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।

Circuits and Pathways in NFPA 72

 Circuits and Pathways in NFPA 72

In Greece, over 2500 years ago, near the small town of Marathon, there was a battle. After the battle, one of the winning Athenians ran all the way from Marathon to Athens carrying the news.

He ran along a path.

Nowadays, the message could be carried by a person running along a narrow mountain road, a verbal telephone call, a news story over the microwave towers, a data signal carried over fiber optics, Etc.; so may choices.

The NFPA would consider all of these to be communication paths. The paths are no longer just copper wires, but wireless radio waves are also used, Ethernet data cables are also used, and fiber optic cables are also used in fire alarm systems.

Because of all the different types of communication paths for fire alarm systems being used nowadays, the NFPA is addressing them all differently than they did in the past.

Beginning with the 2010 edition of NFPA 72, National Fire Alarm and Signalling Code, all of the “styles” of circuits were deleted, and four “classes” were added. A new chapter, Circuits and Pathways, was added during the reorganization of this code. In the past, the styles only described the operation during an alarm or fault condition for initiating device circuits, notification appliance circuits and signalling line circuits. NFPA 72, National Fire Alarm and Signalling Code, defines the performance of fire alarm circuit and pathways in Chapter 12. While the terms “circuit” and “pathway” are often used interchangeably, they are different. The styles of initiating device circuits (IDC), notification appliance circuits (NAC) and signalling line circuits (SLC) were eliminated, and four new classes were added. The intent was to add information about all circuits and pathways, not just IDCs, NACs and SLCs. A circuit is defined in Chapter 3 as “either means of providing power or a connection path between locations”, while a pathway is “any circuit, conductor, optic fiber, radio carrier or other means connecting two or more location.” Basically, a circuit is copper, while a pathway can be copper or any other type of connection.

There are three things considered by the NFPA with the carrying of the signals on the fire alarm system paths:

1.    Supervision - The method of self-checking for faults - the end-of-line resistor continuity check and handshaking using data signals are two common methods

2.    Redundancy - the continued operation of the whole fire alarm system, or a second path to carry signals around a problem is redundancy - an open wire or wire-to-wire short are some of the problems addressed with redundancy

3.    Protection from damage - conduit is one common method used to protect the path

Pathway performance is defined in Section 12.3, using Class A, B, C, D, E, N, or X based on the circuit performance. NFPA 72 does not determine what class is used on a particular pathway, but rather defines the performance of the pathway. The specification, designer, AHJ determine what class of pathway is used. NFPA 72, Chapter 24, “Emergency Communications Systems,” Section 24.3.14 is the only place I have found any requirements for survivability. Survivability for fire alarm pathways is typically only required for systems employing partial evacuation or relocation. Since building and fire codes require systems to be installed in accordance with NFPA 72, they do not have specific provisions for survivability. The Chapter 24 technical committee is proposing important changes to the 2022 edition of the code.

A pathway classification describes more than that. When describing a Class, the NFPA is concerned with is Reliability, Fixability, and Survivability.

Reliability - The NFPA wants to make sure the fire alarm system continues to work in the long run.

Fixability - The NFPA wants to make sure any problems that do occur are found and fixed on a timely basis.

Survivability - The NFPA wants to make sure the fire alarm system will continue to work when fixing it on a timely basis isn't good enough.

In a fire alarm system, there are (at the moment) seven Classes of communication and power infrastructure (paths):

• Class A
• Class B
• Class C
• Class D
• Class E
• Class N
• Class X

The letters after the word Class are not shown in the order of reliability or importance; the letters after the word Class are only the name of the particular classification.

Chapter 12 describes each class. Here are some examples of each you may find useful.

 

Class A

1.    This will include a redundant signal path - If the path is interrupted, the system feeds both ends of the paths so there are now two paths; the original outgoing path which is now cut shorter, and the return path which is now being used as an outgoing path

2.    If wires are used, a wire-to-wire short may shut down the whole path

3.    Both conventional and addressable systems fit into this

4.    Both the IDC (Initiating Device Circuit) and the NAC (Notification Appliance Circuit) fit into this

5.    The panel shows a trouble signal when there is a problem

Class B

1.    There is no redundant path

2.    Any device beyond a break won't work

3.    If wires are used, a wire-to-wire short may shut down the whole path

4.    Both conventional addressable systems fit into this

5.    Both IDC and NAC fit into this

6.    The panel shows a trouble signal when there is a problem

Class C

1.    Uses Handshaking (equivalent to an I'm OK signal) to supervise the path

2.    Can have more than one pathway

3.    The panel shows a trouble signal when there is a problem 

 Examples:

1.    Signals from the fire panel to the monitoring company

2.    The use of IP (Internet Protocol), whether it's local communications or over the Internet

3.    The communicators over the telephone lines that are still in use

 

Class D

1.    Fail-Safe operation - If there is a failure, the device that is controlled by the fire alarm system goes into fire mode

2.    No trouble shows on the panel

Prior to the 2010 edition of NFPA 72, Class D pathways simply referred to as “fail-safe.” A typical application for a Class D pathway is a powered relay used for door release or fan control. Since the relay is powered in normal condition, operation of the relay is accomplished by removing power by control panel operation, or by a failure of the circuit.

 Example of a device going into fire mode when a wire breaks or a signal is lost:

1.    The fire door closes

2.    Emergency door locks release

3.    The damper closes

4.    The fans shut down

 

Class E

Class E pathways are not monitored for integrity and are used in applications where supervision is not required. Section 12.6 of NFPA 72 defines applications where monitoring for integrity is not required. Some examples include interconnection between equipment in an enclosure, interconnection between control equipment within 20 feet of each other where conductors are protected by conduit, and interconnection wiring of a stationary computer to its keyboard, monitor, or mouse where the wiring does not exceed 8 feet.

Class N

This is basically local Ethernet, Token Ring, or other network or IP infrastructure.

1.    Unless a single device is connected, or the path is short (less than 20 feet) and really protected in something like conduit, two pathways are used

2.    These pathways are verified through end to end communication, like data handshaking

3.    Loss of communication between end points on any path show a trouble signal on the panel

4.    Problems with one pathway won't affect the other pathway

Class X

1.    This will include a redundant signal path. Like Class A, if the path is interrupted, the system feeds both ends of the circuit so there are two circuits, the original outgoing path which is now cut shorter, and the return path which is now being used as an outgoing path

2.    Devices on both sides of an open will continue to communicate with the panel

3.    If wires are used, devices on both sides of a wire-to-wire short will continue to communicate with the panel (basically the short has to be isolated on both sides of the short)

4.    The panel shows a trouble signal when there is a problem

In order to be proper classified as Class A or Class X, the outgoing and return path routes for both Class A and Class X have to be separated by a certain distance; the two paths cannot be inside the same conduit, for instance.

Many designers and contractors do not include survivable cable or fire-rated enclosures in their designs for in-building fire emergency voice/alarm communications systems (EVACS) wiring as required in the code—or at least not until the authority having jurisdiction enforces the requirement because a designer missed it the first time around. This may be due in part to some confusion over where survivability is required in the first place. Pathway survivability is not required for all EVACS; it is only required where occupants will remain in the building during an emergency (i.e., relocation or partial evacuation). The intent is to ensure that we can still get subsequent instructions to those occupants if the situation worsens. For those systems where pathway survivability is required, it does not necessarily need to be applied throughout the entire system; it must be applied only where the circuit runs through multiple notification zones, so that a fire in one notification zone doesn’t impair the ability to communicate with occupants in another. Additionally, the current edition of NFPA 72 permits the installer to use Level 1, Level 2, or Level 3, meaning that a sprinklered building (i.e., Level 1 pathway survivability) does not require the use of fire-resistant cabling or an enclosure. No wonder a contractor or installer might not include fire-resistive cable in an initial design.

The reason behind survivability requirements is to maintain the operational reliability of the EVACS during a fire. Pathway survivability for emergency communications systems (including EVACS) is covered in 24.3.14; Section 12.4.5 includes the definition of Level 4 pathway survivability.

The previous requirements for survivability said only that the cable had to be two-hour-rated or installed in a two-hour-rated enclosure. The technical committee changed the requirement so that it is now related to the fire resistance rating of the building construction. This relationship is important because the listing of two-hour fire-rated cable is required to be attached to a concrete wall or floor assembly, constructed with a minimum of two-hour rating or as otherwise identified by the UL FHIT systems assembly.

Additionally, as stated in the Annex A of the code, “installing a pathway survivability Level 2 or Level 3 in a building that is constructed with less than two-hour construction would not be installed within the listing of the product.”

For building construction with a fire-resistance rating of one hour, but less than two hours, the technical committee has proposed a new Level 4 pathway survivability.

With the more common use of timber construction for larger buildings, the expectation is these buildings would be classified as one-hour fire rated. Two-hour cable, as it is presently listed, would not be allowed when using the proposed Level 4 wiring or with wiring that meets the proposed separation requirements. That prohibition is due to the concern that a fire causing an open, ground-fault, or short-circuit fault on the communication and control circuits between rooms or enclosures could affect the operation of the in-building fire emergency voice/alarm control equipment within these rooms or enclosures.

It is well known that the insulation on fire alarm cabling can melt when exposed to heat and flames, causing the conductors to short circuit. When this condition occurs, it is possible for an entire signaling line circuit to fail, seriously impacting communication and control circuits. To help guard against these kinds of catastrophic failures, the proposed code would require the use of fault circuit isolators to ensure that the entire circuit is not disabled during a fire.

These proposed changes to the 2022 code would provide guidance in Annex A to assist designers, contractors, and AHJs in the proper separation of circuits as well as the location of fault circuit isolators to ensure both compliance with the code and a high degree of operational reliability. It is important to remember that for fire alarm systems designed for relocation and partial evacuation, communication must remain operational on all floors other than the fire floor during a fire. The primary fire protection goal is reliable communication during the fire.