GeoffHW
New User
- Location
- Houston, TX
- Occupation
- Electrical Engineer
As a preface, I am a new grad who has only been working as an electrical engineer for three months. The company I work for does not work with fire pumps but we are taking on a fire pump project. I am not well versed in terminology just yet but will try to make my question as clear as possible. I am currently responsible for reviewing Article 695 and NFPA 20 to be sure our design complies with all of the listed requirements.
It is my understanding that OCP on the secondary is not allowed for fire pumps per NEC 695.5(B). Additionally, we are only allowed one disconnecting means between the fire pump service power and fire pump controller per 695.4(B)(1)(a). In our case, we fall under case (3) because we will be using a combination FPC and power transfer switch.
In our design, my colleague has designed a fire pump building consisting of two rooms: a small fire pump control room, and a larger fire pump room to house the motors, controllers, and ATS.
However, I take issue with a part of the design where my colleague has put a 500A OCPD on the secondary of our 15kV:480V transformer which is feeding our control room loads as well as the fire pump room motors and equipment. Additionally, we intend to have protection on the primary sized for all building loads per 695.5(B). This seems redundant to me since we are protecting the loads via the primary OCPD and it is a code violation to have any OCP on the secondary of a transformer as previously stated.
My colleagues reasoning for having OCPD on the secondary is we need a tap box to power each of the FPC's individually. If we do not put any kind of OCPD we are tapping a tap since a transformer's secondary are considered tap conductors, which is a code violation.
However, my solution and suggestion to this issue is we need to feed five separate cables from the transformer secondary winding to power our four pumps, and building ATS which supplies our building loads from a 480:120/240V panel. My colleagues reasoning for not doing this is that he is not aware if feeding five cables off of the secondary is possible with our specific transformer.
Either way, I don't believe OCPD on the secondary of a transformer is allowed in any case. It would only need protection on the primary of the transformer. Additionally, to get around the tap rules, in my mind the best solution is to individually feed each individual FPC power from the secondary of the transformer. I am also aware that fire pump rooms are meant to run until the destruction so in my mind there would be no reason to stop an electrical connection after the transformer. This would just defeat the purpose of running until destruction would it not?
Any additional coded references I may have missed were likely left out just for the sake of brevity. However, do feel free to point them out and give feedback on what you might think. I would have added a design in but it seems pictures are posted in the form of links. All of our designs are PDF's or PNG files. Thank you!
It is my understanding that OCP on the secondary is not allowed for fire pumps per NEC 695.5(B). Additionally, we are only allowed one disconnecting means between the fire pump service power and fire pump controller per 695.4(B)(1)(a). In our case, we fall under case (3) because we will be using a combination FPC and power transfer switch.
In our design, my colleague has designed a fire pump building consisting of two rooms: a small fire pump control room, and a larger fire pump room to house the motors, controllers, and ATS.
However, I take issue with a part of the design where my colleague has put a 500A OCPD on the secondary of our 15kV:480V transformer which is feeding our control room loads as well as the fire pump room motors and equipment. Additionally, we intend to have protection on the primary sized for all building loads per 695.5(B). This seems redundant to me since we are protecting the loads via the primary OCPD and it is a code violation to have any OCP on the secondary of a transformer as previously stated.
My colleagues reasoning for having OCPD on the secondary is we need a tap box to power each of the FPC's individually. If we do not put any kind of OCPD we are tapping a tap since a transformer's secondary are considered tap conductors, which is a code violation.
However, my solution and suggestion to this issue is we need to feed five separate cables from the transformer secondary winding to power our four pumps, and building ATS which supplies our building loads from a 480:120/240V panel. My colleagues reasoning for not doing this is that he is not aware if feeding five cables off of the secondary is possible with our specific transformer.
Either way, I don't believe OCPD on the secondary of a transformer is allowed in any case. It would only need protection on the primary of the transformer. Additionally, to get around the tap rules, in my mind the best solution is to individually feed each individual FPC power from the secondary of the transformer. I am also aware that fire pump rooms are meant to run until the destruction so in my mind there would be no reason to stop an electrical connection after the transformer. This would just defeat the purpose of running until destruction would it not?
Any additional coded references I may have missed were likely left out just for the sake of brevity. However, do feel free to point them out and give feedback on what you might think. I would have added a design in but it seems pictures are posted in the form of links. All of our designs are PDF's or PNG files. Thank you!