I agree that you should ensure that the grounding is appropriate, as the LEAF is very particular about whether the ground pin moves relative to the two hots. There are posts here regarding how to address that safely if the system is ungrounded.
Another idea that I have is to go with EVSEUpgrade.com
which not only allows you to access 240VAC charging, but also it permits you to reduce the current allowed by the system down to 8A (IIRC). If this works with 120VAC charging, then it could give you more flexibility on how you charge when other loads are present.