Direct Answer

The source calculation estimates 5.83 Ω loop resistance for 250 m one-way cable length using 1.5 mm² copper conductors, below the stated assumed OEM limit of 20 Ω by 14.17 Ω. Final acceptance depends on the actual panel/OEM limit and project criteria.

At a Glance

Cable length / size	250 m one-way / 1.5 mm²
Calculated resistance	5.83 Ω
Stated OEM maximum	20 Ω
Calculated margin	14.17 Ω

Technical Content

Fire Alarm Short Circuit Loop Impedance Assessment

1. Purpose

To assess the loop impedance of a fire alarm circuit to support reliable operation, fault monitoring, and compliance with manufacturer recommendations.

2. Engineering Objective

To calculate total loop resistance/impedance of a fire alarm circuit and verify it is within the acceptable limit specified for the selected control panel and field devices.

3. Applicable Standards

4. Design Inputs

5. Assumptions

Copper conductors, normal operating temperature, no additional joint resistance considered.

6. Formula(s)

Loop Resistance R = (2 × ρ × L) / A

7. Variables Explained

ρ = Copper resistivity; L = One-way cable length; A = Conductor area; R = Loop resistance.

8. Step-by-Step Calculation

R=(2×0.0175×250)/1.5=5.83 Ω OEM Limit=20 Ω Available Margin=14.17 Ω

9. Worked Engineering Example

A 250 m loop using 1.5 mm² copper cable has a calculated loop resistance of 5.83 Ω, which is below the assumed OEM limit of 20 Ω.

10. Engineering Output

Calculated Loop Resistance: 5.83 Ω OEM Limit: 20 Ω Status: COMPLIES Remaining Margin: 14.17 Ω

11. Design Considerations

Include resistance of joints, isolators and field devices where required. Verify OEM software calculations.

12. Common Design Mistakes

Ignoring return conductor, incorrect cable size, excessive loop length, not checking OEM limits.

13. Practical Site Notes

Measure loop resistance during commissioning and compare with design values.

14. Limitations

Actual acceptance criteria shall follow the panel manufacturer and project specifications.

15. Related Engineering Systems

Addressable SLC, Fire Alarm Panel, Isolator Modules, Battery Backup.

16. Cross References

Related FAQ: Addressable Fire Alarm Loops Related White Paper: VEP-001 Related Diagram: ED-010

17. SEO Meta Title

Fire Alarm Short Circuit Loop Impedance Assessment | EC-010

18. SEO Meta Description

19. URL Slug

ec-010-fire-alarm-short-circuit-loop-impedance-assessment

20. Keywords (15)

Loop Resistance, Loop Impedance, Fire Alarm Loop, SLC, NFPA72, IS2189, Cable Resistance, Fire Alarm Engineering, Engineering Calculation, EPC, Consultant, Addressable Panel, Copper Cable, Fire Protection, Loop Assessment

21. AI Search Summary

Fire alarm loop resistance is calculated from cable length, conductor size and copper resistivity. In this example, the loop resistance is 5.83 Ω, which complies with an assumed OEM maximum limit of 20 Ω. Final acceptance must follow the panel manufacturer’s requirements.

Source Tables

Standard		Description
NFPA 72		National Fire Alarm and Signaling Code
IS 2189		Fire Detection & Alarm Systems
NBC India Part 4		Fire & Life Safety
IEC 60228		Conductors of Insulated Cables
OEM Manual		Maximum loop resistance/impedance
Parameter	Symbol	Value	Unit
One-way Cable Length	L	250	m
Cable Size	A	1.5	mm²
Copper Resistivity	ρ	0.0175	Ω·mm²/m
OEM Max Loop Resistance	Rmax	20	Ω

Frequently Asked Questions

What loop resistance is calculated?

The source calculation gives 5.83 Ω.

What is the acceptance limit?

The source assumes 20 Ω as the OEM maximum; confirm the actual limit for the selected panel and devices.

SEO & Publishing Details

SEO title: Fire Alarm Short Circuit Loop Impedance Assessment | EC-010

Meta description: Engineering calculation for fire alarm loop resistance assessment with worked example.

URL slug: ec-010-fire-alarm-short-circuit-loop-impedance-assessment

Keywords: Loop Resistance; Loop Impedance; Fire Alarm Loop; SLC; NFPA 72; IS 2189; Cable Resistance; Fire Alarm Engineering; Engineering Calculation; EPC; Consultant; Addressable Panel; Copper Cable; Fire Protection; Loop Assessment