Adiabatic equation calculator for calculating the minimum cpc earth size mm

The Adiabatic Equation for calculating the cpc (circuit protective conductor) and earth minimum csa sizes for earthing conductors.

Adiabatic Equation Calculator Formula

t = Disconnection time (seconds)

k = Conductor k value (From BS 7671 tables)

la = Fault current (PEFC in Amps)

I² = la x la

Values of K obtained from the tables within BS 7671

- 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.

Disconnection times (t) are obtained from the maximum operating time/current characteristics tables within BS 7671

- 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

How to use the Adiabatic Equation

1) Input your voltage value

2) Input your Zs/Ze/Zdb value

3) Select a protective device

4) Select a protective device rating

5) Select a conductor type

6) Select a conductor material

7) Press calculate

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