#12 gauge w/ 20 amp breaker for 4 ton mini split correct?

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mystycs

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Hi folks!

Had my home built 2 years ago but I just noticed something. I noticed that my 4 ton 5 head mini split system has a #12 yellow gauge wire running to it with a 20 amp breaker at the circuit panel. I've never had any trips or issues even with all the units running full in the winter. But from reading through the forum I'm not sure if this will apply to that rule for sizing 440 NEC. Regardless since I haven't had any issues is this an issue due to code or fire hazard? Is #12 sufficient enough and safe? Or do I need something like #10 to replace it?


The specs on my mini split system:

MODEL DAIKIN 5MXS48TVJU

POWER SUPPLY: SINGLE PHASE 208/230V 60Hz

MAXIMUM OVERCURRENT PROTECTIVE DEVICE: 35 A

MINIMUM CIRCUIT AMPACITY: 33.2 A
 
The installed circuit is too small for the unit's rating. It is a code violation.

That is a variable speed system, which means it will draw less power when not heavily loaded. If it was oversized, it may never draw full power. This is probably why it hasn't been a problem _yet_.

Because the #12 wire is properly protected by a 20A breaker, IMHO this is not a safety issue. Rather it is a reliability issue, with the breaker possibly tripping on the highest load days.

If the load regularly exceeds 16A (about half of the unit's max requirement) then this exceeds the breaker's continuous rating, making it more prone to tripping in the future.

Have the builder/electrician fix this now, rather than waiting for peak load season when it might be an emergency.

Jon
 
My understanding is this is Romex NMB so it's 90° rated since it's a new home?

Are you talking about just replacing the breaker or the entire wire?
 
mystycs said:
My understanding is this is Romex NMB so it's 90° rated since it's a new home?

Are you talking about just replacing the breaker or the entire wire?
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The ampacity of NM-B has to calculated as a 60C conductor per NEC Art. 334.80 Even if you could use the 90C rating the ampacity of #12 is 30 amps which is still below your MCA. The 90C rating of NM-B can only be used for adjustment or correction factors.
 
Both wire and breaker need to be replaced. There uis no plausible circumstance where the 12ga wire meets the minimum circuit ampacity requirement.

The electrician can determine if #8 is necessary or #10 sufficient.

Jon
 
You need to have the breaker and wire replaced. 8ga romex is good for 40 amps and you need a 35 amp breaker installed.
 
mystycs said:
My understanding is this is Romex NMB so it's 90° rated since it's a new home?

Are you talking about just replacing the breaker or the entire wire?
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Here is what Rick was pointing to.
334.80 Ampacity. The ampacity of Types NM, NMC, and
NMS cable shall be determined in accordance with 310.15.
The allowable ampacity shall not exceed that of a 60°C
(140°F) rated conductor. The 90°C (194°F) rating shall be
permitted to be used for ampacity adjustment and correction
calculations, provided the final derated ampacity does not exceed
that of a 60°C (140°F) rated conductor. The ampacity of
Types NM, NMC, and NMS cable installed in cable tray shall
be determined in accordance with 392.80(A).
Click to expand...
 
I'll reach out to an electrician/HVAC specialist to look. Does the setup I have now pose any risk or danger or is it just prone to shut offs and tripping? I haven't had any issues even running all of them at full blast. If that's the case should I even bother?
 
mystycs said:
I'll reach out to an electrician/HVAC specialist to look. Does the setup I have now pose any risk or danger or is it just prone to shut offs and tripping? I haven't had any issues even running all of them at full blast. If that's the case should I even bother?
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Yes it should be corrected. I'm surprised thst you haven't had any issues up to this point.
 
I am not sure why the 20 amp breaker is not tripping. My calcs seem to be the unit draws 26 amps.....??????

You are surely doing damage to the breaker. Get it fixed....or wait until it stops working and you have no heat or a/c. hahaha
 
mystycs said:
Do you see #8 romex or #10 romex as the most likely solution?
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Just took a picture of the disconnect you can see the 12 gauge hitting the minisplit. At least they used a smaller gauge there... lol
 

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Are you positive its a 20A breaker. Could be mis labeled.
 
I checked at my circuit breaker in the garage it's 100% a 20amp breaker on a 12/2 romex
 
Dennis Alwon said:
I would get the electrician back and make him/her rewire it.
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Might not really be Sparky's fault.

I can't count the number of times I've tried to get specs because a unit isn't installed, and the HVAC thugs are too lazy to look it up or don't know what they're looking for.

Across the board I'm told "run me a 30 amp circuit" for a standard unit or "run me a 20 amp circuit" for a mini split.

Now I refuse to run an HVAC circuit without having exact specs, but I used to trust those idiots.
 
James L said:
Might not really be Sparky's fault.

I can't count the number of times I've tried to get specs because a unit isn't installed, and the HVAC thugs are too lazy to look it up or don't know what they're looking for.

Across the board I'm told "run me a 30 amp circuit" for a standard unit or "run me a 20 amp circuit" for a mini split.

Now I refuse to run an HVAC circuit without having exact specs, but I used to trust those idiots.
Click to expand...

It is Sparky's fault regardless. He hooked it up with the incorrect wiring. If he left the wiring for the HVAC guy to connect to the unit then he should have come back and made sure it was wired correctly.
 
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