Does anybody know whats going on with the HPWC installation instructions? I've got an installation with a short offset conduit directly attached to a surface mount main panel. I elected to use THHN #6 AWG wire connected to a dedicated breaker (GE THQL type). Only three wires are in the 3" conduit length, each with a length less than 36" from the HPWC junction. Since this is all outside in southern California the ambient temperature is certainly going to be less than 40 deg C. Therefore, I don't believe I need to derate for temperature or bundled cables. Based on this, my code check guide suggests 75A is achievable. Even if I decided to derate for the fuse connection (something I don't think should be necessary up to the fuse limit) or a more typical wiring, this installation should allow me 60A. The other variable is perhaps adjusting for continuous operation but I have not considered that.
However the HPWC installation guide doesn't seem to follow these standard NEC rules. It is has a table of maximum output current vs circuit breaker size. That's odd. I would think the installation instruction should be geared to wire size instead of fuse size. Why shouldn't that be the case? In any case, this table shows a 60A fuse limited to 48A, a 70A fuse limited to 56A, a 80A fuse limited to 64A and to get 80A one would need a 100A fuse.
Let's say I want to get a charge at 64A. The above suggests I need a 80A fuse which in turn would require #3 AWG wire. From NEC tables #3 AWG wire is rated to 110A max. This seems to be highly over designed and doesn't make sense to me.
As another example, consider an existing installation where one has #8 THHN AWG wire attached to a 40A fuse (the wire is rated to 55A but derated to 40A). If I attach a NEMA 14-50 receptacle to this I'd be free to draw up to 40 A (e.g. via a mobile connector). However if I followed similar rules to the HPWC installation I'd be limited to 32A. This would suggest the HPWC is not as sturdy as the mobile connector. However, we know the HPWC is actually designed for use up to 80A!
However the HPWC installation guide doesn't seem to follow these standard NEC rules. It is has a table of maximum output current vs circuit breaker size. That's odd. I would think the installation instruction should be geared to wire size instead of fuse size. Why shouldn't that be the case? In any case, this table shows a 60A fuse limited to 48A, a 70A fuse limited to 56A, a 80A fuse limited to 64A and to get 80A one would need a 100A fuse.
Let's say I want to get a charge at 64A. The above suggests I need a 80A fuse which in turn would require #3 AWG wire. From NEC tables #3 AWG wire is rated to 110A max. This seems to be highly over designed and doesn't make sense to me.
As another example, consider an existing installation where one has #8 THHN AWG wire attached to a 40A fuse (the wire is rated to 55A but derated to 40A). If I attach a NEMA 14-50 receptacle to this I'd be free to draw up to 40 A (e.g. via a mobile connector). However if I followed similar rules to the HPWC installation I'd be limited to 32A. This would suggest the HPWC is not as sturdy as the mobile connector. However, we know the HPWC is actually designed for use up to 80A!