Technical information

Technician’s Handbook

Test/Verify (Ground Start)

Verify the far-end (CO) circuits by using a standard telephone for

incoming calls. Verify outgoing calls by using a Butt Set with a ground-

start lead (momentarily shorting the ring lead to the ground will produce

a dial tone from the far end).

Verify the near-end (PBX Ground Start) circuits by connecting to known

working far end Ground Start circuits.

Verify that appropriate voltages are present on Tip-Ring in each call

state.

During off-hook condition, 18 mA DC minimum should be drawn from the

CO (typical 35-40 mA).

Tip-Ring is polarity sensitive. PBX will be unable to initiate calls if

reversed. Reverse polarity to verify.

Digits

Loop Current toggled

(Rotary) or DTMF

Stop Dial -

Receipt of Digits

Audible Tones - Busy,

Reorder, Ringback depen-

dent upon digits dialed and

called party condition

Answer

Supervision

CO reverses current flow in

Tip-Ring

Disconnect

Supervision

Near-end: PBX opens loop

Far-end: CO removes

ground from ring

Near or Far-end termi-

nation: Loop Current is

broken

Table 7: Ground Start Trunk Summary (continued)

Signal

Ground Start Trunk PBX

Outgoing

Ground Start Trunk

PBX Incoming

(Sheet 2 of 2)