If you don't mind making your own below is some information and diagrams
to do a few different types...
Operation of the surge suppressors
To be able to get rid of surges the surge suppressors have to protect
the equipments against two kinds of surge voltages:
* differential surge = surge voltage between line wires
* common mode surge = surge voltage between ground and line wires
To be able to do this the surge suppressors have to have good ground
connection. If the circuit does not have a good ground connnection is
can only protect against differential surges. The protector must also
act quicly to be effective. A lightning surge has a typical rise time of
10 microseconds and a duration of about 1 millisecond.
When surge protectors
<http://www.epanorama.net/documents/surge/telesurge.html#> are installed
to a telephone/data communications room they are typically connected a
common grounding bar which is connected to a good ground through a heavy
grounding wire. The quality of the grounding (resistance and inductance)
effect very much on how well the surge protector
<http://www.epanorama.net/documents/surge/telesurge.html#> will protect
against common mode surges. Even the best surge protector can't work
well unless it is properly grounded. So it is recommended that you
install the surge protector near the main grounding bar.
Some telephone line surge protectors sold in USA use the mains connector
ground for grounding (those surge protectors which have mains surge and
telehone line surge protectors in some case). The ground in the mains
connector is not very good grounding point and using it as ground for
surge protector can induce par of the surge also to the mains wiring.
The basic surge protectors use metal oxide varistor (MOV) to do the
protection. This circuit below used one MOV between line wires for
protection against differential surges and two MOVs from line wires to
ground connection to protect against common mode surges. *
----------o---------o--------- to equipment
| |
| MOV
TELCO | |
MOV o--- TO GROUND
LINE | |
| MOV
| |
----------o---------o-------- to equipment
*The MOV between the line wire must be selected to have such voltage
that it does not start to conduct at the normal telephone line voltages
but stops the harmful higher voltages. Typica telephone line DC voltage
is 48V and ring voltage is typically 90 vrms or 130V peak but can be upt
to 130V RMS. Some modems use 130V RMS rated VDR which starts to conduct
at about about 190V peak. Bell system Technical Reference #61100
mentions that a worst case telephone line voltage can be 105 VDC + 130
VAC= 289 V peak. If the MOV voltage is set too low the circuit will not
pass "on-hook" requirments because it leaks too much current (for
example FCC part 68 requirments demand 10 Mohm DC impedance in "on-hook"
state).
The MOVs form line to ground connection to line wires have typically
somewhat higher voltage rating to make sure that they do not start to
conduct at normal ground potential differences seen in the situation
where the surge protector is used. For example one AT&T unit has 130 V
RMS MOV's in SERIES to ground, so they won't clip until about 380V peak
and one PATTON says it clips at 310V in 500 Ns.
Because MOVs have limited surge handling capacity some surge protectors
use resistors between the line and the surge protector to somewhat limit
the surge current and dissipate the surge energy. Because the surges can
have high energy the resistors must be able to handle high power surges
<http://www.epanorama.net/documents/surge/telesurge.html#> safely. By
having enough powerful non-flammable resistors (0.5-2W) usually is a
safe choice. The fuses in the circuit are ment to cut the connection if
something hazardous happens. If big surge happens it will quite propably
burn the fuse. The fuse itself does not usually help much in fighting
against surge but it will make sure that if for some reason the ground
potential is no longer ground, no damaging currents will flow to
telephone line (for example mains current accidentally entering to thin
telephone cable wire can burn it and start fire). So the fuses melting
the phone wire in catastrophic failure.
*
FUSE
TELCO >----o/\o------/\/\/\----------o------------> OUT TO EQUIPMENT
|
LINE MOV
|---MOV--> TO GROUND
MOV
FUSE 20 OHMS 2W |
>----o\/o------/\/\/\----------o------------>
*The MOV arrangemen in this circuit is somewhat special. In this
arrangement the rurge voltage in which the MOVs start to conduct ia
approximately double the voltage ratings of the MOVs used in this
circuit. In any surge case the surge energy will flow through MOVs (so
the energy is divided between them). This arrangement is shown here
because it is used also on some commercial surge protectors. The MOV
arrangement in this circuii equivalent to the first circuit if the first
MOVs have half the voltage rating and twice the capacitance of the
second MOVs.
Always just VDRs no not provide enough protoection. DVRs are quite fast,
but have limited surge handling capacity. If nore capacity is needed it
is quite common to use higher power but slower gas tube arrestors in
front of the VDR surge protection circuit. This arrangement (when
derigned correctly) gives high surge handling capacity and quitre fast
operation. If even faster opration is needed then is possible to add
some fast special semiconductor surge protection devices after MOVs
(zener diodes, avalanche diodes, surgectors, TISPs etc.).
------------------------------------------------------------------------
Non-commercial designs
The following non-commercial surge suppressor circuits are collected
from various sources (BBSs, FTP-sites etc). I am only including those
schematics here to make a good collection of surge suppression circuits.
I have not tried those circuits myself, so I can't say if they are
effective or not.
Circuit one
This circuit is designed by Reijo Salminen, who posted it to MITS BBS at
spring 1991. The circuit is designed for protecting modems and
telephones connected to telephone line. The circuit is designed for
telephone lines used in rural areas. The protector is connected between
modem and incoming telephone line. The ground connector is connected to
main electricity ground of the building through good grounding wire.
*
o---------------*----*----------RRRR-------*------
Line A I V ---> to modem
o---------------*----I---*------RRRR-------*------
B B
Ground--------------------*---*
A = 230V surge gas tube protector
B = 600V surge gas tube protector
RRRR = 10 ohm 1 W resistor
V = varistor 250V
*
The resistors in the circuit limit the surge energy passing through the
circuit and they work as fuses in case of large surge. For safety, those
resistors should be non flammable type.
Over voltage protectors B are rated so that in case of electricity
grounding fault where ground pin becomes accidentally hot (220V AC),
those surge protectors does not pass current to telephone line. If the
surge protectors pass current to telephone line when electricity ground
potential is raised against telephone line, there is apparent danger of
fire.
In Finland modems are tested at 2000V voltage pulse and in USA with
1000V pulse, so the protection should be enough in both cases. It shold
be mentioned that the circuit is not 100% proof, so the best protection
is disconnect modem from telephone line connector when thunderstrom is
coming.
Circuit two
This circuit was designed by Tim Jackson at 1990. It was presented in
his article "TELEPHONE LINE SURGE ARRESTOR" found in telecommunication
archives.
The trick is to install the unit in the line between the telephone jack
and your modem (ie: not too far from the modem, like in another room)
and connect the earth lead from the circuit to the earth pin on the SAME
PLUG that feeds your PC. *
10 ohm 5 Watt
>----------+-----/\/\/\/------------------+------------->
Phone Line A | |
<=>300V Gas Arrester ____|_____ To Modem
| | A |
| |TISP2290|
|--------+--------------------------|C |
Earth | | B |
| ----+-----
<=>300V Gas Arrester |
| |
| | To Modem
Phone Line B | |
>----------+-----/\/\/\/------------------+------------->
10 ohm 5 Watt
*Circuit drawn as best as possible with ASCII
<http://www.epanorama.net/documents/surge/telesurge.html#> by Pat Verner.
The phone line has a gas arrestor from each leg to earth. In other
words, two gas arrestors. One from A to earth and one from B to earth.
The line then has a resistor in series with each leg (A and B) before
being connected to the TISP2290 (the Texas Instruments chip mentioned
earlier). This chip has three pins. The outer two (A and B in the
diagram) are connected to the resistors while the centre one (C) is
connected to earth. The metal tag of this component is internally
connected to the earth pin (C), just for the record. The modem is fed
from the outer two pins of the TISP2290.
The bulk of the energy involved in a surge is dissipated by trusted (and
slow as treacle) gas arrestors. The TISP2290 absorbs the high speed
spike that the gas arrestors miss and is itself protected by the two
resistors which provide a little current limiting. The modem, being fed
from the same point as the TISP2290 is protected by the whole circuit.
For those who have to know, the TISP2290 works in a manner similar to a
zener array connected between the A and B wire and earth so as to limit
the voltage between any of three points to about 200 Volts. As you know
this is not entirely effective and so if the voltage rises to 290 Volts
(hence TISP2*290*) then this crafty critter cuts in triacs to crowbar
the offending points to earth until the surge has passed.
Steven McCann wrote:
> Hello,
>
> Does anyone have any experience or know of any products to surge protect
> multiple analog POTS lines?
> I'm in an area that can be hit by lightning often so I need to surge protect
> two incoming FXO lines, and about 8 FXS analog extensions. I see that APC
> offers RJ-11 individual surge protectors (APC PTEL2) for about $25 each,
> but does anyone know of a product that could cover multiple lines at once,
> and idealy that you could crimp directly to rather than having to have
> dozens of small crimped phone cables?
>
> I'm also going to be grounding about 8 cat-5e gigabit lines, but it looks
> like the product offered by APC (PNET1GB) will be fine as I won't need to
> use them as often,
>
> Thanks,
> Steven
>
>
