Re-Feeding Service

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Ericjburgess84

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Maintenance Technician
I have a question about the re-feeding of our service. We have 3 400amp main disconnects that are being re-fed due to construction. One is a 400amp 480V 3 phase, the other two are 120/240 3 phase Delta 400 amp disconnects. The contractor that was hired by the owner of the Industrial building we occupy said that his plans show that they will re-feed all 3 400amp disconnects with one set of 500kcmil feeders (4- 500kcmil and 1-#3 ground} the line coming in is a 3-phase 480v y-service, they plan on connecting the new service feeders by clear taps in a junction box to the existing wires to the existing 400amp 480v main disconnect, setting a 150kva transformer and feeding the other 2 400amp 120/240v delta services. How can you possibly do that?
 
Ericjburgess84 said:
...... the new service feeders
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The mythical service feeder exists! Is this at a unicorn farm 🦄? Sorry I couldn't resist. Ok but seriously, is this something that is being done temporarily? If so it still needs to be code compliant, but it may well be compliant. Perhaps someone investigated the load and found it to be significantly lower than the service size. This is often the case
 
electrofelon said:
The mythical service feeder exists! Is this at a unicorn farm 🦄? Sorry I couldn't resist. Ok but seriously, is this something that is being done temporarily? If so it still needs to be code compliant, but it may well be compliant. Perhaps someone investigated the load and found it to be significantly lower than the service size. This is often the case
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I guess the question is can you feed 3 400amp disconnects off of 1 set of 500kcmil wires? It’s a 3 phase service.
 
Ericjburgess84 said:
I guess the question is can you feed 3 400amp disconnects off of 1 set of 500kcmil wires? It’s a 3 phase service.
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If I understand your description correctly, you are supplying one 400A, 480V service disconnect with one set of 500mcm conductors. The 240/120V disconnects are not service disconnects. There is no problem with that.
 
ptonsparky said:
By putting wire A to point A, etc.

You may be missing some details in your description of what is happening. What exactly is you concern?
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my concern is the contractor is only pulling 4 500kcmil with a #3 ground to 3 separate 400 amp disconnects. Currently each 400 amp disconnect is fed Separately. Is it code compliant to re-feed the service to each disconnect with the above mentioned wire size? Basically we’re going from three separately fed disconnects To it all being on one service with the wires ampacity only at 400 amps. We are in a industrial building with machinery etc. Don’t you have to calculate a continuous load of 125% on your service calculation?
 
david luchini said:
If I understand your description correctly, you are supplying one 400A, 480V service disconnect with one set of 500mcm conductors. The 240/120V disconnects are not service disconnects. There is no problem with that.
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no the 480 V 400 amp disconnect is fed by its own service. And each of the 120 V/240 V 400 amp disconnects Are being fed from a separate service.
 
Ericjburgess84 said:
no the 480 V 400 amp disconnect is fed by its own service. And each of the 120 V/240 V 400 amp disconnects Are being fed from a separate service.
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They want to combine all 3 400 amp disconnects on 1 service and feed them all on the same set of 500kcmil service feeders
 
They want to supply all 3 400 amp disconnects and 150 kva transformer all on 1 set of 500 mcm conductors
 
Sounds like 1 set of 500's serving a 400 amp service disco and a "service tap" (230.40 exception 2) to feed a transformer. The transformer needs a service disconnect ahead of it. No problem here as long the loads are appropriate. The sum of the service OCPDs can exceed the conductors ampacity. If this is an existing building, they are probably using demand data per 220.87 instead of load calcs.
 
What if the disconnects are not grouped at one location? Because ours are not grouped they are on separate floors
 
Ericjburgess84 said:
What if the disconnects are not grouped at one location? Because ours are not grouped they are on separate floors
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If you open the 400A, 480V disconnect, it removes power from the entire building, right? The 240V disconnects are supplied by the 150kVA transformer which is supplied by the 480V disconnect?
 
What is the total load calculation? If under 380 amps not a problem, you will have less room for adding more load than before though.
 
No the 400a 480v disconnect will not remove power to building only certain machines within the building. The 120/240 v 400amp disconnects supply lights and receptacles etc
 
kwired said:
What is the total load calculation? If under 380 amps not a problem, you will have less room for adding more load than before though.
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I was not given the load calculation. But I do know it was done without all our equipment running at the same time
 
If I understand correctly, your existing install is 3 separate services, one 480V 400A and two 240V 400A. Presumably all 3 come from the utility, and you have 3 separate services because of the difference in voltage and maximum service size at the time of the installation.

This is now to be replaced with a _single_ 480V 400A service, supplying 480V loads as well as the 240V loads via a transformer. You are concerned that what was originally supplied by the 3 separate services is being combined into 1, and worried that the service conductors will be overloaded.

This can only be answered by doing an actual load calculation or measurement. If the actual load in the building calculates to less than the capacity of the single 480V service, and the 240V loads calculate to less than the capability of the 150kVA transformer, then the fact that you are replacing all three services with one is not a problem.

The size of the old service is not relevant; what is critical is the actual connected load.

-Jon
 
winnie said:
If I understand correctly, your existing install is 3 separate services, one 480V 400A and two 240V 400A. Presumably all 3 come from the utility, and you have 3 separate services because of the difference in voltage and maximum service size at the time of the installation.

This is now to be replaced with a _single_ 480V 400A service, supplying 480V loads as well as the 240V loads via a transformer. You are concerned that what was originally supplied by the 3 separate services is being combined into 1, and worried that the service conductors will be overloaded.

This can only be answered by doing an actual load calculation or measurement. If the actual load in the building calculates to less than the capacity of the single 480V service, and the 240V loads calculate to less than the capability of the 150kVA transformer, then the fact that you are replacing all three services with one is not a problem.

The size of the old service is not relevant; what is critical is the actual connected load.

-Jon
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Correct supposedly there is a load calculation I have not seen it. I know that it was a calculation of our power bills done over a year. The problem I have is that some of our machines here were not used during that time period.
 
Ericjburgess84 said:
No the 400a 480v disconnect will not remove power to building only certain machines within the building. The 120/240 v 400amp disconnects supply lights and receptacles etc
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How again does the transformer you mentioned come into play. Most of us are assuming it is a new source for the 120/240, but needs something to supply it and since you say you are down to only one set of supply conductors we must assume it is supplied by that set of conductors also.
 
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