CORDLESS, CERTIFIED INTRINSICALLY SAFE
N 513B shown pictured to the right.
These switchboards have been specially designed to meet the demand for an economical article for mines and other places where cast-iron explosion-proof cases are not essential. They are certified intrinsically safe for Group I, and for petroleum vapour in Group II and are therefore suitable for use in fiery mines or the petroleum industry.
The casework is constructed of hardwood of robust proportions and the sloping top is reinforced by a heavy-gauge steel plate which provides ample protection against falling roof material and water. A special triangle-headed screw lock is fitted and a suitable key for same is provided.
The indicators N4781N, mounted on the steel front plate, are totally enclosed and push-button restored.
The connecting keys N5202A, comprised of stout metal plungers fitted with metal tops, will withstand a considerable amount of rough usage. The tops are engraved to indicate the connections made when the keys are depressed.
The terminals are mounted on ebonite strips screwed to the backboard and are very accessible, two of these terminals are for connecting an alarm bell of the N3033 type.
This form of cordless switchboard is widely known as the "Pyramid" on account of the design formed by the keys. The simplicity of operating and obvious low maintenance costs have made them the general favourites for small magneto systems.
A separate telephone is required for operating purposes and any make of certified-safe telephones which have a safety condenser fitted may be used.
A diagram of the connections is supplied with each board.
We can supply a Certified Ringing Delay Unit, N8656, which allows of code ringing,
between stations on a line, without actuating the switchboard indicators. Connecting
facilities are provided on the backboard.
Taken from the Ericsson Telephone Catalogue issue no. 49
Last revised: October 12, 2019