Data Validation and linking columns

I have a work book with 2 sheets in it. One is for the user to enter data and the second sheet (Eq List) is where the pulldowns for Sheet1 are created. I initially had it working fine but had to add 1 more column to the table on Eq List sheet to make it easier to fill in the form. What I need to do, on Sheet1, I need pulldowns for Department, Group, and Equipment Name. When the user selects a category for Department, it should limit the next pulldown, Group, to only the groups within that Department. Once the required Group is selected it should limit the choices in the next pulldown, Equipment Name, to only the names in that group for that department. Once those 3 pulldowns are filled in, the Equipment Number should automatically pull the number from the table on Eq List sheet. I am attaching a sample to make it easier to understand. If anyone could help me out on this would be appreciated.

There will be better methods but using the setup you have - try modifying as follows:
(overwrite what's in the file already if implied by references)

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Now revise / create Define Names:

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Now modify Data Validation settings on Sheet1 - as follows:

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Notes:

a) given your equipment names are duplicated but have differing ID #s this # is included in the description such that each item in the list is unique.

b) given nature of above calcs it won't be quick - you could streamline using Matches etc but I figured the fewer changes the better

If you have more data than listed here the above is not an approach I'd pursue as it will become too slow.

What you want to do will always prove a little cumbersome with formulae given sheer volume of data however perhaps the attached approach will be of interest to you ?

You will note that the yellow range (assumed to be inputs) is sorted by Col A, B & C (in that order) - this is of critical importance - if A:D is not sorted in this manner the approach will not work.
sorting data permits use of more efficient approaches than would otherwise be the case

The remaining cells are formula driven and are used to generate 3 named ranges, specifically:

DeptList
GroupList
EquipList (as before this is a concatenation of MachID & Desc)

These three lists are set as Validation source on Sheet1 for B6, B8 & B10 respectively.

Given the Volatility has been removed using this approach performance should be improved from before.