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For IEC 62368-1, can I conduct single fault testing in lieu of providing a fire enclosure like was allowed for in IEC 60950-1 for some constructions?

You asked if you can conduct single fault testing in lieu of providing a fire enclosure like was allowed for in IEC 60950-1 for some constructions under IEC 62368-1?

The short answer is, no - in most cases not exclusively.

Here is the longer answer.

Clause 6 of IEC 62368-1 requires safeguards to be in place against fire under normal, abnormal and single fault conditions.

Per Clause 6, typically, one safeguard (or safeguard system) is provided to protect under normal and abnormal operating conditions, and another safeguard (or safeguard system) is provided to protect under single fault conditions.

For normal and abnormal operating conditions, the typical basic safeguard consists of limiting temperatures of materials within the equipment to 90% or less of the spontaneous ignition temperature limit of the material.

However, for single fault conditions, manufacturers have the choice of two paths: (a) Reduce Likelihood of Ignition, or (b) Control of Fire Spread. 

(In larger systems it is possible to use both paths for different parts of the system.)

In 60950-1, the Reduce the Likelihood of Ignition path is parallel to the ‘simulated fault test’ option (its Method 2); the Control of Fire Spread path is parallel to the ‘fire enclosure’ option (Method 1).

However, in 62368-1 there is one area that is causing some confusion (compared to 60950-1), mainly the application of the Reduce the Likelihood of Ignition path. 

Based on 60950-1 experience, it is easy to assume a performance test program exclusively of single fault testing can be used to satisfy this Reduce the Likelihood of Ignition path (as was allowed for to a certain degree in 60950-1).  While single fault testing certainly is the primary performance aspect of this 62368-1 safeguard, in PS2 and PS3 circuits there remains (per 6.4.3.2 Ed 2/6.4.3.1 Ed 3) a minimum separation requirement (distance or barrier) from both arcing & resistive PIS (potential ignition sources), which in some cases could require a barrier, flame testing per Annex S, or preselected V-1 or V-0 material, in addition to single fault testing.

Sub-clause 6.4.3.2 (6.4.3.1/Ed 3) of IEC TR 62368-2 (rationale document) provides the associated rationale, primarily that prescribed use of a fire cone (from 60065 experience) is more reliable than single fault testing for predicting risk of fire - single fault testing is not considered by IEC TC108 as wholly representative. Therefore, IEC TC108 included additional material and construction requirements (fuel control area or keep out area) in addition to single fault testing.

It is important to be aware of this difference between 60950-1 and 62368-1 for this performance-based option in lieu of fire enclosure.

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