I want to automate lightings and fans in my home. I am planning to use RPI and SSRs for that. My question is about powering them. Can I have a single 5V 5AMP or 10AMP unit for the entire house, or individual power adapters for each unit? If I want to run the cabling for 5V in the entire house, I suspect power loss due to resistance of the cable. What should be the best approach in this case?
There are a number of problems controlling household loads (120 to 240VAC, often well over 1KVA power, at distances often over 100 feet) with devices like the Raspberry Pi, which are more suited to electronics type loads.
As you mention the challenge distributing 5VDC power through the house is voltage drop. The answer to voltage drop is using a big wire. You can keep the voltage within 1 volt (20% drop) at 5 amps, up to 100' by using 10 gauge wire. That's a big expensive wire.
The more you look at the challenges involved doing automation with the Arduino, Raspberry Pi, etc., the more you appreciate the design of PLCs, commercial building controls, and home automation systems.