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Generators & Electric Motors General Discussion

Add neutral wire to make 240 into 120/240?


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  #1  
Old 09-02-2019, 10:04:01 PM
Graycenphil Graycenphil is offline
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Default Add neutral wire to make 240 into 120/240?

Not really a generator question, but I know there is a lot of great knowledge here.

I am thinking of putting a split system AC/Heat unit in my garage. I have a 240 circuit there that isnít used, but it is only 240 - no neutral wire.

Would it be acceptable to run just a neutral wire from the breaker box out to the garage, instead of running a whole new romex with three wires, plus ground.

Thanks.
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Old 09-02-2019, 11:11:14 PM
Steve Dawkins Steve Dawkins is offline
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Default Re: Add neutral wire to make 240 into 120/240?

It would work, but would not meet electrical code requirements. In my opinion, not acceptable.
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Old 09-03-2019, 09:18:57 AM
brianh brianh is offline
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Default Re: Add neutral wire to make 240 into 120/240?

Why does the system need 120 as well as 240? Check to see if there are any 120V loads in there. If so you could also add a 240/120 transformer for them and just run the whole thing on just 240. If not, it won't care if there isn't a neutral.
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Old 09-03-2019, 10:44:44 AM
Graycenphil Graycenphil is offline
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Default Re: Add neutral wire to make 240 into 120/240?

Thanks Steve. I will not do it if it does not meet code.

Good point Brian. I assumed that it uses 120 for the thermostat, interior fan, etc, but perhaps not. I will write the company (Mr. Cool) and see what they say.
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Old 09-03-2019, 12:03:03 PM
Power Power is online now
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Default Re: Add neutral wire to make 240 into 120/240?

I have Mitsubishi split system. It requires 120/240, but the outdoor portion only uses 240. After the code required outdoor disconnect, the 120 is fed back to inside unit to power blower motor and controls. I looked at it and said I have 120 right here- an outlet just below inside unit, why run all that wire across back of house and back again? Also requires larger size sealtite for extra wires.

Well, it would work that way, BUT if a service person opened outdoor disconnect, outdoor unit would still have 24 volt control voltage to compressor relay, and indoor unit would continue to run, calling for compressor to run. That is no good, and would not meet code, so I drilled more holes and ran #12 BX to inside unit.
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Old 09-03-2019, 12:34:19 PM
Vanman Vanman is online now
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Default Re: Add neutral wire to make 240 into 120/240?

We installed a couple of these at a friend's house, and he was able to order them in 240 volt. We installed the electrical for them before they arrived, and so did include a neutral, just in case. But it was not needed.

240 supplied to the outside unit, and it came with it's own cable to supply power and signal for the inside unit.

Keith
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Old 09-03-2019, 12:40:03 PM
AngrySailor AngrySailor is offline
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Default Re: Add neutral wire to make 240 into 120/240?

^this is how my Fuji’s and Windair are set up. 240v only to outdoor disconnect. See if you can order a 240v unit?
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Old 09-03-2019, 01:38:22 PM
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Default Re: Add neutral wire to make 240 into 120/240?

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Originally Posted by Vanman View Post
We installed a couple of these at a friend's house, and he was able to order them in 240 volt. We installed the electrical for them before they arrived, and so did include a neutral, just in case. But it was not needed.

240 supplied to the outside unit, and it came with it's own cable to supply power and signal for the inside unit.

Keith
SWEET!
Since they recommended a 20 amp circuit, I had to run 12 ga back to indoor unit and a separate thermostat wire for 24 volts.
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Old 09-03-2019, 01:55:51 PM
brianh brianh is offline
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Default Re: Add neutral wire to make 240 into 120/240?

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Originally Posted by Graycenphil View Post
Thanks Steve. I will not do it if it does not meet code.

Good point Brian. I assumed that it uses 120 for the thermostat, interior fan, etc, but perhaps not. I will write the company (Mr. Cool) and see what they say.
You don't need to do that, just look inside and see if there is a place to connect the neutral, and if so, what loads are connected to it. That'll tell you.
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Old 09-03-2019, 02:07:00 PM
Railroads Railroads is offline
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Default Re: Add neutral wire to make 240 into 120/240?

If running a new cable is not an option? Then I'd recommend either, A. Ordering a 240v model if available. B. Using a 240v to 120/240 transformer to obtain a neutral connection. The type of transformer would be a dry type which means it's sealed in epoxy instead of oil filled. The transformer might cost as much as the AC unit though. 20 amps is 5,000 watts or 6.3 kVA. Since you would want to size the transformer to be slightly larger than the load it will be powering, you would want a 7.5KW transformer or 9.4 kVA transformer.


Robert
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Old 09-03-2019, 02:35:41 PM
Graycenphil Graycenphil is offline
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Default Re: Add neutral wire to make 240 into 120/240?

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Originally Posted by brianh View Post
You don't need to do that, just look inside and see if there is a place to connect the neutral, and if so, what loads are connected to it. That'll tell you.
I havenít bought the unit yet. Just sort of planning it all out.
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Old 09-03-2019, 02:37:25 PM
Graycenphil Graycenphil is offline
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Default Re: Add neutral wire to make 240 into 120/240?

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Originally Posted by Railroads View Post
If running a new cable is not an option? Then I'd recommend either, A. Ordering a 240v model if available. B. Using a 240v to 120/240 transformer to obtain a neutral connection. The type of transformer would be a dry type which means it's sealed in epoxy instead of oil filled. The transformer might cost as much as the AC unit though. 20 amps is 5,000 watts or 6.3 kVA. Since you would want to size the transformer to be slightly larger than the load it will be powering, you would want a 7.5KW transformer or 9.4 kVA transformer.


Robert
I can run new wire if necessary. I would prefer not to, if I can help it. Just to save the trouble and expense.
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Old 09-03-2019, 03:52:21 PM
Birken Vogt Birken Vogt is offline
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Default Re: Add neutral wire to make 240 into 120/240?

It would be worth deciding on units that only use straight 240 to avoid the hassle of running new wire. There have to be a lot of straight 240 units available. To be honest I was surprised that there even were units that use 120.
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Old 09-03-2019, 03:54:18 PM
Graycenphil Graycenphil is offline
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Default Re: Add neutral wire to make 240 into 120/240?

But there is only one Iíve found, made by Mr. Cool, that has precharged lines so you can install it yourself. Pretty clever.
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Old 09-03-2019, 05:37:23 PM
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Default Re: Add neutral wire to make 240 into 120/240?

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Originally Posted by Graycenphil View Post
But there is only one Iíve found, made by Mr. Cool, that has precharged lines so you can install it yourself. Pretty clever.
I have seen those, wondered what you do with the extra tubing if you cannot cut it? coil it all up in the attic?
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Old 09-03-2019, 05:47:58 PM
Graycenphil Graycenphil is offline
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Default Re: Add neutral wire to make 240 into 120/240?

Try to plan it to have as little extra as possible. Usually just coil it up behind the compressor, but I suppose you could coil it in the attic, if you are going through the attic. It would make a neater installation.

Most people just go out the wall behind the inside unit and straight down to the compressor.
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Old 09-03-2019, 06:20:04 PM
Birken Vogt Birken Vogt is offline
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Default Re: Add neutral wire to make 240 into 120/240?

I have seen other good looking precharged self installed ones that were not Mr. Cool brand, just so you know. But never paid much attention so I am not sure what they were.
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Old 09-03-2019, 08:51:11 PM
Railroads Railroads is offline
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Default Re: Add neutral wire to make 240 into 120/240?

The 120v no doubt is for the blower motor and 24v transformer. Both of those components can be replaced with 240v components.

Have you considered one of the inverter split AC systems? Most of them call for 240v service. One needs to be careful though if near salt air because of issues with corrosion on the inverter PCB.

Robert
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Old 09-03-2019, 09:55:16 PM
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Default Re: Add neutral wire to make 240 into 120/240?

We just cut the tubing where we needed it and made a new flare. Or in the other case, cut it and brazed in an elbow, due to the nature of the installation. Make sure you are flowing nitrogen through it if you are brazing on it!

On the ones we installed, both fan motors and compressor are all variable speed, 3 phase AC, all controlled by the brains of the thing. They work GREAT. But all that electronic stuff makes me nervous. He's in the desert, so no moisture problems. Lightning could sure be problematic. These units recommended installing surge suppressors, which we did, one at each unit.

If you actually wound up with a unit that does need 120/240 with a neutral, the actual neutral current would likely be very little, and could be derived from a very small autotransformer, couple hundred VA at most, probably less. But as I recall they could be ordered for 120 volt or 240 volt. None required 120/240...

Keith
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