What type of ground fault is used in the C440 and XTOE solid state overload relay?

The C440 uses what is known is a “vector summation” method of ground fault detection. 

The C440 basically monitors each phase current individually, and adds them together. The sum of those three vector phase currents is the ground fault current. In a system without any ground fault current, the three phases would sum to zero.

Operationally, the C440 does this ground fault “monitoring” /summation from the moment it is powered up.  However, the ground fault “protection” is inhibited during a motor start for 30 seconds.

After that 30 seconds, the C440 will trip on Ground Fault based on the following:

1.       A ground fault trip will occur after the 30 second delay in an additional:

a.       120 seconds  --- if the  ground fault current is between 50% and 75% of the FLA dial setting

b.      2 seconds --- if the ground fault current is between 75% and 125% of the FLA  dial setting

c.       1 second --- if the ground fault current is above 125% of the FLA dial setting

2.       If a ground fault occurs after the motor has been running the trip times will occur within the times listed in (1)

3.       Catalog information refers to thresholds with respect to the ground current value.

d.       120 seconds  --- if the  ground fault current is between 100% and 150% 

e.      2 seconds --- if the ground fault current is between 150% and 250%

f.       1 second --- if the ground fault current is above 250%