CO129-464 - Public Offices - 1920 — Page 114

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bong Kong Regn. No. 4:35.2.Item No.!!.....

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110

SPECIFICATION

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for

DRY CORE UNDERGROUND TELEPHONE CABLES.

* 2

101.

"

types of

ables.

Armouring.

Cables.

1. The underground cables are to be to the

latest specification of the British Post Office for twin wires, each weighing 10 pounds per mile, paper

insulated and lead oovered.

The electrostatic capacity of each wire measured

against all the remaining wires of the cable and the

lead sheathing must not exceed 0.115 microfarad per

mile. The maximum resistance per statute mile at 60

degrees Fahr. to be 87.825 Standard ohms. The insula-

tion resistance of each wire from every other wire in

the cable and from the lead aheathing, must not be

less than 5,000 megohme per statute mile, after one

minute's electrification at a temperature of not leas

than 50 degrees Fahr. when tested with an E.M. F. of

not less than 300 volts.

2. The armoured cable is to be protected outside

the lead sheath by the following coveringe :-

(a)

Two strips of canvas, each 2 inches wide,

saturated with Stockholm tar and ozokerite

composition, to be evenly laid on in reverse

lay, the first strip to completely cover the

lead, and the second strip to completely cover

the first.