Minisplit Wiring

[Andy Delle]

OK a ETL listed 1.5T minisplit nameplate says use 20a breaker, double pole 240V. That's as we know #12. But the install manual claims #14/3 to the indoor unit. Now we know the indoor unit only takes a few amps at most and there's no other loads so #14 is fine for that application. But all there is on the condenser is a relay connected across the incoming line to control the fan and electronics. No internal fuse.

So by strict letter of the code, shouldn't that run from the condenser to the indoor unit need to be #12/3? This is no different than using #14 for switch legs on a 20a circuit - which is illegal?

How can this be listed that way. I think the manual is a mistake and the listing just overlooked that.

The NEC need to look at these minisplits in more details fro the next code cycle. Also the use of 14/4 SO should be banned as well unless the wire is specifically listed for in-wall use?

 

[Dennis Alwon]

What is the minimum circuit ampacity? If it is 15 amps or less than 14/2 nm can be used to feed the unit and still be allowed on a 20 amp breaker. This can be done because the outdoor unit has overload protection. So 14/3 may be acceptable in this case.

 

[Andy Delle]

What is the minimum circuit ampacity? If it is 15 amps or less than 14/2 nm can be used to feed the unit and still be allowed on a 20 amp breaker. This can be done because the outdoor unit has overload protection. So 14/3 may be acceptable in this case.

Well yes, most motors have internal protection. And if the #14 was shorted out, a 20a breaker would still trip for sure. I know it's prefectly safe as is but is it up to NEC?

 

[Dennis Alwon]

Well yes, most motors have internal protection. And if the #14 was shorted out, a 20a breaker would still trip for sure. I know it's prefectly safe as is but is it up to NEC?

The code allows a 14 gauge wire to be installed on a 20 amp breaker because the breaker is only used for ground fault and short circuit and not for over current protection. The overload protects the wire from over current. See 240.4 (D) which shows then sends us to 240.4(G) to see where it will be allowed to use a larger breaker.

 

[GoldDigger]

The code allows a 14 gauge wire to be installed on a 20 amp breaker because the breaker is only used for ground fault and short circuit and not for over current protection. The overload protects the wire from over current. See 240.4 (D) which shows then sends us to 240.4(G) to see where it will be allowed to use a larger breaker.

This is a special case for motor loads or motor containing appliances. That is why the general rule about wire ampacity versus OCPD amps does not apply.
Usually there will be a nameplate on a motor-containing appliance with two numbers: The Minimum Circuit Ampacity (MCA) which determines the minimum wire size and the Maximum OCPD (MOCPD) which determines the largest breaker you are allowed to use.

 

[goldstar]

I feel your pain and I understand the issue. This is just a guess but the 14/3 is control wiring and does not carry an excessive load. The # 12 is for the condenser part of the unit. I don't know how they got it through UL that way but that's what the installation instructions say. Just an FYI, make sure you look closely at the mfr's instructions. You may have to install a 3-pole disconnect switch at the indoor unit.

 

[Dennis Alwon]

I feel your pain and I understand the issue. This is just a guess but the 14/3 is control wiring and does not carry an excessive load. The # 12 is for the condenser part of the unit. I don't know how they got it through UL that way but that's what the installation instructions say. Just an FYI, make sure you look closely at the mfr's instructions. You may have to install a 3-pole disconnect switch at the indoor unit.

I have seen the inside unit wired with T-stat wire because the unit was a dc motor. There must be some added protection inside the unit

 

[MasterTheNEC]

Typically the load is outside thus the 20A requirements. The Type MC or TC that is being ran inside to the indoor unit in these mini-split cables are 240V with a 24V control wire (thus why Type TC-ER-JP can be used now in one - and two family). The actual load inside is not an issue. See attached image.

 

[petersonra]

I feel your pain and I understand the issue. This is just a guess but the 14/3 is control wiring and does not carry an excessive load. The # 12 is for the condenser part of the unit. I don't know how they got it through UL that way but that's what the installation instructions say. Just an FYI, make sure you look closely at the mfr's instructions. You may have to install a 3-pole disconnect switch at the indoor unit.

if it is control wiring than they are probably class 1 circuits.

725.43 Class 1 Circuit Overcurrent Protection. Overcurrent
protection for conductors 14 AWG and larger shall be
provided in accordance with the conductor ampacity, without
applying the ampacity adjustment and correction factors
of 310.15 to the ampacity calculation. Overcurrent protection
shall not exceed 7 amperes for 18 AWG conductors
and 10 amperes for 16 AWG.

 

[kwired]

I have seen the inside unit wired with T-stat wire because the unit was a dc motor. There must be some added protection inside the unit

AC or DC wouldn't matter so much, if it can use typical T stat wire then the circuit in question would need to be rated as a class 2 or 3 circuit, if powered from the supply line it won't be class 2 or 3.

 

[GoldDigger]

AC or DC wouldn't matter so much, if it can use typical T stat wire then the circuit in question would need to be rated as a class 2 or 3 circuit, if powered from the supply line it won't be class 2 or 3.

In Mitsubishi units there is one two wire power feed and a third control/signal wire. But the control circuit uses either L1 or L2 as the return, so no way could it be any Limited Power Class IMHO.

Sent from my XT1585 using Tapatalk

 

[kwired]

In Mitsubishi units there is one two wire power feed and a third control/signal wire. But the control circuit uses either L1 or L2 as the return, so no way could it be any Limited Power Class IMHO.

Sent from my XT1585 using Tapatalk

My thoughts also.

I also have no issue with running 14 AWG for it even if protected by a 20 amp breaker it has SC/GF protection and the motor will have overload protection, control circuits actually can have higher overcurrent protection levels in some instances so I am not so concerned with that either.

 

[jap]

Wouldn't all this reduction of wire size just because there's a motor in the system be null and void if the unit was capable of having backup heat strips added?

JAP>

 

[Andy Delle]

Typically the load is outside thus the 20A requirements. The Type MC or TC that is being ran inside to the indoor unit in these mini-split cables are 240V with a 24V control wire (thus why Type TC-ER-JP can be used now in one - and two family). The actual load inside is not an issue. See attached image.

This image (see post #8) is interesting as it implies the 24v is referenced to the line neutral. Nothing wrong with that as long as the product is listed but if someone were to attach any external devices to that 24v, it would be line referenced. Of course the neutral ideally should be at or within a few volts to of ground.

Most standard residential HVAC and heating uses an isolated 24v ac system. One side of the 24v may be grounded but it's certainly not tied to the neutral.

 

[MasterTheNEC]

This image (see post #8) is interesting as it implies the 24v is referenced to the line neutral. Nothing wrong with that as long as the product is listed but if someone were to attach any external devices to that 24v, it would be line referenced. Of course the neutral ideally should be at or within a few volts to of ground.

Most standard residential HVAC and heating uses an isolated 24v ac system. One side of the 24v may be grounded but it's certainly not tied to the neutral.

Just for reference the image itself came directly from the techs at Mitsubishi for their systems.

 

[Dennis Alwon]

I think we are missing what the op was saying. The circuit needs to be #12 (maybe) but the wire between the units was #14. These units have really complicated my understanding of what is allowed.

Tray cable was not allowed in residences prior to the 2017 -- big change specifically for thesde units- so it seems

(9) In one- and two-family dwelling units, Type TC-ER cable
containing both power and control conductors that is
identified for pulling through structural members shall
be permitted. Type TC-ER cable used as interior wiring
shall be installed per the requirements of Part II of Article
334.
Exception: Where used to connect a generator and associated
equipment having terminals rated 75°C (140°F) or higher, the
cable shall not be limited in ampacity by 334.80 or 340.80.

 

[MasterTheNEC]

Tray cable was not allowed in residences prior to the 2017 -- big change specifically for thesde units- so it seems

Indeed and I expect there to be even bigger changes in 2020..:thumbsup:

technically speaking nothing prohibited Type TC Cable in residential applications prior to 2017...if installed in a raceway..

 

[Dennis Alwon]

technically speaking nothing prohibited Type TC Cable in residential applications prior to 2017...if installed in a raceway..

Well, duh... LOL. If I had a raceway why would I use tray cable, huh?

Seriously, so what's the bigger change for 2020-- come on, you let the cat out...LOL

 

[MasterTheNEC]

Well, duh... LOL. If I had a raceway why would I use tray cable, huh?

Seriously, so what's the bigger change for 2020-- come on, you let the cat out...LOL

LOL....well I am just saying..if you wanted to do it you could...lol

Ummm....well it isn't a change unless it is accepted. Lets just say this, there is no legitimate excuse/reason to not expand the use of Type TC-ER-JP to other locations inside buildings (of all types) no differently than Type SE-R. In fact, the only folks who voted against the expansion in 2017 was three manufacturers, two of which do not even make such a cable assembly.

So while I expect bigger changes it will as usual depend on the votes at the table. While some would argue from a manufacturers perspective the expanded use of Type TC-ER-JP would reduce the sales of a competing product like Type MC and Type SE-R but we just see it differently I guess. The argument against the expansion is that Type TC-ER is rated for industrial applications to which I reply so then why not in less harsh environments like within walls of single family, two family and to be quite honest anywhere that currently permits Type SE-R cables.

The only real difference in Type TC-ER and Type SE-R is the fiberglass wrap binder. It adds no rating value to Type SE-R but is part of UL 854's specifications. Also the portion of the section you quoted that is also kinda foolish is the requirement for it to have BOTH power and control conductors within the Type TC-ER-JP Cable for use in one and two family dwellings. It should make no difference at all.

So these are upcoming debates and things that are being targeted with PI's....but no real cat out of the bag so to speak since the fight for expanding the use of Type TC-ER-JP continues.

 

[Dennis Alwon]

I saw TC once and it looks like se cable. Is it really that different?