4x 1080 ti psu spec

Would 1600watt psu suffice for 4 1080 ti’s? If the CPU is roughly 60 watts + mobo + risers?

It’s more than enough. Each 1080 Ti use approximately 250W-280W on stock (depending on the manufacturer) so you will need max 1100W for the 4 cards. The 1600W psu would be sufficient for you to add 1 more card or perform a bit of overclocking beyond 100% power.

Yah 1600W would work, but your math is just wrong.
First of all, you did not take into account the CPU and fan. The 1100 W might not work for certain model. Also running pass 90% rating is not save, because most PSU’s efficiency drops dramaticall above 90%.
Second, you forgot to consider the efficiency of the PSU. 1600W*efficiency=power you can supply to the load. In order to provide 1600W you need to pull more then 1600W from your outlet, which exceeds your PSU’s input power rating.

Also, you should not exceed 80% of your breaker rating. If it’s a 15A breaker @ 120 V. You should only be drawing like 15A0.8120V=1440W from your 15A @120V breaker.

I think I might need to emphasize what I meant earlier. When I said 1100W is sufficient for the 4 cards, I meant literally only for the 4 cards. The power consumption of the other apparels would need to be put into consideration (cpu, MB, risers). However you did mentioned something that I have not put into consideration, the PSU efficiency. Thanks for pointing that out. To put this back into the topic, 80% efficiency should be a safe gauge for calculation if the PSU has a 80 plus rating(https://en.m.wikipedia.org/wiki/80 plus).