CORDLESS, CERTIFIED INTRINSICALLY SAFE
These boards are certified intrinsically safe for Group I, and for petroleum vapour under Group II gases and are therefore suitable for use in fiery mines or the petroleum industry.
They are designed to meet the case where a larger ultimate capacity than six lines is required.
Constructed on very similar lines to the N513 type but a micro-telephone with battery switching key and induction coil is fitted so that a separate instrument is not required for operating purposes.
The indicators N4781N and keys N5202A are mounted on a hinged steel front plate which is locked by means of special triangle-headed screws. The keys are of exactly the same design as those used on the "Pyramid" mining boards but are arranged to provide a limited number of connecting circuits as given in the table below. The indicators are totally enclosed and push-button restored. The alnico generator is inside the board, except in the case of the 30-line switchboard, when it is in a separate box screwed to the bottom, in order to keep the overall size of the case to a minimum.
These switchboards may be used with any make of certified-safe telephones having safety condensers fitted.
A stand built of angle iron and having a hardwood top, can be supplied for mounting any of these switchboards.
A certified Ringing Delay Unit N8656 can be supplied for use with these switchboards.
Similar switchboards can also be supplied for use with certified battery call telephones.
Last revised: October 12, 2019