Surge / Ground / Lightning

[w_tom]

According to W_, surge protection is impossible unless there is
a direct and short connection to earth ground. Does the PC
power supply come with a built-in earth ground?

Again trader reads only what he wants to see. Surge protection
without that short connection to earth ground is *ineffective*.
trader, who understands propaganda in the Rush Limbaugh tradition,
changes the message - uses the word 'impossible'. Misrepresenting
reality is trader.

PC power supply has no built-in earth ground. How do others know?
They learned before knowing. For example, they read both front page
EE Times articles entitled “Protecting Electrical Devices from
Lightning Transients". trader did not. Those electrical concepts
were too complex. trader knows rather than first learn technology.

Had trader learned facts before posting, he would have read what
IEEE Standards also said (and is posted elsewhere). Defined by the
IEEE is effective protection - with numbers:

Still, a 99.5% protection level will reduce the incidence of direct
strokes from one stroke per 30 years ... to one stroke per
6000 years ...

What do 'whole house' protectors use? Enough MOVs so that protector
is sufficiently sized. So that direct lightning strikes does not
destroy the protector.

What do MOVs need to provide effective connection? That short (ie '
less than 10 foot') connection to earth.

What provides surge protection? Earth ground - where surge energy
is harmlessly dissipated.

What does the effective MOV do? Connects to earth so that surge
energy gets dissipated harmlessly rather than destructively inside the
building.

What must those MOVs inside appliances do (and why did Apple stop
using them after Apple II)? Those MOVs must somehow stop or absorb a
surge that even three miles of sky could not stop. So few joules will
somehow absorb all that energy. Such little devices will block what a
sky could not?

What happens when MOVs are too close to appliances and too far from
earth ground? Page 42 Figure 8 from another IEEE citation - surge
earthed 8000 volts destructively through the adjacent TV.

Provides were numerous professional citations that say this. Where
does trader even post technical numbers? He does not. trader is like
most who recommend plug-in protectors. They need not first learn
facts. They know. Their proof is by using insults – just like Rush
Limbaugh.

A protector is only as effective as its earth ground.

 

[Mike Tomlinson]

Phone wires were clamped to ground before the 1960s?

It was common to earth one leg of the incoming pair to either the house
ground or to its own rod. An earth connection also allowed "party
lines", where two houses could share one physical phone line pair, each
house with its own number. Disadvantage was that both lines could not
be used simultaneously.

http://en.wikipedia.org/wiki/Party_line_(telephony)

My previous house still had its telephone earth rod and earth wire,
though it had not been connected to the phone line for many years.

 

[salty]

How does a protector decide how many of its joules to use?

Nick

Bwhahahahahaha!

 

[Guest]

Also required for UL approval is total number of joules. That says
nothing about how many joules actually participate in protection.
Typically, plug-in protectors use as little as 1/3rd and never more
than 2/3rd of its joules for protection.

How does a protector decide how many of its joules to use?

Nick

 

[Guest]

... Surge protection without that short connection to earth ground
is *ineffective*.

Wrong, wrong, wrong (say it 3 times and it's true

Nick, ex-K3VZW, BSEE, MSEE, Senior Member, IEEE

 

[fl_fly_boy]

How can one find this rating for a particular device?

Look for ul1449 330v or 400 for example, or surge voltage rating SVR
330v or Clamping Category 330v

"The unpredictable nature of surges makes it difficult to suppress them;
you never know when, how long or how powerful they will be. In some
cases, asurgemay have a higher energy level than the device can
handle. When this happens, thesurgesuppressor may be damaged and lose
its ability to provide protection against future surges."

MOV’s and surge protectors are like tires on your car, the more you
use them the shorter useful life, mistreat them, the shorter the
useful life, too small or light weight the shorter the useful life.
Ul 1449 certification take care of the too small or light weight.
Proper selection for problem locations is the key to protection.

I'm happy to see that UL agrees! They don't seem to put any evaluation
of this parameter, unless the "suppressed voltage rating" includes the
Jules rating of the MOVs.

Don’t pay attention to joules on surge protectors, no standard to
measure, a better and recommended rating is “Peak Surge Current” the
higher the better.

 

[bud--]

That is a quote from UL. Contrast that with Martzloff:
"The fact of the matter is that nowadays, most electronic appliances
have an inherent immunity level of at least 600 V to 800 V, so that the
clamping voltages of 330 V widely offered by TVSS [surge suppressor]
manufacturers are really not necessary. Objective assessment of the
situation leads to the conclusion that the 330 V clamping level,
promoted by a few manufacturers, was encouraged by the promulgation of
UL Std 1449, showing that voltage as the lowest in a series of possible
clamping voltages for 120 V circuits. Thus was created the downward
auction of 'lower is better' notwithstanding the objections raised by
several researchers and well-informed manufacturers. One of the
consequences of this downward auction can be premature ageing of TVSS
that are called upon to carry surge currents as the result of relatively
low transient voltages that would not put equipment in jeopardy."

Look for ul1449 330v or 400 for example, or surge voltage rating SVR
330v or Clamping Category 330v

I believe it is required by UL to be on the package or literature.

MOV’s and surge protectors are like tires on your car, the more you
use them the shorter useful life, mistreat them, the shorter the
useful life, too small or light weight the shorter the useful life.
Ul 1449 certification take care of the too small or light weight.
Proper selection for problem locations is the key to protection.


Don’t pay attention to joules on surge protectors, no standard to
measure, a better and recommended rating is “Peak Surge Current” the
higher the better.

I would like to know the Joule ratings. The problem, as you say, is
there is no standard way to measure the energy rating and some
manufacturers apparently use questionable ratings. That has led some
other reputable manufacturers, like SquareD, to not include Joule ratings.

Peak surge current is directly related to the energy rating. w_'s
recommended 50,000A surge current rating is way beyond what you will get
at a service panel, but it represents a high energy rating which means
long life.

 

[bud--]

UL makes no effort to measure a protector's protective ability.

Cuttler Hammer says you are wrong.
http://tinyurl.com/63594d

Approval may be obtained by undersizing MOV's thermal fuses so that
a protector will disconnect MOVs faster during a surge; leave the
appliance to fend for itself.

Of course that applies to service panel and plug-in suppressors. But CH
says a suppressor has to have tested functionality (above).

w_ just buys cheap Chinese knock offs, so his suppressors fail regularly.

Also required for UL approval is total number of joules.

Provide a cite. Why does your favored manufacturer SquareD not provide
Joule ratings?

A 'whole house' protector uses all joules during all types of
surges.

Depends on the surge.

How effective are 'whole house' protectors? Well, a friend suffered
when the 33,000+ volt transmission line fell upon his 4000 volt
distribution line. Literally everyone powered from that B phase had
electric meters explode up to 30 feet from their pans. Many had
damage to plug-in protectors and to powered off appliances plugged
into those protectors. But my friend suffered no damage, except to a
meter that exploded off his building. He had a properly earthed
'whole house' protector. A protector is not rated to provide that
protection. But properly installed protectors with sufficient joules
will provide more protection than rated.

Neither service panel or plug-in suppressors will survive extended
overvoltage. It rapidly kills MOVs. w_ is using anecdotal evidence
(with no cite) to suggest service panel suppressors protect from crossed
power lines. More lunacy.

Which protectors actually provide better protection? Products from
a list of responsible manufacturers such as Intermatic, Square D,
Siemens, Polyphaser, GE, Cutler-Hammer, Keison, and Leviton.

Being responsible, they all make plug-in suppressors except SquareD.
SquareD, for the ‘best’ service panel suppressor, says "electronic
equipment may need additional protection by installing plug-in
[suppressors] at the point of use."


Still missing - a link to another lunatic that says plug-in suppressors
are NOT effective.

Still missing – answers to embarrassing questions:
- Why do the only 2 examples of surge suppression in the IEEE guide use
plug-in suppressors?
- Why does the NIST guide says plug-in suppressors are "the easiest
solution"?
- Why do all but one of w's "responsible manufacturers" make plug-in
suppressors?
- Why does SquareD say in addition to their "whole house" suppressors
"electronic equipment may need additional protection" from plug-in
suppressors.
- Why aren't airplanes crashing daily when they get hit by lightning (or
do they drag an earthing chain)?

For accurate information read the IEEE and NIST guides. Both say plug-in
suppressors are effective.

 

[bud--]

Good question. In the MW oven case, the switch was a relay controlled
by the timer circuit. It was probably easier to locate the MOV at the
line input.

I have seen cases with a "blown" MOV and the circuit protector tripped.
The MOV, if it tripped the protector, may have saved the following
circuits from the over-voltage condition for a longer period of time. I
haven't tried to calculate the conditions under which this would work.

Normal MOV failure is by high current and overheating (as below). A fuse
may provide protection. Plug-in suppressors likely use the heat as part
of the disconnect. For overvoltage, the disconnect would have to survive
the higher voltage.

As you know, MOVs lose their capacity each time a "spike" causes them to
conduct. This reduces the remaining capability to handle "surges".

You may already know all of this -

MOVs are damaged by heat from energy dissipated in their clamping
action. The defined end of life of a MOV is when the voltage that
produces a 1mA current decreases 10%. At that point the MOV is still
clamping the voltage across it. Further dissipation continues to lower
the voltage until the MOV conducts at ‘normal’ voltages and goes into
thermal runaway. For surge suppressors, UL required protection
disconnects the MOV when it overheats. It should still be clamping at
that point.

The energy (Joule) rating is for a single event. If the individual hits
are far below the rating, the cumulative energy rating is far above the
single event rating. High ratings give longer life than you might expect.

Service panel and plug-in suppressors do not protect by absorbing
energy. But they absorb energy in the process of protecting.

True, but some are marketed as "surge protected" with minimal capacity.
I've replaced the MOVs in several cheap multiple socket strips with
higher rated MOVs from Radio Shack.


I think the UL requires only that the MOVs don't start a fire when
exposed to conditions which cause their break-down. They don't rate
their ability to function as "surge protectors".

A Cuttler-Hammer tech note:
http://tinyurl.com/63594d
has some information on UL tests. Suppressors have to remain functional
through an initial set of surges (20 surges - 6kv, 3kA). They can fail
safely after that. (This sounds more like the service panel suppressor
test.)

 

[bud--]

It was common to earth one leg of the incoming pair to either the house
ground or to its own rod. An earth connection also allowed "party
lines", where two houses could share one physical phone line pair, each
house with its own number. Disadvantage was that both lines could not
be used simultaneously.

http://en.wikipedia.org/wiki/Party_line_(telephony)

My previous house still had its telephone earth rod and earth wire,
though it had not been connected to the phone line for many years.

I am pretty sure we had a party line long ago when I was a kid.
Wikipedia's reference to "20th century telephone systems" makes me feel
even older.
One side of the ringer is all that was connected to earth.

Not clamping phone wires to earth is a major surge suppression flaw. It
allows high voltage from phone to power wires (like at a modem), and
increases the stress on a multiport plug-in suppressor. A service panel
suppressor doesn't help the voltage difference at all.

Surprising since the UK seems to be very good on electrical protection
in general.

 

[fl_fly_boy]

I would like to know the Joule ratings. The problem, as you say, is
there is no standard way to measure the energy rating and some
manufacturers apparently use questionable ratings. That has led some
other reputable manufacturers, like SquareD, to not include Joule ratings.

Here is a couple of nice article for evaluating SPD’s.

Is the Joule rating of an SPD important?
While conceptually an surge protection device (SPD) with a larger
energy rating will be better, comparing SPD energy (Joule) ratings can
be misleading. More reputable manufactures no longer provide energy
ratings. The energy rating is the sum of surge current, surge
duration, and SPD clamping voltage.
In comparing two products, the lower rated device would be better if
this was as a result of a lower clamping voltage, while the large
energy device would be preferable if this was as a result of a larger
surge current being used. There is no clear standard for SPD energy
measurement, and manufacturers have been known to use long tail pulses
to provide larger results.
Additionally confusing this issue is the possibility that the rating
is just the energy absorbed, diverted, or the sum of both. NEMA LS 1
by specific omission does not recommend the comparison of SPD’s energy
ratings. Comparison of single shot surge ratings and let-through
voltages is considered sufficient.
http://www.nemasurge.com/help.html

http://ecmweb.com/mag/electric_comparing_spd_performance/
http://www.control-concepts.com/pdfs/01_005.pdf
http://www.lightningsafety.com/nlsi_lhm/IEEE_Guide.pdf 2.5.1 Joule
Rating

 

[krw]

I had a party line as a 10 year old. I used to screw with the other
party if I heard them when I picked up the phone.. strange noises, etc.
Of course I got caught, corporal punishment, etc.

We had a party line when I was very young. ...until about '56, or
so. Ma Bell had gotten rid of them in the area by '59.

I think they used to ring between the red green for one party, yellow
green for the other party, black green, etc.

No, that would defeat the purpose of the party line. The ringers
either had "distinctive ring" (once for Mabel, twice for Maude) or
were frequency tuned.

 

[w_tom]

Is the Joule rating of an SPD important?
While conceptually an surge protection device (SPD) with a larger
energy rating will be better, comparing SPD energy (Joule) ratings can
be misleading. More reputable manufactures no longer provide energy
ratings. The energy rating is the sum of surge current, surge
duration, and SPD clamping voltage.
In comparing two products, the lower rated device would be better if
this was as a result of a lower clamping voltage, while the large
energy device would be preferable if this was as a result of a larger
surge current being used. There is no clear standard for SPD energy
measurement, and manufacturers have been known to use long tail pulses
to provide larger results.

MOV manufacturers do not play the 'joules' games that some plug-in
protector manufacturers play. Plug-in protector typically uses as
little or less than 1/3rd and never more than 2/3rds of rated joules
during protection. During some surges, a plug-in protector may use 0%
of its joules because the massive surge voltage is same on all wires -
as surge seeks earth ground destructively via electronics. No voltage
between wires means the protector never sees any of the destructive
surge - does nothing for protection. So how many joules does it
really use?

An effective 'whole house' protector uses 100% of its joules for all
types of surges which is why 'whole house' protectors can routinely
earth direct lightning strikes without damage - why these protectors
suvive and absorb less energy due to an exponentially longer life
expectancy.

Joules that actually get used during each surge provide a ballpark
measurement for a protector's life expectancy. Further numbers are in
an above reply to VWWall on 7 May 2008.

SVR, typically 330 or 400 volts, printed on the box, required by the
UL, and more often called "let-through voltage". A vague number so
that consumers can make ball park comparisons. No useful for making
engineering decisions.

A plug-in protector rated at 330 volts will start conducting at
maybe 200 volts. When a larger surge occurs, it conducts at 900
volts. Protector rated at 330 volts conducts between 200 and 900
volts. What happens when conducting at or above 900 volts? MOV self
destructs - vaporizes. Also called those 'scary pictures' - what every
MOV manufacturers defines as unacceptable operation.

So what does that SVR (threshold or let-through) voltage really
measure?

Discussed is a 70 SVR difference. Irrelevant since the difference
between ineffective and proper earthing is thousands of volts. If not
properly earthed, then even a tiny 100 amp surge puts that protector
at something approaching 12,000 volts. 70 volts or even 330 volts is
completely irrelevant.

Properly routed ground wire (no sharp bends, etc) can make
thousands of volts difference as described by so many professional
citations. What defines protection? Quality of and connection to
earth ground can make thousands of volts difference.

Page 42 Figure 8 from Bud's IEEE citation. Will a 330 or 400 volt
protector make any difference? Of course not. With either protector,
that surge is still >8000 volts destructively finding earth ground
through an adjacent TV. How to eliminate up to 12,000 volts?
Shorten the 50 feet AC electric wire between protector and earth
ground to zero feet.

Bud posts that electronics contain internal protection of 600 or 800
volts. Intel ATX specs demand that internal protection exceed 1000
volts. Just another reason why 330 or 400 let-through volts is
irrelevant. Relevant is 900 volts during a typically destructive
surge on a 330 or 400 volt protector.

"My surge protector sacrificed itself to save my computer".
Reality. A protector was so grossly undersized that voltage exceeded
900 volts. MOV did what no MOV must do - vaporize. What protected
that computer? Computer's internal protection protected the
computer. But a naive computer assembler *knows* the protector
provided protection. A myth promoted by grossly undersizing plug-in
protectors. To be effective, a protector must earth a direct
lightning strike and remain functional.

Why argue over which jelly bean is prettier when the room will be
engulfed by a flood. 70 volts difference in SVR is trivial when
improper earthing can mean another 8000 or 12,000 volts during the
typically destructive type of surge.

 

[w_tom]

Cuttler Hammer says you are wrong.
http://tinyurl.com/63594d

Again Bud misrepresents what professional say. Cutler-Hammer says:

2. Surge Test. Let through voltage tested at lower current
than 1st edition. 10 kA (IEEE Cat C3) used for the first
time, however, it was used only to see if products fail
safely.

Only tests a product for a safe failure – does not threaten human
life. Does not measure the performance of protection. Same citation
further states:

2. UL does not verify that the TVSS device will achieve
the manufacturer's published surge current ratings.

Of course not. That would be measuring a protector's protection
abilities. UL does not measure protection - in direct contradiction
to what Bud posts. A protector can completely fail during UL1449
testing and still be approved. UL only cares that is completely fails
– provides no effective protection – without threatening human life.

UL does determine functionality. Otherwise an empty box would be
submitted by Bud’s peers as a surge protector and get UL1449
approval. A protector must demonstrate some protector function. But
UL makes no effort to measure abilities of that protector. UL only
tests that it functions like a protector and does not harm humans.
Bud must deny those which is why his post again lies about what Cutler-
Hammer, IEEE, NIST, and so many others say.

Meanwhile, Bud repeatedly claims that protectors create fires
because UL1449 was created in 1998. UL1449 was approved in 1987 as
Cutler-Hammer also says. Again, Cutler-Hammer disagrees with what
Bud posts. Numerous plug-in protectors after 1998 with UL approval
still create a fire risk – the scary pictures:
http://www.hanford.gov/rl/?page=556&parent=554
http://www.westwhitelandfire.com/Articles/Surge Protectors.pdf
http://www.ddxg.net/old/surge_protectors.htm
http://www.zerosurge.com/HTML/movs.html
http://tinyurl.com/3x73ol
http://www3.cw56.com/news/articles/local/BO63312/

Finally, Bud claims a plug-in protector protects from a surge
that typically destroy appliances. 400 times Bud has been asked to
provide those specs. He refuses because no plug-in manufacturer will
claims what Bud posts. Bud lies about his own IEEE, NIST and Cutler-
Hammer citations. Bud even claims that UL measures a protector's
protection abilities. UL does not. UL addresses threats to human
safety. Protector can completely fail during UL testing and still be
approved as long as the protector does not spit flame during that
failure.

Bud provides not one manufacture spec that claims protection. Bud
cannot provide what does not exist. No wonder Bud will also post
insults He cannot dispute facts even from his IEEE, NIST, and Cutler-
Hammer citations. A protector is only as effective as its earth
ground. UL makes no effort to rate protection for each protector.

 

[Mike Tomlinson]

Not clamping phone wires to earth is a major surge suppression flaw.

It's simply not necessary in towns and cities in the UK. Occurrences of
damage caused by surges on phone lines are practically unheard of.
There are reports of damage caused by direct or nearly lightning
strikes, but of course nothing is going to protect against that.

Houses in villages and remote locations would probably benefit most from
additional protection. You can be sure that critical installations
(hospitals, data centres, etc.) will install additional protection.

British Telecom fit NTE (network termination equipment), also known as a
master socket, which does have surge arrestors built in, but they don't
clamp to earth, they're just across the line:

http://www.buzzhost.co.uk/nte5.php

has a circuit diagram of the NTE, and an interesting photo of damage
caused by a direct lightning strike further down the page (which, of
course, none of w_'s equipment would have prevented.)

An additional factor is that adding further surge protection devices can
affect the line characteristics, causing ADSL sync speeds to drop.

A service panel
suppressor doesn't help the voltage difference at all.
Obviously.

Surprising since the UK seems to be very good on electrical protection
in general.

As I said in an earlier post, a calm, intelligent assessment (not w_'s
level of hand-waving, gibbering hysteria) of each situation is needed
before deciding on the level of protection required.

It's clear that it's simply not needed for most UK domestic phone lines;
this will have been borne out by years and years of experience, looking
at the number of insurance claims, etc. I should think BT's attitude is
that if the customer wishes to install additional protection after the
demarc (NTE), that's up to them.

In the end, It's all about assessing risk and mitigating it.

I found this webpage rather amusing:

http://www.satcure.co.uk/tech/phonesurge.htm

but will leave it to others to comment

 

[bud--]

Again Bud misrepresents what professional say.

Sorry I picked up the wrong URL. The correct one is

http://tinyurl.com/5m3wrf

UL does not measure protection - in direct contradiction
to what Bud posts.

Using the correct URL, the CH cite above says suppressors have to remain
functional through an initial set of surges (20 surges - 6kv, 3kA). That
is significant functionality.
They can fail safely after that. (Although CH does not say it, I believe
the test for plug-in suppressors is at a lower current.)

A protector can completely fail during UL1449
testing and still be approved.

It can fail after significant functionality (above) has been
established. For instance when subjected to long overvoltage a
suppressor can fail safely.

Meanwhile, Bud repeatedly claims that protectors create fires
because UL1449 was created in 1998.

w_ is so stupid he still can’t figure out the difference between a
creation date and a revision date.

UL1449-2ed (1998) requires thermal disconnects.

UL1449 was approved in 1987 as
Cutler-Hammer also says. Again, Cutler-Hammer disagrees with what
Bud posts.

With minimal intelligence w_ could read in old link "UL1449(2nd edition
1996 [publication date])".

In the new link, 1st sentence: "The Second Edition of UL1449 became
effective August 17, 1998."

Numerous plug-in protectors after 1998 with UL approval
still create a fire risk – the scary pictures:

Lacking valid technical arguments, w_ continues to lie about scary pictures.

None of the links say a damaged suppressor even had a UL label.

Still missing - a link to any source that says UL listed plug-in
suppressors made after 1998 are a problem.

A protector is only as effective as its earth
ground.

w_'s religious mantra will protect him from evil.


Still missing - a link to another lunatic that says plug-in suppressors
are NOT effective.

Still missing – answers to embarrassing questions:
- Why do the only 2 examples of surge suppression in the IEEE guide use
plug-in suppressors?
- Why does the NIST guide says plug-in suppressors are "the easiest
solution"?
- Why do all but one of w's "responsible manufacturers" make plug-in
suppressors?
- Why does SquareD say in addition to their "whole house" suppressors
"electronic equipment may need additional protection" from plug-in
suppressors.
- Why aren't airplanes crashing daily when they get hit by lightning (or
do they drag an earthing chain)?

For reliable information read the IEEE and NIST guides. Both say plug-in
suppressors are effective.

 

[bud--]

Plug-in protector typically uses as
little or less than 1/3rd and never more than 2/3rds of rated joules
during protection.

Depends on the surge that arrives. Like a service panel suppressor, buy
one with adequate ratings.

An effective 'whole house' protector uses 100% of its joules for all
types of surges

Depends on the surge that arrives.

A plug-in protector rated at 330 volts will start conducting at
maybe 200 volts. When a larger surge occurs, it conducts at 900
volts.

Large surges can hit service panels so you might get 900V at the
service. The significant impedance of a branch circuit for surges
greatly limits the current that can reach a plug-in suppressor. Many
sources recommend adding a plug-in suppressor at "sensitive"
electronics to further limit the service panel let-through voltage.

Bud posts that electronics contain internal protection of 600 or 800
volts. Intel ATX specs demand that internal protection exceed 1000
volts.

bud quotes Martzloff who says 600-800V.

Just another reason why 330 or 400 let-through volts is
irrelevant.

As usual, w_ can’t understand Martzloff. Voltage let-through is
important to Martzloff because the lowest values cause suppressors to
conduct on surges that are not damaging to connected equipment, which
shortens the lifetime of the suppressor.

"My surge protector sacrificed itself to save my computer".
Reality. A protector was so grossly undersized that voltage exceeded
900 volts.

In w_'s mind, plug-in suppressors have minuscule ratings, service
panel suppressors have mega ratings. Plug-in suppressors are readily
available with very high ratings for relatively low cost.

And w_ only buys special MOVs that self destruct at 900V. All the others
depend on energy absorbed.

MOV did what no MOV must do - vaporize.

w_ buys also only buys unlabeled Chinese suppressors that do not have
the UL required thermal disconnect.




Still can't find another lunatic that says plug-in suppressors are NOT
effective?

 

[bud--]

No, that would defeat the purpose of the party line. The ringers
either had "distinctive ring" (once for Mabel, twice for Maude) or
were frequency tuned.

They did frequency and distinctive rings. But for 2 parties you can ring
red-to-ground for one and green-to-ground for the other. It is in Mike's
Wikipedia link above. My recollection is black was ground and yellow was
sometimes used for a light in the phone (red and green are phone wires).

 

[krw]

They did frequency and distinctive rings. But for 2 parties you can ring
red-to-ground for one and green-to-ground for the other. It is in Mike's
Wikipedia link above. My recollection is black was ground and yellow was
sometimes used for a light in the phone (red and green are phone wires).

Princess phones used the yellow green pair for the dial light. A
transformer was hidden somewhere in teh house to supply the power
(IIRC, a standard 24VAC door bell transformer, but it's been a lot
of years).

 

[Mike Tomlinson]

Similarly, I would question the reliability of ring on a single line
referencing
ground, since party lines tended to be out longer distances -- the ground
resistivity
would make it more difficult to get ring current to the phone(s).

It did work though. The mechanical bells in older phones in the UK had
a lower impedance (500 ohm coils vs. 2000 ohm coils in newer phones), so
the ringer would draw more current. The ringer was also two bells
either side of a balanced clapper, so it took little to make it ring -
the more current it was able to draw from the line, the louder it rang.

I remember a neighbour with a party line whose phone had problems -
calling her would give a ring tone in the earpiece, but she would claim
that she had never heard the phone ring. Several visits from the GPO
(as was BT) engineers found no fault, the phone always working when they
visited.

Eventually it was discovered that her party line was grounded via the
waste pipe (lead pipe into a cast iron stack disappearing into the
ground) of her cloakroom toilet, which was little used, and in the
summer, when the ground dried out and the water in the toilet pan
evaporated and ran low, the phone lost its earth and failed to ring.
Flushing the toilet restored normal operation to the phone