A fusible resistor is a tailormade dual purpose component –
- In normal conditions it functions as resistor
- In high overload/fault conditions it acts as a fuse/safety device
There are basically two types of fusible resistors:
- Tailor made fusible resistor to suit a customers particular application
- Safety fusible resistor
(a) Tailor Made Resistors
In order to correctly design a Tailor made fusible resistor to suit the customers specific application, the following data is required
- Power rating in terms of watts.
- Resistance in ohms.
- Maximum continuous working voltage across the resistor , at which the resistor must continue to function.
- Fusing Voltage – The voltage at which the resistor must fuse or blow.
- Fusing time – The duration within which the resistor must blow or fuse on being subjected to the fusing voltage.
- Frequency of Power source , voltage waveform.
- Brief details of the application.
In certain cases the customer must be made aware that the compromise inherent in the trade off between resistive and fusing function make certain exact combinations not possible. Having said this that does not mean that it is not possible to make a functional fusible resistor capable of that particular application.
(b) Safety Version Resistors
At HTR, special “Safety versions” are available in our FRS series and HFW series for resistance values => 10R where the resistor will fuse instantaneously when Mains Voltage is applied with no flame or explosion.
The FRS series “Safety version” will fuse when mains voltage 220/240V is experienced and the HFW series “Safety version” will fuse when mains voltage of 110/120V is experienced.
These “Safety versions” are suffixed with the alphabet ‘S’ after the HTR type to signify that this are safety fusible resistors.