Three Phase Definition

Did you catch the other question i asked you today? It was buried in your response to another post as an off topic response.

I wanted to be sure ALL single phase 230V (208V) power in the continental USA was in fact 2 phase, not the "real" European single phase. I have a mixer control for one of our tanks we are shipping to a customer in Louisianna that was built in Europe. The 230V single phase equipment is wired with a single fuse and a neutral terminal block. (one of the phases will not be fuse protected). I insisted we re-build this panel with double pole fuses to protect the conductors on what was the European neutral, as they are smaller than I would ever consider on a power circuit. Over all the system is assumed to be protected by the customers 20A feed, but that is too large for what appears to be AWG 18 conductors on some of the smaller devices.

You don't know of any 230V to neutral systems in the USA do you? We have sent these to the same customer before without modification, as I missed the intended final destination on the previous order, but the customer never complained about the wiring. Their plant electrician should have "blown a fuse" when he saw how the control was wired/fused, unless they are on a Euro style 230V system.

In the US, generally, residential is considered split phase 220VAC, and commercial can be whatever the customer wants based on their line-up.

208VAC is normally derived from a three-phase system by utilizing two of the three phases (is that what you meant?).

However, if a customer's line-up allows trafo strapping for 230VAC, then you wouldn't hear any complaints from the engr or electrician...they would just know their jobs and make it so.

230VAC single phase in the US? Not "normal"...but there is a lot of outside of the norm stuff here.

Yes - that's it exactly - I expect the voltage source to be 208V with two phases being utilized. Maybe that isn't so in all areas of the USA or as you imply, some industries may have different voltage feeds. But you would agree that generally for use in the USA there should be a double pole fuse with fusing in both sides, not one fused and the other treated like a neutral or common - right?

I am a bit concerned about bringing this up now with the customer since we already sent out panels wired in the European style on a previous project, or I would have them called and the plant voltage confirmed.

The costly solution to this would be to replace the 230V VFD with a 120V one that creates a 3 phase 208V output. (VFD manufacturer has such a model for this small HP motor) Then the single fuse and neutral block could remain intact, as the other equipment is universal and will run on 120V to neutral just as well as on 230V, and we could just have the unit plugged into a general wall receptacle.

Yours is a good post, except for even suggesting that 2 phases give a useful 208 volts!

I have removed one of your Off Topics with a GA.....

Remember that when using two of three phases, they are 120° apart......whereas the split single phase is only one phase.....as needed for say UK equipment....I have never put a scope only across 2 phases, but I would imagine a rather large variation in voltage.....

I would guess 5 OTs are your own and one from someone who does not understand the problems....

OK in the UK and the rest of the sensible world a "hot" return rail is not used. It would be grounded, no control contacts allowed between the coil and the return rail. There are numerous reasons for this, the main being an earth fault can't short out sections of the control.

If you look in to why the US allows a hot return rail you need to look back a long way. To journeymen that were house bashers being employed in industry, they simply couldn't understand the drawings.
Like a lot of things a recognised standard boils down to catering for the stupid.

Yes - but - in the USA we have a maximum of 120V to neutral for our residential appliances and lighting. Not terribly dangerous - most people just get a good tickle from this. However in the UK, you get 230V when you are stupid and touch something you shouldn't - a whole lot more serious. My Father taught me well - he rewired our house when I was still a young boy standing on a rubber tire without turning off the electricity - try that in the UK.

I know, I know - no reprimands - this is not a funny subject.

Always a weird one the differencse across a puddle. Live working is a real hot potato with us at the moment, it's the crotchety old ones (like me) that shake our heads in disbelief at the "safety" regulations.

The IET 17^th edition (rev2) that we are saddled with is a farce. So many contradictions that you need a whole stack of books to make any sense of them. Some sections have recommendations that fly in the face of the laws of physics. But the youngsters in the industry blithely quote then with out thinking what they are doing.

You dad sounds my sort of person.