Fire pump fed from customer owned transformer multi building campus style complexes

[hhsting]

I have fire pump, jockey pump fed from customer owned 13.8kV to 480/277V three phase delta to wye transformer. The setting is multibuilding campus-style complex and in accordance with NEC 2017 Article 695.3(C)(2). The customer owned 13.8kVA to 480/277V also feed another switchboard downstream as well as the fire pump and jockey pump. See attached below.


NEC 2017 Article 695.5(C) allows this. However I am confused with NEC 2017 Article 695.5(C)(2) where it says the following “..overcurrent protection is provided for the transformer in accordance with 450.3 and for the feeder in accordance with 215.3 and such that the overcurrent protection device(s) is selected or set to carry indefinitely the sum of locked rotor current of the fire pump motor(s), the pressure maintenance pump motor(s), the full load current of the associated fire pump accessory equipment and 100 percent of the remaining loads supplied by the transformer. The requirement to carry the locked rotor currents indefinitely shall not apply to conductors or devices other than overcurrent devices in the fire pump motor circuit(s).”

It is very confusing what exactly is feeder in this case such as transformer secondary conductor
For feeder protection does the NEC 2017 require transformer secondary overcurrent protection for secondary side conductor feeding the fire pump sized per locked rotor current or not?

 

[Joe Villani]

See 695.5(B)

Secondary overcurrent protection is not permitted.

For carrying your locked rotor you have to do the calculation and verify the primary ocpd is sufficient

 

[Elect117]

If I am not mistaken, only 695.5(C) is allowed to supply loads other than the fire pump and related circuits. To which this transformer is feeding a 4000A main and the fire pump + jockey pump.

695.5 Parent text, "Only transformers covered in 695.5(C) shall be permitted to supply loads not directly associated with the fire pump system."

 

[Elect117]

To better answer the question, yes and no. OCPD can be installed but is not required to be installed. It is more important that the transformer's primary OCPD will not operate. You might have a grounding and bonding problem on the low side of the transformer with the ATS and the fire pump circuit. Mind you the available fault current is going to be ~100kaic for the ATS and fire pump controller AND jockey pump.

You will need to evaluate whether or not the "loads" or generation on the 4000A panel + the fire pumps LRA + 125% of loads on the fire pump's feeder are less than 150A on the primary side. And that the wire is sized appropriately.

It is typically better to install a separate transformer for the fire pump service. That way if you need to service the transformer you don't need to run the generator. It also reduces the necessary kAIC rating of the equipment.

Or, you can feed the fire pump solely from the generator.