Bonding and Grounding on funky trough service at late 1700's build home

[ShauwnC]

The service after we upgrade will be as follows. A 400A fused switch ( existing to remain ) Feeding a 8" x 8" x 48" wireway. From the trough two 200A main breaker panels will be fed( one with a 200A service rated transfer switch before the panel it feeds) . The main question I have is since there are parallel 4/0 thhn cables per phase and the disconnect is old an has no current neutral block, Am I correctly grounding and bonding the new setup. I am running 1/0 GEC to the primary electrode which stops at the disconnect isolated neutral busbar ( installing since there isn't one in the existing disconnect ). The ground rods will have #6 to the same busbar and that busbar will be bonded to the enclosure. From the neutral plate/busbar I will run the neutral to a tap in the trough as well as the two ungrounded phase conductors which will also be tapped to serve the two panels. From the Neutral plate/bus bar I will run a # 3 cu based upon 250.122 to a lug in the trough. The neutrals and grounds will of course be separated in my panels and a #4 from each panel will go through the trough without terminating in the trough and then terminate on the neutral busbar in the disconnect. I am attaching a riser diagram ( not my best or cleanest diagram ) aand want to know if my install is correct primarily bonding and grounding related.

 

[augie47]

1st let me suggest that you simply run one set of your 4/0s (oversized) to each of the disconnects.
There is no need to "parallel" them as long as you comply with the 240.21 tap rules.
Beyond that, a qualifying metal raceway could service as your grounding conductor to the raceway and the switches but if you wish to install a grounding conductor it should be sized as a #3 to each disconnect since the protection is the 400 amp fuse.
Your grounding electrode conductor plan looks fine.

You did not indicate, but how is the 400 amp being fed ? Do the service wires come thru your wireway.

 

[ShauwnC]

This is the funky part. The 400A disconnect is technically utility incoming but this home was built in the late 1700's and the meter is a pole mount CT meter on the pole approx. 200' away. The really funky part is the A phase is two 4/0 cables, the B phase is two 4/0 cables and the neutral is one 4/0 cable all in one 3" RMC. Load side is also paralleled off the disconnect so since I will be utilizing the 25' tap rule to feed the ATS and then on to the gen panel, I might as well have taps in the trough. I was considering using PVC from disco to trough and on to panels to eliminate bond bushings as well. Here is a picture of the existing setup.

 

[kwired]

This is the funky part. The 400A disconnect is technically utility incoming but this home was built in the late 1700's and the meter is a pole mount CT meter on the pole approx. 200' away. The really funky part is the A phase is two 4/0 cables, the B phase is two 4/0 cables and the neutral is one 4/0 cable all in one 3" RMC. Load side is also paralleled off the disconnect so since I will be utilizing the 25' tap rule to feed the ATS and then on to the gen panel, I might as well have taps in the trough. I was considering using PVC from disco to trough and on to panels to eliminate bond bushings as well. Here is a picture of the existing setup.

That smaller neutral may seem funky but code says it can be as little as a single 1/0 conductor if you can show calculations that it will not have any more load then the 1/0 can carry. That is for the portion that is service conductors, for a 400 amp feeder it can be as little as a single 3 AWG if the neutral load is less then what a #3 can carry.

If you have a lot of straight 240 volt load this makes it easier to consider such a reduction of neutral size. The more 120 volt load you have the harder it is to determine what the maximum neutral current may be at any point in time.