TWO PARTY LINE.
No. 1 Set.
(The battery side of the line goes to the L2 post.)
Gives two hook clicks, and can be tested in very much the same way as
a straight set, but the following points should be remembered: on sets
that ring to ground an open ground will, like ringer open, cause the
bell not to ring and only one hook click.
Resistance in the ground may cause poor ring.
Reversal of the three wires on top of the bell may cause only one hook
click, bell not to ring, and transmitter nearly dead.
Transmitter very poor may be caused by the ground side of the line
being open outside. (You can still call the operator and talk, with
difficulty through the ringer and ground.)
No. 2 Set.
Gives but one hook click, but otherwise can be tested in very much the
same way as a straight set. Remember the following points:
On sets that ring to ground:
Ground open will prevent bell from ringing.
Resistance in the ground may cause poor ringing.
A ground on the ground side of the line may cause the bell to ring
poorly or not at all by taking the generator current off to ground
before it reaches the instrument.
Condenser short-circuited will not only put a ground on the ground side
of the line through the ringer, but on exchanges which use pulsating
current for ringing will also cause bell to ring poorly or not at all.
Reversals of the three wires on top of the bell may cause two hook
clicks, bell not to ring, and transmitter nearly dead.
On two-party sets, to find reversals of the wires at the top of the
bell, trace out the wire to the protector, or else find out with your
head receiver which one of the three wires is alive to both of the
others, or to an independent ground. This one is the battery side of
the line.
To test for reversal of the ground wire with the ground side of the
line, bridge your head receiver from an independent ground to the two
doubtful wires successively. You will get induction on the line wire,
and none on the ground wire. Or, bridge your receiver from the battery
side of the line to the other two wires successively; the one that
gives the most induction in this case is the ground wire. Or again,
test by bridging your lamp from the battery side of the line to the
other two wires successively. If the ground is good, bridging to it
will give a brighter lamp than bridging to the ground side of the line;
only a little brighter if the line is short, much brighter if the line
is long.
The above is also the way to test for a poor ground. The resistance
of the ground return back to the central office should be less than
the return through the cable, therefore the lamp should burn brighter
on the ground wire than on the ground side of the line; very little
brighter if the line is short, much brighter if the line is long.
An extension bell open will prevent the main bell from ringing, just
as in a straight set. Test by running a temporary ground, or by
short-circuiting out the extension bell.
If you are in doubt when testing a two party set, disconnect the ground
wire and strap the bell, making it a straight set temporarily, and
then test the ringing, transmission, and hearing. A straight set will
respond to all rings, direct, two-party, and four-party.
If on a two-party set the ground side of the line is open outside,
temporary service may be given, if necessary, by working to the local
ground.
If the ground is open, temporary service can be given, if necessary, by
converting to a straight set; but in this case the bells will respond
to both calls.
If second instrument is properly poled and bell rings when first
station is being called, the trouble is probably due to party at first
station taking his receiver off the hook before the operator has
stopped ringing, and vice versa.