Why Fast Acting, Ceramic Tube Fuses they are not HRC replacement for DMM?

[Kiriakos GR]

Fast Acting, Ceramic Tube Fuses these are found within several HH DMM, of low price and at medium price ones.
But can we replace a HRC DMM Fuse by using Ceramic Tube Fuse instead?
The answer is no, for technical reasons.


This rabbit hole starts from a factor named as Typical Cold. Resistance (mOhms) per fuse type, and next rabbit hole this is named as Typical Voltage Drop (mV).

According data found at ASTM (Fuses brand), the typical 1000V DC/AC, 6x30mm 400mA (ceramic) for DMM.
This has typical Cold. Resistance of 1845 (mOhms)
This causes Typical Voltage Drop of 860 (mV)

From the end of SIBA, 400mA this mention Typical Voltage Drop of 650 (mV).
This translates to similar manufacturing process.

Now and according my testing at larger in size HRC Fuses for DMM, these 440mA Fuses they have half or less typical Cold Resistance.
(Bussmann documentation this mention use of silver at their manufacturing process.)
https://www.ittsb.eu/forum/index.php?topic=1380.0

How we should filter this pack of information?
Here is how, at low current measurements, one DMM designed supporting high precision measurements, onboard electronics design this also take under consideration Typical Voltage Drop caused by fuse resistance as this be a plain resistor.
This apply to high precision bench-top DMM 6 1/2 counts, and also for HH DMM categorized as high-end.

From the other hand, HH DMM these using Ceramic Tube Fuse, at AC and DC Current ranges, these has less tight measuring accuracy specification.
But the most important is, that their circuitry, this is designed to include a higher in resistance fuse.

In conclusion:
For the ones even thinking if an Ceramic Tube Fuse, it can become a replacement of HRC Fuses for DMM?
They better stop thinking of it.