Back-to-back sockets on a shared wall in a multi-tenant office
You are cabling a small office fit-out. The tenant leases suite 4 and suite 5, separated by a single 92 mm steel-stud plasterboard wall with no fire rating and no cavity services. The client wants two data outlets back-to-back: one in suite 4 and one in suite 5, both fed from the same comms cabinet located in suite 4. The wall cavity is only 90 mm deep and already carries two 240 V circuits in surface-mounted conduit on the suite 5 side. The client argues that back-to-back is cheaper and faster. You have a drum of Cat 6 UTP and standard modular sockets. The building manager has asked for a written method before work starts.
1. Evaluate whether running a single cable through the wall to serve both sockets is acceptable, and state what you would install instead.
Read the worked answer
A single cable passing through a wall to serve outlets in two different tenancies is not acceptable. The cable would leave the tenant's demarcation and enter another party's space, creating a security and separation problem, and the outlet in suite 5 would not be a proper termination point on that tenant's side. The correct approach is to treat each tenancy separately.
Install a socket in suite 4 fed from the cabinet, and a separate socket in suite 5 fed by its own cable run back to the cabinet or to a point the suite 5 tenant controls. Each outlet must be a discrete termination, not a pass-through.
Where the cable crosses the wall, it must be protected and the penetration sealed. Because the wall is not fire rated, a simple sealed penetration is adequate, but if it were rated you would need an approved fire-stop system and would not be permitted to breach it without reinstatement.
Also note the separation from the 240 V circuits: maintain the required segregation from mains cabling, and do not share the conduit.
2. The suite 5 side of the wall has two 240 V circuits in surface conduit. What separation issues arise and how do you resolve them?
Read the worked answer
Communications cable must be kept separated from mains cabling to limit induced interference and to prevent a fault in the mains from damaging or energising the comms cable. The exact separation distance depends on the applicable standard and the wiring method, but the principle is consistent: do not run comms cable in the same conduit or enclosure as mains cable, and maintain physical spacing where they run parallel.
On the suite 5 side, the conduits are surface-mounted, so you have two options. First, route the comms cable on the suite 4 side of the wall and penetrate only at the outlet position, keeping the crossing perpendicular and short. Second, if you must run parallel on the suite 5 side, use a separate conduit with adequate spacing and cross the mains conduit at right angles rather than running alongside it.
Do not drill through or attach to the mains conduit. Confirm the circuits are de-energised only if you need to work near them, and if the work requires altering mains wiring, that is outside a restricted cabling registration and must be done by a licensed electrical worker.
3. The client asks you to certify the installation as compliant so they can claim the fit-out is finished. What is your position?
Read the worked answer
Certification follows the work actually performed and tested, not the client's schedule. Before any compliance documentation is issued, the installation must be tested and the results recorded: continuity, length, and the appropriate performance tests for the cable category, with results retained.
If the design as requested cannot be installed compliantly - for example, because the client insists on a shared pass-through cable - you cannot certify it. You should document the non-compliant request, propose the compliant alternative, and only certify the work you actually completed and tested.
You should also confirm that the work is within the scope of your registration. Altering or connecting to mains wiring, or working on the electrical circuits, is not covered. Your certification covers the communications cabling you installed and tested.