# AC disconnect - fused or not?



## Roadhouse (Oct 16, 2010)

I don't know about in Cali but here in Houston, Tx hvac supply houses mainly sell non fused disconnects and all I or anyone installs. I'm an hvac technician, btw. It's a service disconnect, not a protection. That's the breaker and to code.


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## erics37 (May 7, 2009)

Nameplate on the HVAC unit should tell you the maximum fuse/circuit breaker size required. If your breaker matches that then you're fine, no fuses necessary.

On the other hand, a fused disconnect is an extra bit of redundancy. Especially helpful if the breaker size specified on the HVAC unit is an oddball.


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## Jlarson (Jun 28, 2009)

We only use fused ones when actually necessary. So almost never these days as most every unit can be protected by a breaker or fuses.


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## tates1882 (Sep 3, 2010)

Under the 2011 nec if the nameplate calls out max fuse/breaker then either will work but if it says max fuse size then the ocpd has to be a fuse. Falls into art 100.


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## frenchelectrican (Mar 15, 2007)

tates1882 said:


> Under the 2011 nec if the nameplate calls out max fuse/breaker then either will work but if it says max fuse size then the ocpd has to be a fuse. Falls into art 100.


The main thing is look at the nameplate if that did mention fuse only then there is no other way around with it.

But if mention both so it can go either way.

Merci,
Marc


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## greenlee (Feb 7, 2012)

I noticed that you say to go with the maximum fuse size. Why would the name plate state minimum and maximum fuse or breaker size if the minimum would'nt be a compliant install?


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## BBQ (Nov 16, 2010)

greenlee said:


> I noticed that you say to go with the maximum fuse size. Why would the name plate state minimum and maximum fuse or breaker size if the minimum would'nt be a compliant install?


You can use the minimum, but it might trip or blow.

The great thing is you can base your wire size on the minimum but base your fuse or breaker on the maximum.

So if you have a unit with an MCA of 15 amps and a maximum over current protection of 30 you can run 14 AWG and still use a 30 amp breaker or fuse. 

The code allows this to make sure the starting inrush does not trip the breaker. 

Motor loads have the same kind of rules.


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## Jlarson (Jun 28, 2009)

BBQ said:


> You can use the minimum, but it might trip or blow.
> 
> The great thing is you can base your wire size on the minimum but base your fuse or breaker on the maximum.
> 
> ...


Wonder how many posts will pop up saying this is wrong and the wire has to match the breaker and the code is only a minimum and voltage drop and blah blah freaking blah.... :laughing: :laughing:


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## Pete m. (Nov 19, 2011)

Yea... but what about voltage drop and the wire having to match the breaker???? Anyone ever consider that?:laughing::laughing::jester:

Pete


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## Meadow (Jan 14, 2011)

joe cool said:


> Well?
> Homeowner acting as own GC is doing permitted minor remodel including AC. Asks me to do the smokes and replace the AC disconnect. No AC or AC contractor present so I put in a non-fused disconnect. AC is fed by (existing) dedicated 10/2 line on (existing) 30/2 breaker and looks sufficiently protected to me. AC contractor now shows up and is bitching that it isn't fused. Did I do wrong? I offered to replace it (I can replace the guts without replacing the box) but HO wants to wait and see what the inspector says. But I want to know now.
> Thanks.


No, as long as the breaker matches the circuit protection requirements on the AC plate. 

Most fusing I see is on Commercial jobs where different setups are taking place.


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## joe cool (Jun 4, 2009)

#10 Cu and 30A/2 breaker. AC guy wanted 30A fused disco (must be time delay fuse says he!) but homeowner who pulled own permit believes in me and wants to see inspector prove otherwise.
0ur inspectors in Sacramento County are an effing joke so this could go any way.


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## Meadow (Jan 14, 2011)

joe cool said:


> #10 Cu and 30A/2 breaker. AC guy wanted 30A fused disco (must be time delay fuse says he!) but homeowner who pulled own permit believes in me and wants to see inspector prove otherwise.
> 0ur inspectors in Sacramento County are an effing joke so this could go any way.


 
Ask your AC guy for a code reference. If he cant find one and starts bluffing his ego ask him if he is an electrician. 

Bottom line people like that do tick me off when they start going outside of their tech area. If I was there Id showering him with information than tear him a new one. 


As for the inspector he has to give a code reference if he decides to red tag it.


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## Jlarson (Jun 28, 2009)

joe cool said:


> #10 Cu and 30A/2 breaker. AC guy wanted 30A fused disco (must be time delay fuse says he!) but homeowner who pulled own permit believes in me and wants to see inspector prove otherwise.
> 0ur inspectors in Sacramento County are an effing joke so this could go any way.


Tell the ac guy to go knock some tin and stop worrying about electrical.


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## Arc'n'Spark (Jul 21, 2011)

Jlarson said:


> Tell the ac guy to go knock some tin and stop worrying about electrical.


That's funny coming from a damn dirty roofer. :jester:


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## emeralddragon (10 mo ago)

you most certainly cannotE="BBQ, post: 1011753, member: 16226"]
You can use the minimum, but it might trip or blow.

The great thing is you can base your wire size on the minimum but base your fuse or breaker on the maximum.

So if you have a unit with an MCA of 15 amps and a maximum over current protection of 30 you can run 14 AWG and still use a 30 amp breaker or fuse.

The code allows this to make sure the starting inrush does not trip the breaker.

Motor loads have the same kind of rules.
[/QUOTE]
you most certainly cannot. you must use slow blow fuses ir adjustable breakers in that case. the only purpose of the breaker is to protect the wire, not the unit. in your example the wire would melt and never trip the breaker. hope you dont wire many homes


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## Almost Retired (Sep 14, 2021)

emeralddragon said:


> you most certainly cannotE="BBQ, post: 1011753, member: 16226"]
> You can use the minimum, but it might trip or blow.
> 
> The great thing is you can base your wire size on the minimum but base your fuse or breaker on the maximum.
> ...


you most certainly cannot. you must use slow blow fuses ir adjustable breakers in that case. the only purpose of the breaker is to protect the wire, not the unit. in your example the wire would melt and never trip the breaker. hope you dont wire many homes
[/QUOTE]

can you edit that post and clarify a bit please ?


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## micromind (Aug 11, 2007)

emeralddragon said:


> you most certainly cannotE="BBQ, post: 1011753, member: 16226"]
> You can use the minimum, but it might trip or blow.
> 
> The great thing is you can base your wire size on the minimum but base your fuse or breaker on the maximum.
> ...


you most certainly cannot. you must use slow blow fuses ir adjustable breakers in that case. the only purpose of the breaker is to protect the wire, not the unit. in your example the wire would melt and never trip the breaker. hope you dont wire many homes
[/QUOTE]

With motors and HVAC units, the breaker protects against short circuits and ground faults only. Overcurrent protection of the wire is provided by the HVAC unit or motor overloads. 

Lets say you are the inspector and you're looking at a job I did where I installed a 40 amp single pole breaker and #14 THHN to supply a 1 HP single phase motor operating at 115 volts. Would you fail the job? If so, provide code references. 

Also, provide a code reference that requires the use of allow blow fuses or adjustable circuit breakers.


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## Almost Retired (Sep 14, 2021)

not to mention that thread is 9 yrs old
im sure they fixed it by now


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