5501RE is the part number of the wall mounting enclosure to suit L5501RBCP 1 channel C-Bus Blind/Curtain/Shutter relay.
Please go to the website via the following links below and check under the Documentation Tab for more information.
Australia -
https://www.clipsal.com/Trade/Products/ProductDetail?catno=5501RENew Zealand - https://www.pdl.co.nz/products/detail?CatNo=5501RE&itemno=5501RE&backto=/search?q=5501RE&tab-document-1=0