diff --git a/config.py b/config.py
index 9d7da2d..4240f2f 100644
--- a/config.py
+++ b/config.py
@@ -32,6 +32,13 @@ currency_type   = "$"   # Currency Symbol to show when calculating cost to run j
 gpio_heat = 23  # Switches zero-cross solid-state-relay
 gpio_e_relay = 27 # pin 13; emergency cutoff relay
 
+#   Note: `gpio_e_relay` is used to and a redundant mechanical relay in series with
+#   the SSR. Because SSRs normally fail closed (i.e. energized), this provides a 
+#   way for the controller to shut off the kiln in the event that the SSR fails.
+#   It is designed to be used with the SSR input connected to the safety relay's
+#   Normally Open (NC) output; thus, the kiln can only heat when the RPi has
+#   energized the safety relay. 
+
 ### Thermocouple Adapter selection:
 #   max31855 - bitbang SPI interface
 #   max31856 - bitbang SPI interface. must specify thermocouple_type.