Abstract: Electrical wiring trunking includes at least first and second cable running compartments extending parallel to each other in a general lengthwise direction of the trunking and separated from each other by a fixed insulative partition. The partition includes at least one communication opening between the first and second compartments. An electrical insulation box has a lateral wall with a lateral access opening mounted in the first compartment so that its lateral access opening coincides with the communication opening. The space inside the box forms an extension of the second compartment into the first compartment which is electrically insulated from the first compartment and receives an electrical accessory to be connected to electrical cables running in the second compartment.