Warmly Yours controllers incorporate built-in Class A GFCI protection for all new floor heating systems. Class A GFCI provides personnel protection and trips when ground fault current exceeds 5 mA (milliamps). Class B GFCI protection is pretty much obsolete, but older systems may still require it. Warmly Yours controllers with built-in Class B GFCI provide equipment and circuit protection and operates when a fault to ground exceeds 15 mA.