Fuse Recommendation?


The Masso documentation recommends adding a 1 amp fuse between the 24 VDC power supply and Masso controller. The two types of fuse I am currently looking at are Blade Fuses and glass fuses (size: 5 x 20mm). The glass fuses can be either 'slow blow' or 'quick blow' fuses.

Am I on the right track here, are there better options available? Are quick blow better than slow blow fuses for this application?


"Quick Blow" is more appropriate.

"Slow Blow" is for situations where you are driving motors which have a high start current that only lasts for a couple of seconds. If the current remains high for 30 seconds or more then the fuse would blow.

What you are trying to protect is the circuit board power rail between the power in and the various "Power" and "GND" terminal blocks.

There is a recent forum article with a picture of the damage that can occur.

Glass vs Automotive blade fuses: Glass fuses are readily available in smaller current ratings, it can be challenging to find a blade fuse rated at 1A. For reference the MASSO G3 controller idling with keyboard and mouse attached draws 0.3A from a 12V power supply (expect half that with a 24V power supply).


@andrew-h - I don't have sufficient information to give a definitive answer. The following is an information dump so you can make your own decision.
  • The most probable failure mode that will cause an over-current incident is a short between a Masso positive terminal for accessories and ground.
  • The PCB track width on the Masso controller for power appears to be 2mm wide (see this photo)
  • On-line PCB trace width calculators allow 7 Amp continuous for a 40 C temperature rise (1 oz/ft copper cladding)
  • Circuit breakers have two parts:
    • Thermal breaker which is slow to respond (several minutes) but trips slightly above the rated current (could be as little as 110% of rating after 1 hour)
    • Coil/Electromagnet breaker which is nearly instantaneous, for a C curve this trips at 5 to 10 times rated current (B curve is 3.5 to 5 times, D curve is 10 to 14 times)

Then comes the question of when to use a fuse vs circuit breaker (there is a fair amount of justifications for both).

A circuit breaker is better suited for "overload" cases where equipment has been pushed to its limits while for "short circuit" protection a fuse is a better option as it forces (or at least tries) the end user to investigate the cause. For mains powered equipment circuit breakers are generally used to avoid exposure of live contacts. A circuit breaker is a fixed value whereas a fuse could be replaced with a larger rating compromising the integrity of the system.


Andrew H
Thank you for your very thorough reply. I will take my chances with the circuit breaker for now.

I got a test panel and some motors running over the weekend. So far so good.


I use the Phoenix CBMC a lot at my dayjob, they are a bit expensive but you can create 4 seperate 24VDC circuits with 1-4 amps and can save you from a lot of trouble. They protect against short circuit and overload. Murr mico is an alternative for te cbmc.