An electrical adapter is disclosed for connecting a connection contact of a circuit breaker with an associated contact piece of an electrical circuit along which the circuit breaker has to be inserted, including a hollow tubular element having a first end portion and a second end portion configured to be electrically connected to a connection contact and a contact piece, respectively, an inner cavity of the hollow tubular element having, at the first end portion, a first frusto-conical shape. A first connector having a hollow deformable body and configured to be accommodated inside the first end portion. A locking body configured to be securely placed along the inner cavity of the hollow tubular element. A second connector including a first connection portion configured to be accommodated inside the first end portion of the hollow tubular element.