The 3 Things You will learn today are as follows.
- What are the Wiring Classes (A,B,X) defined in NFPA 72
- The World's top Fire & Gas Standard.
- Habits that make you world class.
The Brain [๐ง ]
Last week,
We learnt about
Addressable V/S Conventional F&G Communication System.
Nearly 4,000+ People shared that they found it valuable.
So thought to go a bit in-depth
On how to Wire them.
To Clear the Confusion.
The wiring methods that you will learn today (As per NFPA 72)
Can be used to Implement both Addressable or Conventional Communication System.
Addressable and Conventional describe:
How devices talk to the panel.
Class B, A and X describe:
How the wiring behaves when something goes wrong.
I am so excited to share this with you.
Let just begin the fun ....
Level 1: Class B Wiring
This is the simplest arrangement.
The cable leaves the panel.
Then passes via all devices.
It stops at the last device.
Advantages of Class A
โฐโโค Less cable.
โฐโโค Lower installation cost.
โฐโโค Easier installation and maintenance.
If it is so good ?
Then why is it that NFPA mentions other wiring methods
The Super Danger Risk
If the cable is cut.
Devices beyond the cut are lost.
Example:
Imagine 10 detectors connected on one circuit.
If the cable breaks after Detector No. 3:
- โ
Detector 1 works.
- โ
Detector 2 works.
- โ
Detector 3 works.
- โ Detector 4 to 10 are lost.
The panel reports a fault.
But a portion of your protection is gone.
Now What to do ?
If you know how we engineers think.
This is non-good.
We think smart ways to avoid fault.
Let's look at what engineers designing the NFPA standard though about this.
Level 2: Class A Wiring
So they created Class A.
The cable leaves the panel.
Passes through all devices.
Then returns back to the panel.
Creating a "loop".
Advantages
โฐโโค Higher reliability.
โฐโโค Better fault tolerance.
โฐโโค Survives a single cable break.
Now imagine the cable gets cut.
The panel can "still communicate" with devices from the opposite direction.
Result:
- Detection remains active.
- Devices remain operational.
- Panel reports a fault.
The system is damaged.
But it is still working.
That is the beauty of Class A.
BUT ......
A Big BUT ......
A Big Big BUT ......
What if ? (If there's a Short-Circuit)
What if the cable is not cut?
What if the conductors touch each other?
In simple words : called a short circuit.
A short circuit can be more severe than a simple cable break.
To solve this problem.
Engineers created Class X.
Think of Class X as:
Class A with body armor.
Class X uses short-circuit isolators.
These devices automatically separate the faulty section from the healthy section.
Result:
- Survives a cable break.
- Survives a short circuit.
- Most devices continue operating.
- Highest level of survivability possible.
This is why Class X is commonly used in critical facilities and below industries (Not for all but Critical Areas only).
- Refineries.
- LNG Plants.
- Offshore Platforms.
- Petrochemical Complexes.
Anywhere loss of detection cannot be tolerated.
I like to call it:
"The Special Forces version of Fire & Gas wiring.
Maybe the NFPA Engineering team was watching X-men hence they call this wiring Class X - Hope this makes it easier to remember" ๐
PS: Would you not want to select a Cable (For Fire & Gas) that works when there is an actual fire ?
If yes, then this Video here will help you learn the wiring selection.
The "Most Common" Mistake
Many Engineers think:
Addressable = Class A (Wrong)
Conventional = Class B (Wrong)
This is not correct
You can have:
- Conventional with Class B Wiring
- Conventional with Class A Wiring
- Addressable with Class B Wiring
- Addressable with Class A Wiring
- Addressable with Class X Wiring
These are separate design decisions.
Which One Should You Select?
Class B
Best when:
- Budget is important.
- The system is relatively small.
- Loss of a few devices during a fault is acceptable.
Class A
Best when:
- Reliability is important.
- Continuous detection is required.
- A single cable cut should not disable the system.
Class X
Best when:
โ Maximum reliability is required.
โ Harsh industrial environments exist.
โ Process safety is critical and failure is catastrophic.
โ Loss of detection is unacceptable and the Plant budget allows it.
A Simple Rule to Remember
Addressable vs Conventional = How devices talk.
But Wiring class is how devices are connected.
- Class B = A cable break can disable devices.
- Class A = Survives one cable break and still functions.
- Class X = Survives one cable break and one short circuit.
If you remember only these four lines.
You understand 90% of the topic.
PS: Would you not want to select a Cable (For Fire & Gas) that works when there is an actual fire ?
If yes, then this Video here will help you learn the wiring selection.
#2- Engineering Question
Corrosivity Class
If your outer environmental Corrosivity Class is lets say C5.
Will you select the same Corrosivity Class for Equipment's inside building as well ?
If you will select lower class ?
Then Client could question that the same Air (C5 corrosive air) will also come inside your control room.
How can you select low corrosivity class ?
How will you answer this question ?
Resume PDF were in 1990's since there was no Internet.
People still assume PDF is sufficient for Job Openings.
The best Job opportunities are not in newspapers anymore.
Your LinkedIn profile is your "New Resume".
Update your LinkedIn Bio like a Professional Engineer.
This is very under-rated.
But trust me...... You will reap the fruits in future.
The People from Exxon / Shell / Technip etc have always reached out to me on LinkedIn and never via Job Portal.
Your linkedin presence matters.
#4 - Your Feedback
How was todays email lesson?
Reply "1" - Found Super Valuable
Reply "2" - Somewhat valuable
Reply "3" - Needs Improvement
Until next week,
Happy Learning and Keep Smiling.
โAsad Shaikhโ
Your super passionate Instrumentation Friend!!
See you next Week!
โwww.Asad-Shaikh.comโ
PS : Here is the video to learn the Wiring Selection (Especially if you want your Fire and Gas Cable to work in Actual Fire)
โ