4#2/0 multiple lighting ground wire

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I am an electrical designer working on a change of plan for a project I didn't design. The project is for a bridge. 2000 feet of underground conduit has 4#4/0 & 1#1/0 Ground then continues to 2 conduits within a bridge parapet - one is spare and the other is 4#4/0 & #1/0 ground to feed roadway lighting. The circuit is protected by a 70A circuit breaker.

My 2 questions are:
Why did the original designer indicate for #1/0 ground? I think there is a restriction to Table 250.122 that I wasn't able to find. (Perhaps, it was due to 4 conductors being installed within a conduit or due to possible future use of the spare conduit).

During my change of plan, the load was reduced and voltage drop decreased. The 2000 feet of 4#4/0 & #1/0Ground is already constructed. Only the wiring within the parapet is being reduced to 4#2/0. I don't know what to do with the ground wire. Can the ground wire be reduced and per what section of the code?
 
The EGC is based on the size of the OCPD but if the circuit conductors are increased for any reason, ie voltage drop then the egc must be increased proportionately-- 250.122(B)
 
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If the first 2000 feet has a #1/0 ground already installed, are my able to only reduce the ground within the parapet which is spliced into the existing #1/0 ground according to NEC Section 250.121B?
 
It's been discussed previously (I'll try to find the link) but, as I recall, the consensus of opinions was that when you tap and reduce your ungrounded conductor, you can reduce the grounding conductor accordingly.
 
Malteser said:
If the first 2000 feet has a #1/0 ground already installed, are my able to only reduce the ground within the parapet which is spliced into the existing #1/0 ground according to NEC Section 250.121B?
Click to expand...
It is permissible reduce the size of the equipment ground if the size of the ungrounded conductors are reduced anywhere in the circuit.
 
Equipment grounding conductor run with feeder taps does not need be any larger than the tap conductors. 250.122(G)
 
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