Custom Format for totalling hh:mm

Hi Guys,

I am looking to total up times spent on tasks in a spreadsheet.

I record the times in hh:mm format

eg: 10:30 = 10 hours and 30 minutes spent on task.

The trouble is, then the hours clock over 24 the total resets to zero and shows incorrect times:

eg: time spent on task: 30 hours = this will display total time as 06:00 (24 hours + 6 hours)

Is there a way to total this so that hours will continue increasing past 24?

many thanks