At almost 1300 watts I think I'm done chasing the mining train. I may have mentioned it before, but most home outlets let you pull about 1200-1300 watts for the entire room (circuit). That means you're asking your ancient home wiring to pull 100% for 24/7 mining. Fires are a real possibility once you get in this range. Imagine all the 17 yr old kids that have a few BTC, order a S7, and plug it into their mom's basement unknowingly overloading the circuit like a Christmas tree with too many lights. Spark, spark, and two huge fans to kick the flame up. Now you're looking at a home burning down and possible lawsuits, though with BM being in China a successful suit is unlikely.
If you are talking about circuits inside U.S. homes, 15 amps x 120 volts = 1,800 watts. A 1300 watt rig would consume 72.2% of an 1800 watt/15 amp circuit. That's approximately 3% under the 75% recommendation by the NEC for a 15 amp circuit with 14 AWG wiring.
If they have other devices (lamp, clock, etc...) plugged into other outlets on the same circuit, there will not be as much heat as you might think at that one outlet the PSU(s) is plugged into when powering one S7. Most of the heat would be at the breaker in the Main Service Panel (MSP) while the current is distributed to multiple outlets for that circuit. It is the circuit breaker that would be at fault of any potential fire [For not tripping]. You are mistaken if you think the PSU(s) and rig would catch on fire for pulling only 72% of the available current for that circuit.
Even if the circuit is a "loop" circuit instead of a "branched" circuit [with the rig being the first device in the loop] there could potentially be quite a bit of heat at the outlet the rig is plugged into. Yes, in that case, there would be a lot of heat at the breaker and the wire leading up to the first outlet in the circuit. Then less and less heat for each outlet after the first in the loop, providing the rig was plugged in the first outlet in the loop closest to the breaker. Is this the fault of the rig? No... It's the fault of the owner if old defective wire catches fire. It could potentially be the fault of the manufacturer of the breaker under certain circumstances.
As the customer plugs in and turns on more devices at different outlets on the same circuit, the circuit breaker should trip once 15 or more amps flowed on that circuit. If it does not trip and a fire is created, it will not be at the outlet where the rigs are located. It would be in the MSP where the defective breaker is located. This is assuming the wire gauge in the home is 14 AWG. If the wiring is old in the home, that's the home owner's fault for running devices on defective wiring. It's not the manufacturer of the device fault.
It is my opinion that one should proceed with caution when mining with multiple S7's. In that case [Multiple S7's] one should consider creating a space with circuits dedicated just for the rigs; preferably with a 240 Volt circuit(s) and PDU's or whips.
Bitmain really should change some policies. I ordered several batch 6's at $1625 each. And now batch 7 w/ 5th shipping the same time mine are, arg. 
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