Bungalow: buried cable to hut and bike shed

A single-storey bungalow, 12 × 9 m inside the outer walls: living room, kitchen, study, bedroom, bathroom and utility room around a central hall. The garden with the terrace lies behind the house and ends at a garden hut; in front of the house is the driveway with a bike shed. Hut and shed each have a small sub-board of 1 × 12 TE.

Both trenches start in the utility room, where the main board hangs. The trench to the hut runs 27.7 m along the side of the house and through the garden, 60 cm deep. The one to the bike shed is 6.1 m long and runs under the driveway, so it is 80 cm deep. About 60 cm under lawn and paths and 80 cm under surfaces cars drive on is the usual depth. Every cable lies in protective conduit, and the outdoor-rated Cat.7 network cable to the hut in a conduit of its own. The material list comes to 73 m of conduit, 42 m of warning tape and six watertight wall entries.

The cable in the ground is NYY-J; NYM-J is not intended for laying in soil. The hut gets NYY-J 5 × 10 mm², the shed NYY-J 5 × 6 mm². The cross-section follows from the length: the cable route to the hut is 39.7 m, 28.9 m of it in the trench. With 5 × 10 mm² the voltage drop to the farthest outlet behind the hut comes to about 2.5 %, with 5 × 6 mm² it would be about 3.3 %, both at the breakers’ rated current and 70 °C conductor temperature. DIN 18015-1 provides for 3 % from the meter.

In the main board a three-pole B32 protects each feed. That is three steps above the B16 in the sub-board; two steps is the usual rule of thumb for selectivity. The feed breakers sit behind no RCD, and each sub-board has its own four-pole type A RCD, 40 A, 30 mA. In the hut it covers the sockets, the lights inside and outside, and the socket post in the garden, which is connected through a 3.5 m branch trench. In the shed it covers two double sockets for charging e-bikes and the light.

The four bollard lights along the garden path hang on the main board, with NYY-J 3 × 2.5 mm² in the same trench as the hut’s feed, and are switched at the terrace door. Indoors the circuits are spread over two type A RCDs, two arc fault detection devices (AFDD) for the bedroom and one lighting circuit, and an RCBO each for the microwave and the dryer, behind the main switch and type 2 surge protection. 4 TE stay free.

Open the project in the room planner for the trenches, cable routes and material list, or the three boards in the panel planner.