ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat
Recent Posts
Increasing demand factors in residential
by gfretwell - 03/28/24 12:43 AM
Portable generator question
by Steve Miller - 03/19/24 08:50 PM
Do we need grounding?
by NORCAL - 03/19/24 05:11 PM
240V only in a home and NEC?
by dsk - 03/19/24 06:33 AM
Cordless Tools: The Obvious Question
by renosteinke - 03/14/24 08:05 PM
New in the Gallery:
This is a new one
This is a new one
by timmp, September 24
Few pics I found
Few pics I found
by timmp, August 15
Who's Online Now
1 members (Scott35), 260 guests, and 19 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Page 1 of 2 1 2
#84314 03/17/03 10:08 AM
Joined: Mar 2003
Posts: 25
S
steve66 Offline OP
Member
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?

Stay up to Code with the Latest NEC:


>> 2023 NEC & Related Reference & Exam Prep
2023 NEC & Related Reference & Study Guides

Pass Your Exam the FIRST TIME with the Latest NEC & Exam Prep

>> 2020 NEC & Related Reference & Study Guides
 

#84315 03/17/03 10:48 AM
Joined: Jan 2002
Posts: 163
D
Member
Fuses are generally preferred over breakers but NOT required....as long as you use HACR breakers. See Art. 440 for AC requirements, Section B - Disconnecting Means.

#84316 03/17/03 11:12 AM
Joined: Jan 2003
Posts: 4,391
I
Moderator
You must follow what is on the Tag of the unit if the only type of protection listed on the tag is fuses you must use fuses.

Some tags will say "Fuse or HCAR Breaker" then you can use either

You must also use the size listed. If the tag says 25 Amp fuse that is what you must use even if your branch circuit is #10 with a 30 amp breaker.

2002 NEC 440.52(A)(3) and as always 110.3(B)

[This message has been edited by iwire (edited 03-17-2003).]


Bob Badger
Construction & Maintenance Electrician
Massachusetts
#84317 03/17/03 11:15 AM
Joined: Oct 2001
Posts: 597
E
Member
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.


Al Hildenbrand
#84318 03/17/03 11:34 AM
Joined: Jan 2003
Posts: 4,391
I
Moderator
Read 2002 NEC 440.52(A)(3) this requires the makers to state fuses or inverse time breaker, if the overcurrent is part of the motor current protection

Now look at table 430.52 and you will see that fuses and inverse breakers react differently.

Units still come with a specification as to minimum circuit ampacity as per 440.4(B) and overcurrent device requirement as per 440.52(A)(3)

But I agree if the unit does not state a specific type of overcurrent device it is up to you.


[This message has been edited by iwire (edited 03-17-2003).]


Bob Badger
Construction & Maintenance Electrician
Massachusetts
#84319 03/17/03 12:09 PM
Joined: Oct 2001
Posts: 597
E
Member
Thanks Bob,

You are saying this clearer than I.

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.


Al Hildenbrand
#84320 03/17/03 07:34 PM
Joined: Mar 2003
Posts: 25
S
steve66 Offline OP
Member
It sounds like I can't go wrong if I just follow the manufacturer's instructions and recomendations.

Thanks everyone.

#84321 03/18/03 08:55 AM
Joined: Jan 2003
Posts: 46
B
Member
Hello All,

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.

#84322 03/18/03 12:42 PM
Joined: Oct 2001
Posts: 597
E
Member
You're probably not missing anything [Linked Image] Big A.

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.


Al Hildenbrand
#84323 03/18/03 08:18 PM
Joined: Apr 2001
Posts: 518
J
Member
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.

Page 1 of 2 1 2

Link Copied to Clipboard
Powered by UBB.threads™ PHP Forum Software 7.7.5