Fire Pump Service Calculations

[Dengineer]

Hello All,

I am working on a project where we are adding a new fire pump late into the design of a mixed-use building. An issue has come up regarding the service calculations and the RLC requirements for the fire pump. We currently have a 600A service pulled to the space and are being requested to upsize to 800A. I would appreciate some insight from other engineers, since I have gotten a lot of mixed opinions.

Project Information:

• General: Commercial/Residential 2FL building, 5000 Sqft
• Location: New Hope, PA
• Service size: One 600A utility pole that has been split into two services to feed a 200A residential and 400A commercial space.
• Code in effect: 2017 NEC
• Current Load on service per load calculations with fire pump (FLA * 125%): 520A
• Reason for fire pump: Well system and low PSI

Situation:

We are designing the main power service tap for a 7.5HP (34.6 FLA) 230V/1PH fire pump and plan to tap directly into our commercial CT cabinet. This would allow the fire pump to be metered without a dedicated service meter and ensure it remains powered independently of any main service disconnect.

Problem:

The code inspector has approved the CT tap but has informed us that the main service must be capable of carrying the locked-rotor current of the fire pump motor indefinitely per 695.3(A) and requested we add a minimum 208A (FLA x 600%) to the service size.

Argument:

To my understanding, we shouldn't size the service based on the RLC and the unrealistic expectation that the building would be running at 100% during an emergency fire situation. My assumption would be to size per the FLA and ignore the RLC for service calculation, but follow all other RLC requirements to compensate for inrush, so that the system does not trip before the fire pump can activate.

Our service is currently calculated at 520A, which includes the fire pump load at 43.25A (FLA * 125%). We are expected to add the RLC at 600% of the FLA, which would be a service load calculated at 684.75A (FLA * 125% removed for RLC) and would require an 800A service.

In NYC, high-rise buildings with fire pumps can exceed 150 HP and can have RLCs that would exceed 1000A, but I don't see 1000A being added to the service loads. There seem to be mixed opinions on the subject even on the forums.

My solution is to add a load-shed panel that would turn off the main mechanical units when the fire pump starts as to compensate for the RLC, but I still wanted other people's opinions on the subject.

 

[d0nut]

If I am understanding this arrangement, you are proposing to run two services through your commercial meter, connecting at the CT cabinet ahead of any overcurrent devices. If that is the case, all of the load is on the utility side, not yours and your commercial service on the customer's side wouldn't be carrying the fire pump at all. No equipment on your end would need to change and the utility company would be the proper entity to state whether there is capacity or not.

 

[Dengineer]

If I am understanding this arrangement, you are proposing to run two services through your commercial meter, connecting at the CT cabinet ahead of any overcurrent devices. If that is the case, all of the load is on the utility side, not yours and your commercial service on the customer's side wouldn't be carrying the fire pump at all. No equipment on your end would need to change and the utility company would be the proper entity to state whether there is capacity or not.

The service was originally upsized from 400-600A at the start of construction and the incoming conduit/conductors have already been ran. The fire pump was added much later during construction. The customer is the owner of the building and would like to avoid upsizing the building service.

I believe my solution avoids the requirement to upsize the service per the LRC load, but I would like to understand how do we take the LRC under consideration when sizing the entire building service.

Essentially how is a fire pump load calculated in a building service load summary.

 

[garbo]

Side note: Lucky you performing electrical work in dukes of hazard Pa. When my dad took the city if Philadelphia electrical license exam back in 1964 they told him Harrisburg is working on a state license. Maybe ten years ago the great officers at the Philly IAEI sent several electricians & believe inspectors to Harrisburg to talk to several politicians about finally getting a state electrical license. Believe at least one politician stated he would look into it. I had a Philly electrical license for years and turned down work in neighboring towns because they did not recognise other location licenses. Some were no problem but one little hick town had the only electrical contractor issue the license but after my inspector passed the job he failed me because I spliced two #14 wires in a panel that I replaced. Asked him if that was written in the non existing acement town code . Nope his own rule. Gave him the NEC article that allows what I did so he said he would allow me to get away with it that one time. One time I asked one of the inspectors at an IAEI meeting question on a 250 HP fire pump and he told me to talk to thier fire pump expert. Guy was a walking talking fire pump expert. Took CHOP (hospital ) a year to get approval on 50 year old existing fire pump new switchgear upgrade. The city wanted them to install a separate 13,200 to 480 transformer to only feed the two fire pumps ( one was a booster to feed water to helicopter landing pad on 10th floor roof ). There was no room in or near the switchgear room for such a transformer. Did not make sense demanding an expensive transformer to be installed because they had a dual 13.2 service and fire pumps were backed up by three 2,000 KW generators.