Adiabatic Equation Calculator

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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