Adding an expansion rack requires an Extension rack Module (BMXXBE1000), Extension rack Cable and Terminators.
The BMXXBE2005 is an Extension rack kit that contains everything that you need including:

• 2 BMXXBE1000 extension rack modules
• one BMXXBC008K 0.8 meter extension cable
• one TSXTLYEX set of 2 line terminators

Other cable lengths available:
BMXXBC015K - 1.5m extension rack cable.
BMXXBC030K - 3m extension rack cable.
BMXXBC050K - 5m extension rack cable
BMXXBC120K - 12m extension rack cable