Not sure about US/CA, but in Eurasia you can get low-amperage modular circuit breakers, like 2A ones. Was useful for example while playing with my tube oscilloscope having a dying power transformer.

Yush, we have lots of small circuit breakers here that are normally used for things like electrical control cabinets. 0.5A and 1A is not at all uncommon. I have used some C1A at work to protect smaller control power stuff, we also use it a lot at 24V.

Has anyone seen LPF ballasts like F40 single lamp go up in smoke?


Also whats the difference between the white fuses and the clear? The white ceramic ones are more expensive, and ive seen glass ones used in fluorescent before, including inside T8 ballasts ive opened.

Not really familiar with fusing so im very appreciative of everyone's thoughts on it, and I hope this thread serves to help others run their lights more safely. After all, an 80s advance ballast seeks modern, but is actually about 40 years old (i know its wild to realize its that long ago) lol

I've had a look at digikey and found what looks to be suitable for my needs, ill paste the links.

Fuseholder: https://www.digikey.ca/en/products/detail/littelfuse-inc/01500332H/3425489

Fuse 1a slow blow: https://www.digikey.ca/en/products/detail/bel-fuse-inc/3SB-1-R/1009830

Fuse 1.5a slow blow: https://www.digikey.ca/en/products/detail/eaton-electronics-division/BK-MDL-1-1-2-R/954317


I intend to use the 1A on single lamp F40 ballasts. The 1.5A for 2 lamp ballasts.

For reference, I linked the 3 choices I made earlier in this thread

I've seen these Phoenix Contact style DIN rail breakers used inside things such as control and automation cabinets and it seems like they come on fairly low current ratings as well.

For something a bit more compact, you can also get small panel mounted circuit breakers. You'll have to drill a 1/2" hole on the fixture to mount it though.

As a precaution I generally fuse most of my magnetic ballasts in use designed for 40w lamps. I used to only fuse the older equipment from the 1960s and earlier before thermal protection was mandatory but as the ballasts age I decided to just spend the additional cost and fuse all the other 40w magnetic ballasts as well. When you think about it, magnetic HPF 2x40w ballasts were last produced in 2010 so even the newest examples are 15 years old now. 

Has anyone seen LPF ballasts like F40 single lamp go up in smoke?


Also whats the difference between the white fuses and the clear? The white ceramic ones are more expensive, and ive seen glass ones used in fluorescent before, including inside T8 ballasts ive opened.

Not really familiar with fusing so im very appreciative of everyone's thoughts on it, and I hope this thread serves to help others run their lights more safely. After all, an 80s advance ballast seeks modern, but is actually about 40 years old (i know its wild to realize its that long ago) lol

To be fair I even have seen a 230V 36W ballast going in flames, but later it was so screwed up, so no idea if it was a choke itself or power factor capacitor fire. So nothing is impossible, but it is rare.

We said before, ceramic fuses are just better, better breaking capability and they do not crack when tripped. Obviously, you can tell a blown  glass fuse visually though. For single pieces purchase price difference is not significant, get better ones, but a large ballast manufacturer may save a little $$ using thousands of glass fuses. And for today's European style electronic ballasts, internal fuses are routinely completely omitted, specially formed zigzag traces on the circuit board are used instead.

Breaking capability means than in event of short circuit the current can vary depending on the wiring cross section and the distance to substation (wiring loop resistance). If the current exceeds the fuse breaking capability, it may shatter, projecting hot pieces outside, or even stay arcing both leading to a possible fire.

I selected the 250v 1.5A and 1A rated fuses, which are glass slow blow type.

My goal isn't to compensate for the mains breaker or wiring. I want to add an inline fuse to each ballast individually. The majority of my ballasts are Philips/Advance from around the Kool koil era, which are good performers but can fail by internal shorting.

The problem is, magnetic ballast fault is not black and white normal current into a hard short circuit, it could lead to virtually any current from zero to a short circuit. And ironically both extremes are pretty safe - zero (open circuit fault) means no currents at all, short circuit means immediate trip of the circuit breaker, so then no current either.
But when the fault current happens to become above 20A, the glass fuse isn't guaranteed to be able to break the circuit, at least without causing dangerous effects. It will burn an arc there and that arc causes the fuse holder to melt, even ignite something and a lot of hot fragment to fly out.

Yes, there is "upstream" breaker, but an 16A may still not trigger at all (due to allowed tolerances the 20A may not trigger it at all) and if it does trigger, it will take quite a long time (minutes or even 10's of minutes), way longer than the assembly would be able to tolerate the arcing where the glass fuse has been and long enough to allow it to e.g. start a fire.

To guarantee immediate trip of the upstream breaker (so do not allow sufficient time for the fuse to ignite something even when the current is above its breaking capability), the fault current must be above the "short circuit" electromagnetic trigger threshold. For typical wiring B165 breaker we are talking about 80A (you need to use the upper limit, as breaker components have tolerance), with C16 used at some places we are talking about 160A. So fault currents above that would cause immediate breaker trip so the thing won't be that dangerous, even when the fuse itself fails to break the current.

But when there does exist a range between the fuse current breaking capability (20A for the glass fuses) and the electromagnetic trigger of the upstream breaker (80A or so), you have a room for dangerous fault (20..80A) where the fuse itself becomes a fire starter and the current allowed to flow long enough to allow that condition to really do severe damage or fire.

If you use the ceramic fuse, up the 1500A of fault currents the fuse is guaranteed to break the circuit, but any current above the 80A (or even 160A with the C16) causes the breaker to break the current. So whatever fault current there will be, at least one of them will break it safely, there is even very comfortable overlap between them (the 80..1500A range is guaranteed to be interrupted by both devices).


I would also argue no fuse would be even safer than use of the glass one: Ballasts are usually mounted so the thing is able to handle quite a heat there. But an inline fuse may slip somewhere, where the things could get easily ignited once the fuse starts arcing and spitting white hot fragments.
Plus a fuse adds another few connections, moreover in questionable place, which can go bad and start arcing. And arcing faulty connections are one of the leading house fire starters when speaking about electrical faults, so adding more of them won't help.
Another aspect: Any fuse has rather wide tolerance of the blow current. If you add the square law between the current and the extra heat generated by the ballast, plus the tight margings the ballast are usually designed at, it is even question whether an overcurrent fuse will really make the ballast any safer than it is on its own.

In my view a nonresettable (or requiring some form of manual intervenbtion reset, so either a push butrton or at least cycling the power, but it won't reconnect on its own just by the ballast cooling down) thermal cutout on the ballast will yield to way better safety than just an overcurrent fuse. Not only it directly monitors the dangerous aspect of the ballast (its temperature), but its thermal coupling to the ballast means it will be placed in the area where eventual connection faults will be better contained.