ATS incoming source 1 & 2 Designation

[leur2011]

This question is mainly in regards to consequences. I have a 480VAC open transition Automatic Transfer Switch (ATS) to put in service soon; and I'm wondering what happens if we designate single ended 480V switchgear SG-002 fed from existing upstream generators as normal “N” (preferred) power source-1 of ATS and utility fed double ended 480V switchgear SG-001 designated as emergency “E” (alternate) power source-2 of ATS as illustrated in the below diagram?

I understand that governing standards and codes stated that emergency DG set has to be standby (alternate power); not normal power (preferred). If we swap the two feeders does it impact the existing configuration of the electrical network system and maintenance of the emergency loop power supply system of the existing facility.

 

[waross]

I can not make out where the diesel generator is in your drawing.
You have not told us which codes you work under.
That said:
There are applications where my code calls for an emergency generator, such as emergency lighting and life support systems.
There are applications where operating conditions or security concerns dictate an emergency generator installation.
In the first case my code also stipulates a minimum testing procedure that must be followed.
An emergency generator is a defined piece of equipment that must meet minimum standards.
For non-critical equipment a standby generator may be used.
The rules for a standby generator in regards to regular testing are much less stringent than the rules for an emergency generator.
Then there is the case for a prime power generator.
Operating a prime power generator may put you in the position of a utility operator. Many of the conditions of my normal codes do not apply to a prime power application if the AHJ agrees that the application is a self owned utility.
However, for a small scale installation, that works in conjunction with a grid supply I would probably follow my normal codes.
If you are able to re-classify your generator from emergency to standby or prime power, many of your concerns may go away.
Note: If a failure may result in an insurance claim, it may be prudent to check with your insurance company. They may have a minimum standard that must be followed to avoid voiding your insurance policy.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[leur2011]

Thanks waross, to describe more of my question in my first post, our local standard state that critical security system loads should be supplied by emergency power regardless of how emergency power is defined in NEC or IEEE. My question was if we swap the two feeders does it impact the existing configuration of the electrical network system and maintenance of the emergency loop power supply system of the existing facility?

 

[waross]

The emergency generator must be ready to start at any time. It must be regularly checked to ensure that it is ready to supply energy should the primary source fail.
If there is a power outage or maintenance shutdown of the grid the emergency generator must be ready to run.
If you are using the generator for the primary source of supply, you may have a tough time avoiding power failures or shutdowns of the grid in the event that the generator fails.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[leur2011]

Your last paragraph is the present situation of the connection of the two incomer feeder cable of our ATS. We used the emergency generator as normal “N” (preferred) power source-1 of ATS and we used the utility grid as emergency “E” (alternate) power source-2 of ATS base on facility existing configuration of electrical system and practice for all facility previous projects. However, the AHJ did not agree. He want to swap the two feeders so that the emergency generator is the alternate power supply.

I'm afraid that if alter the connection by swapping the two feeders it may impact the operation of the ATS, configuration of the facility electrical network system, and maintenance of existing emergency loop power supply system due to faults may impact operations and reliability of critical security systems loads.

 

[waross]

I have had to convert an ATS in the field. The first choice is to interchange the incoming feeders on the transfer switch.
I had an existing failed ATS (flood water).
The existing cables would not reach to the proper terminals. Switching the operation of the switch allowed us to use the original cables. The saving in copper costs was roughly equal to my charges for the work, including air fare and hotel accommodation.
The control wiring was swapped between the normal contactor and the emergency contactor.

Listen to the AHJ. Sometimes an AHJ will make a mistake but I don't think this time.
If the available fault currents from the grid supply are too great then the system is not compliant with most codes.
The system must be capable of safe and compliant operation in any operating mode. That is, both grid operation and generator operation must be compliant.
Another issue, Generator rating;
For continous operation the generator should be rated for prime power.
For emergency operation you may be able to use a standby rated set. Check your local codes.
For comparison, a 125 KVA standby set will only be rated at 100 KVA for prime power.
This sounds as if someone made a mistake sometime in the past and the mistake has been copied several times.
Running a generator and using the grid for back-up is NOT general practice, NOT recommended, Expensive for both fuel and repairs and for greatly reduced set lifetime, not in operating hours but in calender years.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[catserveng]

Have you checked with the vendor of the the ATS? Many ATS controllers allow for what is called sometimes "dual source" (sometimes dual prime). Allows you to select which of the sources is preferred. Sometimes just requires the change in the decal over the front of the controller and/or adding a switch.

Some ATS switches do not offer this option, and depending on the area you're in and the AHJ, your only option may be to swap the leads. A forum can give you general suggestions, but your best info is likely to come from the supplier of the ATS, a local engineer familiar with your codes and applications and your AHJ.

MikeL.