Soft loading systems are utility paralleling systems capable of sustained paralleling. Whereas many load curtailment systems transfer loads from the utility power source to the generator all at once (in 100 milliseconds or less), soft loading systems parallel the two live power sources, allowing a more gradual transfer of loads (up to 20 seconds or longer). This eliminates any momentary dip in voltage and the disruptive effects of block loading. Conversely, retransfer from the generator source to the utility source is accomplished through soft loading.
System specifiers should be aware that soft loading systems usually require utility-approved protective relaying and control measures.