Donald,
The numeric suffixes key Table 0.1 to Figure 5A:
* OP1 through OP6 are all OPERATIONAL INSULATION (clause 1.2.9.1) which does
not provide protection from electric shock.
* B1 through B8 are all BASIC INSULATION (clause 1.2.9.2) which provides one
level of protection from electric shock.
* S1 and S2 are both SUPPLEMENTARY INSULATION (clause 1.2.9.3) which provides a
second level of protection from electric shock.
* R1 through R4 are all REINFORCED INSULATION (clause 1.2.9.5), which is
equivalent to DOUBLE INSULATION (clause 1.2.9.4),
which consists of BASIC plus SUPPLEMENTARY INSULATION.
* S/R is SUPPLEMENTARY or REINFORCED INSULATION that meets Table 0.1 notes 3 &
4.
The insulation requirements cover not only the expected peak voltages, but also
the transient voltages that may appear on the different circuits. They also
cover the possibility of a pinhole or insufficient overlap of the insulation
permitting an arc to occur. Insulation requirements are mainly covered by IEC
950:
* Section 2.9 Clearances, creepage distances and distances through insulation.
* Section 5.3 Electric strength.
* Section 5.4 Abnormal operating and fault conditions.
* Annex F (normative) Measurement of creepage distances and clearances.
Clearance is distance through the air. If an arc occurs, and then stops, the
air is assumed to completely return to normal. Creepage is distance over the
surface of an insulator. If an arc occurs and then stops there can be damage
that leaves the surface conductive or otherwise more prone to arc again. The
required creepage distances are a function of:
* Transient voltages.
* Pollution class-- how much crud can build up on a surface & its likelihood of
getting wet.
* Comparative Tracking Index (CTI)-- how badly insulator gets damaged by an
arc.
John Barnes Advisory
Engineer
Lexmark International
donald%hq.rossvideo....@interlock.lexmark.com on 04/12/99 11:11:56 AM
Please respond to donald%hq.rossvideo....@interlock.lexmark.com
To: emc-pstc%majordomo.ieee....@interlock.lexmark.com
cc: (bcc: John Barnes/Lex/Lexmark)
Subject: IEC 950 Insulation Requirements
I have just received a copy of the IEC 950 standard and after
reviewing the insulation requirements outlined in section 2.2.6 I
have a question that the group maybe able to shed some light on.
The question relates to the two table 0.1 and Table 5 which is
intended to give examples for the application of the various
insulation requirements.
In the two table it appears there are numerical reference to the
different categories of insulation, for example OP1, OP2, B1, B2
etc. I have reviewed the entire standard and I can not find any other
reference other then these tables to these numerical references of
the different categories of insulation.
Could some one provide some insight in the the intent and use of
these tables? Are the numerical references simply to identify
various circuits to circuit situations and which of the five categories
of insulation applies?
Thanks before hand
Donald McElheran
Product Engineering
Ross Video Ltd.
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