Fuse drawer

Protection against electric shock (against direct contact with live parts) for fuseholders. The assessment of the protection against electric shock assumes that the fuse holder is properly assembled, installed, and operated as in normal use, e.g. on the front panel of the equipment. IEC 60127-6 and EN 60127-6 divides into three categories:

Protection against contact with live parts is an important aspect when dealing with electrical connecting devices. Both your customers and your servicing engineers will appreciate the greatest possible protection against accidental contact with live parts – something which can easily happen as a result of inappropriate use, or during servicing or repair work.

In particular, our “shock-safe”, “extra-safe fuse-drawers” and “protective covers” precautions are effective ways of protecting against accidental contact when using the power entry modules.

The extra-safe versions of shock-safe power entry modules are now available.

They are thus also able to satisfy requirements of the following standard: IEC 60601-1 (medical equipments).

The design engineer of electrical equipment is responsible for its safety and functioning to humans, animals and real values. Above all, it is his task to make sure that the state of the art as well as the valid national and international standards and regulations be observed.

In view of the safety of electrical equipment the selection of the most suitable fuseholder is of great importance. Among other parameters, one has to make sure that the maximum admissible power acceptances and temperatures defined by the manufacturer are followed. Differing definitions and requirements in the most important standards for fuse-links and fuseholders are time and again origin for the incorrect selection of fuseholders.

To equate the rated current of a fuse-link with the rated current of the fuseholder, may, especially at higher currents, cause high, not admissible temperatures, when the influence of the power dissipation in the contacts of the fuseholder was not taken into consideration.

For a correct selection the following influence factors depending on the application and mounting method, have to be followed:

1. Rated power dissipation of the suitable fuse-link.
2. Admissible power acceptance, operating current and temperatures of the suitable fuseholder.
3. Differing ambient air temperature outside and inside of the equipment.
4. Electrical load alternation
5. Long time (> 500 h) operation with load > 0.7 In.n
6. Heat dissipation/cooling and ventilation. Heat influence of adjacent components.
7. Length and cross section of the connecting wire.

The value of current assigned by the manufacturer of the fuseholder and to which the rated power acceptance is referred. 

Power dissipation at rated current. See Product Catalog for fuses. 

The rated power acceptance of a fuseholder is determined by a standardised testing procedure according to IEC 60127-6. It is intended to be the power dissipation caused by the inserted dummy fuse-link at the rated current of the fuseholder and at an ambient air temperature of TA1= TA2 = 23 °C (over a long period). During this test the following temperatures must not be exceeded on the surface of the fuseholder:

NOTES:
1) When the fuse-holder is properly assembled, installed and operated as in normal use, e.g. on the front panel of equipment.
2) The maximum allowable temperature of the used insulating materials corresponds to the Relative Temperature Index (RTI) according to IEC 60216-1 or UL 746 B.

Illustration of temperatures experienced

TA1 = ambient air temperature, surrounding the equipment A1
TA2 = ambient air temperature in the equipment A2
TS1 = temperature of accessible parts on fuseholder surface S1
TS2 = temperature of inaccessible parts on fuseholder surface S2

This correlation is demonstrated by derating curves.

I =operating current of the fuseholder
In =rated current of the fuseholder

The derating curves demonstrate the admissible power acceptance of a fuseholder depending on the ambient air temperature TA1 for the following fuseholder operating currents: I << In, I = 0,7 · In and I = 1,0 · In. This power acceptance corresponds to the max. admissible power dissipation of a fuse-link.

A calculation example can be looked up in the technical information for fuses.