Grounded service conductor

[greenspark1]

Hello,
We have a standard 208/120V commercial service from a utility pad mount transformer. The transformer has the neutral and ground bond via a nice copper strap. We will carry three phase conductors to our main service panel. The question came up about the neutral & ground conductors.

1. I believe we only need a neutral since it will be bonded on both ends to ground. It can be sized smaller than the phase conductors by table 250.102(C)(1)(NEC 2017). Intuitively this makes sense to me since it is just carrying any imbalance in the loads.
2. Others want to run a fullsize neutral and a separate ground conductor. This seems wrong since the neutral is bonded on both ends. If anything this creates parallel paths for the neutral or ground current.

Thanks for any help.

 

[augie47]

The grounded conductor on a service that is grounded at any point must be brought to the service disconnect(s){250.24(C)} and sized per 250.102(C) or 220.61 whichever is greater
(sized no smaller than the grounding electrode conductor or calculated load)

On a utility supplied service there is no need for a grounding conductor from the transformer to the service panel(s)

 

[greenspark1]

Thanks. I think I've seen fullsize neutrals on about 95% of all the padmounts I've opened.

 

[kwired]

I have hardly ever ran a full size neutral - exception maybe being when just using two phases and a neutral of a wye system (still depends on how much line to line vs line to neutral load there is going to be). Some maybe don't realize you can reduce the neutral, or don't want to bother figuring out what size they can run if they do know. No inspector has ever even questioned it if it was no more then two sizes smaller then ungrounded conductors in my experiences.

Running a grounded and equipment grounding conductor is pointless for service conductors - electrically they will be parallel to one another if you have bonding jumpers at both ends.

I did rework a 1800 amp single phase service a couple years ago (converted to 1200 amp three phase), pulled new conductors through existing raceways. For some reason whoever installed the original thought they needed 500 aluminum neutrals in each conduit and 1/0 aluminum EGC's in each conduit - all it should have done is put them in parallel to one another - but also part of the switchboard frame and part of the transformer case was in the parallel path, let alone one conductor was quite a bit larger then the other.