single phase 208y Mini split control voltage cable required

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mgawatt

Member
Location
Buxton maine
Okay, ist thing, I am an electrician not an HVAC tech. I recently got involved in rfunning 12 mini split sytems that call for 60 amp 208Y to the outside unit and 20 amp 208Y to the inside head...no problem...Probelm started to manifest itself with the interconnect (control) PEQ terminals. On the units thart had the outside unit mounted inside (this is a huge factory installation), I used 18/3 t-stat cabvle (as the manufactuter suggested) and had no problems.
For the units wired outside, we used 14/3 UF solid, and had communications missues. The HVAC tech siad it was because the units needed stranded wiring to communicate properly, Yet, the 18/3 t-stat wire is solid and we have had no problems with that.
My wholesaler said there was a newer coated MC calble that the techs around here were using that contains 3 runs of 14 stranded...Has anyone here had more experience with these 4 ton units and can recommend the correct cable and size (face plate states =either 22/4 shieleded or 18/3)(Everything is installed seperate in a pvc conduit system for shielding requirements.
 

sparkyrick

Senior Member
Location
Appleton, Wi
If you have access to the installation manual, they may spec out a specific Belden cable, that may have stranded conductors. If any cable will do, just run the 18/3 and call it a day.

FWIW, these mini split systems suck. Seems that everyone I do is different from the last and makes it hard to rough-in for.
 

sparkyrick

Senior Member
Location
Appleton, Wi
Is that interconnect line voltage or low voltage? I wouldn't have even toughed it if it was low voltage. That's the first thing I check on these mini splits. If it's line voltage control, then yes I do the work. If it's low voltage control, then I tell the HVAC installers to take care of it.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Is that interconnect line voltage or low voltage? I wouldn't have even toughed it if it was low voltage. That's the first thing I check on these mini splits. If it's line voltage control, then yes I do the work. If it's low voltage control, then I tell the HVAC installers to take care of it.
Those mini splits for which I have seen schematics all have only line voltage interconnections, but they include one or more signalling wires which will carry that signal as an offset voltage from L1 or L2 rather than as an isolated low voltage system.
There is some indication that some of them carry much more than simple on/off information and they do it by either pulse train encoding or encoded RF signals.
There is the slightest possible chance that the details of the wiring could affect RF signalling, but it seems awfully far fetched.
 

sparkyrick

Senior Member
Location
Appleton, Wi
Those mini splits for which I have seen schematics all have only line voltage interconnections, but they include one or more signalling wires which will carry that signal as an offset voltage from L1 or L2 rather than as an isolated low voltage system.
There is some indication that some of them carry much more than simple on/off information and they do it by either pulse train encoding or encoded RF signals.
There is the slightest possible chance that the details of the wiring could affect RF signalling, but it seems awfully far fetched.

The last two mini splits I've done had line voltage connections to each unit, plus a 24V control cable between the two, like a standard AC unit would have.
 

curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
On most of the projects I have been involved with the HVAC contractor has installed the wiring between the outside and inside units. We just supply a circuit and disconnect adjacent to the outside unit. The HVAC guys have been running Mini-Split Cable. http://www.southwire.com/products/ez-in-mini-split-cable-600-volt.htm

I have not seen a Mini-Split system that requires separate circuits for the inside and outside units. The inside units have always received their supply from the outside unit.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
To the op

There is no reason the 14/3 wouldn't work. We have installed units like that and have used 14/3nm. Not an issue. Something else is amiss
 
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