1200 Amp Service Change Out

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dvcraven052256

Member
Location
St. Louis, missouri
Occupation
Electrical Engineer
I am in the process of changing out an existing 1200Amp 480/277V, 3Ph, 4W service and replacing with the same size.

In essence the existing service is stand alone 1200a with CT and PT built into cabinet with 1220Amp MCB. We are mounting a new J-box adjacent to the existing J-box to make room to splice the feed thru conductors. The MTS (manual transfer switch) will feed a new 1200amp MCB w/feed thru lugs as shown. This will allow for us to use the new 1200a panel MCB as the means of disconnect so we can prep the new service. The existing will be demolished once the new service is installed.

I will need to coordinate shutdowns with the utility to perform the work. I have attached a overall riser diagram and wiring diagram for reference. I would like your thoughts if the wiring diagram show on E2.0 accurately reflects my intent.

Your thought are most appreciated.

Dan Craven
 

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Dan, It's unclear to me if the existing 1200A MCB will remain or be demolished. The existing neutral ground bond in the 1200A will need to be removed regardless. Your new N-G bond will be at the 'MTS', not panel 'P1', as the MTS is considered your service disconnecting means.

Is there a reason you are providing 500kcmil? For a 1200A service I would provide 4 sets of 350s in 3" conduit unless voltage drop is a factor.

Also, I think your L1 and L2 legend is backwards?
 
tjdilly said:
Dan, It's unclear to me if the existing 1200A MCB will remain or be demolished. The existing neutral ground bond in the 1200A will need to be removed regardless. Your new N-G bond will be at the 'MTS', not panel 'P1', as the MTS is considered your service disconnecting means.

Is there a reason you are providing 500kcmil? For a 1200A service I would provide 4 sets of 350s in 3" conduit unless voltage drop is a factor.

Also, I think your L1 and L2 legend is backwards?
Click to expand...
Yes the existing 1200 will be removed. The 500kcmil are what is existing. Yes the legend needs to revised. Thx
 
Is the transfer switch the equivalent to an outside disconnect per fire code? Is there a back up generator or something? What is "transferring"?

You might need an isolated outdoor 1200A disconnect.
 
Joe Villani said:
Is the transfer switch 3 pole or 4 pole? With GFPE involved I would be going with a 4 pole transfer switch
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I understand what you are saying. If the power system had two grounding electrodes simultaneously some current could return through the earth without passing through ground fault sensing equipment. This might cause sensing equipment to falsely detect faults, causing nuisance tripping. But in this case once the new service is set we will deenergize the existing service and remove.
 
We are no
herding_cats said:
Is the transfer switch the equivalent to an outside disconnect per fire code? Is there a back up generator or something? What is "transferring"?

You might need an isolated outdoor 1200A disconnect.
Click to expand...
We are not really transferring anything. We are using the manual transfer switch to assist in making the switch over from the old service to the new without a long shutdown.
 
A couple concerns: note that the MTS must be your service disconnect. As such, it must be "immediately adjacent to" the overcurrent protection (P1). Also you might want to confirm the SCCR, usually it is 10K for a switch only. Also this has been mentioned, but note the GFPE requirement, I didn't see it mentioned on the plans.
 
dvcraven052256 said:
There are emergency lug if the power goes out they can bring in a temp generator and hook to the MTS.
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Probably much more expensive than your original method, but I have used a Trystar DBDS-1 docking station to do this in the past. It has kirk key interlocked mains with camlock connections for a temp generator. 1751038053587.png
 
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