Double Fusing

[Cicada]

The reason for double fusing is due to the American system for providing 220V from a 110V supply.
The 220Vac supply is generated by an anti-phase winding of 110Vac.

The term you need to search for is "split phase", try starting here: https://en.wikipedia.org/wiki/Split-phase_electric_power

Brilliant thank you guys. I think the picture is becoming clear now. This video explains 'split phase' 'anti phase'. Both descriptive names seem correct to me.

The double fused power inlets that I am using http://bit.ly/1P4ZurI have no L and N stamped on the plastic of the connector like the single fused inlets that I also have. It is obvious that the single fused units should have the L and N stamped on it so that you do not accidentally do a phase reversal when wiring them. You will then have a single fuse in neutral only. That is if you are careless and do not adhere to the iec 60320 standard. See attached iec_60320_plug_and_socket_definitions.png and iec_60310-1_c13_c14_pin_definitions.png

The double fused units do not have L and N stamped on the body of the housing but it does have L and N (in the correct orientation according to iec 60320) on the mains filter sticker.


So in summary. It seems that the double fused IEC power inlets are mainly used:
1. in such 'split phase' systems where you want a fuse in both phases because both are actually at some voltage above safety earth.
2. in non-'split phase' systems where you (as equipment manufacturer) cannot guarantee that there will be no phase reversal from the supply side where the product is used. So live will always be fused. And I think in non-'split phase' systems you should be safe with an additional fuse in the neutral (although redundant) and an upstream RCCB.

Feel free to complete the picture. Thank you very much for everyone's contribution.