My boss is under the impression that disconnects for air conditioners have to be fused. Does anyone know a code reference that requires this? If not, is there still a good reason to use fuses? Does commercial vs. residential make a difference?
Historically, there was a problem created by the wording printed on the nameplates attached to the installed equipment. The label listed maximum fuse size, which was taken to mean that a circuit breaker wasn't enough to protect the equipment, when the AHJ considered 110.3(B). Manufacturers have changed the wording on the nameplate to not describe one form of OCP (over current protection) over another.
If the branch circuit OCP at the panel is approved to protect the AC, the disconnect at the AC unit could be just a pullout (non-OCP) or unfused switch.
Re: fusible disconnects#84318 03/17/0310:34 AM03/17/0310:34 AM
The AC nameplate must be in agreement with the choice of the hardware the electrician installs to supply and protect it.
It is interesting to note that even one type of fuse compared to another behaves differently, and the same is true when comparing circuit breakers. 440.52(A)(3) states: A fuse or inverse time circuit breaker responsive to motor current . . . shall have sufficient time delay to permit the motor-compressor to start and accelerate its load
For Steve66's question with respect to residential vs. commercial, the same is true in both cases.
Am I missing something here? I have installed non-overload protected disconnects for AC's and heat pumps lot's of times.
I am talking about the disconnect that is required to be at the condensor outside the home. Usually I just install on of those pull out type disconnects that you flip over. The overload protection comes from the breaker in the panel.
Re: fusible disconnects#84322 03/18/0311:42 AM03/18/0311:42 AM
What Iwire and I are talking about is that the nameplate on the side of the metal enclosure of the condensor will call out whether only fuses, only HACR type circuit breakers or either can be used to provide the overcurrent protection for the machine. We always read the nameplate to get the numbers for the min. circuit ampacity and the maximum overcurrent protection (OCP). . .the wording on that label may vary from model to model when it describes the OCP types the manufacturer allows.
Much of the time, as you are describing, the condensing unit will allow protection by HACR type circuit breaker, and that breaker can be in the service center with a simple unfused pull out disconnect outside at the AC condensor. However, the manufacturers wording on the AC condensor must agree with what you do. Read the nameplate closely to comply with 110.3(B).
The 2002 NEC Handbook has a great example (Exhibit 440.1) of the possible hookups after 440.21.
You almost have to be psychic sometimes... If the plate on the AC says "maximum fuse..." without any mention of a circuit breaker, or other type of overcurrent protection, you are required (see UL white book) to use a fuse somewhere in the circuit. Circuit breakers are not the same as fuses; a fuse, even a "time delay" fuse, will typically respond (blow) a lot quicker than a breaker.