The device I want to install is properly called a "voltage protector". It is not a UPS or AVR ("power conditioner"). I even posted a link to the device.

So what are you confused about?

Confused about your posts. It a real problem, with actual technical people, that can see many more possibilities (as opposed to a OP that thinks they know exactly what they want) than you can with the limited information you gave. We are trying to discover what you really need, not what you think you need.

I used your requested functionality finally posted here to find that device. We are all confused here. You seem to not know that split-phase is single phase with a CT neutral and we listened to your words of that you want, not a link to something likely not to work due to your not knowing/understanding the correct electrical terminology by saying you could not find the needed device when they are easily searchable for IF you know what to look for.

 

Do you have any 240 loads in this system, if so, do you intend to install these devices before or after those loads?

Just curious.

Yes, a few.

I intend to install these voltage protectors at the service panel so everything, whether 240V or 120V, is downstream from there.

I already have both 120V and 240V loads on individual voltage protectors. My objective is to install voltage protectors at the service box to protect all circuits.

 

Confused about your posts.

I used your requested functionality finally posted here to find that device. We are all confused here. You seem to not know that split-phase is single phase with a CT neutral and we listened to your words of that you want, not a link to something likely not to work due to your not knowing/understanding the correct electrical terminology by saying you could not find the needed device when they are easily searchable for IF you know what to look for.

As I understand split-phase: L1 & L2 are 180° out of phase with each other. They share a common neutral. Is that not correct?

Per my original post, what I cannot find is a voltage protector for a split-phase 3 wire install. The example I posted was of a single phase/2 wire device. As stated, I can find single phase (2 wire) devices and 3 phase devices, but not 3/wire split phase. I suspect the voltage protector wont care whether it is split or single phase, but I can't find one at all for a 3 wire install.

The main question becomes: can I [safely] use two single phase devices sharing a common neutral on a 3 wire install?

 

Re: Wikipedia:

"Split phase, also known as single-phase three-wire, is a type of electrical power distribution system.
It's commonly used in residential settings, particularly in North America, to provide both 120V and 240V power from a single transformer.
This system utilizes two "hot" wires, 180 degrees out of phase with each other, and a neutral wire connected to the center tap of the transformer's secondary winding. "

Yes, this. Seems split-phase is not familiar to many.

 

The solution for that is to have the utility correct the supply voltage or for you to have a local voltage regulator. Shutting off the power (not a good solution except in emergencies) will just make a nasty surge that will require a HEPD to suppress the transient voltages from the ON/OFF/ON switching.

Either way the voltage is single phase.

Yeah...thats not gonna happen here (utility providing in spec power).

Re power off causing a surge: You mean like a flyback surge? Even if there are no inductive loads?

 

Keep in mind...if you open either L1 or L2 before a 240 volt load that load can then power the open line.

 

Keep in mind...if you open either L1 or L2 before a 240 volt load that load can then power the open line.

Exactly; both lines would have to be opened up, regardless whether the fault occurred on L1 or L2

 

OK, so how bad is that, if one side of a 240 volt line is opened?? If there is another protective device on the other side it should also protect by switching off.

 

how bad is that, if one side of a 240 volt line is opened??

If one side of the main feeder is opened leaving 240 volt devices with only one leg powered, the 240 volt devices will be in series with the 120 volt devices on the open leg to neutral. That sounds somewhere between undesirable and very bad.

 

If one side of the main feeder is opened leaving 240 volt devices with only one leg powered, the 240 volt devices will be in series with the 120 volt devices on the open leg to neutral. That sounds somewhere between undesirable and very bad.

As soon as the voltage on the other side rises, that device would trip, isolating that side also.

 

Exactly; both lines would have to be opened up, regardless whether the fault occurred on L1 or L2

Good point!

That answers my question: you should not install two single phase 2 wire voltage protectors on a 3 wire split phase unless you add circuitry to open/close them in sync.

Thanks!

 

OK, so how bad is that, if one side of a 240 volt line is opened?? If there is another protective device on the other side it should also protect by switching off.

Potentially very bad.

Ive had it happen before due to a loose connection. Fortunately everything important downstream was protected. What got fried was protection devices, wired smoke alarms, and GFI breakers.

Without protection devices it would have been much worse.

 

Good point!

That answers my question: you should not install two single phase 2 wire voltage protectors on a 3 wire split phase unless you add circuitry to open/close them in sync.

Thanks!

Gives rise to a product idea: individual modules that can be interconnected to create any combination of wires/phase needed. This could be applied across a wide range of devices, not just voltage protectors.