Upgrade from fuse??

Hi HVAC experts,

I know this may seem elementary to some of you, but I am new and still learning. This house was built in the mid 60’s and the furnace was replaced in the late 90’s. Here is the question, the furnace “shut off” has a fuse as seen in the one picture(sorry it is sideways). Would you call this out to be “upgraded”?? The house main has breakers. Not sure where to go with this one. Thanks in advance.


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I’ve seen alot of things like that–a single fuse for a particular appliance. Some AHJs have no problem with it and approve the installation. You might check with the local AHJ and see what they say.

I’ve seen many HVAC’s installed today have fuses. There seems to be installation instructions that require it, do convert them to breakers could violate warranties, and create dangerous situations.

Example: < 15amp breakers are uncommon, but you can smaller fuses, so you might be overrating the furnaces ocp.


Hi. Gregg;

I think the fuse is OK if it is rated for the wire and amperage.

I think you need to note that althought Duct Tape is spelled like Duct, it does not mean that it is for Duct joints. If you know what I mean.

Marcel :slight_smile: :slight_smile: :wink:

Don’t see any problem with fuses unless you are the home owner and the fuse blows and you don’t have a spare:) :slight_smile:

That is when you take your knife and peel the brass threads and bend it under the fuse and put it back it, right.??? Next to the best thing of a penny I believe. ha. ha. Seriously, hope no one does or tries this.

Marcel :wink: :slight_smile: :slight_smile: :slight_smile:

Yeah Marcell,

I am still trying to figure WHY they used that duct tape? I planned on calling it out, but couldn’t figure why they would do it.

I can tell you why they used the duct tape because there are no S’s and Drives below the tape where the transition joints are. Bad install:(

I love this message board, I learn every time I read a post. So I will ask. What do you mean by “S’s and Drives”? Are they like transition strips?

Greg: The two connecting joints of ducts have their ends rolled into the shape of the bottom 1/2 of a S and the drive is a strip of metal that slides down the two S’s holding the two sections of duct together and is air tight you don’t need any tape. That is the way all rectangular duct is suppose to be joined together.

Greg…are you talking about the fuse for the Emergency Shut off application?

And…something a wise 'old inspector told me

It isn’t important WHY the dipsh8t used the duct tape…what is important is that he shouldn’t have.

I planned on calling out the duct tape, but in the process learned about S’s and Drives. This message board is worth its weight (if it had any weight) in Gold :mrgreen:. But I still think you can use duct tape to fix glasses :bandit: :|.)

And yes on the emergency shut off Tony. How are you by the way? Hope your good buddy!


See pp 509 Here:



Thank you for that link!

It is most normal to see a switch fuse unit on a furnace. This is for a several reasons. One, as has already been mentioned, some central heating equipment calls specifically for fuse protection. Second, it would be normal to find these fuse units with 6 or 8 amp fuses installed, as per the heating equipment manufacturer’s specifications. Third, in days gone by, with very small fuse panels protecting homes, the fuse panels had a set of “subfeed lugs” marked “heater lugs”. These were lugs basicaly unfused terminals, and intended to go to future central heating equipment that may require an electrical connection, and required their own fuse protection at the central heating unit. As a result, these switch fuse units were in use from “way back”, and it became tradition for furnace installers to continue to use them to modern times, even if not otherwise expressly required. Fuses continue to provide superior protection over circuit breakers. It is people who install the wrong size fuse or bypass the fuse protection who create the hazards blamed on fuses.

Unless it’s “snap-lock”–which I hate.

Only familiar with snap lock for round pipe

Also, on another note, there is no drip leg installed. I realize this is a very old house, but I always make note of it.

Mine is on the back of the furnace. Possibly installed on the back or other side of furnace where we cant see it?