diff --git a/Hardware-Preparation.md b/Hardware-Preparation.md
index b7783184..ce738643 100644
--- a/Hardware-Preparation.md
+++ b/Hardware-Preparation.md
@@ -8,10 +8,12 @@ Be careful - some so called 3V3 FTDI cables actually supply 5v on the VCC line.
 
 ### Attention ⚠️️⚠️️⚠️️
 
-**Do not connect AC power and the serial connection at the same time** 
+**Be extremely careful if connecting to AC while the cover is open and circuit board is exposed** 
 
 Shorting your serial interface with AC will fry your module or programmer and may also harm or destroy your PC.
-If you are not careful, your own health might be in danger. Always make sure to have all high power cables disconnected from the Sonoff module while being connected via serial/USB or even while the case of the module is opened.
+If you are not careful, your own health might be in danger. It is preferable to always have all high power cables disconnected from the Sonoff module while being connected via serial/USB or even while the case of the module is opened.
+
+Note that contrary to alarmist reports circulating on the internet, the DC power supply is fully isolated from the AC supply. It is perfectly safe to interface with the DC circuit while the unit is connected to AC supply, as long as the GND is tied in common. It is also preferable to keep the +3.3V line *disconnected* while interfacing with the sonoff self powered. If the sonoff is self-powered (connected to AC), connect only GND, TX, RX.
 
 ## Serial Connection