Cable Calculations in Cambridge

Accurate cable calculations are fundamental to the safety, reliability, and efficiency of any electrical installation. At Delta M&E, we offer specialist services to meticulously calculate and specify the correct cables for all power and distribution systems within your building services projects, ensuring full compliance with international and local wiring regulations (e.g., BS 7671/IET Wiring Regulations).

Why Accurate Cable Calculations Matter

Incorrect cable sizing can lead to serious issues, including:

• Safety Hazards: Undersized cables can overheat, leading to insulation failure, fire risk, and the tripping of protective devices.

• Energy Waste: Oversized cables increase capital cost, while undersized cables increase resistive losses, leading to high operational energy bills.

• System Failure: Excessive voltage drop can prevent critical equipment (like motors or IT systems) from operating correctly.

• Non-Compliance: Non-compliant installations face issues during inspection, potentially delaying project handover.

Our Cable Calculation Methodology

We employ industry-leading software and engineering principles to perform detailed calculations based on the specific parameters of your installation:

1. Load Assessment: Determining the accurate design current ($\boldsymbol{I_b}$) for every circuit based on connected and anticipated loads.

2. Cable Selection: Calculating the required current-carrying capacity ($\boldsymbol{I_z}$), taking into account:

   • Installation methods (e.g., buried in walls, clipped direct, in trunking).

   • Ambient and grouping temperatures.

   • Harmonic content and diversity factors.

3. Voltage Drop Verification: Ensuring the voltage drop from the source to the farthest point of the circuit remains within permissible regulatory limits to guarantee stable equipment operation.

4. Short-Circuit & Earth Fault Protection: Verifying that the selected protective device (e.g., circuit breaker or fuse) will disconnect the circuit quickly enough to prevent damage from short circuits and earth faults ($I_k$ and $Z_s$ calculations).

5. Compliance Reporting: Providing comprehensive, traceable documentation detailing every calculation and the rationale behind the selected cable type (e.g., PVC, XLPE, SWA), size, and protective device settings.

Delta M&E ensures your electrical distribution is not only compliant but also optimally sized for both performance and cost-effectiveness.

Protective Device Coordination

Effective protective device coordination (also known as Discrimination) is a specialist service we offer to ensure that in the event of an electrical fault (like a short circuit), only the protective device immediately upstream of the fault operates (trips).

Why Coordination is Critical

Poor coordination leads to nuisance tripping and system failure. If the main circuit breaker trips instead of a sub-circuit breaker for a fault on a minor load, the entire building or floor could lose power. Our service ensures selectivity, keeping critical services running and minimizing disruption.

Our Process

We use sophisticated software and analytical techniques to model your electrical system and determine the optimal settings for circuit breakers and fuses:

• Fault Analysis: Calculating the maximum and minimum fault currents at various points in the distribution network.

• Time-Current Curve Analysis: Creating a visual plot of the time-current characteristics for all devices (fuses, circuit breakers, relays) in series.

• Setting Optimisation: Adjusting the trip settings (time delays and current thresholds) to ensure a controlled and sequential tripping sequence.

• Documentation: Providing detailed reports and single-line diagrams that clearly define the settings and confirm full discrimination throughout the system.

Delta M&E guarantees that your electrical system is protected efficiently, reliably, and with maximum uptime, confining power outages to the smallest possible area.