Page 9 - Fuse link Catalogue

UTILISATION CATEGORIES ‘gG’ AND ‘gM’

Utilisation Categories ‘gG’ and ‘gM’ A class gM fuse link has a dual basis of current rating, the
Some of the fuse link types used in some European smaller one of which is its continuous rating (In), whilst
Countries have only partial range breaking capacity the larger one is its rating with respect to its time/current
(ie, they interrupt short circuit fault currents, but are characteristics (Ich) and is thus an indication of its ability
unable to interrupt overload currents safely). To to withstand motor starting surges.
distinguish these types from the much more widely The two ratings are separated by an ‘M’ in list
used general purpose fuse links, the concept of numbers, eg, 32M63. A class gG fuse link has only
‘utilisation category’ has been introduced in the one, continuous rating.
international standard IEC269. BS88:Part 2:1988 specifies a time/current zone for
Since AS2005 & BS88 are based upon IEC269, it each current rating within which its published
includes the same utilisation classes, each of which is time/current characteristics must lie. The time/ current
defined by a two letter code. The first letter indicates zone for a gM type is defined according to its larger
the breaking range of the fuse link, as follows: current rating, and thus the characteristics of a 32M63
rating must fall within the same zone as a 63A class
‘g’ full range breaking capacity fuse link. gG rating.
‘a’ partial range breaking capacity fuse link. Class gM fuse links exist only to enable economies to
be achieved in the size of equipment used in motor
The second letter indicates utilisation category, as circuits, eg, 32M63 fuse links can be fitted in 32A fuse
follows: holders in a 15kW, 415V, direct on line motor circuit,
instead of 63A gG fuse links in 63A fuse holders,
‘G’ Fuse link for general application, including the because although the motor starting surge required the
protection of motor circuits. use of fuse links with 63A time/current characteristics,
‘M’ Fuse link for protection of motor circuits. the motor FLC is less than 32A (about 28A).
The standards combine these letters to recognise three It should therefore be noted that gM fuse links
classes ie, gG, gM and aM. complement the standard range of ratings, ie, gG
All type ‘T’ fuse links are classified as either gG or gM, types are also used in many motor circuits, with gM
and so have a full range breaking capacity. ratings applied only when there is an economic
advantage to be gained from their use.

IPD INDUSTRIAL PRODUCTS Phone: 1300 556 601 www.ipdgroup.com.au
7