Published October 20, 2026 · Evidence reviewed October 21, 2026
Maincubes reaches substation milestone at Nauen data-centre campus
A topping-out ceremony marks progress on power infrastructure for mainHub Berlin. The operator’s documents give conflicting targets for BER02 to enter service in 2028.
Maincubes has completed the structure of the substation serving its planned mainHub Berlin data-centre campus in Nauen, Brandenburg. Contractor JSM Group confirmed on 19 October that a topping-out ceremony took place on 13 October, with building-services installation due to begin at the end of the month and transformers to follow. The milestone concerns the substation building; it does not establish that the campus is connected or its data halls are complete. JSM construction update
The campus is marketed under the Berlin name but lies in Nauen, outside the German capital. BER02 is the first of up to six planned data-centre buildings. The operator’s live English and German project pages list Q3 2028 for BER02, while its undated English factsheet still lists Q1 2028. The conflicting targets do not establish a confirmed service date; the reviewed documents do not establish a revision chronology or a confirmed delay. The factsheet gives approximately 137,000 square metres as the site area. Live operator page; German operator page Operator project announcement; BER02 factsheet
Three capacity figures, three different measures
Maincubes says it has signed a grid-connection agreement with E.DIS for 200 MW. Its factsheet specifies planned campus IT capacity of 144–186 MW, depending on design. JSM describes the substation as 200 MVA. The figures refer respectively to grid-connection capacity, the planned power available for IT equipment and the substation’s apparent-power rating. They are neither interchangeable nor additive. Grid agreement announcement; Technical specification; JSM update
JSM’s work includes a roughly six-kilometre, 110 kV cable route linking the campus to Wustermark. The October update documents construction progress, while electrical installation and commissioning remain ahead. JSM update
The municipal development plan took effect on 2 July 2025. That establishes the zoning position, rather than an individual building permit. Local reporting from the topping-out ceremony says the first data-centre hall has a permit and is expected to start construction in early 2027; the underlying permit was not available in the reviewed material. Nauen official gazette, pp. 4–5; Unser Havelland report
Financing disclosed at platform level
Maincubes is majority-owned by funds advised by DTCP. A January financing announcement set out a €2.475 billion platform debt package: €1.775 billion in committed facilities and a €700 million uncommitted accordion. The package covers refinancing and several developments, including Nauen. It does not disclose a dedicated Nauen allocation or establish the campus’s construction budget. DTCP ownership disclosure; January financing announcement
The operator is designing the campus for cloud, AI and high-performance computing, with air, liquid or hybrid cooling options. The reviewed disclosures do not identify a tenant or a committed GPU deployment. For now, the documented advance is in power-infrastructure construction, with BER02’s 2028 service timing still unresolved between the operator’s documents. BER02 factsheet