Condenser Breaker Trip

[Anonymous]

Hello I have a "typical" 30 amp outdoor compressor that I relocated to the far end of the deck. This required a 60' wire run from panel. 20' of 10/2 W/Grnd to outdoor disconnect, then 40' of stranded 10G red/blk/grn to compressor. AC company ran line set and charged system. System runs for couple hours then trips the 30 amp breaker. Called back A/C company to check out any overcharge condition (compressor) that might create excessive amps. Company checked system and verified charge etc was ok - they suggested simply replacing the new 30 amp breaker with a 40 amp instead. -- :o My 10G wires require 30 amp breaker protection -absolutely- right? My only other ideas of possible problem areas: Could wire run/distance necessitate larger wire? Wiring and compressor/system is new except inside 10/2 romex and old outdoor disconnect with cartridge fuses. Could the old cartridge fuses (that were slightly abused -not blown- with old malfuntioning condensor) possibly create this condition? I thought I'd finally break down and purchase that new fluke 322 clamp meter to see whats happening with amp pull before breaker trip... Your thoughts? Thank you!

[imeduc]

By my books a 3 tonA/C at 50' call for a #8 wire on it. its like take 50' of hose and fill a 5 gal bucket. Now add 50' more on to the hose thats a 100' . Now you didnt do a thing to the pressure but look how it takes longer to fill the last bucket of water. the same with the electric Get a bigger wire in there before you burn the compressor out :shock: ED

[Wgoodrich]

Look on the name plate of the a/c unit. Look where it says "minimum circuit ampacity". This tells you the minimum amp rated conductor allowed to serve as a branch circuit conductor. Per Table 310.16 of hte NEC 10 awg for a hermatic motor is allowed to carry a maximum of 30 amps. If the MCA [aka minimum circuit ampacity rating] on that name plate says 30 amps or less then you are fine with the wire size you have safety and minimum safety standards wise. Then If you go to Chapter 4 of the NEC it tells you that the internal built in overload of that compressor is designed to protect the branch circuit conductor on the load side of that conductor. The breaker only serves as a short circuit device. Breakers are not that compatible to motor loads. The internal of the breakers tend to heat up causing false tripping. Ampacity of the branch circiut conductor is not the sizing factor of breakers serving motors. The maximum size of a breaker serving a motor with an internal over load may be as much as 225% higher than the full load current of a motor. There is a rule limiting the breaker size serving an a/c unit no larger than the MOP [aka maximum overcurrent protective device amp rating]. Look again on the a/c unit. the MCA tells you minimum circiut conductor size in ampacity. MOP is the maximum breaker size. The two do not relate to each other. This wiring style serving motors is a different world in wiring design than normal wiring found in the first three chapters of the NEC as normal people are used to.

If you wish to know more details read the following linked chapter found on our homewiringandmore.com web site for hermatic motors.
Then read the second link to a second chapter for motors in general. May enlighten your knowledge on the subject.

http://www.homewiringandmore.com/homewiringusa/2002/motordesign/hvac/hvac.html

http://www.homewiringandmore.com/homewiringusa/2002/motordesign/motordesign/motordesign.html

Let us know what you find.

Good Luck

Wg

[Anonymous]

Imeduc - Thank you for the reply.

WG - Thanks for the breakdown information. I now realize there is a whole world of variables regarding conductor/breaker sizing with motors. :oops: I have been reading your reply over and over many times - still trying to wrap my brain around that information. If you could apply the information that I am listing from the compressor and tell me what I require and why, I will eventually get to Indiana and buy you that lunch...
Compressor info:

208-230V
14.1 RLA
78.3 LRA (comp)
.8 FLA - 1/8 H.P. (fan)
Min. Circuit Ampacity 18.4
Max circuit breaker 25

(total circuit lenth is approx. 55')
Thank you gentlemen

[Wgoodrich]

YOU SAID;
Min. Circuit Ampacity 18.4

Read the following rule found in NEC 2002;

440.33 Motor-Compressor(s) With or Without Additional Motor Loads.
Conductors supplying one or more motor-compressor(s) with or without an additional load(s) shall have an ampacity not less than the sum of the rated-load or branch-circuit selection current ratings, whichever is larger, of all the motor-compressors plus the full-load currents of the other motors, plus 25 percent of the highest motor or motor-compressor rating in the group.
Exception No. 1: Where the circuitry is interlocked so as to prevent the starting and running of a second motor-compressor or group of motor-compressors, the conductor size shall be determined from the largest motor-compressor or group of motor-compressors that is to be operated at a given time.

COMMENTS;
If you will check with your installation instructions your instructions will tell you to size your branch circuit conductor by the "minimum circuit ampacity" marked on your a/c unit name plate. This minimum circuit ampacity on your name plate already has the 25% increase calculated in by the manufacturer. Then you take what you found on the a/c name plate "minimum circuit ampacity" being 18.4 amps as you stated. Then you must take that to NEC Table 310.16 and that chart says that you would be allowed at a minimum to install a 12 awg copper wire that is rated at 25 amps for motors. This 25 amp rating is higher than normally accepted in the first three chapters of the NEC. Look at the following rule NEC 240.4 that appies to motors exempting the 20 amp rating of 12 awg for motors.

240.4 Protection of Conductors.
(G) Overcurrent Protection for Specific Conductor Applications. Overcurrent protection for the specific conductors shall be permitted to be provided as referenced in Table 240.4(G).

Air-conditioning and refrigeration equipment circuit conductors
440, Parts III, VI

COMMENT;
That rule above refers you back to the first copied rule above.


YOU SAID;
Max circuit breaker 25

REPLY;

III. Branch-Circuit Short-Circuit and Ground-Fault Protection
440.21 General.
The provisions of Part III specify devices intended to protect the branch-circuit conductors, control apparatus, and motors in circuits supplying hermetic refrigerant motor-compressors against overcurrent due to short circuits and grounds. They are in addition to or amendatory of the provisions of Article 240.

NEC COMMENTARY;
Where an air conditioner is listed by a qualified electrical testing laboratory with a nameplate that reads “maximum fuse size,” the listing restricts the use of this unit to fuse protection only and does not cover its use with circuit breakers. If the air conditioner has been evaluated for both fuses and ordinary circuit breakers, or both fuses and HACR-type circuit breakers, it may be so marked. UL-listed circuit breakers that have been found suitable for use with heating, air-conditioning, and refrigeration equipment comprising multimotor or combination loads are marked “Listed HACR Type.” It is the intent of 110.3(B) to require that the manufacturer's installation specifications be closely followed and that any restriction of the listing be applied to the installation of the equipment, in order to comply with the Code.
The UL Electrical Appliance and Utilization Equipment Directory states the following under Air-Conditioners, Central Cooling (ACAV): “This marked protective device rating is the maximum for which the equipment has been investigated and found acceptable. Where the marking specifies fuses, or 'HACR Type' circuit breakers, the circuit is intended to be protected only by the type of protective device specified.” Exhibit 440.1 illustrates three wiring configurations where the equipment is under fuse protection only.

MY COMMENT;
Then you must refer to NEC article 110.3.B where it tells you that you must follow manufacturer's recommendations.

YOU SAID;
(total circuit lenth is approx. 55')

REPLY;
As a normal rule of thumb you can run a normal distance of approximately 250 feet without concern for voltage drop. However many electical experts including myself advise that your install a branch circuit conductor for an appliance that pulls heavier than normal and may run longer than normal on auto control that is about one conductor size larger than minimum size conductor allowed. This extra cost can be recouped in better voltage serving that unit and profeciency of the appliance concerning electrial usage. While the minimum circuit size is considered safe, you often times expecially in an a/c unit case will recover your added investment in larger wire size the first year then experience that savings and extended life expectancy of that equipment for years to come. This is a personal choice you have to decide on whether to oversize above minimum circuit size or not seeking the better running equipment and extended life expectancy and kw savings involved. Voltage drop should be within normal range of 3% if you installed the minimum wire size allowed.

Minimum per your name plate as stated.

12 awg wire on maximum breaker size of 25 amps per name plate data "minimum circuit ampacity" and "Maximum breaker size".

If you will read the link that I provided for hermetic motors you will find what is being said here and more.

Hope this helps

Wg

[Always-interested]

WG
Good lord! - I really do appreciate the exacting response. As my username implys, I like to know all of the specifics. But, the brain really hurts now. I see the surface of the water but I think I'm still sinking :? ... After reading all of the suggested information -several times- My taxed brain absorbed the following. I need 8 gauge wire with an HVAC listed 30 amp breaker - right? I cannot seem to locate an HVAC listed breaker anywhere. Am I ok using 8G and a standard 40 amp breaker?

I am wondering if an additional part of the problem could be undersized ducts and poorly placed returns etc. - the "old cooling system" ran almost continuously. But that shouldn't trip the breaker??

Again, I appreciate the effort in trying to show me the facts. Thank you.

[Wgoodrich]

Sizing an A/C unit is very important. Too big invites the system to freeze up. Too small make the unit run too long and possibly not maintain room comfort desired.

Improperly designed duct system being both cold air and heat ducts evenly will greatly affect the efficiency of the a/c unit and length of time it has to run to maintain room comfort.

It takes both designs sizing and duct design to provide a properly run a/c unit.

NO. when it pertains to motors you could legally have a 10 awg wire on a 75 amp breaker and be within code. The breaker is not designed to protect a conductor from over amping. The overload of that motor built into the motor is the protection from over amping that conductor and is found on the load side of that conductor.

Normally a motor is allowed while using a breaker to be sized at a maximum of 250% of the full load current of a motor, this breaker serves only as a short circuit protection not an ampacity protection the overload of the motor does the overload protection of the conductor. The conductor is sized at a minimum at 25% more than the full load current amp rating of that motor.

Example motor 3 phase 10 horse power 28 full load amp rated would require a 10 awg copper wire and may be served by as much as a 75 amp breaker on that 10 awg wire. The overload is much more accurate than any breaker or fuse can be and is designed to protect that wire from overheating.

Read the two articles linked in my previous posts. The Code rules are included as well as an explanation in detail for both understanding the a/c nameplate info and also motor design in the second article.

Hope this helps

Wg

[Anonymous]

WG
It did help tremendously! Thanks for patiantly explaning everything. There is so much to being an electrician. So many unseen variables. Kinda blows my mind - and I love it! I hope to some day become as educated and bright as you are.
Thanks again - have a great week! :D John