Erniesone wrote:"All six cards lack additional power connectors and are thus powered through the PCIe slot alone, and have a TDP of 30 W. This is low enough, even for the passively cooled models that use up two slots in order to ensure proper cooling. Accordingly, the actively-cooled models are smaller and only use up a single slot. Despite the fact that the cards only use four PCIe lanes internally, the external connector requires a PCIe x16 slot."
Technically, only the x16 slot is rated to supply up to 75w. x1 and x4 physical slots are only required to deliver up to 25w, but in practice going over spec to 30w is usually not a problem, and an x16 card will plug right into an open-ended smaller slot. Note though that some SFF x16 slots actually have 25w maximum printed right on them.
It's purely a power issue as the GT1030 chip only has external wiring to connect to x4 whether or not all traces are printed on the x16 connector.