Re-classing PLFA Circuit to NPLFA Circuits

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DM2-Inc

DM2-Inc

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Houston, Texas
We're being told to replace the THHN wiring with Power Limited Fire Alarm (PLFA) cable because the fire panel doesn't have fuses on the the circuits that we connected Non-Power Limited Fire Alarm (NPLFA) cable to.

NEC (2017 edition and I suspect previous editions), 760.130(A), Exception 3 allows one to use NPLFA cable in place of PLFA cable:
760.130 Wiring Methods and Materials on Load Side of the PLFA Power Source. Fire alarm circuits on the load side of the power source shall be permitted to be installed using wiring methods and materials in accordance with 760.130(A), (B), or a combination of (A) and (B).
Exception No. 1: The ampacity adjustment factors given in 310.15(B)(3)(a) shall not apply.

Exception No. 2: Conductors and multiconductor cables described in and installed in accordance with 760.49 and 760.53 shall be permitted.

Exception No. 3: Power-limited circuits shall be permitted to be reclassified and installed as non–power-limited circuits if the power-limited fire alarm circuit markings required by 760.124 are eliminated and the entire circuit is installed using the wiring methods and materials in accordance with Part II, Non–Power-Limited Fire Alarm Circuits.

Informational Note: Power-limited circuits reclassified and installed as non–power-limited circuits are no longer power limited circuits, regardless of the continued connection to a power-limited source.​

When you go back to Part II, your faced with article 760.43 which requires overcurrent protection for circuits 14 AWG and larger. As we're using 14 AWG for the audibles, we're forced to follow this. This then brings us to 760.45, which requires overcurrent on the 14 AWG wires stating:
760.45 NPLFA Circuit Overcurrent Device Location. Overcurrent devices shall be located at the point where the conductor to be protected receives its supply.
Exception No. 1: Where the overcurrent device protecting the larger conductor also protects the smaller conductor.

Exception No. 2: Transformer secondary conductors. Non–powerlimited fire alarm circuit conductors supplied by the secondary of a single-phase transformer that has only a 2-wire (single-voltage) secondary shall be permitted to be protected by overcurrent protection provided by the primary (supply) side of the transformer, provided the protection is in accordance with 450.3 and does not exceed the value determined by multiplying the secondary conductor ampacity by the secondary-toprimary transformer voltage ratio. Transformer secondary conductors other than 2-wire shall not be considered to be protected by the primary overcurrent protection.

Exception No. 3: Electronic power source output conductors. Non–power-limited circuit conductors supplied by the output of a singlephase, listed electronic power source, other than a transformer, having only a 2-wire (single-voltage) output for connection to non–powerlimited circuits shall be permitted to be protected by overcurrent protection provided on the input side of the electronic power source, provided this protection does not exceed the value determined by multiplying the non–power-limited circuit conductor ampacity by the output-to-input voltage ratio. Electronic power source outputs, other than 2-wire (single voltage), connected to non–power-limited circuits shall not be considered to be protected by overcurrent protection on the input of the electronic power source.

Informational Note: A single-phase, listed electronic power supply whose output supplies a 2-wire (single-voltage) circuit is an example of a non–power-limited power source that meets the requirements of 760.41.​

I believe my "Get Out of Jail Free" card is Exception No. 2 to 760.45 above, because:
  1. The Panel is connected to a 20 Amp Breaker
  2. The Transformer Primary is 120 VAC and the secondary is 24 VDC, so the ratio is "5"
  3. The output of the power supply to the fire panel is 8 Amps (see Table 12B)
  4. The "...value determined by multiplying the secondary conductor ampacity..." 8 Amps "...by the secondary-to-primary transformer voltage ration..." ((120 / 24) = 5) x 8 = 40
  5. The 20 Amp breaker is less than the above ration of 40

I don't want to replace the cable and think that this would allow me to leave the cable as is. Is my logic correct...
 
I think you are correct in your reasoning. Keep in mind that the transformer for the fire alarm panel is going to have it's own protection, either primary or secondary. You could probably stop right there.

Are you actually re-classifying the circuits? For example, are you intending to run them with Class 1 power and light circuits? If you are simply using THHN as the conductors that doesn't mean you are re-classifying the circuit. It's more about where you are running the cable, not what it's made of. You only have to show that the THHN you are using meets the requirements of the fire alarm cable you would otherwise install; flame spread, ampacity, etc.
 
If you reclassify, make very sure that none of the devices on the circuit(s) require power limited input.
This is similar to the often overlooked issue when reclassifying ordinary power limited circuits (Class 2 and 3).
 
GoldDigger,
Can you elaborate?

Are you referring to requirements from
760.136 Separation from Electric Light, Power, Class 1, NPLFA, and Medium-Power Network-Powered Broadband Communications Circuit Conductors,
part (D) Associated Systems Within Enclosures​
 
DM2-Inc said:
The NEC basically says your "re-classing" the circuit if you use THHN because THHN isn't permitted on Power limited circuits.
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I disagree. It's more about "how used" than "what used". Take a look here. Southwire's product is basically THHN in MC and suitable for NPLFA and PLFA.

I think you'd have a good case to argue that if THHN is good enough for NPLFA it's certainly good enough for PLFA.
 
gadfly56,
With regard to the Red Alert Cable, I'd have to look more into the approvals.

...if THHN is good enough for NPLFA it's certainly good enough for PLFA
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Unfortunately, this isn't about "common sense", but rather what the code allows, and finding the language in the code which permits the use of NPLFA, beyond Exception 3 of 760.130.

If you read 760.45 (as our customer is reading it without the benefit of exception 2), you would either need to put fuses between the fire panel terminals and the field wiring, or revert back to PLFA cable. This is because 760.45 requires "Overcurrent devices shall be located at the point where the conductor to be protected receives its supply", which is at the fire panel terminals.
 
DM2-Inc said:
gadfly56,
With regard to the Red Alert Cable, I'd have to look more into the approvals.


Unfortunately, this isn't about "common sense", but rather what the code allows, and finding the language in the code which permits the use of NPLFA, beyond Exception 3 of 760.130.

If you read 760.45 (as our customer is reading it without the benefit of exception 2), you would either need to put fuses between the fire panel terminals and the field wiring, or revert back to PLFA cable. This is because 760.45 requires "Overcurrent devices shall be located at the point where the conductor to be protected receives its supply", which is at the fire panel terminals.
Click to expand...

Our fire alarm association had someone in from the state and the whole question of PLFA and NPLFA came up for a lengthy discussion. Unfortunately, there's no slide or anything memorializing the results and frankly, I don't recall the conclusion. It seems obvious it should be allowed but I can see your AHJ's point.
 
gadfly56
Our fire alarm association had someone in from the state and the whole question of PLFA and NPLFA came up for a lengthy discussion
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What State are you from?
Do you know who's the chapter head for your states association? Maybe they can shed some light.

We have 5 building that this has become an issue on and it's going to get expensive if we have to change to PLFA cable.
 
DM2-Inc said:
gadfly56

What State are you from?
Do you know who's the chapter head for your states association? Maybe they can shed some light.

We have 5 building that this has become an issue on and it's going to get expensive if we have to change to PLFA cable.
Click to expand...

AFAANJ. Jim Loftus is the current president, although I missed the last meeting and they did have elections.
 
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