ITT grounding Feature

[Babybearjs]

enclosed is a copy it the schematic for the ITT 2565 phones with a #46 dial... I'm trying to understand the Ground Feature (pushbutton) as I don't understand the purpose for the feature. is it a flash key? or does it do something else? I was looking at the schematic for the ITT 501 KSU and there was nothing on this feature... what am I missing, if anything?

[tubaman]

Ground push-buttons on business phones are usually for a PABX earth recall facility. This usually brings back the dial tone so you can access PABX features (divert, hold, callback etc).

[Babybearjs]

so, it is like a flash key....

[countryman]

Those functions are controlled by a flash key on modern PABX. Back in the days an Earth key was used.
An Earth key connects one of the lines to a third, grounded wire.
A flash key breaks the line for a defined, short period (time can vary)
On some old phones like German W48, the Earth key can be turned into a makeshift flash key by removing a jumper. It will then break the line as long as the button is pressed. A brief stroke will do. It must be longer than the dial pulse "1" but short enough not to be interpreted as hookup.

[Jack Ryan]

That seems like a very modern (DTMF) telephone to be using an Earth key but those key systems used multiple wires between stations anyway and one of those was a ground key.

Normal PSTN telephones had been using "flash" for a long time by then.

Jack