A generator, ATS, elevator, and fire pump walked into a bar.

[malachi constant]

It's not really a joke, but I got your attention. I am a consulting engineer and got a call asking me to weigh in on a situation. A 40-year-old high rise is in the midst of having their elevators replaced. As part of the project the elevator consultant called for the original ATS to be replaced. As the contractor was preparing to replace it the building's maintenance team recalled a conversation a decade ago where someone said the generator was not properly sized to handle both the fire pump and elevators. So I get the call to figure it out.

Review of the original plans matches what is installed:
* 205kW / 256kvA 208V/3P generator feeding a single 1200A ATS.
* The ATS feeds two disconnects which in turn feed the 75HP fire pump, and the elevator bank.
* I'm trying to get elevator shops but let's assume all four elevators are replaced with 85A models on VFDs (smaller than what was originally installed).
* Only one elevator will run at a time during emergency power situations.
* The ATS was called out as being replaced because it was assumed to not have presignal functions. In review of the on-site ATS it appears presignal relays were added as part of an elevator upgrade 25 years ago.

Question #1 - can the 205kW generator handle the fire pump and one elevator? I don't know how to determine this. My understanding of NEC 695 is the source must be able to handle the locker rotor amps of the fire pump. I believe the equation for 208/3 RLA is I = 577 x HP x (kva/HP) / 208. Plugging in 75 and either 5.6 or 6.29 yields RLA of 1165 or 1309A. I am asking for shop drawing info for the elevators, but for now am assuming a starting current similar to nameplate since they are on VFDs. How do I determine if the generator can handle this?

Question #2 - do the elevator and fire pump need separate transfer switches? I'm typing this up from home so don't have my code book in front of me. Do they both fall under NEC 701 "Legally Required Standby"?

I haven't done high rises in a long time so fire pumps are not something I spend a lot of time thinking about. Any insight you all have is appreciated.

 

[topgone]

It's not really a joke, but I got your attention. I am a consulting engineer and got a call asking me to weigh in on a situation. A 40-year-old high rise is in the midst of having their elevators replaced. As part of the project the elevator consultant called for the original ATS to be replaced. As the contractor was preparing to replace it the building's maintenance team recalled a conversation a decade ago where someone said the generator was not properly sized to handle both the fire pump and elevators. So I get the call to figure it out.

Review of the original plans matches what is installed:
* 205kW / 256kvA 208V/3P generator feeding a single 1200A ATS.
* The ATS feeds two disconnects which in turn feed the 75HP fire pump, and the elevator bank.
* I'm trying to get elevator shops but let's assume all four elevators are replaced with 85A models on VFDs (smaller than what was originally installed).
* Only one elevator will run at a time during emergency power situations.
* The ATS was called out as being replaced because it was assumed to not have presignal functions. In review of the on-site ATS it appears presignal relays were added as part of an elevator upgrade 25 years ago.

Question #1 - can the 205kW generator handle the fire pump and one elevator? I don't know how to determine this. My understanding of NEC 695 is the source must be able to handle the locker rotor amps of the fire pump. I believe the equation for 208/3 RLA is I = 577 x HP x (kva/HP) / 208. Plugging in 75 and either 5.6 or 6.29 yields RLA of 1165 or 1309A. I am asking for shop drawing info for the elevators, but for now am assuming a starting current similar to nameplate since they are on VFDs. How do I determine if the generator can handle this?

Question #2 - do the elevator and fire pump need separate transfer switches? I'm typing this up from home so don't have my code book in front of me. Do they both fall under NEC 701 "Legally Required Standby"?

I haven't done high rises in a long time so fire pumps are not something I spend a lot of time thinking about. Any insight you all have is appreciated.

Your calculations jibe with mine. The 75HP fire pump will have a starting kVA of 419 kVA (1163A) when starting! Your generator can carry the fire pump + the elevators for as long as they are started one after the other (staged starting). Most generators have skVA capacities, please verify if yours has enough capacity.

 

[Besoeker]

Just an idle thought.
If the fire pump is being used in earnest to combat a fire in the building, wouldn't the elevators be out of use?

 

[GoldDigger]

Just an idle thought.
If the fire pump is being used in earnest to combat a fire in the building, wouldn't the elevators be out of use?

Except possibly by the firefighters under manual override control. And at the very beginning the fire pump may get triggered while the elevators are still in the process of returning to their recall floors.

 

[malachi constant]

Your calculations jibe with mine. The 75HP fire pump will have a starting kVA of 419 kVA (1163A) when starting! Your generator can carry the fire pump + the elevators for as long as they are started one after the other (staged starting). Most generators have skVA capacities, please verify if yours has enough capacity.

I assume skVA = starting kVA. I have a 40-yr-old nameplate and am trying to get generator test reports from the Cummins service agent. Can I figure out sKVA from those? I'm guessing the answer is to call my local Cummins rep and see what he can figure out.

 

[zbang]

Except possibly by the firefighters under manual override control. And at the very beginning the fire pump may get triggered while the elevators are still in the process of returning to their recall floors.

According to the OP, only one elevator is on the ATS, so presumable the others just stop or they have a separate source of e-power. (That doesn't sound right to me, but it's not my area.)

 

[gadfly56]

According to the OP, only one elevator is on the ATS, so presumable the others just stop or they have a separate source of e-power. (That doesn't sound right to me, but it's not my area.)

Sometimes they are arranged so that any one of "n" can be activated, not just one fixed unit.

 

[tw1156]

Question #1 - can the 205kW generator handle the fire pump and one elevator? I don't know how to determine this. My understanding of NEC 695 is the source must be able to handle the locker rotor amps of the fire pump. I believe the equation for 208/3 RLA is I = 577 x HP x (kva/HP) / 208. Plugging in 75 and either 5.6 or 6.29 yields RLA of 1165 or 1309A. I am asking for shop drawing info for the elevators, but for now am assuming a starting current similar to nameplate since they are on VFDs. How do I determine if the generator can handle this?
.

I would recommend using Cummins' sizing software (http://powersuite.cummins.com/en). As you're dealing with motor loads here as others have mentioned you'll have a high in-rush. What won't be obvious from the nameplate of the generator is if they provided it with an upsized alternator to handle any of these motor loads. I've seen applications where you'll have a 175kW generator with an upsized alternator to handle 275kW.

 

[malachi constant]

According to the OP, only one elevator is on the ATS, so presumable the others just stop or they have a separate source of e-power. (That doesn't sound right to me, but it's not my area.)

All elevators are on emergency power, but only one will run at a time. Initially they will lower one by one to the main floor. Then fire fighters will have control of one elevator (they pick which one). I could imagine a scenario where a sprinkler head is flowing and the fire pump intermittently kicks on to pressurize it, while the fire fighters use the elevator to lower victims down to main floor. I don't pretend to understand fire fighting protocol in a high rise, so am just assuming worst case.

The question of can the fire pump share an ATS with the elevators...anyone have insight? I have reviewed NEC 695 and don't see that directly answered. There is a guiding principle evident that the fire pump MUST remain operational at all times, and that load shedding is allowable to achieve this. Load shedding isn't easily achievable with this installation, so it is mainly a question of (1) can the generator handle both and if so then (2) is it legal to have them on the same ATS. I should have #1 figured out by end of the day, but am at an impasse with #2. Any thoughts are appreciated.

Thanks all!

 

[topgone]

All elevators are on emergency power, but only one will run at a time. Initially they will lower one by one to the main floor. Then fire fighters will have control of one elevator (they pick which one). I could imagine a scenario where a sprinkler head is flowing and the fire pump intermittently kicks on to pressurize it, while the fire fighters use the elevator to lower victims down to main floor. I don't pretend to understand fire fighting protocol in a high rise, so am just assuming worst case.

The question of can the fire pump share an ATS with the elevators...anyone have insight? I have reviewed NEC 695 and don't see that directly answered. There is a guiding principle evident that the fire pump MUST remain operational at all times, and that load shedding is allowable to achieve this. Load shedding isn't easily achievable with this installation, so it is mainly a question of (1) can the generator handle both and if so then (2) is it legal to have them on the same ATS. I should have #1 figured out by end of the day, but am at an impasse with #2. Any thoughts are appreciated.

Thanks all!

To answer some of your questions, a fire pump will have to be wired separately from other feeders per NFPA 20. It "shall" be labeled properly to differentiate form other feeders and should be lockable at close position, among others. The idea is to make sure the power supply to the fire pump is not going to be compromised by various factors including fire itself. NFPA 20 requires no more than one disconnecting device to the fire pump also.

 

[malachi constant]

To answer some of your questions, a fire pump will have to be wired separately from other feeders per NFPA 20. It "shall" be labeled properly to differentiate form other feeders and should be lockable at close position, among others. The idea is to make sure the power supply to the fire pump is not going to be compromised by various factors including fire itself. NFPA 20 requires no more than one disconnecting device to the fire pump also.

So in this instance I popped open the ATS and observed feeders of three different sizes coming into the ATS from the generator, then feeders of three different sizes going out of the generator to each of three fused disconnects (elevator, fire pump, em lighting).

So I see one violation for sure, and possible another. The first is that the fire pump is not wired separately from other feeders - where it hits the transfer switch the feeders are all effectively connected. The second (possible) violation is the generator likely has an output breaker - if it did that would mean it has two overcurrent devices.

Appreciate the comments. I haven't read NFPA 20 but will take a look this week.

 

[texie]

So in this instance I popped open the ATS and observed feeders of three different sizes coming into the ATS from the generator, then feeders of three different sizes going out of the generator to each of three fused disconnects (elevator, fire pump, em lighting).

So I see one violation for sure, and possible another. The first is that the fire pump is not wired separately from other feeders - where it hits the transfer switch the feeders are all effectively connected. The second (possible) violation is the generator likely has an output breaker - if it did that would mean it has two overcurrent devices.

Appreciate the comments. I haven't read NFPA 20 but will take a look this week.

Your going to need to study NEC 695 and NFPA 20 carefully. The age of the building and they way things were done at that time will be vastly different from today's requirements. I see AHJ discussion in your future.
While not addressing all of your questions, for starters, I will say that you can not use the same ATS. A fire pump ATS must be specifically rated for fire pump duty and be located in the fire pump room. That's one reason that the vast majority of fire pump installs today use a listed combination fire pump controller/ATS.
There is no requirement for the generator to carry locked rotor current. Normally you would use the genset manufacturer to assist with sizing to be sure it will meet all the requirements. With an old genset this may be difficult.