Fire Pump Service & Utility Company Responsibilities?

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VBE

VBE

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Cincinnati, OH
Does the NEC's requirement for sizing overcurrent protection for fire pumps to accommodate the locked rotor ampacity of the motor apply to up-stream primary overcurrent protection (utility company's equipment), or does the NEC only cover overcurrent devices within or ahead of the fire pump controller (building equipment)?

What I've got is a 200 HP 480V 3PH Electric Fire Pump with a dedicated utility pad mount transformer. The utility company wants to provide a 300 kVA transformer at 19.9 KV 3PH primary and 8 Amp primary fuses.

The 200 HP fire pump LRA per NEC 430.251(B) is 1450 Amps at 480V 3PH. This locked rotor information for the motor would equate to about 1205 kVA and 35 Amps at 19.9 kV 3PH.

Now, the NEC does not require conductors to be sized by the LRA nor does it require transformers to be sized for the LRA. But in order to meet NFPA 20 and be a "reliable service", wouldn't the utility company's transformer and primary fuses need to accommodate the LRA? The utility is saying they want to size the transformer for the 200 HP load and then protect their transformer, hence the 8 Amp fuses. This would not carry the LRA indefinitely as is required by the NEC. But does the NEC get to determine what the utility company does?

Thoughts? Thanks!
 
Agreed. I know they're not governed by the same set of rules as the rest of us. And they're really good at making that evident too! I guess the question then diverts to NFPA 20's definition of a reliable service (and AHJ's interpretation) rather than the NEC.

NEC wants our fire pump to be connected to a reliable source and for our installation to be designed to allow operation at the LRA indefinitely (until equipment is destroyed). The utility company's source meets all conditions in NFPA 20 as far as reliable source is concerned. However, the utility company's equipment would not facilitate such operation at the LRA for more than a few cycles (inrush). Could the utility's service then not be considered "reliable" in the eyes of the NEC based on the fact that it won't allow indefinite operation at the LRA of the motor as NEC requires?

Maybe this is where "under proper engineering supervision" and the AHJ's decision comes into play.
 
VBE said:
Agreed. I know they're not governed by the same set of rules as the rest of us. And they're really good at making that evident too! I guess the question then diverts to NFPA 20's definition of a reliable service (and AHJ's interpretation) rather than the NEC.

NEC wants our fire pump to be connected to a reliable source and for our installation to be designed to allow operation at the LRA indefinitely (until equipment is destroyed). The utility company's source meets all conditions in NFPA 20 as far as reliable source is concerned. However, the utility company's equipment would not facilitate such operation at the LRA for more than a few cycles (inrush). Could the utility's service then not be considered "reliable" in the eyes of the NEC based on the fact that it won't allow indefinite operation at the LRA of the motor as NEC requires?

Maybe this is where "under proper engineering supervision" and the AHJ's decision comes into play.
Click to expand...

I'm going to suggest the source is not "reliable" since 695.3(A) specifically says:

(A) Individual Sources. Where reliable, and where ca-
pable of carrying indefinitely the sum of the locked-rotor
current of the fire pump motor(s) and the pressure mainten-
ance pump motor(s) and the full-load current of the asso-
ciated fire pump accessory equipment when connected to
this power supply, the power source for an electric motor
driven fire pump shall be one or more of the following.

(1) Electric Utility Service Connection...etc
 
Client Coverage

Client Coverage

What I've done in the past is perform a voltage-drop calculation that determines the minimum size transformer based on starting and running VD per NEC 695. Then publish those findings to the Utility and the client. I would also plot the Utility's ocpd against the motor locked rotor amperage for determination of appropriate fusing.
I think the client is covered because they've done their due-diligence and they only have control of the secondary devices.
 
mayanees said:
What I've done in the past is perform a voltage-drop calculation that determines the minimum size transformer based on starting and running VD per NEC 695. Then publish those findings to the Utility and the client. I would also plot the Utility's ocpd against the motor locked rotor amperage for determination of appropriate fusing.
I think the client is covered because they've done their due-diligence and they only have control of the secondary devices.
Click to expand...

They may have control of only the secondary devices, but the AHJ is well within his/her rights to consider the fusing on the primary side in evaluating the reliability of the source. It puts the client in a tough spot if the utility won't budge. I would guess it gets passed on to the Board of Public Utilities or equivalent in that case.
 
gadfly56 said:
I'm going to suggest the source is not "reliable" since 695.3(A) specifically says:

(A) Individual Sources. Where reliable, and where ca-
pable of carrying indefinitely the sum of the locked-rotor
current of the fire pump motor(s) and the pressure mainten-
ance pump motor(s) and the full-load current of the asso-
ciated fire pump accessory equipment when connected to
this power supply, the power source for an electric motor
driven fire pump shall be one or more of the following.

(1) Electric Utility Service Connection...etc
Click to expand...

That's an interesting point, and I would say you are probably right.

mayanees said:
What I've done in the past is perform a voltage-drop calculation that determines the minimum size transformer based on starting and running VD per NEC 695. Then publish those findings to the Utility and the client. I would also plot the Utility's ocpd against the motor locked rotor amperage for determination of appropriate fusing.
I think the client is covered because they've done their due-diligence and they only have control of the secondary devices.
Click to expand...

True, they don't have control of the utility, but they do have the option of installing a alternate source. In this case, I would say the alternate source is required, unless the utility will increase the delivery capacity. That alternate source could either be a generator, or even a diesel motor pump.

It's apparently been a while since I've designed electrical for a fire pump. The NEC 2011 handbook has some commentary I've never read before on some exact requirements for a "reliable source". It's extracted from NFPA 20.

Overhead lines are not allowed since the fire dept. might have to cut them for firefighting. And any outages caused by other than natural disasters or grid management failure (i.e. regional blackouts) cause the utility to be considered unreliable.
 
steve66 said:
That's an interesting point, and I would say you are probably right.



True, they don't have control of the utility, but they do have the option of installing a alternate source. In this case, I would say the alternate source is required, unless the utility will increase the delivery capacity. That alternate source could either be a generator, or even a diesel motor pump.

It's apparently been a while since I've designed electrical for a fire pump. The NEC 2011 handbook has some commentary I've never read before on some exact requirements for a "reliable source". It's extracted from NFPA 20.

Overhead lines are not allowed since the fire dept. might have to cut them for firefighting. And any outages caused by other than natural disasters or grid management failure (i.e. regional blackouts) cause the utility to be considered unreliable.
Click to expand...

Just to be clear, the prohibition on overhead lines is only on the user premises, not on the POCO right-of-way outside the property.
 
gadfly56 said:
Just to be clear, the prohibition on overhead lines is only on the user premises, not on the POCO right-of-way outside the property.
Click to expand...

Yes, I was trying to summarize, assuming the OP would refer to the full text in the handbook or even NFPA 20.

Chances are, if you trace the supply back far enough, you are going to find some overhead lines somewhere:)
 
steve66 said:
Yes, I was trying to summarize, assuming the OP would refer to the full text in the handbook or even NFPA 20.

Chances are, if you trace the supply back far enough, you are going to find some overhead lines somewhere:)
Click to expand...

In NJ that would be nearly everywhere.
 
Found some additional info specifically on transformers while researching another issue (NFPA 70-2014 695.5(B)):

(B) Overcurrent Protection. The primary overcurrent pro-
tective device(s) shall be selected or set to carry indefitely
the sum of the locked-rotor current of the fire pump motor(s)
and the pressure maintenance pump motor(s) and the full-load
current of the associated fire pump accessory equipment when
connected to this power supply. Secondary overcurrent protec-
tion shall not be permitted. The requirement to carry the
locked-rotor currents indefinitely shall not apply to conductors
or devices other than overcurrent devices in the fire pump
motor circuit(s).

So yeah, the transformer needs to be fused at not less than 35 amps on the primary side. Note that no protection is allowed on the secondary side.
 
gadfly56 said:
Found some additional info specifically on transformers while researching another issue (NFPA 70-2014 695.5(B)):

(B) Overcurrent Protection. The primary overcurrent pro-
tective device(s) shall be selected or set to carry indefitely
the sum of the locked-rotor current of the fire pump motor(s)
and the pressure maintenance pump motor(s) and the full-load
current of the associated fire pump accessory equipment when
connected to this power supply. Secondary overcurrent protec-
tion shall not be permitted. The requirement to carry the
locked-rotor currents indefinitely shall not apply to conductors
or devices other than overcurrent devices in the fire pump
motor circuit(s).

So yeah, the transformer needs to be fused at not less than 35 amps on the primary side. Note that no protection is allowed on the secondary side.
Click to expand...

But 695.5 would not apply to a utility transformer. It's for a transformer owned by the customer. Notice where it says "where the supply voltage is different than the fire pump voltage' or something similar.

I still think you have it right. I just don't think its covered in this paragraph.
 
steve66 said:
But 695.5 would not apply to a utility transformer. It's for a transformer owned by the customer. Notice where it says "where the supply voltage is different than the fire pump voltage' or something similar.

I still think you have it right. I just don't think its covered in this paragraph.
Click to expand...

695 doesn't care who owns the transformer, it still has to meet the requirements. The POCO isn't bound by it but the customer is. Now, if you're trying to provide what your customer wants then you should pay attention to the to the NEC in this case.
 
ActionDave said:
Welcome to the forum.

The NEC does not cover power company equipment. Basically the NEC starts where the power company ends and that is called the Service Point.
Click to expand...

On the one (100 hp) electric fire pump I work on, there is a note on the one line about the fuse size for the primary.
so maybe our POCO has some engineering notes or standard to coordinate with the customer
 
gadfly56 said:
695 doesn't care who owns the transformer, it still has to meet the requirements. The POCO isn't bound by it but the customer is. Now, if you're trying to provide what your customer wants then you should pay attention to the to the NEC in this case.
Click to expand...


Read the first sentence again: "Where the service or system voltage is different from the utilization voltage of the fire pump motor....."

This only applies to transformers after the service connection point.

All electric services are supplied by a utility transformer, so if this section applied to utility transformers, there could never be any overcurrent protection on a fire pump service. That would make 695.4B a total waste of ink.
 
steve66 said:
Read the first sentence again: "Where the service or system voltage is different from the utilization voltage of the fire pump motor....."

This only applies to transformers after the service connection point.

All electric services are supplied by a utility transformer, so if this section applied to utility transformers, there could never be any overcurrent protection on a fire pump service. That would make 695.4B a total waste of ink.
Click to expand...

I don't see how you can say that. If the distribution voltage from the POCO is 19K and they drop a transformer that supplies my facility with 460 which is also what my fire pump runs at that POCO transformer has to supply the locked rotor current for my fire pump(s).
 
gadfly56 said:
I don't see how you can say that. If the distribution voltage from the POCO is 19K and they drop a transformer that supplies my facility with 460 which is also what my fire pump runs at that POCO transformer has to supply the locked rotor current for my fire pump(s).
Click to expand...

I have to agree with you..In NEC section 695.5 it says that

Transformers. Where the service or system voltage
is different from the utilization voltage of the fire pump
motor, transformer(s) protected by disconnecting means
and overcurrent protective devices shall be permitted to be
installed between the system supply and the fire pump controller
in accordance with 695.5(A) and (B).

So even if the utility supply voltage is different from the firepump controller voltage you have to size them based on 695.5(B) where it clearly states that the "The primary overcurrent protective
device(s) shall be selected or set to carry indefinitely the sum of the locked rotor current of the fire pump motors and the pressure maintenance pmp motors and full current associated fire pump accessory equipment when connected to this power supply"
 
Guys,

I think you have drifted to far back in your book. Section 90.2(B)(5) places installations under the exclusive control of a utility outside the scope of the code, so you can stop reading right there. The customer may need to install an alternate source of power but the AHJ has no say in the protection of a utility transformer.

RB
 
gadfly56 said:
I don't see how you can say that. If the distribution voltage from the POCO is 19K and they drop a transformer that supplies my facility with 460 which is also what my fire pump runs at that POCO transformer has to supply the locked rotor current for my fire pump(s).
Click to expand...

I'm paraphrasing here, but the first sentence basically says "Where the service voltage is different than the fire pump voltage a transformer shall be permitted between the system supply and the fire pump controller."

So this only applies when the source voltage is different than the fire pump voltage. Note that "source" or "service" refers back to the sources listed in 695.3, so the source or service is the "Electric Utility Service Connection". As a result, 695.5 only applies for a customer owned transformer after the service, or a transformer connected to a generator or an on site power production facility.


Again, I still agree with you that the utility primary fusing should carry the locked rotor current, or an alternate source must be provided, but that's just not the right paragraph to quote.

I do not agree with this:

gadfly56 said:
Note that no protection is allowed on the secondary side.
Click to expand...

And overcurrent protection is permitted on the secondary side of a utility transformer that supplies a fire pump, just not on the secondary of a privately owned transformer.
 
steve66 said:
And overcurrent protection is permitted on the secondary side of a utility transformer that supplies a fire pump, just not on the secondary of a privately owned transformer.
Click to expand...
I dont agree with that statement...As per 695.4 B(1) it states that A single disconnecting means and associated overcurrent protective device(s) shall be permitted to be installed between the fire pump power source(s) and one of the following
1) A listed fire pump controller
(2) A listed fire pump power transfer switch
(3) A listed combination fire pump controller and power transfer switch

As per your statement you are saying there is a protection on the primary as well as on the secondary which violates the code.....
 
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