Can I install this heat pump on a 15 amp breaker?
I’m in Canada if that matters. I have a 15 amp circuit wired to a receptacle on my porch and I’d like to use that to power this Toshiba heat pump. Model TW12HQ1B8A. The data shows a MCA of 20A and an MOCP of 30A. This is what the experienced contractor has recommended. I’m uncertain about how to map the electric specs of the heat pump to the required breaker size. Also, as a retrofit do I need the heat pump to be on a standalone circuit or is it OK if there are other outdoor receptacles on this same circuit (obviously understanding that I increase the risk of tripping the breaker if I plug other things in.)
https://tosotamerica.com/wp-content/uploads/2020/05/TOSOTANCAT20_V13_LR.pdf
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Short answer: NO.
MCA (Minimum Circuit Ampacity) of 20A means you need at least a 20-amp circuit; MOCP (Maximum Over Current Protection) of 30A limits the branch circuit to a 30 amp over current device (circuit breaker or fuse). The heat pump also needs to be on its own circuit.
Thanks. I understand that you need a dedicated circuit in a new building. If you hook a heat pump up to a plug, are you allowed to plug it into a GFCI receptacle in an existing building?
And just to expand on this... this can lead to things that most people find odd but is acceptable. For example, a minimum circuit ampacity of 20A and maximum over current protection of 30A could be met with 12 gauge conductors in most cases and a 30A breaker, which is not a combo you'd expect on a "normal" circuit.
I assumed that just meant you could run 10 gauge on a 30 amp breaker.
You cannot run 12 gauge on a 30 amp. No? What am I missing?
Being in Canada may well matter. This article has a lot of useful info: https://www.greenbuildingadvisor.com/article/heat-pump-electrical-requirements
To add my two cents: Wiring the heatpump to the existing circuit likely isn't causing a dangerous situation -- but it may well be that the breaker will occasionally trip when the heat pump ramps up to full load. I'm quite certain that it's not up to code (needs a dedicated circuit, and a proper breaker, and appropriate wiring). It may be possible to legally use the existing, presumably 14 gauge, wiring with a 20 amp breaker if it is rated to 75 C, and if the rest of the components (breaker, connector in the heat pump) are rated for 75 C. Though I think I also remember somehow that NM-B cables can only be used at 60 C ampacity even if they are rated for higher temps.
In any case, I'm not an electrician, it's always better to consult an actual professional. I'd run a dedicated 20-amp circuit, but how much work that is depends on your circumstances, of course.
>”It may be possible to legally use the existing, presumably 14 gauge, wiring with a 20 amp breaker if it is rated to 75 C, and if the rest of the components (breaker, connector in the heat pump) are rated for 75 C. ”
No, that is not permissible. There is an exception in the code that states that 14, 12, and 10 gauge wire may only be used for 15, 20, and 30 amp circuits, respectively. You are not permitted to size those wires based on the 75 or 90 degree columns in the ampacity chart. There is another exception that types NM and NMB cable (the common “romex” used in residential construction) can only be used as 60 degree rated wire.
You can try running the heat pump on a 15 amp circuit, but it probably won’t be reliable. You really need a 20 amp circuit here, which would have to be wired with at least 12 gauge wire.
Bill
"You can try running the heat pump on a 15 amp circuit, but it probably won’t be reliable."
Bill, is tripping the breaker essentially the only concern with putting the heat pump on a 15-amp shared circuit instead of a 20-amp dedicated circuit?
Or are there also safety concerns with doing that? I assume that if everything is operating as designed, the breaker should trip before any safety issues manifest?
No, there is also the risk of sustained heavy amp draw on that circuit. The code has a rule, commonly known as "the 80% rule", which says that anything that is a continuous load (with "continuous" being defined as more than 3 hours of operation), you have to de-rate the circuit to 80% of capacity. That means your "15A" circuit is a "12A" circuit for long duration loads.
What this all means in practice is that running the circuit at or near capacity may not trip the breaker, but WILL heat up the wire and all the connections along the way. You're also likely to actually run the circuit at MORE than 15A at some times, and this is a problem too: a 17A load probably won't trip a 15A breaker in any reasonable length of time, if ever. That's because circuit breakers don't trip as soon as you exceed their rating, they trip when you exceed their rating by some amount as a percentage of the rating, and the more you exceed their rating, the faster they trip. Small overloads of 10-15% or so may never cause the breaker to trip, but the wire WILL heat up more than it should. That's the big risk you take doing something like this.
My recommendation would be to put in a proper circuit for this unit to know that you are safe. Some homes may actually have 12 gauge wire for receptacle circuits, in which case you could safely up the circuit to a 20A circuit, but a unit like this heat pump should really be on a dedicated circuit.
Bill
Short answer is yes. It will work as this thing at full tilt will use about 1500 watts
… but it needs to be on its own circuit with outdoor shutoff
You might run afoul with an overzealous inspector in case he decides to compare stated equipment ampacity to actual wire gauge. Unlikely, but might happen in case some other bigger event takes place and insurance has to pay- in those cases they might look at anything that will allow them to not pay you.
"… but it needs to be on its own circuit with outdoor shutoff"
Asked above to Bill, but will ask here as well:
Is tripping the breaker essentially the only concern with putting the heat pump on a shared circuit instead of a dedicated circuit?
Or are there also safety concerns with doing that? I assume that if everything is operating as designed, the breaker should trip before any safety issues manifest?
Bill's explanation and suggestion is spot on. The MCA is on the name plate for a reason, to avoid people trying to do exactly what you are. If you do proceed, I would at least make sure you have newish smoke detectors installed in the proper location with new batteries.
It’s a pretty minor cost to do this correctly.
In the US it would not be allowed because the unit did not come from the factory with a plug and cord.
The factory intended it to be hard wired to circuit. US code requires hard wired appliances IE fixed appliances to be on dedicated circuits.
Walta
Do you have the correct voltage at that receptable?
Am I crazy, what am I missing? What's the outdoor unit model? It appears the model you mention is an indoor unit which doesn't take the main feed, no? Your standard receptacle has correct voltage?
Besides the circuit that is too small and not dedicated, adding a plug in cord to a device that is meant to be hard wired is a code violation.
Too many issues with this plan. If you want to use that plug, I would look at a PTHP instead of a minisplit. If you don't need cold temperature heat, something like a Midea MAW12HV1CWT is a pretty good deal.