Pool Heat Pump Tripping Electrical Breaker
If you have an electric heat pump for your swimming pool that is tripping the electrical breaker then this article will help you to understand some of the reasons why this would happen. It is important to note that electric heat pumps are not the same as natural gas or propane heaters. Nor are they the same as the electric motor that runs your filtration system. If your electric pump motor for your filtration system is tripping the breaker then you should read this article on pool pump troubleshooting for information on pool pumps, as well as this article on pool pump overheating.
Electric heat pumps require special consideration when sizing the electric service and electrical disconnects (breakers) and unfortunately mistakes are quite often made from people when installing these - even experienced and licensed electricians and technicians can make mistakes here if electric heat pumps (or air conditioners) are not something that they work with regularly. The reason for this comes down to special considerations that the NEC (National Electrical Code) has for air conditioners (and electric heat pumps which essentially operate like a reverse air conditioner). Before we can cover this stipulation we first need to cover some basics for how electrical wiring and breakers are installed.
The sizing of the wire (AWG, American Wire Gauge) and the current value for the electrical breaker work in tandem to protect circuits from fire or damage from heat that is generated. Before the days of standardized and safe electrical standards it might be common to find a wire too thin for a given application in use. Even if an electrical breaker was being used, if the current passing through a wire exceeds a certain value this will cause the wire to get hot. If the wire gets too hot it could start a fire. This is why electrical breakers and electrical wire size has been standardized to make sure that your wires never get overheated, and if something happens that tries to draw more current than the wires would be able to handle, an appropriately sized electrical breaker would trip and open the circuit.
14 AWG - 15 Amps
12 AWG - 20 Amps
10 AWG - 30 Amps
8 AWG - 40 Amps
6 AWG - 60 Amps
As a general guide from the NEC this is how you would expect to see wire size matched with circuit ampacity. Even this however is a simplification and far from a one size fits all rule about wire sizing. For example there are conditions where 14 AWG is used for 20 Amp circuits, and 12 AWG for circuits up to 25 Amps. Additionally there are exceptions to standard breaker and circuit ampacity pairings such as those covered in Section 240.4 of the NEC. One of these exceptions is for appliances like air conditioners...or in this case an electric heat pump.
Electrical Ratings For Pool heat Pumps
If you buy a blender and read the electrical nameplate is probably says something like 12 Volts, 6 Amps, 60 Hz...depending on where you live of course because electrical appliance values are different the world over. Still they will all follow a fairly familiar and straight forward format. Electric heat pumps are not straight forward like this. When you get into voltage, current and power ratings for dynamic devices like electric motors, compressors, air conditioners and electric heat pumps the ratings are not as straight forward as with simple appliances. Consider the following:
MCA (minimum circuit ampacity) - The minimum circuit ampacity is the calculated amperage value that the heat pump needs to run continuously. This is the value typically used to determine the wire size that is needed to feed the branch circuit to the heat pump.
Maximum Breaker Size - When stipulated by the manufacturer on the nameplate the maximum breaker size indicates the largest (highest amperage value) breaker that you can safely use on this particular heat pump.
Minimum Breaker Size - Opposite to the maximum, the minimum breaker size when listed by the manufacturer indicates the minimum size (lowest amperage value) breaker that the heat pump will require in order to not cause nuisance trips of the electrical circuit during normal operation.
Phase - Electrical phase refers to voltage, and residential electrical services are almost all single phase voltage which is the 110/220 (also 115/130 and 120/240 since voltage is a range, not a hard number) Volts that you are probably already familiar with. If your heat pump said 3 phase on the nameplate, this would be a common voltage used in commercial and industrial electrical applications and not something you can use with standard household voltage.
RLA (rated load amperes) - The rated load amperes of a motor is a calculated value to determine the sum total amperage that the appliance can draw sustained with an allowance for oversizing. Specifically the manufacturer will use the RLA value and multiply this by 1.25, or 125%, and then add to this any other electrical demands from the appliance, and the sum of these numbers will be the MCA, or minimum circuit ampacity value on the nameplate.
LRA (locked rotor current) - The current needed to operate the electric heat pump, or RLA, is the maintaining current. This would be similar to gas mileage you get in a car while cruising in overdrive at a steady speed on the highway...or in other words good gas mileage / low consumption of energy. The LRA is how much current draw there will be to get the motor moving from a dead stop. This is similar to the mileage that you would get accelerating your car (at full throttle) from zero up to highway speeds. It takes a LOT more energy to get something moving than it takes to keep something moving. This heavy current demand on startup needs to be accounted for in the electrical calculation for heat pump service installations and the manufacturer provides this information on the nameplate.
FLA (full load amperage) - Until the early 1970's the FLA was the calculation of how much running energy was needed for a circuit, but as it relates to HVAC systems FLA is now replaced by RLA. The FLA value provided by heat pump manufacturers refers to the secondary electrical system demands such as the fan motor, not the AC compressor motor. So RLA tells you how much current your large compressor needs to run, and the FLA tells you how much all the other stuff (fan, electronics) needs to run.
According to the NEC section 440.22(a) the breaker size for electric heat pumps can be between 175% and 225% of the RLA value on the nameplate. If you take the RLA value and multiply this by 2.25 this will give you the maximum breaker size for the disconnect. You can use a smaller breaker than 225% of RLA so long as it still meets the MCA value. This is how you can end up with a heat pump with #8 AWG wires, typically intended for 40 Amp installations used in conjunction with a larger breaker size such as 50 Amps or 60 Amps, for AC compressor and electric heat pump systems specifically - and this is approved by the NEC.
Heat Pump Tripping Electrical Breaker
Now that you have an understanding, or at least an appreciation, for how (complicated) electrical service, wire and disconnect sizing is for electric heat pumps you can probably appreciate how easy it would be for someone to make a mistake when installing yours. For electricians familiar with these sections of the NEC, and familiar with AC compressor motor ratings and electric heat pumps, this is all pretty straight forward stuff. Even if you don't understand it terribly well, you just need to know what a few of these ratings are, and which apply to selection of wire size and disconnect size. Many electricians, good electricians even, might not be familiar with these unique heat pump considerations.
In many cases the electrical wires will be selected based on the minimum circuit ampacity, which is the right thing to do. The mistake comes from then matching the normal electrical breaker size to the AWG wire size standards. If this were not an electric heat pump (or AC) then that would be the correct move. In this case sizing the breaker to the wire size might actually undersize the breaker by quite a bit. The LRA current draw when first starting up the heat pump pulls a lot more amperage than the unit needs once it is up and running. That heavy draw is the reason why the electrical breaker can be up to 225% higher than the RLA value of the appliance. If the breaker is selected based on the MCA value and not 1.75 to 2.25 times the RLA value, then it is entirely possible that the starting amperage draw will cause the heat pump to trip upon initial start up...but that is not always the case.
A very common situation is that a breaker is selected based on the MCA and is too small for the startup current draw. However since the heat pump is new, and the breaker is new, the breaker might just hold out long enough to not trip and once the unit is up and running the MCA is able to be held indefinitely by the breaker...or so it would seem. But after a few months or a few years of operation the heat pump is incrementally less efficient than it used to be. Additionally electrical breakers can wear out from constant use, too much on-and off use, or from heat damage. It is possible that over time the breaker has weakened slightly from what it once was, and the heat pump draws just a little more current than it used to. Where the breaker was always sized wrong for your heat pump, it once was able to just get by without tripping. With age, and wear, it now is unable to hold during the motor startup and trips the breaker.
To double check your heat pump installation double check the MCA value and the RLA value and compare this to the electrical breaker rating on your installation. Multiply your RLA number by 1.75 and if your electrical breaker is smaller (lower amperage) than this value it is possible that your breaker was sized based on the MCA and not the RLA.
DO NOT attempt to change a breaker on an existing installation based on this information you have just read. This information is intended to help you determine if you should hire an electrician. If your breaker appears to be sized from the MCA and not the RLA calculation then the appropriate next move would be to contact a local electrician who is familiar with AC and electric heat pump installations.
Please note that this information is intended to help heat pump owners and installers to better understand how heat pumps work and the variables involved with determining wire and electrical breaker size for their installations. This information is not a replacement for professional advice from an electrical authority in your area. You should not attempt to modify or change any electrical systems on your own, nor should you attempt to to install, wire or modify an electric heat pump without the assistance of a licensed electrician.
Pool Heat Pump Tripping Breaker
In addition to the common problem of undersized breakers on heat pumps detailed above there are many other reasons that an electric heat pump might start tripping the breaker. Unfortunately none of these are DIY or homeowner level troubleshooting or repair steps. The size of electrical installations for heat pumps is as large as some small / older homes have as an electrical service. Would you open up a main electrical panel for a house and start testing things looking for a problem? You should definitely not unless you have appropriate electrical training and experience. A pool heat pump has a huge electrical service by residential standards and you need to respect the power and danger of this appliance.
Loose electrical connections - A poorly made electrical connection will have more resistance than a properly made electrical connection. Resistance in an electric circuit causes heat. A poor electrical connection under load would be much hotter than the rest of the wire and connection points. This is exactly how poorly done or damaged wiring can cause fires. The poor connection builds heat, but heat can damage electrical connectors and cause them to increase in resistance. This perpetuates the problem and the heat causes more resistance and the increased resistance in turn causes more heat. This process continues until either the circuit starts a fire or until the electrical connections burn and open, effectively disconnecting the circuit. The heat around the connection point will also damage the insulation on the wires and over time the insulation can crumble away or fall off which leaves current carrying conductors exposed. This could easily result in a short circuit if the wire touches another wire or anything metal, which would result in a dead short, and the electrical breaker tripping.
Low voltage - If loose connections have not deteriorated to the point where they are shorting out or burned open, you sometimes can experience a "brown out" situation. This describes a situation where the circuit is still live, but the required current or voltage is being supplied at less than the value the heat pump needs. Damage from heated conductors would do this, especially under heavy load. You also could have pest damage like frayed or partially chewed wires like from rodents. Voltage drop is normal when the end of the circuit is located physically far from from the souce panel. Too much of a voltage drop in a long run can cause brown out and under-voltage problems and the amount of voltage drop over a given distance can change (for the worse) as the wire itself ages and is exposed to heat.
Faulty start capacitor - Start capacitors are often used on motors to help them overcome the LRA. Capacitors hold a charge, and when used as part of a starting circuit can help to get the motor started from a dead stop. Without the capacitor, or with a failing capacitor, the motor takes too long to get moving and the heavy draw current LRA value exceeds what the circuit breaker can handle. It builds heat very quickly and as designed it will trip out before fire or appliance damage can occur.
Seized motor or compressor - Especially with a heat pump that has not been run for a while, like one that has been sitting all winter in a seasonal pool location, the motor can seize from the accumulation of rust. The amount of rust it takes to seize a motor is very little. Unlike with a pool pump where you can jog the motor with a mallet, or spin the impeller manually, if your motor on your heat pump is seized you will need a service call to inspect, repair and probably replace your motor. Symptoms from a seized motor would be humming from the appliance when it tries to turn on followed by an electrical breaker that trips.
Faulty electrical breaker - Electrical breakers can be faulty, or become faulty over time, especially when they are operated at, near or past their intended current limits. This heat can cause damage internally inside the breaker and make it begin to trip out at a lower current value than it was originally manufactured. Similar damage can also happen from using an electrical breaker like a light switch or motor controller. An electrical breaker is a safety disconnect device and not intended to be used regularly like a light switch.
Dirt, debris or lack of maintenance - Inside of an electric heat pump there are moving components such as a fan. Over time grime and debris can build up on these moving parts which causes the motor to have to work harder. Over time this increase in friction and weight of moving parts can cause an increase in the current draw to the motor, which can manifest eventually as a tripping breaker if it is let go long enough. If the condenser coils or air filter become plugged this will also cause the heat pump to pull a larger amperage which generates additional heat inside the unit and in the wires feeding it. Regular service and maintenance by an HVAC professional is recommended to avoid this problem with your heat pump.
Again it is critically important that you do not attempt to work on an electric heat pump yourself, or do anything other than look and observe the symptoms (and manufacturer ratings) for your device. This information, along with the information on this page, should give you a much better idea as to what might be wrong with your heat pump. This will allow you to engage a professional electrician or HVAC installer more efficiently in discussing your problem and help you to better understand how you can avoid down time with your heat pump in the future.
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