Mini Splits

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Dennis Alwon

Dennis Alwon

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The last few days I spent at an electrical conference in Raleigh. Over 700 people attended- contractors, ec,electricians, inspectors etc.

We do this every year and this year it was quite good because they changed the format and more questions got answered.

One particular question came up about mini splits and whether or not a disconnect was needed at the inside unit.

The opinion was no disconnect was needed based on 440.8 except and 430.87 exception.

They did bring up that many of these units have dc motors and that it would not be compliant to install a standard snap switch on a DC circuit. They stated that if you tried to turn the snap switch on under load you would be in for a surprise. They did not elaborate.

Does anyone know anything about this. There are tons of units out there with a/c switches
 
Can you elaborate on the "opinion". Since the motors are in a different location, I don't see 440.8/430.87 Ex 1 applying.
I can see it for a compressor/condenser fan but not a mini-split...

no comment yet on the DC switch
 
augie47 said:
Can you elaborate on the "opinion". Since the motors are in a different location, I don't see 440.8/430.87 Ex 1 applying.
I can see it for a compressor/condenser fan but not a mini-split...

no comment yet on the DC switch
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I think what they are getting at is that this is one machine and thus the outside unit is the controller for the inside unit. This being the case the disconnect only has to be within sight of the controller
 
I always wondered if the indoor unit of the mini-splits really were considered something that could be serviced anyhow. I guess I haven’t looked real hard at them since the hvac guy does most of the work hooking up.
 
Dennis Alwon said:
I think what they are getting at is that this is one machine and thus the outside unit is the controller for the inside unit. This being the case the disconnect only has to be within sight of the controller
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I understand the single machine argument but 450.87 does not seem to support the idea, IMHO
 
Dennis Alwon said:
They did bring up that many of these units have dc motors and that it would not be compliant to install a standard snap switch on a DC circuit. They stated that if you tried to turn the snap switch on under load you would be in for a surprise. They did not elaborate.
Click to expand...
I would think that turning the switch off under load would be much more interesting, as DC is more likely to cause arcing, since there is no zero crossing which helps extinguish the arc.
 
LarryFine said:
I would think that turning the switch off under load would be much more interesting, as DC is more likely to cause arcing, since there is no zero crossing which helps extinguish the arc.
Click to expand...

He may have said turning it off under load-- I don't recall
 
I have never noticed 440.8 before, but is one more thing that should allow not requiring a disconnect for inside portion of this system.

My thought has always been that 440 only applies to items with a hermetic compressor, it mentions this in 440.1.

The indoor unit, unless the whole system is deemed a single unit, does not contain a hermetic compressor and therfore IMO does not fit in the scope of 440. It is simply a motor operated appliance and is covered by art 422. They also are typically under 300 VA or 1/8 HP and 422.31 allows the branch circuit device to be the disconnecting means, and does not require it to be within sight.

The motor may be a DC motor but the question about a typical AC toggle switch not being rated for DC becomes a question of whether it is interrupting DC or not. If the rectifier is in the outdoor unit then it is wrong to use a switch only rated for AC. I don't know enough about what is typical for these units to know where the rectifier is located.
 
kwired said:
The motor may be a DC motor but the question about a typical AC toggle switch not being rated for DC becomes a question of whether it is interrupting DC or not. If the rectifier is in the outdoor unit then it is wrong to use a switch only rated for AC. I don't know enough about what is typical for these units to know where the rectifier is located.
Click to expand...

I would find it odd that the switch would actually be disconnecting only the portion of the circuit that's DC and not some AC component upstream from the motor.
 
rcarroll said:
I have a mini split in my house, no inside disconnect.
I don't require inside disconnects when I inspect them. Right or wrong,homeowners would hate them.
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For Aesthetic reasons I take it?


JAP>
 
I have never seen a disconnect on a residential or commercial mini split on the inside. Take that with a grain of salt though as Virginia is still under the 2011 NEC for commercial, and a good number of these units could have been wired under the 2008 or even 2005 NEC.

Are the DC motors even of a high enough voltage and amperage to cause an arc worrying about? Interesting is too vague a term... I find that light switches that Arc internally interesting... Some might find a bolted fault across 480 3-phase interesting, or a 500 KV transmission line opening in throwing a lightning bolt a hundred feet in the air interesting
 
JFletcher said:
I have never seen a disconnect on a residential or commercial mini split on the inside. Take that with a grain of salt though as Virginia is still under the 2011 NEC for commercial, and a good number of these units could have been wired under the 2008 or even 2005 NEC.

Are the DC motors even of a high enough voltage and amperage to cause an arc worrying about? Interesting is too vague a term... I find that light switches that Arc internally interesting... Some might find a bolted fault across 480 3-phase interesting, or a 500 KV transmission line opening in throwing a lightning bolt a hundred feet in the air interesting
Click to expand...
High enough voltage is a good possibility. These units are usually 208-240 volts input - if directly rectified from input volts I'd say it is high enough to be a concern.
 
JFletcher said:
I have never seen a disconnect on a residential or commercial mini split on the inside. Take that with a grain of salt though as Virginia is still under the 2011 NEC for commercial, and a good number of these units could have been wired under the 2008 or even 2005 NEC.

Are the DC motors even of a high enough voltage and amperage to cause an arc worrying about? Interesting is too vague a term... I find that light switches that Arc internally interesting... Some might find a bolted fault across 480 3-phase interesting, or a 500 KV transmission line opening in throwing a lightning bolt a hundred feet in the air interesting
Click to expand...

I would agree.

Also if it were a high enough DC voltage and current I wouldn't think a standard snap switch would be used for the disconnecting means to begin with.

JAP>
 
Never liked the idea of having a 3 pole switch required for the indoor unit and always wondered:

1. Is a 3 pole switch rated to have both ac and dc on the same yoke?
2. Often times people install a plastic old work box next to the unit to accommodate the switch (metal ow is too narrow), but the switch didn't have a grounding screw, so the switch itself would not be grounded.
3. Why is the requirement for a disconnect (i.e. padlockable device) for a wall oven hardly ever enforced, but was strictly enforced for mini splits? I realize we are talking about 2 different animals, 440 vs 422.
4. Why the heck don't the manufacturers just put an on-off switch on the unit and call it a day?

Glad to see this requirement go away.
 
Actually many of these units use small VFD's on the compressor and possibly the fan motor although as small as these indoor fan is, it would seem a simple multi winding motor would be far more cost effective.

The point is while a DC inverter may be inside the unit, the indoor unit disconnect still sees 120v or 240v AC. And a double pole should be fine as the third wire usually is low voltage control or data signal.

There are a lot of myths about the indoor unit wiring. Such as you can't splice it, you can't use solid wire. Hogwash IMO as an EE. The data signals that go ever the control wire are low bandwidth and have to be immune from EMI anyway. There is no reason 12-14/3 NM, BX, AC can't be used for that. The expensive cables the manufactures sell is in no way specially shielded either that I have seen.

I think these "special" cables are just a money grab from the unit manufacture. Of course they could void the warranty if you don't use them. Then comes the question of listing. Some of these OEM cables look like nothing more than foreign 14/4 SJT. Are these cables even listed for in-wall use under the NEC?
 
Andy Delle said:
Actually many of these units use small VFD's on the compressor and possibly the fan motor although as small as these indoor fan is, it would seem a simple multi winding motor would be far more cost effective.

The point is while a DC inverter may be inside the unit, the indoor unit disconnect still sees 120v or 240v AC. And a double pole should be fine as the third wire usually is low voltage control or data signal.

There are a lot of myths about the indoor unit wiring. Such as you can't splice it, you can't use solid wire. Hogwash IMO as an EE. The data signals that go ever the control wire are low bandwidth and have to be immune from EMI anyway. There is no reason 12-14/3 NM, BX, AC can't be used for that. The expensive cables the manufactures sell is in no way specially shielded either that I have seen.

I think these "special" cables are just a money grab from the unit manufacture. Of course they could void the warranty if you don't use them. Then comes the question of listing. Some of these OEM cables look like nothing more than foreign 14/4 SJT. Are these cables even listed for in-wall use under the NEC?
Click to expand...

I am not sure this is accurate as many of these units are run with T-stat wire between the indoor and outdoor units. I have seen the line voltage units also and I agree that they are fine wired with 14/3 nm or whatever.... But some of these units are run with low voltage to the indoor unit
 
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