David,
Very good advice in general.
In this particular case, the original poster was in the US which is much
more relaxed about withholding mains power from older residences that do
not conform to the newer electrical codes (grandfather clauses, etc.).
In addition, here in the US, one side of the 120 volt receptacles is
connected to neutral - and the neutral is connected to earth ground at
the mains service entry point. I believe in the UK, both sides of the
240 volt service are isolated from ground which can create more exposure.
In this specific case, there has to be an existing ground rod at the
electrical mains entry, and rather than driving an additional ground
rod, it would be safe practice to add a direct wire from that mains
ground to the location where the anti-static mat and wrist strap are
located - Warning - if an additional ground rod is driven, it must be
connected to the service entry ground by a #6 or larger wire to comply
with NEC code. The actual ground rod may be buried under the surface of
the earth since many building inspectors and power companies insist on
it to keep the ground rod from being removed by the unaware homeowner
who finds an 'ugly obstacle' which interferes with his lawn mowing
efforts. When I built my house, the building inspector strongly
suggested that I sink my ground rod under the surface, but I explained
my reasons for not doing so, and he backed off. I like to check and
tighten my ground rod clamps once a year.
73,
Don W3FPR
David Woolley (E.L) wrote:
Apologies for breaking threading.
Paul G4LNA wrote:
> Just run a wire to a rod outside, it doesn't matter how long the
> wire is, as you say it's not an RF ground. I wouldn't use the gas
> pipe for safety reasons.
This advice is dangerous and doesn't even really achieve what one
needs to achieve.
It's dangerous because, if there is a fault which connects live to any
exposed metalwork, you have introduced a low resistance path to earth
into an environment where the the fault was much less dangerous
because only high resistance return paths existed.
What you are really trying to do make sure that all, even partially,
conducting surfaces are at the same voltage, including you and the
soldering iron tip. Normally you can rely on internal surfaces being
insulated or connected to mains earth, because that is what modern
electrical codes require, so it is normally appropriate to connect the
mat to mains earth.
As far as I know, in the UK, you would have electricity supply refused
if you had two wire mains sockets (shaver sockets are specially
isolated), except for environments which are specifically designed to
be earth free, in which case you would not be allowed to have anything
connected to earth.
If you only have two wire sockets, or, more generally, if you do not
know how the mains earth is arranged, you really need to consult a
competent electrician before doing anything that involves earthing at
DC to mains frequencies. You should treat any metal connected to true
earth, and inside, as though it was at mains voltage, and you should
treat any wires going to the outside, as being at mains voltage, when
outside.
My own guess is that you either need to completely rewire to include
an earth wire and properly earth all relevant appliances and bond
other conductive surfaces to that earth, or to establish a work area
that is a body's length from any electrical outlet, or equipment,
provide conductive flooring, bond all surfaces electrically and use a
battery powered soldering iron. (Your electrical codes may be more
specific about the separation distance.) I think there are variations
on this that provide some mains power, but I wouldn't want to suggest
anything without detailed knowledge of local electrical codes.
In general, if you put in earth rods, they must be connected to the
mains earth or completely isolated from the electrical system, by
sufficient distance that it is impossible to touch anything that can
come into contact to one of them at the same time as anything that can
come into contact with the other.
WY5Q wrote:
>
My house does not have grounded electrical outlets. What is the best
way to protect against static during assembly of the K3 kit? Ground
the mat to a ground rod outside? Or to a metal gas pipe (for
grounding me, not as RF ground!)? There are no water pipes accessible
my build location.
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