Which side should cars not be coupled?

Cars should not be coupled on the wire side or the inside of a curve because this position can create several hazardous conditions. When cars are coupled on the inside of a curve, it can lead to an increased risk of derailment. This is primarily due to the dynamics involved when the train navigates the curve; the pull on the coupling points can be greater due to the forces acting on the cars. Coupling cars in this position may not provide the necessary stability needed during operation, particularly on tighter curves where the tracking of the cars can be compromised.

Additionally, coupling on the inside of a curve may obstruct visibility and access for inspections or maintenance, further increasing safety risks. Thus, coupling should always occur in a safer, more stable position to minimize potential dangers during train operations.