INGRESS PROTECTION CHART

The ingress Protection (IP) for all low voltage enclosures up to 1000 V a.c. and 1500 V d.c. is defined in identical fashion by the standards BSEN 60529 - IEC 529 it comprises the letters IP followed by two character numerals:

The first character numeral - protection against solid substances indicates the degree of protection provided by the enclosure with respect to persons, also to the equiptment inside the enclosure.

DEGREE OF PROTECTION OF ENCLOSURES

The degree of protection provided by an enclosure is indicated by the IP code in the following way -

For example, an enclosure with an index IP20 would provide protection against solid bodies greater than 12mm but offer no protection against water; however an index IP31 would provide protection against solid bodies greater than 2.5mm and in addition against vertically dripping water.

Sometimes the letter 'X' is used in place of the first or second numeral to indicate that tests have not been made or are not considered relevant. For example IP4X provides protection against a 1mm probe but has not been tested for the ingress of water.

SHORT-CIRCUIT WITHSTAND

The British Standard requires the manufacturer to state the following:

For a panel having incoming device, offering over current protection e.g. fuses

• The maximum allowable value of prospective short-circuit current at the terminals of the incoming fuse.

For a panelboard where a short-circuit protective device is not incorporated in the incoming unit (Main Isolator or Terminals) -

• The rated short-time withstand current
• The rated peak withstand current
• The withstand time period if different from one second

Internal Seperation

The internal seperation of assemblies is described in the British Standard BS EN 60439 and is concerned with three requirements, which can be met by the suitable arrangement of barriers or partitions.

• Protection against contact with live parts belonging to adjacent functional units.
• Limitations of the possibility of initiating and spreading of arcing faults
• Prevention of the passage of solid foreign bodies from one unit of an assembly unit.

Form numbers are given to some typical forms of seperation -

Form 1 - No seperation
Form 2 - Seperation of bus-bars from the functional units
Form 3 - Seperation of bus-bars from the functional units and seperation of all functional units from one to another, but not their outgoing terminals.
Form 4 - Seperation of bus-bars from the functional units and seperation of all functional units from one another including their outgoing terminals.

Fuse - Cobination Units - BS EN 60947-3

Many people are attracted to fuse-combination units by their simplicity in application and their reliability in operation. They are particularly usefull for use on very high prospective fault level systems where the high energy limiting characteristic of the HRC fuse can be effectively utilised. In the past fuse-combination untis came in two forms -

However, in order to keep the selection of fuse-combination untits as simple as possible, Switchgear Systems LTD. offer a range of high performance double break switch switch-fuses, which also satisfy the isolating requirement of the British standard. These are correctly shown as and defined as a Switch-Disconnector-Fuse.

Switch disconnectors and switch disconnector fuses - BSEN 60947-3. A range of switch disconnectors (isolators) and switch disconnector fuses are available for use on lower current ratings from 20A to 125A, these switches are rated at AC-22 and provide a cost effective alternative to the fuse combination switch especially where the utilisation catagory AC-23 is not required. ie; mixed resistive and inductive loads.

Utilisation categories

utilisation categories are not new but they are important because they help the designer or specifier identify the correct unit for a particular application.

The designation of the utilisation category i made up up of three parts:

(1) The prefix ac or dc, which indicates the nature of the current.
(2) The two digit number, which indicates the type of application the unit is suitable for -

20 Connecting and disconnecting under no-load.
21 Switching of resistive loads.
22 Switching of mixed resistive and inductive loads.
23 Switching of highly inductive loads.
(3) The suffix A or B, which indicates whether the unit is suitable for frequent or infrequent operation.

A - frequent operation
B - infrequent operation

For example a fuse-combination unit feeding a 400V ac of mixed resistive and inductive loads which would need to be operated frequently would require a minimum utilisation category of AC-22A.

If the load was highly inductive, i.e. motor loads, then the minimum utilisation category would be AC-23A

Generally, category AC-23 does not cover the switching of capacitors. For this application it is essential that full details are presented to Switchgear Systems LTD. who will then specify the correct device.

Motor Power Circuit Protection

Fuse-combination units can be used very effectively for motor power circuit protection, the energy limiting HRC fuse offering very good protection to its associated starter. Category AC-23A should be specified for this duty. Special motor circuit protection fuse links are available which eliminate the need to fit a larger bodied fuse just to take care of the starting current of the motor.

The protection of motor power circuits should not be confused with the direct switching of a single motor. If a fuse-combination unit is required to perform this functionthen it must comply with the requirements of Appendix A of BS EN 60947-3 which makes provision for different utilisation categories for this application.