Wiring method for both wet location AND place of assembly

[ckelley3]

The whole mini-split scene has been a nightmare for many inspectors and electricians.
Many of the systems are foreign and many are covered by various listing agencies. Some come with instructions calling for wiring methods that are not NEC allowed (cord), most ignore the need for a disconnecting means on the interior motor and some of the larger units ignore the fact that the smaller conductors to the interior unit do not, on some units, have overcurrent protection.
Add to that a myriad of "special" instructions added by the manufacturer.
I talked with some UL folks concerning some of the problems where manufacture instructions clashed with NEC and they noted the units were not UL listed but rather ETL. ETL folks said they would "look into it" (twice).
FWIW, I know of several Mitsubishi splits that have had switches added and wires spliced that seem to be operating fine... (not saying your unite would)

I do agree with most of you on the fact that splicing is not likely to be an issue. The use of a three pole disconnect switch for the indoor unit is optional, according to the manufacturer (req'd by the NEC) and I cannot imagine it having much different of an effect than a properly spliced junction. What I do know is that Mitsubishi takes warranty claims VERY seriously and prides themselves on their quality. They say their warranty claim rate is 0.05% of all units and industry standard for spilt systems is 2%. It is my opinion that they do not want splices in their system because too many HVAC guys don't know how to properly install them, as one responder commented. They market heavily to end users and their reputation is on the line when someone does an improper install.

That being said, this is only my second install for these units (the first was a residential application where I used UF to be able to meet both indoor and outdoor NEC code) and I am doing 7 of them. I do not want any issues that a field service rep would deem a problem, as it is 7X the problem for this particular job.

So in light of that, I will be doing a single, unspliced run and am thankful for the feedback given thus far and would appreciate any additional feedback as it relates to the original post.

Oh, and Augie, a quick comment on your post regarding the indoor unit wiring not being protected at an appropriate level if it is smaller than the outdoor unit's power circuit: The circuit boards for the Mitsubishi units contain a couple of 7A fuses to protect the 14 AWG wire powering the indoor units. I had the electrical inspector ask the same question and this is what the manufacturers rep told me and I later confirmed by the line drawings in the product docs.

 

[cadpoint]

Install Insulation in all vertical walls! If not insist on all ceiling be insulated! The problem is you installing so many, they also need disconnects at point of use! I mean you did get the training!

IMO. You will be also installing a lot of thermostat's - it's a very demanding and addressable at use of each service! You might think about some total controls and some relays to push button for service to demand air on a timer, till thermostat takes over.

 

[kwired]

They are becoming data signals more than control signals.

The outdoor unit has to recognize the indoor unit and they 'talk' to each other.

Not all that new of technology either, X10 and other similar products have been talking to each other over power lines for a long time now, with who knows how many splices between units. Really the third conductor in these mini split systems is not all that necessary as we have the ability to send data over the power lines between the two, or even over lines that do not run directly between them.

 

[darekelec]

To be 100% legal I would use option;
2. Use sealtite or NM conduit outside to a JB just inside the interior wall, where the remaining run will be EMT or FMC. Wire with continuous THWN.

 

[wasabiian]

Mini split (Ductless) systems

Mini split (Ductless) systems

There are several issues with wiring ductless systems.
On a Lennox system the installation instructions,
1. specify tray cable as the wiring method between the indoor and outdoor unit... The Lennox part no is a Tray Cable. The NEC says that tray cable is required to be installed in conduit or a tray. There isnt enough room for conduit in the back of the indoor unit.
2. the instructions also specify that you tape the type TC cable to the line set. In my area we dont attach one trades work to another trades. The mechanical guys aren't licensed to run the wire in our state.
3. and the most aggravating, I had an install fail because i used solid wire and the installation instructions call for stranded only. its in italics so Im told by the AHJ. there are no products available that I am aware of that can be run inside the building, and outside the building and is stranded. I did find a special order of the sealtite MC type in stranded but its a special order. our local supply houses only had solid.

The company I work for installs all brands of these things and I have been using 14/3 UF to comply with the interior/exterior wiring NEC code issues, but this stranded issue just threw this last job in the tank. Most inspectors in my area don't care about the stranding issue because its not life safety.
Johnstone supply, a supply house for the HVAC industry sold me a roll of "mini-split" wire. its 300 volt CL3R wire. its Stranded 14/4 but according to my AHJ it doesn't meet the voltage requirements of the circuit unless the manufacturer specifies the circuit has a class 3 rating. I called Lennox and they agreed it didn't meet design requirements.

it sounds like maybe the Mitsubishi at the beginning of this thread could use the mini-split wire..

My question is... if the manufacturer shows taping the wire to the line-set and they specify type TC does the manufacturers instructions trump the NEC?

interestingly,

 

[kwired]

There are several issues with wiring ductless systems.
On a Lennox system the installation instructions,
1. specify tray cable as the wiring method between the indoor and outdoor unit... The Lennox part no is a Tray Cable. The NEC says that tray cable is required to be installed in conduit or a tray. There isnt enough room for conduit in the back of the indoor unit.
2. the instructions also specify that you tape the type TC cable to the line set. In my area we dont attach one trades work to another trades. The mechanical guys aren't licensed to run the wire in our state.
3. and the most aggravating, I had an install fail because i used solid wire and the installation instructions call for stranded only. its in italics so Im told by the AHJ. there are no products available that I am aware of that can be run inside the building, and outside the building and is stranded. I did find a special order of the sealtite MC type in stranded but its a special order. our local supply houses only had solid.

The company I work for installs all brands of these things and I have been using 14/3 UF to comply with the interior/exterior wiring NEC code issues, but this stranded issue just threw this last job in the tank. Most inspectors in my area don't care about the stranding issue because its not life safety.
Johnstone supply, a supply house for the HVAC industry sold me a roll of "mini-split" wire. its 300 volt CL3R wire. its Stranded 14/4 but according to my AHJ it doesn't meet the voltage requirements of the circuit unless the manufacturer specifies the circuit has a class 3 rating. I called Lennox and they agreed it didn't meet design requirements.

it sounds like maybe the Mitsubishi at the beginning of this thread could use the mini-split wire..

My question is... if the manufacturer shows taping the wire to the line-set and they specify type TC does the manufacturers instructions trump the NEC?

interestingly,

Anybody know what NRTL's have to say about it? Their requirement to use a specific cable you would think would part of listing. If that is so we have a conflict between the listing and NEC requirements for that type of cable, or even the listing of the cable itself is conflicting with a specific use.

 

[GoldDigger]

Anybody know what NRTL's have to say about it? Their requirement to use a specific cable you would think would part of listing. If that is so we have a conflict between the listing and NEC requirements for that type of cable, or even the listing of the cable itself is conflicting with a specific use.

Yes. If the wiring had been inside the UL-listed assembly, the NEC would not apply, and if the wiring is outside the UL-listed assembly, now can the manufacturer control anything but the part of the wiring that terminates on their equipment?
The mini-split is a strange beast.
When you get down to it, there is room to argue that the wiring between the two parts of the mini-split is not building wiring in the purest sense (although it is still covered, I am not disputing that....).

If the manufacturer provided an interconnecting cable harness, available in different lengths, which was sold as part of the UL-listed product would that be a possible escape from the dilemma?

 

[kwired]

If the manufacturer provided an interconnecting cable harness, available in different lengths, which was sold as part of the UL-listed product would that be a possible escape from the dilemma?

I think it would be, as it would be a listed component. But problem is they don't sell this cable they just specify a particular cable that otherwise has no business being used in the same manner.

 

[wasabiian]

But problem is they don't sell this cable they just specify a particular cable that otherwise has no business being used in the same manner.

Lennox does have a "Lennox" part number that they spec, and it is a tray cable type TC printed down the side of the cable. its likely made by southwire or someone else???

 

[wasabiian]

"1. Use a PVC coated MC (TECK) cable for a continuous run. Deal with the expense/availability of wet rated connectors outdoors."

I am the electrical supervisor for a Heating and AC company. I would use the plastic coated MC.
You are fortunate that the specs dont require stranded wire as stranded is a special animal whereas the solid stuff is easy to get from most supply houses.

 

[wasabiian]

Why not option #4 if you really don't want to splice?

EMT.

you'd have to be a magic man with emt to bend it into the wiring channel provided with the unit. there isnt enough room for carflex with the line set in there. the units are designed to be used with Tray Cable.

 

[SmithBuilt]

they are adamant that S1-S2-S3 conductors CANNOT be spliced ANYWHERE between the units.

I have wired many Mitsubishi units with splices. I do not see in the installation instructions that you cannot splice. They actually show a 3 pole disconnect for the indoor unit, wouldn't that be a splice.

They must be 14AWG, no bigger, no smaller, and can be stranded or solid.

The Mitsu instructions say 16 awg. I run 12 awg for this and never had a problem.

2. Use sealtite or NM conduit outside to a JB just inside the interior wall, where the remaining run will be EMT or FMC. Wire with continuous THWN.

I have never had to run exposed on the inside to a unit. Most of the time the line set goes thru the exterior wall directly into the indoor unit and I run along side it. It is almost impossible to run a conduit to the factory ko. I normally run nm flex to a disco mounted directly against the indoor unit.

 

[cpinetree]

An interesting take on not needing the disconnect at the inside unit at least for residential installs, Oregon 8/14/2009
http://cbs.state.or.us/bcd/boards/electelv/board_pack/09/20090924/EE_092409_IVa.pdf

partial quote from above:

Question:
Is a separate disconnect required at the indoor unit or component of a mini-split system used in a residential application?

Answer:
Indoor components, with a unit switch that complies with NEC article 424.19(C) or 422.34, are adequate to meet the intent of the OESC for personnel protection. Where there is no switch on the indoor unit, article 422.31(A) applies, and a lockable disconnect at the outdoor unit shall be permitted to serve as the disconnecting means.