Adiabatic Equation Calculator

– CPC EARTHING SIZER –

Don’t give yourself a headache, let the app do the math for you!

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Adiabatic Calculator

Description

CPC EARTH SIZE CALCULATOR

The Adiabatic Equation Calculator is for calculating the absolute minimum permitted circuit protective conductor size, or for verifying an existing protective conductor is adequately sized.

CALCULATING PROTECTIVE CONDUCTOR CSA

The current edition (at time of writing) of BS 7671 states:
The cross-sectional area of each protective conductor, other than a protective bonding conductor, shall be:

  1. (i) Calculated in accordance with regulation 543.1.3 or
  2. (ii) Selected in accordance with regulation 543.1.4

This Adiabatic Equation Calculator App is designed to assist in satisfying option (i) above.

- Calculating the Adiabatic Equation need not be daunting, get the app!

Features

CALCULATES
  • Conductor mm²
  • la = Fault current
  • I² = Fault current²
  • k = Conductor k value
  • t = Disconnection time

App Reviews

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Adiabatic Equation Formula

Adiabatic Calculator

SIMPLE TO USE

The Adiabatic Equation Calculator couldn’t be any easier to use, just enter your voltage and Zs values, then select your choice from the following drop down options.

Options:

  1. Protective Device
  2. Protective Device Rating
  3. Protective Conductor Type
  4. Protective Conductor Material

Then tap the “Calculate” button to get the results, its that simple!

Protective Device

DEVICE TYPE | DEVICE RATING

We have pre-programmed in the operating time / current characteristics for the protective device circuit breakers, fuses and RCBO’s so you don’t need to look them up.

Protective Devices:

  • MCB’s
  • RCBO’s
  • Fuses

Device Ratings:

  • Depends on selected protective device

Protective Conductor

TYPE | MATERIAL

Select your choice of protective conductor type, then conductor material. The options available for protective conductor material depends on the selected conductor type.

Types of Protective Conductors:

  • Single cable not bunched
  • Incorporated in a cable or bunched with cables
  • Sheath or armour of cable
  • Steel conduit or trunking

Protective Conductor Material:

  • Copper
  • Aluminium
  • Steel
  • Lead

Protective Conductor k Values:

Conductor k values have already been set, your protective conductor type and conductor material selections will automatically set the values of k for you.

Adiabatic Calculation

RESULTS

Once you have completed the quick steps mentioned above, tap the calculate button to get the results.

In addition to calculating the protective conductor size the Adiabatic Equation calculator also displays all the other relevant calculation results associated with the final calculation of the earth / earthing conductor / protective conductor size.

Adiabatic Equation Calculation Results

Resulting Parameters:

  • Conductor size mm²
  • la
  • k
  • t
Adiabatic Equation Formula
Adiabatic Equation Results.

FAQ's

FREQUENTLY ASKED QUESTIONS

What is the minimum cpc size?

The minimum csa of a cpc can be selected from the appropriate table in BS 7671 or can be calculated using the adiabatic equation for a specific circuit, this will determine the actual minimum csa of a cpc required for the specific circuit in question.

BS 7671 Earthing Conductor Sizes

BS 7671 earthing conductor sizes can be found in the current edition of the IET wiring regulations and Guidance Note 8: Earthing & Bonding.

Protective Conductor k Values

BS 7671 Conductor k Value Tables:

Table 54.2 – Conductor not incorporated in a cable and not bunched with cables.
Table 54.3 – Conductor incorporated in a cable or bunched with cables.
Table 54.4 – Sheath or armour of a cable.
Table 54.5 – Steel conduit or trunking.

How to use the Adiabatic Equation Calculator

To calculate the minimum protective conductor (cpc) size using the Adiabatic Equation is fairly simple.

The required tables, times and k factors are already programmed and will auto calculate the values depending on your selections.

  1. Enter a measured voltage value
  2. Enter a measured Zs value
  3. Select a protective device
  4. Select a protective device rating
  5. Select a conductor type
  6. Select a conductor material
  7. Tap Calculate

The Adiabatic Equation Calculator will then calculate PEFC, conductor k value, disconnection time (s) and conductor size mm for you.

Adiabatic Equation Example

Here we demonstrate an adiabatic equation example, we will explain how the adiabatic equation calculator works.

1. Enter a measured voltage value Uo = 230V.

The voltage value needs to be a measured value in-order to carry out an accurate calculation. Uo is the voltage to earth.

2. Enter a measured Zs value = 0.26 Ohms.

The Zs value needs to be a measured value in-order to carry out an accurate calculation. Zs is the earth (fault) loop impedance.

3. Select a protective device type = BS EN 60898 Type B.

4. Select a protective device rating = 10 Amps.

5. Select a conductor type = Single cable not bunched.

6. Select a conductor material = Copper – 70°C Thermoplastic.

Adiabatic Calculation Results:

la (PEFC) = 884.62
I² = 782552.54
k = 143
t (s) = 0.1
Conductor csa = 1.956 mm²

As 1.956 mm is not a standard cable size the next available larger cable size shall be used.

la is the prospective earth fault current, I² is the fault current squared, k is the conductor k value, t is the disconnection time in seconds and conductor csa is the cpc earthing conductor size in millimetres.

Maximum Operating Time Current Characteristic Tables

BS 7671 Maximum Operating Time Current Characteristic Tables:

Fig 3A2 (a,b) – BS 3036 Semi-enclosed Fuse
Fig 3A3 – (a,b) – BS 88-2.2
Fig 3A4 – BS EN 60898 / 61009-1 MCB/RCBO Type B
Fig 3A5 – BS EN 60898 / 61009-1 MCB/RCBO Type C
Fig 3A6 – BS EN 60898 / 61009-1 MCB/RCBO Type D
BS 1361 Fuse

Tablets and Phones

OPTIMISED FOR MULTIPLE SCREEN SIZES

Adiabatic Equation Calculator is optimised to work on all screen sizes and resolutions from the iPhone 5 up to large tablets such as the iPad Pro and all Android devices.

Features:

  • Easy to use
  • Preset data
  • Quick and instant results
  • Dedicated support team
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