Primary & Backup Pumps Run Simultaneously?

9/9/2022

We have two fire pumps on a project which are to be connected to one emergency generator. One is a primary pump, the other is a backup.

Will these ever run simultaneously?

The Electrical Engineer on the project is concerned about running supply for both pumps simultaneously and overburdening the generator.

Is there an NFPA limitation for this, or requirement either way?

Thanks in advance.

Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe

10 Comments

Glenn Berger

9/9/2022 08:12:33 am

Fire Pumps typically start on pressure drop, with the secondary pump starting on a further pressure drop and after the sequential start timer elapsed.

As such it is very possible that multiple fire pumps can operate simultaneously.

Jesse

9/9/2022 08:20:13 am

Its not ideal but it could happen.

I had a warehouse that had a partial roof collapse that sheared the top of two 8" risers. I can attest that both of the 2000-gpm pumps ran just fine filling the warehouse with water...

What Glenn said is on the money. It could happen.

Sanjeev

9/9/2022 08:59:08 am

Normally primary fire pump will be feed with normal power and backup fire pump will have own diesel engine or feed from emergency generator thinking both pumps can start together based on pressure drop settings.

Tim

9/9/2022 09:01:38 am

Yes, fire pumps can both run at same time if the the pressure in system drops below pre-set set start pressure of both primary and secondary pump set. The demand on electrical power is therefore doubled up.

This is all due to the pump design and setup and there is not much you can do unless the second pump is diesel driven.

ray hardy link

9/9/2022 09:13:11 am

In my experience duplicate pumps need 2 sources of power supply with demonstrable diversity in the supply arrangements and where supplies to each pump are controlled by individual automatic power transfer switches.

1 No power supply taken from the mains power supply grid

1 No power supply from an emergency generator set.

Battery based UPS are not acceptable as a source of emergency power supply for a sprinkler system

The power supply feeder from the mains supply to the pump controller should be separate from the normal services feeder and all other circuits.

The generator should be sized to accept the combined current of the electrical sprinkler pumps, assuming one to be in a locked rotor condition and the other at full starting current, plus any other connected loads.

Franck

9/9/2022 09:14:56 am

Normally it shouldn't (otherwise the second would not be a back up, but a complement), but in reality it could happen, as indicated above.
Sometimes for good reasons : there are more sprinklers operating than initially designed, or use of more water for manual firefighting purposes, when fed by the same water supply. Having both pumps running in that conditions could save your buildings.
Sometimes for bad reasons: the pressure switch starting the pumps are not accurate and both pumps starts simultaneously, or you have a huge water demand as per the example of Jesse.

9/9/2022 09:33:34 am

The generator and overcurrent protection devices must be properly sized to handle the intended load. This includes both load from the primary and secondary fire pumps.

700.4 Capacity.
(A) Capacity and Rating.

An emergency system shall have adequate capacity and rating for all loads to be operated simultaneously. The emergency system equipment shall be suitable for the maximum available fault current at its terminals.

ENHANCED CONTENT
Collapse
The emergency system must be designed with adequate capacity an rating to safely carry, at one time, the entire load connected to the emergency system. It must be capable of restarting emergency loads that have been interrupted, such as motors that may have stopped, and it must be suitable for the available fault current.

Greg

9/9/2022 11:09:03 am

Your one line diagram will be the best reference as design progresses. The electrical component selected for the automatic transfer switch will dictate how the pumps are called following power loss and emergency generator start.

Typically, your sizing the generator to run pump 1 OR pump 2. But make you to size it to the largest motor demand, that is if there is a difference and they are not perfect twins of each other.

It's all in the automatic transfer switch and panel arrangement. The common objective is to transfer one pump to the Emergency generator and that should be sized to handle a start from zero (i.e. the electric motor is not spinning).

The sequence; Main power lost, the generator engine goes to full speed, the load is made available to the emergency line, the line transfer is made (e power available to the pumps) , call for pump 1

Jose Manuel Cruz

9/9/2022 02:14:14 pm

The controller for each unit of multiple pump units
shall incorporate a sequential timing device to prevent any one
driver from starting simultaneously with any other driver
NFPA 20

Rob B

9/12/2022 07:32:22 am

This squarely an issue for the EE to figure out. There is a fair amount of work that goes into generator load calculations and since it is a motor load, you have start up considerations and such.

Leave a Reply.

Home
Our Cause

The Blog
The Forum

PE Exam Prep
The Toolkit
MeyerFire University

Pricing
Login
Support
Contact Us

MeyerFire.com is a startup community built to help fire protection professionals shine.
Our goal is to improve fire protection practices worldwide. We promote the industry by creating helpful tools and resources, and by bringing together industry professionals to share their expertise.

MeyerFire, LLC is a NICET Recognized Training Provider and International Code Council Preferred Education Provider.
All text, images, and media Copyright © 2016-2024 MeyerFire, LLC

We respect your privacy and personal data. See our Privacy Policy and Terms of Service. The views, opinions, and information found on this site represent solely the author and do not represent the opinions of any other party, nor does the presented material assume responsibility for its use. Fire protection and life safety systems constitute a critical component for public health and safety and you should consult with a licensed professional for proper design and code adherence.

Discussions are solely for the purpose of peer review and the exchange of ideas. All comments are reviewed. Comments which do not contribute, are not relevant, are spam, or are disrespectful in nature may be removed. Information presented and opinions expressed should not be relied upon as a replacement for consulting services. Some (not all) outbound links on this website, such as Amazon links, are affiliate-based where we receive a small commission for orders placed elsewhere.

Primary & Backup Pumps Run Simultaneously?

Leave a Reply.

ALL-ACCESS

SUBSCRIBE

COMMUNITY

YOUR POST

PE EXAM

FILTERS

ARCHIVES

PE PREP SERIES