HVAC FUSE OR BREAKER

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Just wondering
Location
Hillsdale, NJ
Occupation
Contractor
Hi,
I see on name plate of ac condenser says " Min Fuse size 30A."
Does this mean no circuit breaker is allowed?
Thanks
 
Generally the entire circuit is protected by a CB and the disconnect is fused.
 
If the nameplate says “Maximum Over Current Protective Device” or specifically lists a fuse OR breaker size, then a breaker is OK. If it only lists a fuse, then it is only a fuse.
 
Min or Max is not my issue. I just gave an example.
OCPD can be fuse or breaker. Why it doesn't say "fuse only"? I'm aware of article 110. But, it still bothers me why I can't use a breaker.
 
IMO, It will be hard to do "fuse only" if your system is circuit breakers.
 
So I was skimming UL 1995 "Heating and Cooling Equipment" and I found the section (44.3(i)) that says the nameplate shall be marked with "Max Fuse" or "Max Ckt Brk" or "Max OCPD".

However, without reading the whole standard, I didn't find any language directing the use of one wording or the other in particular situations, or any testing portion that was specific to one labeling or another. I easily may have missed it, though, since you can't do a word search on the free on-line UL viewer. I did see Section 76 "Loading Test" which basically says that if the equipment comes with a cord and plug, you have to test it with regular fuses, and it if blows the regular fuses, label it "for use with time-delay fuses only" or something like that.

So if that's correct, that there's nothing in the standard that directs you when to use which of the language choices in 44.3(i), and none of the testing requirement depends on the language choice used, then I would think that would mean the choice of language is meaningless, and the "Max Fuses" language doesn't actually require fuses. But again, maybe I just missed part of the standard?

Cheers, Wayne
 
wwhitney said:
. . . the nameplate shall be marked with "Max Fuse" or "Max Ckt Brk" or "Max OCPD".

However, without reading the whole standard, I didn't find any language directing the use of one wording or the other in particular situations, or any testing portion that was specific to one labeling or another.
Click to expand...
Seems self-explanatory to me.

Max Fuse = fuse only
Max Ckt Brk = breaker only
Max OCPD = installer's option
 
In getting the equipment UL listed, it must be tested with the OCPD that the mfr wants to pay to list it with. Each destructive test is very expensive, in the neighborhood of $50k (last time I did it we paid $25k, but that was almost 30 years ago now). Testing with fuses is generally more likely to pass. But if you test it only with fuses, that’s what has to be used. To be able to say it’s OK to use breakers, it has to be tested and pass with breakers, so another $50k with less chance of success. So it becomes a financial decision based upon ROI (Return On Investment) and how the lack of CB rating might affect sales. So if they do not test it with breakers too, they have to say Fuses Only.
 
Jraef said:
In getting the equipment UL listed, it must be tested with the OCPD that the mfr wants to pay to list it with. Each destructive test is very expensive, in the neighborhood of $50k (last time I did it we paid $25k, but that was almost 30 years ago now). Testing with fuses is generally more likely to pass. But if you test it only with fuses, that’s what has to be used.
Click to expand...
The above is certainly logical, and so I skimmed UL 1995 some more. I didn't find anything that explicitly says the above, but the sections on short circuit testing are certainly consistent with the above.

I'm just surprised that UL 44.3(i) which says label it "A" or "B" or "C" doesn't go on to give explicit guidance as to when you should use "A" or "B" or "C". In my limited experience reading the standards, that's the way it usually reads: if such and such is true under clause XYZ, label it like so.

So is there a different UL standard that would apply more generally that would spell out what you described?

Thanks,
Wayne
 
Yes, but it is ALL ABOUT the short circuit testing. So you can’t dismiss that aspect just because it’s the “only” thing.

Before the equipment that has a control panel can be connected to a power source, it must be labeled with a “Short Circuit Current Rating” or SCCR and that SCCR must be equal to or greater than the Available Fault Current at the installation. The NEC outlines how the SCCR is determined, but it really boils down to being done as part of the UL (or NRTL) listing process as either being calculated from known test data or determined by testing. Each UL listing standard doesn’t lay out this requirement over and over, somewhere in there it will reference that any control panel will need to reference UL 508A, which is where the SCCR listing process is laid out.

If there is no testing or listing done, then they can apply a “courtesy” untested SCCR value of just 5kA. Considering that even the lowliest of residential panels is going to be rated at 10kA, it becomes a real problem to actually connect a 5kA rated piece of equipment. Some places may actually be 5kA or less at the point where it is connected, but that has to be proven to the AHJ.

So in that process of getting their SCCR listing, it is usually very simple to attain a higher level using fuses, as MOST power circuit components such as contactors, overload relays, terminal blocks etc., will have been series tested and listed with fuses, and once listed with a class of fuses, any brand of fuses in the same class is fine. It’s more difficult with circuit breakers because components must be series listed with SPECIFIC breakers. It’s an expensive test, so that means for the most part, the series listings will only exist when the breaker manufacturer is the same as the other components. So a Square D contactor is likely listed with a Sq. D breaker, but not with a Siemens breaker. That in itself is not really that difficult to accomplish with a little effort, but what it means is that if using circuit breakers, the OEM cannot just pick the cheapest components for their control panels by mixing brands. As a result, fuses win by default since they are brand-agnostic and that makes the listing process cheaper and easier for the OEM.

It MIGHT complicate things for the installing contractor, as you have pointed out, but the OEM doesn’t really care about us.
 
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