Max fuse ratings

[David C. Macy]

I have been observing numerous exterior air conditioners where the max fuse rating at the data plate is smaller than than whats int he shut off box.

.....example max fuse is 35 Amps at data plate and then the exterior shut off box has 60 Amp fuses.

Would you report this as a repair or a safety concern?

What are the potential problems that this may cause.

Thanks

Dave

[Jay Schwartz]

David,

Check out the archives. There was a thread not to long ago about it. I am sure the 60 AMP is overfused, but inside the disconnect box, there should be a rating based on wire size that the manufacturer will approve.

Good Luck.

[Dean Call]

The fuses in the service disconnect are not necessarily normally there to protect the line.
Sometimes the disconnect has no fuses at all or has blanks in the place of fuses, both would be considered a non fused disonnect.
The circuit breaker that supplies power to the A/C line is the one that counts.

Some cities do require fused disconnects but many do not.
In my area, only non fused disconnects are used on condensing units.

Having said that, if they were going to use a fused disconnect, why not use the proper size fuses in it if possible even though the fuses are not needed.

Maybe the installer only had a 60 amp disconect in the truck.

[Mark Reagin]

One reason to disallow such breaker sizing is because it will void the manufacturers warranty.

[David P. Valley]

The fuses are simply used as a shut-off at this point. I don't call out overfusing unless there is improper protection on the supply side.

[Rick J. Hinck]

I am constantly reporting overfusing in the service panel as compared to the max. fuse called out on the outdoor spec plate. Anyone else seeing a lot of this?

Rick

[jrupert]

The disconnect is not the protection for the system and in most electric codes the size only needs to be larger then the draw of the unit. Over sizing is not an issue since the protection is provided by the breaker in the main electrical box.

Some boxes are fused others have a breaker and others junt a pull bar, to stop the flow of electricity, the intended purpose is so that the service person has easy method to kill the power. 60amp is often used here because it is actually cheaper then 30 amp boxes, one size fits all so less to stock, etc

The 60 amp disconnect will not disallow any manufacture warranty, if this would happed it would again be based on the breaker I the main box.

[pdacey]

Originally Posted by jrupert

Over sizing is not an issue since the protection is provided by the breaker in the main electrical box.

I find breakers in the main panel that are over/under sized just about every day. It is usually the result of the AC being replaced and the tech. not going back to the panel to check for the required breaker size.

[Michael W. Gault]

I see 10 over (compressor to panel) all the time, prevents nuisance trips and the AHJ's here allow it.

[Paul W. Abernathy]

Originally Posted by dmacy

I have been observing numerous exterior air conditioners where the max fuse rating at the data plate is smaller than than whats int he shut off box.

.....example max fuse is 35 Amps at data plate and then the exterior shut off box has 60 Amp fuses.

Would you report this as a repair or a safety concern?

What are the potential problems that this may cause.

Thanks

Dave

Ok...great stuff here guys...but I need to remind you....if the nameplate says FUSED on it...does not say circuit breaker then the disconnect has to be fuse protected...............


Now....their are ways to do this........just so you all know this...
1.) If the AC unit says FUSED and does not say breaker it MUST be fuse protected...either AT the disconnect, at the panel.....either way it MUSt be fuse protected...

Now....you can have a circuit breaker panel....and have a fused AC unit outside that is old and says fuse and no mention of circuit breaker...well you know then the FUSES either have to be in the disconnect and RATED as the nameplate states... or at a disconnect that is fused and fed from the circuit breaker panel....either way it would have to be fuse protected.

Now...you can also have a circuit breaker disconnect....BUT then you must still FUSE protect it........either again at the disconnect or at a disconnect next to the panel with fuses in it...being FED from the existing circuit breaker panel....

Hope that is easy to understand........any questions just refer to the UL Electrical Appliance and Utilization Equipment Directory which states the above information....and we all know it overrides the code in requirement.

[dspencer]

Those are 60amp rated boxs....meaning they handle up to 60amps and can be used on any circuit under 60amps.

[dspencer]

These are also used on radon systems.

[Paul W. Abernathy]

Remember....it is VERY important to know what the Data Plate dictates.....yes, the enclosure is rated as such..60 AMPS...so it can handle up to 60A applications.....however rating OCPD and Name Plate Ratings are the focus here.

[jrupert]

Great point that Paul makes, all the A/C’s I install do call out what the max fuse size is……but I have never been turned down for any HVAC inspection in central Ohio when the protection is a breaker in the main box regardless of the disconnect, we normally use a non fused box. Think I will run this past the local inspectors this week to see what they have to say.

I do find that when the out door unit is replaced the breaker is often over looked, the older breaker is over sized and some times 10+ years old. The HVAC guys just don’t want to tackle the electrical side properly.

Interestingly enough here this error may result because the city allows (overlooks?) the HVAC guys to handle the wiring from the main box to the unit on change outs with out having an electrical license, no electrical permit and no electrical inspections on simple jobs. New construction does require an electrician but again, no fuse just breakers.

[Paul W. Abernathy]

Yep.......just remember if the HVAC outside unit says Fused and does not mention circuit breakers...it MUST be fused protected.....somewhere..either at the main panel or at the disconnect.

As I said before....you can have a circuit breaker panel....feeding a fused disconnect next the panel and the feeding a circuit breaker or pull out at the unit outside....BUT their has to be fuse protection in their somewhere....

You would be surprised how confused this makes local AHJ's...but it is clear in the code..if they read it correctly.