Archived from groups: alt.sys.pc-clone.dell (
More info?)
1967 means the building was probably safety grounded for
earthing to cold water pipe. Earthing via water pipe is no
longer acceptable. Today, a safety ground connects to water
pipe only to remove electricity; not dump electricity into
earth. Today, there must be an earth ground rod or equivalent
connected right at mains circuit breaker box - the one with a
mains disconnect breaker. IOW all receptacle safety grounds
(green wire), the incoming utility neutral wire, all
receptacle neutral wires (white), safety ground wire to cold
water pipe (bare copper), and the earth ground wire (bare
copper) meet inside this mains box at a safety ground bus.
Also code requires that incoming utilities (telephone and
cable) make a less than 20 foot connection to the same earth
ground that connects to breaker box. NEC requires this for
human safety. The earth ground (and not the bus bar inside
breaker box) is referred to in previous posts as the single
point earth ground.
For human safety, a 50 foot wire to the cold water pipe is
sufficient. Resistance is low. But for transistor safety,
that same wire is too long; impedance is too high. Wire is
not a perfect conductor. Wire is an electronic component.
For human safety, the electrical numbers are so small that we
say water pipe and breaker box are, essentially, bonded
together. But for radio frequency transients that destroy
transistors, that 50' distant water pipe is just too far
away - impedance numbers are too high.
And so we need have all incoming utilities make a 'less
than 10 foot' connection to earth. IOW all utilities must be
earthed to same point for human safety AND be earthed short
for transistor safety.
If incoming utilities are not entering at the same point
(the 'preferred' solution in figure), then this 'right'
solution using a buried bare copper wire to interconnect the
grounds may be necessary:
http://www.cinergy.com/surge/ttip08.htm
Underlying concept is demonstrated in this figure:
http://www.xantrex.com/support/docserve.asp?id=337
Same is demonstrated by an example of how the fax machine is
protected in:
http://www.epri-peac.com/tutorials/sol01tut.html
Why is the typical plug-in protector ineffective? Distance
between that protector and the earth ground rod is how far?
For example, a trivial 100 amp surge to be earthed by
protector on 50' of electric wire inside wall. Wire impedance
is maybe 130 ohms. That 100 amps attempting to transverse 130
ohms impedance would leave protector and adjacent computer at
something less than 13,000 volts. IOW the surge will also
find other (and destructive) paths to earth ground. Adjacent
plug-in protectors is essentially not earthed; therefore not
effective.
Furthermore, that ground wire inside walls is bundled with
other wires. A 100 amp transient attempting earth ground on
that safety ground wire will induce transients on all other
adjacent wires. What kind of protection is that?
Ineffective. IOW we want earthing ground to be short, direct,
and routed independent (separate) of all other wires.
Plug-in protectors instead avoid discussing this to make
their highly profitable sales. Notice that plug-in protectors
never discuss earth ground.
First off, inspect your building's earth grounds. To meet
post 1990 National Electrical Code, then all incoming
utilities must be bonded together either by connecting to the
same earth ground OR having the separated earth grounds bonded
by a buried conductor. Utility cold water pipe is no longer
acceptable for earth grounding.
Second, a surge protector connects each AC electric 'hot'
wire so that a less than 10 foot connection to that earth
ground exists. If earthing is in a box with the meter, then a
'behind the meter' protector can be installed. Either you buy
one or rent one (at a very expensive $5 per month) from the
utility.
Most mains breaker box protectors attach outside the box -
ie Intermatic IG1240RC that is sold in Home Depot. Some snap
into circuit breaker positions such as Siemens QSA2020.
Minimally sized protectors start at about 1000 joules and
50,000 amps. For example, one Square D product that snaps
inside breaker box is undersized. However something is better
than nothing.
Of course, being in CA, CG lightning is often not a
problem. Although I viewed massive damage to a Bay area radio
station, their location was the exception to CA. Location and
geology also determine protection requirements. Surges occur
typically once every 8 years. How your location varies from
the norm may determine how much work you want to do for
transistor safety. But at minimum, all incoming utilities
must share a common earth ground. Not just for human safety.
Also for transistors safety.
Timothy Daniels wrote:
> "w_tom" replied:
>> As a condo owner, you should be able to install a 'whole
>> house' protector in the mains breaker box. If properly
>> installed after 1990, then that 'whole house' protector would
>> then make the 'less than 10 foot' connection to earth ground;
>> may protect all household appliances from direct strikes to AC
>> electric. But first identify and verify the earth ground.
>
> By "mains breaker box" do you mean the main breaker
> box for the building or for an individual unit at the point of
> service entry (where the meter is) or the breaker box inside
> an individual condo unit?
>
> In our case, the building was built circa 1967 in California.
> Does that suggest the type of earthing that was used?
>
>> If it is a seriously compromised installation, then this may
>> be your only alternative. First, learn where the building's
>> earth ground is located. All incoming utilities such as cable
>> and phone must connect 'less than 10 feet' to this earthing
>> point. Even a buried, bare copper, 4 AWG ground wire
>> joining these grounds (if they are separate) would help.
>
> The entry point for the communication utilities is
> different from that for electrical power, and they are
> about 120 feet apart. What to do?
>
>> Now find the nearest 3 prong AC receptacle to breaker box
>> and therefore to earth ground. Buy a protector with largest
>> joules. Cut 6 foot power wire as short as possible and plug
>> modified protector into that nearest AC receptacle. That
>> 'upgraded' plug-in protector will at least provide some
>> earthed protection on half of the condo receptacles that share
>> same AC electric phase.
>
> Is there a surge protector that will fit inside a typical
> condo breaker box inside the unit? How about inside
> the main breaker box where the meter is?
>
>> Of the three AC electric wires, one must make a direct
>> connection to earth ground. That becomes your single point
>> earth ground. Other two incoming AC electric wires must be
>> earthed through a 'whole house' protector (or via the kludged
>> protector).
>
> As I interpret you, the ground wire in a branch circuit is
> to act as the "single point earth ground" for equipment in the
> condo unit. How is this different from the typical Home
> Depot surge protector setup?
>
> *TimDaniels*
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