey via EV
wrote:
On 10 Mar 2024 at 23:41, (-Phil-) via EV wrote:
Based on what I know, [the US NEC is] one of the most rigorous codes in
the world.
Agreed. I've seen some ... interesting ... wiring practices elsewhere,
including Spain, Italy, France, Canary Islands, Puerto Rico, and South
Korea.
Some of them look like old USA practices. Example: junction boxes aren't
usually used for surface mounted luminaires in France. The cable or smurf
tubing emerges from the ceiling or wall.
I've seen single conductors run through ceramic cleats on the ceiling
surface in South Korea, similar to early 20th century US wiring. It
appeared
to be a recent installation.
Service capacities are also lower. A typical western EU service will be
6kW
or 12kW, a size the US hasn't seen in probably 70 years. Spain has a lot
of
3kW services. I'm sure that that's a problem for EV home charging there.
On the other hand, as Bill says about NZ, in most (all?) western EU
nations,
the whole house is GFI (RCD) protected at 30ma leakage current.
David Roden, EVDL moderator & general lackey
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