Criteria for externally fitted fuses in the input lines of a Lambda power supply.
Normally the internal fuse fitted in the power supply is rated approximately 20 - 25% greater than the maximum I/P current at low line and maximum load to overcome nuisance blowing.
The addition of external fusing is usually for one of the following reasons:
1. The supply is to be used in a medical application and therefore must have dual fusing.
2. To allow the customer to change fuses in the event of a problem because the unit fuse is NOT accessible. WARNING: If the fuse blows immediately after being replaced the Power Supply must be viewed as having a serious malfunction and must be returned to Lambda.
3. The Power Supply is to be connected to a non-polarised mains supply (where it is not certain which line is live).
It is important therefore, to consider the following when selecting fuses to be fitted externally to the Power Supply:
Any external fuse:
1. Should not be rated higher than the fuse fitted inside the power supply (the internal fuse rating is stated in the installation manual).
2. Should be a minimum of one rating below the fuse fitted in the Power Supply (see note 1)
3. Should have at least the same speed of response as the fuse fitted inside the power supply. e.g. FAST or SLOW acting.
4. Should have High Breaking Capacity.