Separation distance calculator, IEC 62305-3
The simplified method of §6.3.2: one current-division coefficient over the whole length. Enter five inputs. The answer comes with every coefficient, the table it is read from, and the formula with your numbers in it.
A published worked example, shown until you calculate your own: LPS Class IV, concrete walls, Type A earthing in the dissimilar-resistance case, at the roof edge (l = 15 m). The source gives 1.2 m. How it reconciles →
Required separation distance
s = 1.200 m
s = ki · kc · l / km
= 0.04 × 1 × 15 m / 0.5
= 1.200 m
| ki | 0.04 | LPS class (Table 11). |
|---|---|---|
| kc | 1 | Type A earthing whose neighbouring electrode resistances are not shown to be within a factor of 2 of each other: k_c = 1 (Table 13, note). |
| km | 0.5 | What fills the gap (Table 12). |
| l | 15 m | As entered. |
IEC 62305-3:2024 §6.3.2, eq. (6); Tables 11, 12 and 13.
Every internal metal installation closer than s to the conductor must be bonded to it, or the distance increased.
This separation distance is not altitude-corrected. §6.3.2 requires a correction for an LPS installed at high elevations, following IEC 60071-2. Site elevation is not an input here and no correction has been applied, so where the site is at elevation, read §6.3.2 against it and adjust s accordingly.
What this calculator does not compute
- The tip of an air-termination rod. At the point of strike the current has not divided yet, so kc = 1 over the rod before the down conductor's kc applies (§6.3.1, eq. (5); Annex B, Figure B.4 a)). This page gives s at a point on the down-conductor run.
- The general method. Where ring conductors interconnect the down conductors, the current divides again at every ring, kc falls level by level, and s becomes a sum over segments (§6.3.1, eq. (5); Annex B, Figure B.3). It often gives a distance you can build to. The guide works through it →
- Where l runs. l is a path length along the conductor, not a straight line between two things, and bonding higher up the structure shortens it for everything above. Measure it on the layout.
On your own building
LPS Design computes s from your model: on the down-conductor run and at the tip of each air-termination rod, and by the general method where you choose it. The report prints each value with its derivation.