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Old 08-09-2010, 01:44 PM   #1
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Default A/C Mini Splits and Code

A couple of quick questions. For some reason we are doing our first mini split in a school. I figured alot of you have done or will be doing them so this might be a good topic.

The 2 fuzzy things I'm not sure about is the wire size, fusing, and securing.

There are 2 Fujitsu's. Powered by 2-2pole 20 amp Breakers (12.5 amps RLA). The supplier tells us that they just use a 14-3 SO wire (which they sell for $50 per 50 ft) and just run them (ties) out of unit with the line sets and wire into unit.

A couple of things I see wrong with that.

Securing the 14-3 out of unit to brick or tie to line set? The supplier tells me everyone just zip ties them to line sets, but, that does not sound kosher.

14-3 How can you run 14-3 out of condensor when unit is protected with 20 amp OCPD? This will carry 208v at 0.5 amps to fans in unit

Do you need a disconnect above acoutical ceiling at unit?? Some distributors so no, and some have told me yes.

Any thoughts?

On a side note: I've had this thing in my head that anything commercial "must" be 12-2 or larger (branch circuits). Is this a myth or the truth?

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Old 08-09-2010, 01:53 PM   #2
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I've never used an so cord between the compressor and the fan coil unit. In commercial jobs I just pipe the thing all the way. In dwellings I run (whatever size required)-3 wire cable. ** You are correct, running a 14-3 connection between compressor and fan coil is a code violation when the unit is protected at 20 or 30 amps, but yet millions of the same violation is performed in that instance. In the ac industry, it seems that factoid is universally overlooked.
Most electrical inspectors will not find a problem with it either. I have looked at most of the big boys schematics carefully to see if they have internal current limiting protection of the control cables for 15 amp but they do not. As far as putting a disconnect at the fan unit, if you first put a locking disco method at the compressor or a lock out unit on the circuit breaker at the panel you should not have to add a switch at the fan coil.

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Old 08-09-2010, 07:12 PM   #3
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I thought that the connection between the two units was low voltage. When I have done these, all I have ever done was run power to the disconnect and flex to the outdoor unit. The power cable was run to inside unit along with the line sets, sometimes under some sort of sleeve. The plumber/HVAC guys have always done between the inside and out, at least on my jobs.
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Old 08-09-2010, 07:20 PM   #4
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The ones I have done have all been 120 volt control wiring. We are talking about mini-split systems right?
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Old 08-09-2010, 07:26 PM   #5
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uh oh, I may have assumed...
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Old 08-09-2010, 08:55 PM   #6
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Default Mini

Well, this is new to me as well. In our case, we feed 2 condensors with #12 - 208 volt single phase and then run 2 sets of 14-3 solid to units in ceiling grid. I talked with tech of fujita today and said 2 leads L1 and L2 carry 208 volts to unit, 1 is return path (his words?), and 1 is a signal wire.
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Old 08-09-2010, 10:17 PM   #7
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I saw this gal do some mini splits one time, wow! Things are probably different in Sweden I would imagine. Bet the gals can really do mini splits over there : )
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Old 08-09-2010, 10:18 PM   #8
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Quote:
Originally Posted by nrp3 View Post
I thought that the connection between the two units was low voltage. When I have done these, all I have ever done was run power to the disconnect and flex to the outdoor unit. The power cable was run to inside unit along with the line sets, sometimes under some sort of sleeve. The plumber/HVAC guys have always done between the inside and out, at least on my jobs.

When we install mini split systems, we use either 18-5 t-stat wire if the interconnect is low voltage, or 14-12 gauge wire in carflex. Also, we zip tie the wiring to the lineset.
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Old 08-09-2010, 10:37 PM   #9
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I see the load on the evap unit is .5 amps. Is it protected somehow? With that small of an amp draw you could use t-stat wire. Even if you have to add a fuse (or two) to protect the wiring it'dbe a hell of a lot cheaper than using 14/3 SO

Most of the units we install with high voltage evaps have fuses in em.
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Old 08-10-2010, 12:39 AM   #10
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Lets put this a different way. Mitsubishi, Sanyo, Fujitsu mini split systems- Larger than 9,000 btu are 208/240 volt two wire and ground fed. The compressor calls the fan coil functions with a three wire plus ground control scheme. I have seen MG units that supply a SO type cord for the same control, but around here the electrical inspectors will give you trouble for those (machines are nice units though). The control wiring for the above mentioned units is spelled out in the installation manual to be #14. However there is no built in current limiting devices so that seems to me to be a conflict with the nec wire size protection ruling, especially when the nameplate on the compressor on some units calls for minimum 24 amps feed wire. Still I am a capitalist, and therefore am able to overlook certain limitations, especially since all the local authorities pat my installs on the back and say "nice job Mike". So I will often use 14-3 to a wp box on the building exterior where I switch to sealtite and thwn. Never had a fan coil go into loc rotor on me yet, but I have wired thousands.
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Old 08-19-2010, 10:07 PM   #11
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Default 1 conduit

Hey Mc or whomever. The HVAC guys came and went and sealed their hole. Do you see anything against code on running the 2 condensor circuits line side with the 4 wires going out from condensor to the Mini Splits. 7 Current carrying conductors total in same 3/4 EMT conduit ? It's all 120/208 but 1 signal wire??

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Old 08-20-2010, 02:18 AM   #12
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Quote:
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Hey Mc or whomever. The HVAC guys came and went and sealed their hole. Do you see anything against code on running the 2 condensor circuits line side with the 4 wires going out from condensor to the Mini Splits. 7 Current carrying conductors total in same 3/4 EMT conduit ? It's all 120/208 but 1 signal wire??

Sven
I don't see a problem Sven doing it that way, so long as all other wiring conditions are met like using the right size wire and temperature ratings and so forth and so on..

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