A second sensor located externally of the vessel and within {HEAD ~ a coupling} in fluid communication with {TAIL ~ the vessel} serves as a backup safety device and is connected to a second relay coil also having contacts interrupting the flow of electrical energy to the heating element when the water level is below the outside sensor 
with
A second sensor located externally of the vessel and within { HEAD ~ a coupling } in fluid communication with { TAIL ~ the vessel } serves as a backup safety device and is connected to a second relay coil also having contacts interrupting the flow of electrical energy to the heating element when the water level is below the outside sensor
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH