Modeling components below a functional group in series or parallel makes a difference. Typically one would model electrical circuits in series (as they typically work that way).

 

 

 

The advantage to this method is that if hoist brake 1 is working, we know that the other components below it are all working as well.

 

If we modeled it in parallel, the system would not see the dependency (links) between the items and you would have to test them ALL to know it they were all good or bad.

 

However - with mechanical systems, it is sometimes better to model items in parallel as the dependencies in those cases are not always so clear.

Thus to summarize.

 

Parallel

 

Series