When overload or short-circuit protection may be omitted (§433.3/§434.3)

The §433 overload protection guide and the §434 short-circuit protection guide both cover the general rule: every circuit must be protected against overload and against short-circuit. Both articles end with the same caveat: exceptional cases exist where the standard deliberately does not require this. This article covers those exceptions themselves — §433.3 (overload) and §434.3 (short-circuit).

Why an exception can sometimes be safer than the general rule

This sounds contradictory — how can omitting protection be safer? The answer: in a small number of specific circuits, unexpected disconnection itself is the greater hazard, greater than the risk of the overload or short-circuit the protection would otherwise prevent.

§433.3 — when overload protection may be omitted

The standard lists, among others, the following circuit categories where unexpected disconnection would create danger or damage:

Excitation circuits of rotating machines — an unintended loss of excitation current can create a far greater hazard than the overload itself.
Supply circuits of lifting magnets — a lifting magnet that unexpectedly loses power while carrying a load is a direct fall hazard.
Secondary circuits of current transformers — an open secondary loop of a current transformer under load can generate dangerously high voltage; disconnecting via a protective device in this circuit is therefore precisely what should be avoided.
Supply circuits of fire-extinguishing installations.
Supply circuits of burglar-alarm and gas-alarm installations and comparable safety systems.

§434.3 — when short-circuit protection may be omitted

Omitting short-circuit protection requires two conditions to be met simultaneously:

The wiring is installed in such a way that the risk of a short-circuit is reduced to a minimum (for example through mechanical protection, a short, fixed connection without branches, or double insulation).
The wiring is not installed near combustible material.

A commonly cited practical example: the conductors connecting generators, transformers, rectifiers and accumulator batteries to the associated switchboard, provided both conditions above are met.

What these exceptions are — and are not

Note: these are not blanket permissions to omit a protective device "because it doesn't seem necessary". Both articles name specific, limited circuit types with a demonstrable reason why disconnection itself is more dangerous than the absence of protection — and §434.3 additionally requires two cumulative conditions, not a free choice.

The difference from the general rule of §433/§434 is therefore not that the cable needs less protection, but that the form of protection shifts: from a switching protective device to constructive measures (mechanical protection, functional need for uninterrupted supply) that manage the underlying risk in a different way.

Practical relevance

When assessing an installation where a circuit appears to lack overload or short-circuit protection, it should not automatically be treated as a fault. First establish whether the circuit falls under one of the specific exception categories of §433.3/§434.3, and whether the associated conditions (for §434.3: minimisation of short-circuit risk and distance from combustible material) are actually met. If not, the absence of protection remains a valid finding.

Common mistakes

Treating any circuit without dedicated protection as a fault without checking whether it falls under a valid exception of §433.3/§434.3.
Checking only one condition of §434.3 and forgetting the other — the two conditions (minimising short-circuit risk and distance from combustible material) must both be met simultaneously, not just one of them.
Applying the exception more broadly than the standard allows — for example leaving an ordinary final circuit unprotected "because it will never overload", when this does not fall under any of the listed exception categories.
Confusing §433.3 and §434.3 — one exception concerns overload (based on the danger of unexpected disconnection), the other short-circuit (based on minimising the risk itself); these are two separate tests with their own conditions.