  We measure a triple quantum dot in the regime where three addition lines,
corresponding to the addition of an electron to each of three dots, pass
through each other. In particular, we probe the interplay between transport and
the tridimensional nature of the stability diagram. We choose the regime most
pertinent for spin qubit applications. We find that at low bias transport
through the triple quantum dot circuit is only possible at six quadruple point
locations. The results are consistent with an equivalent circuit model.
