Compaq Prosignia 150 User Manual page 119

11-22 Government Approvals
A clearance distance is the measurement of the shortest path (in air)
between two points; whereas a creepage distance is the distance
measured along the surface between two points.
For a host or other expansion card fitted in the host, using or generating
voltages greater than 300V (rms or dc), advice from a competent
telecommunications safety engineer must be obtained before installation
of the relevant equipment.
Except at the edge connector which plugs into the host's expansion slot,
clearance distance (Xmm) and creepage distance (Ymm) as given in the
table shown above, must be maintained between the communications
card and any other assemblies which use or generate a hazardous
voltage.
1. The modem is suitable for connection to the Public Switched Telephone
Network (PSTN) direct exchange lines and relevant branch systems
(PBXs).
2. A ringer equivalent number (REN) is a value given to all apparatus to be
connected to the PSTN. Its value can be taken and used to calculate the
maximum number of equipment items that can be connected in parallel
without impairing the performance of the standard bell circuit.
a.
b. The maximum REN of a line is 4; therefore, the total REN of all
c.
d. The REN for this piece of equipment is 1.0.
e.
REN = 3/n where n is the maximum number of units that may be
used in parallel.
apparatus connected to the line (obtained by summing the individual
REN values) should not exceed 4. This value includes any BT
provided instrument, each of which is assumed to have REN value
of 1.0 unless otherwise stated. Exceeding the REN value of 4 may
cause your telephone(s) to ring weakly or not ring at all.
Only one modem should be connected to a telephone line.
Connecting a modem in parallel with one or more telephone
instruments is not allowed.
The exchange should provide facilities for either loop disconnect
(pulse) dialing or multifrequency (tone) dialing. The modem can be
configured to operate with either system.