120v 20 Amp to 220v circuit 20 Amp

[Mark]

And if you go to Ford Motor on the south side of Chicago they use 480 volt b phase ground that runs about 530 volts between phases

[Mark Lloyd]

I have heard 110/220, 115/230, 117/234, 118/236, 120/240, and 125/250.

[trader_4]

Me too, but what is actually there in homes US today and has been for a very long time is 240/120.

[gfretwell]

Not exactly It is 120/240.

240/120 means 3p Delta center tapped. (the big number first is 3p) 208/120 is 3p Wye. More obscure, 240/3p or 240/240 would imply corner grounded delta. (Looks exactly like a regular 120/240 single phase service but there is no 120v. Every combination is 240v.

[dpb]

I thought I had seen a chart of when US NERC standards were updated over the years that listed the nominal voltages but a quick gargle search didn't uncover it...would be kinda' interesting to see the history chart 'cuz for old fogies like us the 110/220 was definitely the thing; then there was the period of 115 and a while for 117 seems like I also recall...

But what were "official" and when I don't know.

--

[gfretwell]

I think I read an article in IAEI magazine some years ago about this so that might be a place to start. The designation of single phase vs 3 phase that I just referenced was in an article in ECM recently but most people in the business already know it. The only one that is fairly obscure is corner grounded delta. The only place I ran into it was in sewer lift stations. It will confuse you if you don't recognize it right away. It had me dragging my meter out the first time I saw it.

[Dean Hoffman]

A couple utilities here in central Nebraska have used it. I see it on irrigation hookups sometimes. Crescent Electric list price is almost $200 for the

200 amp dummy neutral fuse. The real price problem would be having to over size a variable frequency drive for a well motor. My area typically has 60 to 100 horse power well motors.

[Mark Lloyd]

[snip]

I put a meter on a receptacle recently, and measured almost exactly 120V.

[gfretwell]

They don't fuse the neutral in the installations I have seen. the 3p corner delta looks exactly like a regular single phase installation. 2 ungrounded conductors, 2 pole breakers and a white grounded conductor on a buss bar. I am also not sure why you would need to oversize a VFD unless they are doing this with 2 transformers. I typically see that with center tapped delta with a larger transformer on the winding that is center tapped because they expect most of the load will be on the 240/120 legs. The 3p would just be for incidental loads like computers, elevators or HVAC and one transformer provides that phase. The 3d side of the delta is open (Hence Delta Vee).

[Ralph Mowery]

Look at the meter several times a day and see how much it changes. I have a meter that monitors the voltage all the time. I have seen it go from about 117 to 125 volts over a months time. It has been calibrated with a known source that is accurate to about .5% so it could be off about a half a volt or so.

[gfretwell]

Mine is very stable at 123v but I have a pole pig in my front yard connected directly to the drop.

[Ralph Mowery]

I have a transformer that feeds my house and one other smaller one. There is about 200 feet of underground cable from the transformer to the house. It does not seem to matter all that much as to how much I have running as to the voltage going about 8 volts from low to high.

[gfretwell]

That sounds like your primary is overloaded. They will just keep adding transformers in a slowly evolving neighborhood until the birds start getting blisters on their feet. I bet your neutral to ground current is scary when you have that low voltage. (assuming single phase of a wye distribution, one hot wire on the top of the stack) At a certain point you and the other people on that primary (take a walk and look up) could have a chat with the PoCo. One customer bitching is a pain in the ass. Twelve is a problem.

[Dean Hoffman]

Just about everything is disconnect switches. Circuit breakers were considered unreliable in the dirt, heat and cold of the outdoors. The modern soft starts and vfds use breakers. L2 is always supposed to be the odd one, either in the corner ground or center tap configurations. I don't know the reason for the larger vfds. It's 3 transformers with the grounded legs. All I know is the resident expert where we buy them says so. He knows his stuff. I ask questions out of the blue and he answers off the top of his head and accurately.