When does 'it'refer to a person?

[nado92]

When does 'it' refer to a person?
Like

It is my friend Tom.

 

[bhaisahab]

When does 'it' refer to a person?
Like

It is my friend Tom.

"Who is that on the phone?" It's my friend Tom.

 

[nado92]

"Who is that on the phone?" It's my friend Tom.

Thanks.
so ,is there any rule for that?


who is at the door?
It is Tom.

what else?

Thanks

 

[nado92]

yet ,no rule.