T1 Voltages and Crosstalk

Question:
The cisco router built-in CSU by default transmits at 0 dBm. It can be set for
-7.5 or for -15. If telco is sending at -7.5 and the cisco is sending at 0 dbm
could this cause a problem ?

Answer:
Yes, this can cause near end cross talk but only in longer DEMARC extensions.
The file below discusses this in detail:

Also, if interference is coming from a 3rd, foreign source that is leaking
energy, like a pots line, or even a high voltage electrical circuit that
is generating emf noise then many transmission problems can result.

Verizon Answer about differing signal strength and crosstalk:

The actual DS1 rate signal is preset to -7.5 dBm. It was common in
the past to set them for 0 dBm, but somewhere in FCC regulations in
tiny, tiny print the -7.5 setting is prescribed and Verizon tries to
adhere to it.

The 0 dBm from the Cisco should be fine, the HTU-R is pretty tough.
The only time I've noticed an issue with CPE power levels is when
they are connected thru a particular type of smartjack to a fiber
mux.

Some of the low-speed cards on the muxes are sensitive to input
levels. So it is a circuit-by-circuit kind of issue depending on the
design.

Crosstalk or other interference can be an issue. Generally you want
to run signal cables perpendicular not parallel to power cables, and
in the case of DS1 signal cables as far from 56-64K (like ISDN BRI)
signal cables.