Pillars or Cross Connect Units are used to provide an accessible distribution/break-down point in the copper cable network between the Exchange and Customer. They are fed by main copper cables from the Exchange that, in turn feed smaller size, outgoing Customer Distribution cables. The connected copper cable pairs are used to provide a telecommunication service to Customers. The main cables are connected to the distribution cables using cross-connection jumper wires. The 900 pair pillar will typically feed a Distribution Area of up to 300 Customers (maximum). The pillar provides an access and test point in the network, as the Customers circuit can be tested both back to the Exchange and forward to the Customers residence, if ever the line develops a fault. Typically a ratio of about 1:2, is provided between Main Exchange Pairs and Customer Distribution Pairs of copper cables.