Direct Answer

Voltage drop in ELV circuits is calculated from cable length, load current and conductor resistance. In this example, the estimated voltage drop is 6.78 V (28.23%). Final cable selection should be verified using manufacturer data and applicable installation standards.

At a Glance

Resource ID	EC-070
Cable Length (one-way)	L | 80 | m
Load Current	I | 3.5 | A
Cable Resistance	R | 0.0121 | Ω/m
Supply Voltage	Vs | 24 | V
Source detail	Refer to Technical Content
Source detail	Refer to Technical Content
Source detail	Refer to Technical Content

Calculation Method & Worked Example

Voltage Drop = 2 × L × I × R

Percentage Drop = (Voltage Drop ÷ Supply Voltage) × 100

Voltage Drop = 2 × 80 × 3.5 × 0.0121 = 6.78 V

Percentage Drop = (6.78 ÷ 24) × 100 = 28.23%

Preliminary engineering result as stated in the source document.

Applicable Standards Listed in the Source

IEC 60364	Low-voltage electrical installations
IEC 60228	Conductors of insulated cables
BS 7671	Electrical Installations
Manufacturer Data	Device voltage tolerance

Technical Content

1. Purpose

To estimate the voltage drop in an ELV power circuit supplying field devices and verify that the operating voltage remains within acceptable limits.

2. Engineering Objective

To calculate the preliminary voltage drop for cable selection and power supply sizing. Final verification shall be based on manufacturer requirements and detailed circuit design.

3. Applicable Standards

Standards and references are reproduced as listed in the source document.

4. Design Inputs

Cable Length (one-way) = L = 80 = m; Load Current = I = 3.5 = A; Cable Resistance = R = 0.0121 = Ω/m; Supply Voltage = Vs = 24 = V

5. Assumptions

Single-phase DC ELV circuit with return conductor included. Cable resistance is assumed at operating temperature.

6. Formula(s)

Voltage Drop = 2 × L × I × R
Percentage Drop = (Voltage Drop ÷ Supply Voltage) × 100

Voltage Drop = 2 × L × I × R
Percentage Drop = (Voltage Drop ÷ Supply Voltage) × 100

Final result: refer to the source calculation and engineering output.

7. Variables Explained

L = One-way cable length; I = Load current; R = Cable resistance; Vs = Supply voltage.

8. Step-by-Step Calculation

Voltage Drop = 2 × 80 × 3.5 × 0.0121 = 6.78 V
Percentage Drop = (6.78 ÷ 24) × 100 = 28.23%

Voltage Drop = 2 × 80 × 3.5 × 0.0121 = 6.78 V
Percentage Drop = (6.78 ÷ 24) × 100 = 28.23%

Calculation result: refer to the engineering output below.

9. Worked Engineering Example

A 24 V ELV circuit with an 80 m cable run carrying 3.5 A experiences an estimated voltage drop of 6.78 V (28.23%).

10. Engineering Output

Calculated Voltage Drop: 6.78 V
Percentage Voltage Drop: 28.23%

Calculated Voltage Drop: 6.78 V
Percentage Voltage Drop: 28.23%

Refer to the source calculation.

Calculated Voltage Drop: 6.78 V
Percentage Voltage Drop: 28.23%

11. Design Considerations

Verify minimum operating voltage, cable size, ambient temperature, grouping factors and future load growth.

12. Common Design Mistakes

Ignoring return conductor length, undersized cables, incorrect resistance values and excessive circuit loading.

13. Practical Site Notes

Measure voltage at the farthest device during commissioning to confirm acceptable operating voltage.

14. Limitations

This is a preliminary engineering calculation. Final verification shall use actual cable data and manufacturer requirements.

15. Related Engineering Systems

Fire Alarm, Access Control, CCTV, IBMS Controllers, Power Supplies.

16. Cross References

Related FAQ: ELV Cable Sizing
Related White Paper: WP-005
Related Case Study: CS-005
Related Engineering Diagram: ED-070

Related White Paper: as identified in the source document.

Related Case Study: as identified in the source document.

Related Engineering Diagram: as identified in the source document.

17. SEO Meta Title

Voltage Drop Calculation for ELV Power Circuits | EC-070

18. SEO Meta Description

Engineering calculation for estimating voltage drop in ELV power circuits.

19. URL Slug

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20. Keywords (15)

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21. AI Search Summary

Voltage drop in ELV circuits is calculated from cable length, load current and conductor resistance. In this example, the estimated voltage drop is 6.78 V (28.23%). Final cable selection should be verified using manufacturer data and applicable installation standards.

Frequently Asked Questions

How is the preliminary detector quantity calculated?

The calculation method and result are stated in the source document and reproduced in this website-ready version.

What is the result for this example?

A 24 V ELV circuit with an 80 m cable run carrying 3.5 A experiences an estimated voltage drop of 6.78 V (28.23%).

Does this establish the final detector layout?

This is a preliminary engineering calculation. Final verification shall use actual cable data and manufacturer requirements.

What design factors should be checked?

Verify minimum operating voltage, cable size, ambient temperature, grouping factors and future load growth.

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