240 split phase vs 230v European inverter and US split phase devices

[1201]

In North American equipment the L1 and L2 are isolated from ground. For a simple element water heater, it probably wouldn't matter. For most other equipment (with electronics or control circuits) it would be a problem.
Like a dryer, or range.
The older ones have a 3 wire cord. The newer ones have a 4 wire cord. But all require a split-phase ground. (120v from L1 or L2 to ground)

Ok so if it's a USA 240v only load, like my water heater or heat pumps then it's no problem but for dual 120/240 loads it's a big no no? I think I'm tracking.

Another question- you said L1 and L2 are isolated from ground. Ie not bonded? I just want to make sure I understand this- if one of those makes contact with ground say via a metal case, the current will still travel back to the transformer via the neutral wire right?

 

[timselectric]

Ok so if it's a USA 240v only load, like my water heater or heat pumps then it's no problem but for dual 120/240 loads it's a big no no?

Heat pump would be a maybe. Depending on how old it is. If it just has a contactor, it's probably fine. If it has a fancy control board, maybe not.

Another question- you said L1 and L2 are isolated from ground. Ie not bonded? I just want to make sure I understand this- if one of those makes contact with ground say via a metal case, the current will still travel back to the transformer via the neutral wire right?

It would travel back the ground wire, through the N/G bond, and then through the neutral to the transformer (if one is installed).

But, if you have a transformer. None of that matters. You are installing a split-phase system. And everything will work as designed.

 

[1201]

Heat pump would be a maybe. Depending on how old it is. If it just has a contactor, it's probably fine. If it has a fancy control board, maybe not.


It would travel back the ground wire, through the N/G bond, and then through the neutral to the transformer (if one is installed).

But, if you have a transformer. None of that matters. You are installing a split-phase system. And everything will work as designed.

You mean an auto transformer?

 

[timselectric]

You mean an auto transformer?

An autotransformer would be fine for creating a split-phase ground point.
But I wouldn't recommend it if you are running the grid through the AIO.

 

[zanydroid]

In North American equipment the L1 and L2 are isolated from ground. For a simple element water heater, it probably wouldn't matter. For most other equipment (with electronics or control circuits) it would be a problem.

So to throw another chunk of complexity into here. My understanding is that, because of the large variance in how L-N-G are installed onto receptacles in Europe / overseas (even within the same country), imported plug-in appliances are generally pretty tolerant of being operated out of spec, EG with L-N tied to L1-L2. Since half the time you can't trust the L-N polarization anyway in the plugs/receptacles.

I'm not sure if that applies to hardwired appliances however. Hopefully the standards for L-N-G identification are less crazy than for receptacles.

 

[CoolWill]

I know of no air conditioners that use 120/240 volts. I saw some window units from the 60s that did, but I don't think that's what we're talking about here.

In an off grid setup, using a 230 volt L-N inverter and bonding the N to ground would work just fine for any 240 V-only appliances. But if you feed it with gride 240, you're most likely going to have a problem, depending on how the input connects to the output.

 

[zanydroid]

I know of no air conditioners that use 120/240 volts. I saw some window units from the 60s that did, but I don't think that's what we're talking about here.

I interpreted those posts as - 240V to outside unit, 120V to air handler. Pretty standard, right?

(or are 120V air handlers only for gas furnaces)

 

[timselectric]

I interpreted those posts as - 240V to outside unit, 120V to air handler. Pretty standard, right?

(or are 120V air handlers only for gas furnaces)

Electric furnaces are usually all 240v. Except for the controls , which are 24vac created from an internal transformer.
Gas furnaces in North America are usually 120v. Also with their own control transformer.

But a lot of the new equipment control boards verify that there is a ground before starting up.
To do this it's checking for line to ground as 120v.
When L2 is bonded.
If it checks from L1 , it would see 240v.
If it checks from L2 , it will see 0v.

 

[zanydroid]

Yes, they need to do a ground check, and for furnace the flame sensor relies on a ground bond for basic operation so it's not just for safety.

Anyway, going down the transformer rabbit hole is basically a "Great power / Great responsibility" situation... you're trading off some minor equipment savings against no longer being code compliant / significant responsibility to either get smart about it and really understand what is going on (which is a worthy goal, education never hurts) or being super YOLO about it (not good).

 

[RCinFLA]

Some 240vac air conditioners use 120vac for their electronic control board power.

NEC rules now require GFCI to outside units like 240vac air conditioners and sprinkler water pumps.

I do not know the rule for unit replacements. I am sure if you have a new AC main panel replacement you have to bring everything up to code.

Not sure about replacement air conditioner or sprinkler pumps. Since it could be an expensive additional cost to upgrade to GFI protection, I presume you can get away with a replacement A/C or pump without upgrading to GFI protection on them.

You should always check to make sure there is grounding wire to metal case of A/C and pumps. An induction AC motor 240vac stator winding can short to metal case so you need a case ground wire return to blow the breaker.

 

[zanydroid]

NEC rules now require GFCI to outside units like 240vac air conditioners

NEC extended the exemption for HVAC until something like 2026 because of all the false trips that have been happening due to shitty American HVAC engineering.

I'm pretty scared of doing the ground wrong on HVAC system. That means a ton of exposed metal in your house is potentially not grounded correctly, since there is potentially a circuit from each register all the way back to the air handler (depending on type of duct used of course).

 

[SparkyJJO]

HVAC ground is no harder than anything else. There is a ground terminal in the air handler to connect the griund wire to. Same as any other appliance. As long as you connect it to the ground at your panel, and your panel is also grounded properly no problem.

 

[RCinFLA]

NEC extended the exemption for HVAC until something like 2026 because of all the false trips that have been happening due to shitty American HVAC engineering.

I'm pretty scared of doing the ground wrong on HVAC system. That means a ton of exposed metal in your house is potentially not grounded correctly, since there is potentially a circuit from each register all the way back to the air handler (depending on type of duct used of course).

Only for mini-splits and variable speed inverter units.

 

[zanydroid]

HVAC ground is no harder than anything else. There is a ground terminal in the air handler to connect the griund wire to. Same as any other appliance. As long as you connect it to the ground at your panel, and your panel is also grounded properly no problem.

Sure, that case is normal and easy.

I was referring to when people start talking about stuff like adding a transfer switch on the furnace to plug it into their auto transformer, isolation transformer, or ungrounded generator.

 

[RCinFLA]

HVAC ground is no harder than anything else. There is a ground terminal in the air handler to connect the griund wire to. Same as any other appliance. As long as you connect it to the ground at your panel, and your panel is also grounded properly no problem.

That assumes the A/C service personnel know what they are doing. The ruling was partially motivated by a 12 year old girl jumping over a chain linked fence onto top of an ungrounded outside A/C units getting electrocuted.

When I had to replace my sprinkler pump, the original new house pump, presumably with new house electrical inspection, had no ground wire connected to pump 240 vac motor case.

 

[FilterGuy]

Lets do some N-G Bond 101.



Let's look at how this works with 240V circuits



Notice that in the above 240V circuit, Neither hot leg is bonded to ground.

Now let's look at a typical 230V circuit in the EU.



There are several key things to notice.
* The color coding on the wires is different.
* The utility does the N-G bond. (this is common but not necessarily always true. A few old systems have no NG bond)
* The utility does the earth grounding. (This can vary, but it is common)
* The hot wire is a full 230V in reference to the ground (In the US each hot wire is 120V in reference to the ground)
* One of the 230V lines is the neutral line. (In the US, neither of the 240V lines is the neutral line)


SO.... you could make a 230V EU inverter work on a 240V US load, but you must be extremely careful to understand what is happening with grounding and bonding so you don't end up with energized metal surfaces or dead shorts. Furthermore, once you get it working it would be such an odd set-up, it is just begging for someone to do something that will be dangerous.

I could probably draw something up that would work, but I am so against doing it I won't assist others by showing how.

 

[zanydroid]

Furthermore, once you get it working it would be such an odd set-up, it is just begging for someone to do something that will be dangerous.

Unpopular opinion: If someone understands it well enough to implement a 100% safe and functional system due to the necessary professional or educational experience, they should probably treat themselves to the more expensive proper 120/240V hardware instead of living dangerously (if they end up not really understanding it as well as they think) to save a few bucks. And the day job probably pays well enough to support that.

 

[timselectric]

Trust no one else with your life, or the lives of your family.

 

[Hedges]

240V would be a few percent above the 230V (or 220V) it expected. Then if line was running high, it would be further from expected. Works until beyond limits.

I interpreted those posts as - 240V to outside unit, 120V to air handler. Pretty standard, right?

(or are 120V air handlers only for gas furnaces)

I have 120V feeding gas furnace blower and controls transformer.
240V to outside A/C compressor.

Since it could be an expensive additional cost to upgrade to GFI protection, I presume you can get away with a replacement A/C or pump without upgrading to GFI protection on them.

If available for your model and space in the box (not overstuffed with tandem including this circuit), GFCI addition would be $50 to $150.
I've put in 30A 2-pole GFCI for my dryer circuits. They are available at least up to 50A. I haven't for A/C or pool pump (already GFCI for pool lights and outdoor outlets) but maybe I will in the future.

You should always check to make sure there is grounding wire to metal case of A/C and pumps. An induction AC motor 240vac stator winding can short to metal case so you need a case ground wire return to blow the breaker.

Definitely. And any tools you pick up. I used a pipe-threader power head for quite some time before I changed its power cord, and discovered ground wire not connected.


Don't use a 120 or one pole of 120/240V breaker for 240V. Get a breaker rated for that.

GFCI, there are 2-pole, but circuitry powered by 120V. From McMaster-Carr I was able to get a portable 240V GFCI with 3-wire not 4-wire plug. (Hmm, gotta make sure it isn't using ground to power circuitry!) My application is 208 or 240V bench testing at work, decided to use GFCI to power the DUT (old dog learning new tricks, after the horse got out of the barn.)

 

[RCinFLA]

Don't use a 120 or one pole of 120/240V breaker for 240V. Get a breaker rated for that.

There are many 240vac air conditioners that use single pole contactors. That should not be allowed.