Disco, Mitsubishi mini splits.

[chris kennedy]

What do you guys use on the indoor units for a disco? Single throw double throw switch? Although there are 3 ungrounded conductors between the inside and outside units, the wiring diagram appears that a switch as mentioned above would be sufficient.

Thanks

 

[iwire]

 

[luckylerado]

Dryer plugs are a cheaper way to go. Probably could go 20 amp in many cases.

Do these fall under 422 or 440?

 

[augie47]

Locally most guys use a general use switch, two pole for 208-240, single pole for 120v motors.

From comments made by local installers, many jurisdictions allow the condenser disconnect to serve as the disconnect.

 

[kwired]

Dryer plugs are a cheaper way to go. Probably could go 20 amp in many cases.

Do these fall under 422 or 440?

The unit containing the compressor definitely is 440. The indoor unit - maybe not, but is not designed to really stand alone without the outdoor unit either - and is typically supplied by same circuit, sort of making it one unit. Maybe listing information gives us that answer?

I doubt these are an acceptable use for flexible cord and with that comes receptacles and cord caps.

Locally most guys use a general use switch, two pole for 208-240, single pole for 120v motors.

From comments made by local installers, many jurisdictions allow the condenser disconnect to serve as the disconnect.

What about the third ungrounded conductor between inside and outside units if using a two pole switch as a local indoor unit disconnect?

If 1/8 hp or less does it need a local disconnect?

 

[augie47]

.................................................


What about the third ungrounded conductor between inside and outside units if using a two pole switch as a local indoor unit disconnect?

If 1/8 hp or less does it need a local disconnect?

My understanding is that the 3rd conductor is a signaling circuit and low voltage. Some of the mini-split installers have related that the mfg ask that it be installed without splice or joint.
I have discussed the 1/8hp situation with fellow inspectors and we don't see that altering the requirement of 430.102

 

[kwired]

My understanding is that the 3rd conductor is a signaling circuit and low voltage. Some of the mini-split installers have related that the mfg ask that it be installed without splice or joint.
I have discussed the 1/8hp situation with fellow inspectors and we don't see that altering the requirement of 430.102

May be low voltage - but where is the return path, or better yet what return voltage from one of the other two leads is on this conductor? I ask with little experience with these units.

Have only had a small number of them inspected, but a big variance from the installers about how to connect them - some even say you do not put a switch in that line between the inside and outside units or their warranty is void.:?

 

[peter d]

Not that it's relevant, but I have never seen a disconnect installed for a residential indoor mini-split unit (and quite a few commercial ones too). I'm fully aware that it's a code violation, but it seems to be something that is not practiced or enforced around here.

 

[ActionDave]

Not that it's relevant, but I have never seen a disconnect installed for a residential indoor mini-split unit (and quite a few commercial ones too). I'm fully aware that it's a code violation, but it seems to be something that is not practiced or enforced around here.

Same here. We put discos on the outside only.

 

[augie47]

A number of our local inspectors have been involved in numerous discussions on these and have built up a huge folder of info and correspondence from UL, ETL, manufactures, dealers, , etc. in an effort to work out the dependencies between Codes, instructions and hear-say.
I can't say we have all the answers but the result has been to install a switch within sight from the outside and inside units to satisfy 430.102 and suggest using Southwire's mini-split MC to resolve other wiring method issues.
Installation techniques and enforcement seem to vary widely.

 

[chris kennedy]

The 3rd conductor (S3) comes off the S2 terminal to a set of dry contacts that closes when the unit needs to cool. So a 2 pole switch to open S1 and S2 opens all three conductors. At least that's what the wiring dia indicates.

 

[kwired]

The 3rd conductor (S3) comes off the S2 terminal to a set of dry contacts that closes when the unit needs to cool. So a 2 pole switch to open S1 and S2 opens all three conductors. At least that's what the wiring dia indicates.

Where does other side of this control circuit come from though? You need a load (maybe relay coil)n and a return conductor to a source to have a complete circuit.

Low volt signal that is ground referenced for one side of the source? If it comes straight from one of the other supply conductors then it is not low voltage.

 

[iwire]

The 3rd conductor (S3) comes off the S2 terminal to a set of dry contacts that closes when the unit needs to cool. So a 2 pole switch to open S1 and S2 opens all three conductors. At least that's what the wiring dia indicates.

I have wired split systems that the wiring diagram showed a field installed three pole switch.

 

[GoldDigger]

On at least one system diagram that I have seen there are two hots for 240V and the signal lead is referenced to one of the hots so no neutral is required. That means that you absolutely must interrupt the control wire too.

 

[goldstar]

Is this requirement specific to Mitsubishi mini splits ? I know they call for it in their diagrams and product specs. If other mfr's don't show it in their specs is it required ? Also, the condenser unit provides the working and signaling voltage for the indoor unit. If not called for in the specs, wouldn't the condenser disconnect be a sufficient disconnect means ?

 

[iwire]

Is this requirement specific to Mitsubishi mini splits ? I know they call for it in their diagrams and product specs. If other mfr's don't show it in their specs is it required ? Also, the condenser unit provides the working and signaling voltage for the indoor unit. If not called for in the specs, wouldn't the condenser disconnect be a sufficient disconnect means ?

There is a motor in the indoor unit, NEC 430.102(B) requires a disconnecting means within sight for motors.

 

[infinity]

This is all so confusing I'm glad that I don't install these things for a living. :slaphead:

Maybe we need a separate code section that specifically addresses these units.

 

[iwire]

This is all so confusing I'm glad that I don't install these things for a living. :slaphead:

Maybe we need a separate code section that specifically addresses these units.

I don't understand the confusion.

The indoor unit is an air handler and I think most folks are used to putting local disconnects on closet or attic mounted air handlers.

Why is there a difference with these small split systems? Is it because the indoor unit is indirectly supplied by the outdoor unit? :huh:

 

[goldstar]

I don't understand the confusion.

The indoor unit is an air handler and I think most folks are used to putting local disconnects on closet or attic mounted air handlers.

Why is there a difference with these small split systems? Is it because the indoor unit is indirectly supplied by the outdoor unit? :huh:

I understand the reasoning for the disconnect and I'm in agreement with you. I think a problem starts to arise (in a residential situation anyway) when you have to install an ugly looking disconnect next to a very neat looking AHU. It's one thing to locate a disconnect in an attic or a closet but quite another to put a big ugly switch on a wall in someone's dining room.

 

[peter d]

I understand the reasoning for the disconnect and I'm in agreement with you. I think a problem starts to arise (in a residential situation anyway) when you have to install an ugly looking disconnect next to a very neat looking AHU. It's one thing to locate a disconnect in an attic or a closet but quite another to put a big ugly switch on a wall in someone's dining room.

:thumbsup: