APPENDIX
Appendix 1
Appendix
Generally Accepted Criteria for Plain Old
Telephone Service
Parameter
Acceptable
Marginal
Unacceptable
Loop Current mA
≥
23
2
≥
20< 23
2
<20
1, 2
Circuit loss dBm
≤
8.5
–
>8.5
Metallic Noise dBrnC
≤
20
>20< 30
≥
30
Power Influence dBrnC
≤
80
>80<90
≥
90
Balance dB
≥
60
>50<63
≤
50
*Station Ground Ohms
≤
25
–––
> 25
Slope dB
≤
7.5
–––
> 7.5
Parameter
Insulation Light Fault
Heavy
Good
(Service
Fault
Affected)
3
(Out of
Service)
Insulation
Resistance
≥
3.3 MOhms
>2.8 kOhms
≤
2800 Ohms
< 3.3 MOhms
1
These are negative values.
2
>18 to <20 mA acceptable for emergency service only.
3
Lines having good insulation but equipped with ringer
isolators or selective ringing devices will test as having light
faults on tip and ring.
NOTE:
>
means “more than”
≥
means “more than or equal to”
<
means “less than”
≤
means “less than or equal to”
* On some floatingĆtip switches, such as #5 ESS, ground
resistance cannot be measured because the switch
operates on a floating ground.