Fire Pump Across the Line Starting on Generator Power

All,

Having a real hard time here trying to figure out how to size the generator for the fire pump. We are in a high-rise, have a 120 HP fire pump, and we need to have this fire pump on the emergency generator. We know about limiting the voltage drop to 15% when starting under locked rotor conditions. We also know that the fire pump has to be able to start with all of the other emergency loads running simultaneously. Last but not least, we know that in case the soft starter fails that this fire pump can be started in manual mode but when it does, it starts across the line.

I plug in the other emergency loads and have a 230 kW generator with a soft starter on the fire pump. I change the fire pump to across the line and I get a whopping 500 kW genset. So here is the pickle I am in...I have to tell the Owner now that he has to more than double his generator size in case the normal power is out, there is a fire in your building AND your soft starter fails and we have to start the fire pump manually. This single requirement is driving all of this. Where does it say/stipulate this in the code - how do I get around it - or am I just stuck. Any help here would be greatly appreciated. If you could cite code that I could go back to the AHJs with that would be even better.
 

mike7330

Senior Member
Location
North America
You should not design this system! You need an electrical engineer! You are taking one hell of a liability if something fails. That's my two cents! And yes a diesel fire pump is a good way to go. But get a licensed engineer to help you.
????
 

GoldDigger

Moderator
Staff member
You should not design this system! You need an electrical engineer! You are taking one hell of a liability if something fails. That's my two cents! And yes a diesel fire pump is a good way to go. But get a licensed engineer to help you.
????
Hi Mike, I just took a look at crazy's profile, and he is an EE. Maybe not a licensed PE though.
 
NFPA 2010 9.4.2 & A10.5.3.2

NFPA 2010 9.4.2 & A10.5.3.2

Thanks everyone. I am a PE in 5 states. Looks like NFPA 2010 9.4.2 and A10.5.3.2 do not require the 15% voltage dip requirement to be met when the fire pump is started in emergency mechanical bypass mode if a soft starter is specified. I knew there was some snippet of code out there - and thanks for pointing me to it.
 

Npstewart

Senior Member
You should not design this system! You need an electrical engineer! You are taking one hell of a liability if something fails. That's my two cents! And yes a diesel fire pump is a good way to go. But get a licensed engineer to help you.
????
Just because someone is a licensed engineer doesn't mean they automatically know how to design something. The OPs question was really a code question. I have been to engineering school and they teach you NOTHING about any code at all..ever..Most (if not all) of the professors have never designed anything real using any code. Engineering school teaches you the fundamentals, its up to you to do your own research which many times leads to a article or a forum which can point you in the right direction.
 

GoldDigger

Moderator
Staff member
Thanks everyone. I am a PE in 5 states. Looks like NFPA 2010 9.4.2 and A10.5.3.2 do not require the 15% voltage dip requirement to be met when the fire pump is started in emergency mechanical bypass mode if a soft starter is specified. I knew there was some snippet of code out there - and thanks for pointing me to it.
Being able to work with a 30% voltage dip instead of 15% may help you meet code witj a smaller generator, but resistive voltage drop is not your only problem. Just make sure that the engine of your generator can supply enough short term power to start the pump across the line without stalling or tripping out on engine protection or speed regulation.
 
Last edited:

Canton

Senior Member
You should not design this system! You need an electrical engineer! You are taking one hell of a liability if something fails. That's my two cents! And yes a diesel fire pump is a good way to go. But get a licensed engineer to help you.
????
Not every design and electrical calculation requires a PE.....?
 

Canton

Senior Member
Just because someone is a licensed engineer doesn't mean they automatically know how to design something. The OPs question was really a code question. I have been to engineering school and they teach you NOTHING about any code at all..ever..Most (if not all) of the professors have never designed anything real using any code. Engineering school teaches you the fundamentals, its up to you to do your own research which many times leads to a article or a forum which can point you in the right direction.
I know a couple of electricians that can't wire 3 way switches.....:huh: ......"Licensed" Master Electricians
 

kingpb

Senior Member
un

un

Thanks everyone. I am a PE in 5 states. Looks like NFPA 2010 9.4.2 and A10.5.3.2 do not require the 15% voltage dip requirement to be met when the fire pump is started in emergency mechanical bypass mode if a soft starter is specified. I knew there was some snippet of code out there - and thanks for pointing me to it.
I don't care what the code allows; dumping a fire pump on a DEG that pulls the voltage down 30% is, in all likelihood going to cause the DEG to go into load rejection. Somebody better be doing a transient starting analysis.

Give the loads to the DEG supplier; they can do it most easily. But then, most likely they want to sell the 500kW unit as well, so roll the dice. The owner's cost should have no bearing on the proper engineering solution.
 
Top