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Searching for wire pairs (double wires)
When searching for double wires and identifying overdrafts, one test lead of
the KE890/895 is connected to each wire of a twisted pair of wires. This can
be done automatically by plugging it into a junction box or by connecting it to
the open cable end.
With the KE420, the pair is found at the other end or at each distributor when
the
HIGH
key is held down. The
LOW
key is pressed to find the exact wire
pair with the strongest signal. If the pair is twisted over the whole distance,
this pair will be found exactly. If, for example, there is a wire break, an exch-
ange of a single wire or even an overdraft (split pair), several wires with the
search signal are found at the distributor. Such a result would be an indication
of an error in the wiring. By walking back along the cable, the location of the
error can be narrowed down.
If the cable ends are open, the procedure is similar – the wires are fanned out
and the KE420 moves over them while holding down the
LOW
key. If the test
probe of the KE420 is led over the wires, a high level is displayed over the
first wire of the correct wire pair, a minimum level in the middle and a high
level again over the second wire. This allows you to clearly identify the pair
you are looking for.
If no minimum can be found, it is either not the pair you are looking for or
there is a cable fault, e.g. caused by an interruption, an exchange, or an
overcurrent (a so-called split pair).
The KE890/895 also transmits the search frequency on lines with a termi-
nating resistor down to 50 Ω. This means that the transmitter unit can also
transmit a search tone on telephone or data lines carrying supply voltage.
