60 amp breaker feeding two condensing units

Hey everyone,

I have a home where the ac disconnects and circuit breakers are questionable. Background: 1983 home, two Ac units (2019/30 amp max and 2009/30 amp max). Here is my question/concern. Each unit has an individual disconnect. The conductors for both disconnects go into a junction box where they are fed from a 60 amp circuit breaker. In other words, there is one 60 amp breaker feeding power to both electrical disconnects. I normally see each unit with its own individual max breaker and disconnect. They are having ac issue and the panel is an FPE so professionals are already going to be recommended. I would appreciate others insight and opinion as to this situation.
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Do you know what the max amperage say on the condensing units? Not that it matters at this point.

It’s wrong in various aspects. Take a minute to think about it and the operation of the units and you will see why.

Both condensing units have a max amperage of 30 amps. I am guessing they thought 30 is 30 is 60 and it is food enough. I will be referring to an electrician, thank you Larry.

I have never seen an installation like this so I knew there were several issues. I just wanted other professionals insight for my personal knowledge as to what and why it is wrong. I dont like to point things out as wrong without giving a reason why. Thank you Emmanuel.

It’s still improper, as they require dedicated circuits, but where the disconnect fused?

No sir, they were non-fused disconnects. Thank you Chuck.

I am an Ohio ESI. There must be 2 separate disconnects at 30A each. This is illegal and common sense tells you why. If one unit is off and the other is running, it will not trip the breaker until it is pulling over 60A. It is supposed to trip at over 30A. At best it could burn components , at worst it would cause a fire.

Look on the Name Plate of the condenser unit to find1 the maximum overcurrent size; and 2 the minimum circuit conductor size. First lets segregate the terms Overcurrent and Overload. Overcurrent can have multiple causes such as Ground Fault, Short Circuit, and Overload. Overload means that the conductors of a circuit are carrying more current than they can safely carry. Customarily an overload is associated with a motor which is itself Overloaded in that it lacks the torque it takes to carry the mechanical load it is intended to turn.

The following is from the US National Electric Code (NEC) Article 100 Definitions. viz.

"Overcurrent. Any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault.

Informational Note: A current in excess of rating may be accommodated by certain equipment and conductors for a given set of conditions. Therefore, the rules for overcurrent protection are specific for particular situations.

Overload. Operation of equipment in excess of normal, full-load rating, or of a conductor in excess of rated ampacity that, when it persists for a sufficient length of time, would cause damage or dangerous overheating. A fault, such as a short circuit or ground fault, is not an overload."

The circuit Overcurrent Protective Device (OPD) is selected to open the circuit under any overcurrent condition. In the case of most circuit breakers the greater the overcurrent is the faster it will open. In Heating Ventilating and Air Conditioning (HVAC) service OPDs are often selected to provide protection of only fault conditions with a rating that is above the ampacity of the circuits conductors. The reason that is an accepted practice is that the load supplied is fitted with Overload protection. In the case of Overloads it is not critical were in the circuit the overload protection is located since the current is the same at all points in the circuit.

The circuit Overcurrent Protective Device and the minimum conductor size that are on the name plate label are wedded to each other. If you use this minimum conductor size then you may not use an OPD with a set point higher than that setting and that type. If the supply conductors are protected by a properly sized OPD and are larger than the minimum circuit size on the Name Plate it is possible; although admittedly unusual, that there is no Violation of the US National Electric Code in such a case.

The problem in this case is that the circuit conductors are reduced in size in the junction box for the one unit and at the disconnect load connections for the other unit. That could still be compliant because of the 10 foot tap rule.

From the US NEC section as stated.
"240.21 Location in Circuit. Overcurrent protection shall be provided in each ungrounded circuit conductor and shall be located at the point where the conductors receive their supply except as specified in 240.21(A) through (H). Conductors supplied under the provisions of 240.21(A) through (H) shall not supply another conductor except through an overcurrent protective device meeting the requirements of 240.4.

(B) Feeder Taps. Conductors shall be permitted to be tapped, without overcurrent protection at the tap, to a feeder as specified in 240.21(B)(1) through (B)(5). The provisions of 240.4(B) shall not be permitted for tap conductors. (1) Taps Not over 3 m (10 ft) Long. If the length of the tap conductors does not exceed 3 m (10 ft) and the tap conductors comply with all of the following:
(1) The ampacity of the tap conductors is a. Not less than the combined calculated loads on the circuits supplied by the tap conductors, and
b. Not less than the rating of the equipment containing an overcurrent device(s) supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors.
Exception to b: Where listed equipment, such as a surge protective device(s) [SPD(s)], is provided with specific instructions on minimum conductor sizing, the ampacity of the tap conductors supplying that equipment shall be permitted to be determined based on the manufacturer’s instructions.
(2) The tap conductors do not extend beyond the switchboard, switchgear, panelboard, disconnecting means, or control devices they supply.
(3) Except at the point of connection to the feeder, the tap conductors are enclosed in a raceway, which extends from the tap to the enclosure of an enclosed switchboard, switchgear, a panelboard, or control devices, or to the back of an open switchboard.
(4) For field installations, if the tap conductors leave the enclosure or vault in which the tap is made, the ampacity of the tap conductors is not less than one-tenth of the rating of the overcurrent device protecting the feeder conductors. From what I can see in the photographs this installation may meet the requirements of this section of the US NEC."

All of that is to reinforce what some of the more experienced home inspectors here keep counseling. Don’t write anything that may be beyond your level of qualification in a report. I’ll leave wording suggestions to the home inspectors here. I’m a retired electrician.

Tom Horne

On a related note: I always check the lable on the AC/Heat-Pump Condenser for the MAX Breaker size and then compare to the Breaker used at the panel (also check if a fuse or breaker is incorporated at cut-off , if used) I find about 50% have too large of a breaker and is called out regularly in my reports. Two reasons for this, The Electrician on new construction usually has no idea what the Condenser unit will call out and is finished with their work before the unit is installed …OR new replacement units require much less energy and will show a smaller max breaker than the old unit. In my state an HVAC guy can not change out a breaker in the panel unless also a licenced electrician, so they never get changed.
I have a canned statement for the report and I add a picture of the unit’s data plate and a picture of the breaker and I’m done.

Code inspectors have started checking this in recent years here before issuing the CO.

Great information. Thank you everyone that took the time to give me some great information and knowledge. May you all have a blessed week.

There are ways to run a 60 amp feeder for two units but this isn’t one of them. One way would require tap rules and an OCPD at the end of the each tap.

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Good to know, Robert. Thanks!

The challenge here is that when the branch circuit conductors are not the minimum called out on the name plate then the maximum breaker size given is also wrong. Keep in mind that the breaker in a Heating Ventilating and Air Conditioning (HVAC) circuit is often providing only fault protection and not any kind of motor protection The overload limiter of the Recognized Testing Laboratory listed motor compressor unit provides the circuit supplying the unit and the unit itself with all of the overload protection required. In HVAC work conductors are often permitted to carry a load that that size of conductor would not be used for under the more general rules of the NEC. Name plates often show a conductor and breaker size that would not be permitted in another use. That is because the built in motor controller will prevent any prolonged overload of the conductors from occurring. The Breaker’s only job in that application is to open the circuit on a fault or short circuit. That purpose is much easier to achieve because the current will rise very high and very fast.

Tom Horne

Gentlemen…it is said that one unit is from 2019 and of 30A current and the other is 2009 and 30A current…the procedure is to refer a certified electrician and when the 2nd. inspection is made you have to see each AC unit with its own circuit and breaker of 30A and 10 AWG wire each…also each one have to have its own disconnect that doesn’t have to be fused because it already have a dedicated circuit protected by a 30A breaker…by the way 2 units with 10 years diffrence is a concern…will also recommend a certified HVAC technician on this issue.

No. The wire gauge requirement is determined by the label on the equipment, not the breaker size. The conductor must be at least as large as required for the label minimum ampacity. The minimum will likely be 12AWG. It can be as large as the terminals are rated for.

I agree with Chuck, the aforementioned 30 amps is the Maximum OCPD size not the conductor size. As he stated it’s likely that a #12 AWG conductor is all that’s required and there may even be a scenario where the conductors could be #14 AWG with a 30 amp OCPD.

Gentlemen, I came across this thread late but have similar issue on a duel ac units wired the same as described. Because of an issue with one ac unit discovered I have a faulty contactor which I am waiting on replacement. While testing the bad ac I had turned off the cut off breaker to it. When I turned it back on it cut power to the good unit. Nothing was changed or altered on either unit. I did however unstick the bad contactor on the faulty unit. Other than that nothing was changed. What I did wonder was if because the contactor is bad on one unit, and since both the 30 amp cut off breakers are wired to a single 60 amp in main panel is this due to a shared breaker in main panel?

are you trying to fix your ac units?

Based on your post, you need help from HVAC tech. You need to know how things work and have equipment to test & troubleshoot the issue. Until then you’re just playing around and can make an otherwise easy fix into a much bigger problem. If you have something more specific, let us know :slight_smile:

Well thanks for replying. I guess I was not specific so I will try again. The wiring described in the original post referred to using a 60amp breaker in the main panel wired to two 30amp breaker/cut off for two separate ac units outside. On face value this does not appear to be a best practice in wiring of such a circuit. So I was asking for insight from more experienced people on this site, which seems the reason it exist. The concern, the issue, and my question is can such a configuration be prone to failure or faults that could cause the present symptom. That being that when moving cutoff of unit 2, which experienced a stuck contactor but has since been unstuck to the on position, unit one compressor turns off? As I stated in my first post, nothing was changed or altered in wiring. The operation of the units had been working normal. The only thing done was freeing up the stuck contractor.