Adding / to concatenate a cell

Hi All

As an example:

Unit # St # Combined
1 123 1234 John Street

In column Unit # I need to add a / in every cell. This then has a concatenate formula to make the combined look like 1/234 John Street, however when I change the number format to add a / it will not concatenate.

If you add a / manually to each cell it will.

Any ideas?

Thanks
Tammy