Fused disconnect or non- fused disconnect. When must it be fused?

zappy

Senior Member
Location
CA.
I noticed that some furnaces have the SSU fused switch, and some A/C units have the fused disconnect. So when do they or don't they need to be fused. Thank you for your help.
 

texie

Senior Member
I noticed that some furnaces have the SSU fused switch, and some A/C units have the fused disconnect. So when do they or don't they need to be fused. Thank you for your help.
If the installation instructions say to connect to, say, a 15 amp branch circuit you don't need it. If it says to provide a supplemental over curent device at XX amps you need it. But I can tell you from experience that many AHJ's just automatically require it, but I think it is erroneous as a blanket statement.
 

Gac66610

Senior Member
Location
Kansas
just did a skim through 440.11 - 14 (2011 code)
unless i missed it (i am sure i'll be corrected if i did) it only mentions "disconnecting mean" not "fused disconnecting means" as long as the disconnecting means is rated 115% of the name plate or branch circuit with ever is higher, and insight of
 

texie

Senior Member
If the installation instructions say to connect to, say, a 15 amp branch circuit you don't need it. If it says to provide a supplemental over curent device at XX amps you need it. But I can tell you from experience that many AHJ's just automatically require it, but I think it is erroneous as a blanket statement.
This was in reference to the first part of your question. For the A/C unit, if the data plate says "Max Fuse XXX" that means you must use fuses (not a HACR breaker) because that is the way the unit was tested and listed. Used to be common, but not so much anymore.
 

hurk27

Senior Member
I used to see the FSU's on oil furnaces mainly for the oil pump protection and when furnaces were allowed on any branch circuit, but now I thing it is just a carry over that someone would either use the same fsu when it was upgraded to a gas fired furnace or someone who was used to installing it that way just kept doing it.

As for AC condensers as texie said it is in the manufactures instruction and on the label that will tell you when you are required to use fuse protection, as as he said any more its a rare requirement, I don't think I have seen any in some time, Trane was one of them that still require fuse protection till a few years ago, (at least I think it was Trane)?
 

renosteinke

Senior Member
Location
NE Arkansas
We're hitting on a policy change at UL. No, I can't 'document it,' so you'll have to trust my memory.

UL tests things 'as submitted.' If an air conditioner came with a fused disconnect, UL had the nameplate specify 'maximum fuse,' and you were supposed to derive from that that there HAD to be a fuse somewhere in the circuit. Part of this was a carry-over from 'the old days,' where it was assued that the final overcurrent protection would be a fuse.

After all, UL maintained, it wasn't evaluated with a breaker.

Well, sometimes even UL can 'see the light.' UL finally figured out that the folks who make the air conditioners are not the ones supplying the disconnecting means- and there are plenty of disconnects out there that take breakers. Breakers are also readily available to match most any fuse size.

Thus, about five years ago, UL changes its' marking requirements to have the nameplate simply read 'max overcurrent protection.' Fuse or breaker, it doesn't matter.

Older equipment, with the older marking? While there might be a 'paperwork' violation, were one to use breakers alone on an air conditioner marked "Max Fuse," I would sleep perfectly fine with such a unit outside my window.
 

cowboyjwc

Moderator
Staff member
Location
Simi Valley, CA
HACR=heating air condition rated.

Let's say you run #8's on a 40A breaker out to the unit and the unit calls for maximum 35A Fuse/HACR breaker, then you would have to put in a fused disconnect. If you did it the way I said and it called for maximum 40A Fuse/HACR breaker, then you could use a non-fused switch.
 

rbalex

Moderator
Staff member
HACR=heating air condition rated.

Let's say you run #8's on a 40A breaker out to the unit and the unit calls for maximum 35A Fuse/HACR breaker, then you would have to put in a fused disconnect. If you did it the way I said and it called for maximum 40A Fuse/HACR breaker, then you could use a non-fused switch.
The "R" in HACR is Refrigeration

"HACR" = Heating/Air Conditioning/Refrigeration
 
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