Relays used for in Fire Alarm Systems

Relays used for in Fire Alarm Systems 

In an emergency you may wish your fire alarm system to perform a number of automated tasks – this could include grounding a lift or closing doors. To do this you will require fire alarm relays, devices which allow the automation of certain functions.

A relay is a simple electromechanical switch. While we use normal switches to close or open a circuit manually, a relay is also a switch that connects or disconnects two circuits. But instead of a manual operation, a relay uses an electrical signal to control an electromagnet, which in turn connects or disconnects another circuit.

The function of relay module in fire system control is to provide a way for a high-voltage device to be controlled by a low-voltage signal. This is done by closing a switch that activates the device when the fire alarm sends a small current to it. In practice, a relay in a fire alarm system may be used to perform the following functions:

·        Close Doors: A fire alarm relay can be used to automatically shut fire doors in a building when the fire alarm is triggered. This helps to contain the fire and prevent it from spreading.

·        Activate Sprinklers: The fire relay module can be used to activate the sprinkler system in a building when the fire alarm is triggered.

·        Sound Alarms: A fire alarm relay module is often used to activate a sound alarm in an emergency. This warns people in the vicinity of the fire and helps them to evacuate the area.

·        Switch OFF AC Systems: The stream of air coming out of an air conditioner can spread the fire in a building or even smoke and fumes. A fire alarm relay can be used to switch off the AC system and prevent the fire from spreading.

·        Switch On Smoke Exhaust Systems: The smoke exhaust system in a building helps to clear out smoke and fumes. A fire alarm relay can be used to switch it on.

·        Switch Off Loud Music: During a fire, it is important to be able to hear fire alarms and other warnings. a fire alarm relay module is often used to switch off loud music when the fire alarm is triggered so that people can hear the warnings.

Relays can be used to control voltage feeding a particular supply and either apply or drop voltage in the event of a fire activation.

Relays can be used to signal to monitored inputs, these inputs would monitor a nominal EOL resistance and in the event of a fire alarm activation would switch to pick up the trigger value resistance.

Relays can also be used to signal a simple NO/NC contact.

The relay’s load may be AC or DC, but must be within amperage rating of the relay contacts. The relays must be fire alarm listed and supplied by the FACP manufacturer, or be a Listed Fire Relay from a manufacturer.

Off-the-shelf electrical supply relays are not permitted to be directly wired to a fire alarm system. Additionally, polarity must be observed because of the integrated diode used in the relay.

Testing of the fire alarm system includes only verifying the relay changed state, and not necessarily the operational performance of the fire-safety function itself. Proper fire alarm relay operation will be verified by using a meter or by observing an activation LED on the relay.

Question 1: Will your relay be used to supply electrical power or turn it off? You are not responsible for the connection and operation of any other trade’s equipment or function, but you cannot allow the relay to be used improperly. If your relay states it has contacts rated at 10 amps and the owner wishes to turn on 20 amps of outdoor lighting, then they will have to use your relay to switch another device having the proper load rating (i.e. 20 amps or less).

While it is true that the relay, wiring, contactor or equipment could fail without causing a trouble signal on the fire alarm system, you are only responsible for the relay and circuit that you provide up to the switched contacts of the relay. All equipment after your relay contacts is the responsibility of another trade or another contractor.

 

Question 2: Will your relay be used to switch a small current and low voltage signal used by another electrical system, rather than the safety equipment load? Sometimes the load you need to switch amounts to an electrical control signal of just 5V – which another system’s data input needs in order to perform a function. Since you must supply a relay that is used to perform a certain function, you are not responsible for performing everything the owner wants to do. For example, your relay cannot pulse an illuminated street address sign.

 

Question 3: Is the safety function to be performed a code-required fire alarm feature such as controlling elevators, or is it a customer nicety such as opening a driveway gate or turning on outdoor lighting? For a code compliant relay, its wiring must be either fail-safe or cause a Trouble Signal when power to the relay fails.

For Illustrated Relay A

Power to certain emergency safety functions may need to be turned off during an alarm. Examples of these functions commonly include power to electro-magnetic door holders or electro-magnetic door locks. These two examples are normally well within the electrical rating of a fire relay, but a contactor may also be needed if you intend to cut power to a club’s DJ booth, for example, that is providing amplified sound, light and stage effects. If a contactor/relay is also needed, the electrician will supply it.

Relay A rules: Common and Normally Open relay contacts are used to supply a CLOSED circuit to keep safety equipment operational.

This relay’s wiring is “Fail-Safe,” since loss of power to the relay coil will cause the fire-safety function to be performed. No EOL resistor or power supervision relay is required if the emergency function is performed when loss of power to the relay causes the safety function to be performed.

For Relay B

Power to safety functions may need to be turned on during an alarm. This may include smoke exhaust fans and indoor/outdoor lighting. Typically, a 10 amp relay will be used to switch an additional contactor/relay that would be needed for a large rooftop fan, for example.

 

Relay B rules: Common and Normally Open relay contacts are used to supply a CLOSED circuit to deactivate safety equipment upon a polarity reversal signal from the FACP upon alarm conditions.

This relay wiring is NOT “Fail-Safe,” since loss of power to the relay will not cause the fire-safety function to be performed. Instead, this wiring method will cause a FACP trouble signal should there be a fault on the wiring supplying power to the relay.

A circuit fault or any other loss of power to operate the life safety function may need to be supervised. For example, supervision of the electrical power to operate the elevator’s shunt controller is required to ensure the 110vac power to perform the emergency shunt trip is constantly present. The modern self-contained elevator shunt-trip panels contain a set of relay contacts that will close should the shunt-trip lose its operational power for any reason. Wire a dedicated IDC with an EOL resistor across these provided open terminals. Any loss of that 110vac operating power will cause their relay contacts to close and initiate a Supervisory signal. This signal must be specifically and descriptively annunciated (ie “elevator shunt-trip power loss”).

For Relay C

Use only for non-life safety applications or as allowed by the exception (see below).

Relay C rules: Common and Normally Closed and/or Normally Open Relay contacts may be used to activate or to deactivate customer’s equipment. This Relay is NOT “Fail-Safe,” since loss of power to the relay will not cause the fire-safety function to be performed. Also, power wiring to the relay coil can experience a fault without causing a FACP Trouble signal.

An exception allows this relay’s wiring configuration to be used to perform code-required safety functions. This is when a relay output within a control unit is used to activate a function performed by another control unit. This happens when an FACP on-board relay is used to close a set of input contacts of another control panel. For example, you can trip a NAC power booster using the alarm output relay of the main control panel. This exception allows a relay circuit to connect two control units even though the relay wiring is neither monitored for integrity nor provides fail-safe operation.

This wiring exception is only permitted if both control units are located in the same room, the control units are within 20 feet of each other, and the relay wiring connecting both panels is protected against mechanical injury by running it either inside the wall or on the surface using conduit

An elevator company provides a shunt-trip panel whenever the machine room or hoist way includes sprinklers. This panel ensures the elevators will be shut down before sprinkler water can reach sensitive electrical and mechanical components. Your job will be to provide a fail-safe relay (example A) or power-supervised relay (example B), and contacts that will close upon an alarm signal from the hoist way or elevator equipment room detectors.

রিলে কি? 

রিলে একটি সুইচিং ডিভাইস। রিলে এমন একটি সুইচিং ডিভাইস যা সার্কিটে কোন ধরনোর শর্ট সার্কিট সৃষ্টি হলে নিজে ধংস হয়ে সার্কিট কে রক্ষা করে। এই জন্য রিলেকে অতন্দ্রী পহরি বলা হয়ে থাকে।  রিলের মধ্য দিয়ে যদি কারেন্ট প্রবাহিত হয় তাহলে কয়েল মেগনেটাইজ হয়ে কন্টাকের মাধ্যমে সার্কিট কে অন অফ কন্ট্রোল করে থাকে। জরুরি অবস্হায় সার্কিট পুড়ে যাওয়া বা ধংস হয়ে হাত থেকে রক্ষা করে থাকে রিলে। 

রিলে কতো প্রকার কি কি 

ভোল্টেজ অনুযায়ী রিলে দুই প্রকার 

১. এসি রিলে 

২.ডিসি রিলে 

*এসি রিলে আবার ভোল্টেজ উপর ভিত্তি করে অনেক ধরনের হয়ে থাকে

1. 5VAC,6VC,12VAC,24VAC,36VAC, 110VAC,220VAC,440VAC

 কয়েলের ভোল্টেজের উপর ভিত্তি করে এসি রিলে এতো ধরনের হয়ে থাকে।

*ভোল্টেজ উপর ভিত্তি করে ডিসি রিলে বিভিন্ন ধরনের হয়ে থাকে 

1. 5VDC,6VDC,12VDC,24VDC,36VDC, 110VDC,220VDC 440VDC

কয়েলের ভোল্টেজের উপর ভিত্তি করে ডিসি রিলে এতো ধরনের হয়ে থাকে।

রিলে কেন ব্যাবহার করা হয়

১.এসি ভোল্টেজ কে ডিসি রিলে দিয়ে কন্ট্রোল করার জন্য রিলে ব্যাবহার হয়। 

২.সার্কিটে কোন ধরনের ক্রটি বা ক্ষতির সম্মুখীন হলে রিলে হতে জানা যায়। 

৩ রিলে নিজে নষ্ট হয়ে সার্কিট রক্ষা করে।

৪.সার্কিটে কোন ফল্ট হলে রিলে থেকে জানা যায়।

রিলে ব্যাবহারের নিয়ম

প্রতিটি রিলেের গায়ে ডায়াগ্রাম দেওয়া থাকে,  কতো ভোল্টেজ কতো এম্পিয়ার,  কোনটা কোন কন্টাক।

যদি রিলের বডিতে কিছু লিখা না থাকে তাহলে ভিতরে কয়েলের মধ্যে ভোল্টেজ এম্পিয়ার লিখা থাকবে।সেই ভোল্টেজ এবং এম্পিয়ার দেখে কোন জায়গায় ব্যাবহার করা যাবে তা নির্ধারণ করতে হবে। 

রিলে প্রকারভেদ 

সাধারনত তিন প্রকার রিলে হয়ে থাকে 

1.SPST  (Single Pole Single Throw)

2.SPDT (Single Pole Double Throw)

3.DPDT (Double Pole Double Throw

       *SPST রিলে মূলত ৪ পিনের হয়ে থাকে 

       *SPDT রিলে মূলত ৫পিনের হয়ে থাকে 

       *DPDT রিলে মূলত ৮ পিনের হয়ে থাকে

রিলে পিন পরিচিতি 

রিলেতে মূলত তিনটি পিন থাকে 

1.Common 

2.NO 

3.Nc 

1.Common: কমন কয়েলে সার্কিটের সুইচিংয়ের মান অনুযায়ী ভোল্টেজ প্রবাহিত করা হয়। রিলে কয়েলে কোন পজিটিভ নেগেটিভ প্রান্ত নেই তাই এটি পজিটিভ নেগেটিভ যে কোন প্রান্তে সংযোগ করা যায়। রিলের পরিচিত প্রকাশ পায় মূলত তার কয়েল ভোল্টেজ উপর ভিত্তি করে। যে ভোল্টেজে রিলে চালু হয় সেটি রিলের ভোল্টেজ ধরা হয়। 

2.NO: NO এর ফুল মিনিং Normally Open,  অর্থাৎ রিলে যখন নরমাল অথবা কয়েল না ধরা অবস্হায় থাকবে তখন Common এবং NO প্রান্ত বিছিন্ন অবস্হায় থাকবে।  যখন রিলে কয়েল ধরবে তখন অথবা রিলে কয়েল এবনরমাল হবে তখন Common এবং NO প্রান্তটি নিরবিচ্ছিন্ন অবস্হায় কাজ করবে। 

 3.NC: NC এর ফুল মিনিং Normally Close, অর্থাৎ রিলে নরমাল অবস্থা বা কয়েল না ধরা অবস্হায় Common এবং NC প্রান্ত নিরবচ্ছিন্ন অবস্থায় থাকবে বা সংযোগ থাকবে। যখন রিলে কয়েল ধরবে বা রিলে এবনরমাল অবস্হায় থাকবে এখন Common এবং NC বিচ্ছিন্ন অবস্হায় থাকবে। 

রিলে কয়েল পরিচিতি:

রিলে কয়েল ভোল্টেজ অনুযায়ী অনেক ধরনের হয়।  আমরা যে রিলে ব্যাবহার করবো তার কয়েল ভোল্টেজ অনুযায়ী ভোল্টেজ সাপ্লাই দিলে কয়েলটি ধরবে এবং রিলের উপরে থাকা ইন্ডিকেটর লাইটি জ্বলে উঠবে। আবার যখন ভোল্টেজ সাপ্লাই বন্ধ হয়ে যাবে ইন্ডিকেটর টি বন্ধ হয়ে যাবে এবং কয়েলটি বন্ধে হয়ে আগের অবস্হানে চলে আসবে।

Stair Pressurization Fan & Fire Detection integration

Stair Pressurization Fan & Fire Detection integration

According to the National Fire Protection Association, the process of evacuating some of today’s largest high-rise buildings may take upwards of two hours.  This is by far the most compelling argument for effective smoke control in building stairwells. 

Pressurized staircases keep exit routes smoke free in the event of a fire, lending precious minutes to building occupants during an evacuation. The pressures specified to keep a stairwell pressure positive vary by code.  However, the universal goal is to restrain smoke but still allow the opening of doors in the stairwell shaft.

In case of fire in a high rise building, a Stair Pressurization Fan (SPF) uses clean outside air to pressurize the air in stairwells. The pressurized air helps people escape the fire and firefighters battle the fire. It should be work during fire condition through FACP.

When there's a fire, clean outside air is forced by a Stair Pressurization Fan into a stairwell. The pressurization is used to push back on smoke, keeping the smoke out of the escape route.

Stairways are Fire Escape Routes

Nowadays, stairwells have better fire ratings than the rest of the building. In other words, so people can get out when the rest of the building is on fire, stairways don't burn.

Stairways Full of Smoke

The stairways may not burn, but they can still fill up with smoke. The smoke can not only make it harder to see as one is getting away from a fire, but it can:

·        Make it harder to breathe - possibly causing injury or death

·      Close off the escape route - possibly causing people to seek another pathway of escape

Open Doors

The problem is, as people are escaping the fire, they have to open the door to the stairway. When the door is open, preventing the stairway from being used by later escapees, smoke follows and billows into the stairway.

Smoke Push Back

The idea behind the stair pressurization is that during a fire the stairway should have more pressure than the rest of the building. That way, when the doors open, the higher pressure in the stairwell pushes the smoke back onto the floor, keeping the escape route clear of smoke.

The smoke free escape route also doubles as a smoke free entrance route for the firefighters as they combat the fire.

Turning On the SPF

Except when there's smoke, the stair pressurization fans aren't needed, so normally they're turned off. When the fire alarm system detects smoke, they're automatically turned on.

As firefighters battle the fire, if the fire alarm system has not turned on the stair pressurization fans, they're turned on by the firefighters.

Escape

As people are escaping a fire, and open the doors to get into the stairways, smoke would naturally billow from a fire floor into the stairwell. Keeping the smoke out of the stairwell by pushing it back onto the floor, a Stair Pressurization Fan pressurizes the air in the stairwell.

Integration

In every Fire Detection system has one devices named Control Module / Relay Module. This Module operate through FACP loop line. Module has Loop IN /OUT & NO COM NC. Module can be programed as NO / NC condition. An External relay may require (Depend on Module relay capacity) for integration. If Stair Pressurization Fan starter panel has an auxiliary circuit for Fire Alarm then only no need to put any external relay. During external relay operation you required one adjust power supply to energized relay coil.

Here’s a practical case study applying NFPA 92 and ASHRAE methods 👇
🏗️ Project Overview
🏢 Total Levels: 32 (2B + G +28 +Roof)
🧱 Internal Stair Interface Wall Area: 66.38 m² per level
🚪 Door Size: 2.15 m (H) × 1.055 m (W) → 2.27 m² per door
➡️ Total Stair Doors: 32
🧮 Design Conditions
1️⃣ All doors closed: Maintain max. 50 Pa
2️⃣ Single door open: Maintain up to 50 Pa
3️⃣ Three doors open: Maintain min. 20 Pa (above 12.5 Pa)
🔸 Max door opening force: ≤ 133 N

⚙️ Step 1: Basic Data
• Total leakage area (A): to be derived below
• Each door opening area: 2.27 m² = 24.42 ft²
• Face velocity through open door: 1.0 m/s = 196.85 fpm
• Pressure conversion: 1 in.w.g. = 249.09 Pa

⚙️ Step 2: Formula (IP Method)
Q=2610×A×(ΔP)1/2
Where:
Q = airflow leakage (CFM)
A = total leakage area (ft²)
ΔP = pressure differential (in. H₂O)
🔍 Simplified Leakage Calculation (How A = 1.479 m²)
A = A_walls + A_doors_closed
1️⃣ Stairwell walls (A_walls):
Leakage ratio (LR) = 3.5×10⁻⁴ (loose construction)
Wall area per level = 66.38 m² × 32 levels = 2,124 m²
A_walls = 2,124 × 3.5×10⁻⁴ = 0.743 m²
2️⃣ Closed doors (A_doors_closed):
Single-leaf door leakage ≈ 0.023 m² per door × 32 = 0.736 m²
→ Total leakage area, A = 0.743 + 0.736 = 1.479 m² (15.92 ft²)
This area represents the total equivalent leakage the fan must overcome during pressurization.

⚙️ Step 3: Calculations
Case 1 – All doors closed (ΔP = 50 Pa = 0.2007 in.w.g.)
Q = 2610 × 15.92 × √0.2007 = 18,616 CFM (8.79 m³/s)
Case 2 – Single door open (ΔP = 50 Pa)
Door flow = 2.27 m² × 1 m/s = 4,807 CFM (2.27 m³/s)
Total airflow = 18,616 + 4,807 = 23,423 CFM (11.05 m³/s)
Case 3 – Three doors open (ΔP = 20 Pa = 0.0803 in.w.g.)
Q = 2610 × 15.92 × √0.0803 = 11,774 CFM (5.56 m³/s)
Total airflow = 11,774 + 3 × 4,807 = 26,195 CFM (12.36 m³/s)

✅ Governing Design Case
Three-door-open condition controls:
➡️ Q = 12.36 m³/s (≈ 26,200 CFM)
➡️ Maintain pressure between 20–50 Pa
💡 Engineering Insight
A well-engineered system isn’t just about airflow — it’s about balancing:
✔️ Leakage (walls + doors)
✔️ Pressure stability
✔️ Door opening forces
✔️ Fan & damper control logic
Proper VFD tuning, DP switch placement, and humidity control ensure that the system remains stable and compliant under all conditions .

🌍 Design Tip
In hot, humid GCC environments:
✅ Add humidity control at fan inlet
✅ Use normally closed motorized smoke damper for standby sealing
✅ Set pressure range Above 12.5 Pa–Below 50 Pa
✅ Ensure door opening ≤ 133 N per NFPA 92 / ASHRAE 62.1

🔧 Testing Procedure
System compliance is verified using calibrated instruments under different door conditions:
1️⃣Door Open Scenario – Check pressure differential & airflow.
2️⃣Doors Open Scenario – Ensure minimum pressure is maintained.
3️⃣Doors Open Scenario – Validate performance under maximum leakage condition.
🌬️ Air Velocity Requirement:
At any open door, minimum 1 m/s airflow is required to prevent smoke entry.

🔹 Pressurization Strategy (based on sprinkler protection, building height & occupancy)
Buildings Without Sprinklers
Staircase → Lobby: 5 Pa
Lobby → Corridor: 5 Pa
Corridor → Smoke Zone: 25 Pa
Staircase only: 25 Pa to smoke zone
Buildings With Sprinklers
Staircase → Lobby: 5 Pa
Lobby → Corridor: 5 Pa
Corridor → Smoke Zone: 12.5 Pa
Staircase only: 12.5 Pa to smoke zone

🔥 The choice between staircase-only pressurization or staircase + lobby/corridor pressurization depends on building height and occupancy type – ensuring compliance with NFPA 92 & ASHRAE while providing maximum life safety.