Norchard UAX13 Exchange Trunking Diagram
Vertical Marking Bank Strappings
The above arrangement allows telephones on the Norchard site (connected to levels 3-5 on the linefinders) to have access to all group selector levels but prevents telephones which are off site from dialling 2 and setting off the 222 fire warning system. It prevents museum demonstration telephones from dialling any phone other than a demo phone. This stops demo phones from ringing administration phones connected to the exchange.
Note : Group selector levels that are spare are connected to an NU Tone circuit rather than have the levels strapped as spare on the VMBs. This arrangement saves restrapping of the VMBs each time a new level is taken into use.