Do Away With Ring Final Circuits?

[bernardgreen]

This is where a little knowledge confuses.

Exactly. The little knowledge some people have has been learnt parrot fashion and is not the result of thinking about and questioning what it is they are being told.

Mind you some of the "trainers" are probably only repeating what they learnt parrot fashion.

( apologies to parrots )

 

[SUNRAY]

missed my point, At the red line I trust there is no dispute that this is a single phase circuit:

and equally these are both 3 pase:

But is this single or 2 or 3 phase?

 

[Harry Bloomfield]

It is two phases.

 

[SUNRAY]

And this?

 

[bernardgreen]

To my way of thinking to the left of the red line is a 3 ph supply and on the right of the red line is a bi-phase connected load

 

[JohnW2]

But is this single or 2 or 3 phase?

As bernard has said, that would best be described as a 3-phase supply with a single-phase load connected between two phases.

However, that is surely something which would rarely, if ever, be done with a 3-phase supply isn't it? What are these (single-phase) "~400V loads" you had in mind?

Kind Regards, John

 

[SUNRAY]

As bernard has said, that would best be described as a 3-phase supply with a single-phase load connected between two phases.

However, that is surely something which would rarely, if ever, be done with a 3-phase supply isn't it? What are these (single-phase) "~400V loads" you had in mind?

Kind Regards, John

Just as starting points:
- Heaters in grain hoppers and
- I've worked in many control panels with no incoming neutral and 400V single phase pumps, fans, transformers, relays, contactors, etc.

Please bear in mind I'm putting forward other peoples arguements here, to me it's '2 phase'.

 

[JohnW2]

Just as starting points: - Heaters in grain hoppers and - I've worked in many control panels with no incoming neutral and 400V single phase pumps, fans, transformers, relays, contactors, etc.

OK, I can't argue with your experience, but I've personally never seen, or heard of, such a thing as a ~400V single-phase load.

Please bear in mind I'm putting forward other peoples arguements here, to me it's '2 phase'.

I'm not sure that there are (m)any people who will ever have considered what they should call such an arrangement, since it is, I feel sure, very rare.

In any event, the concept of phase does not exist in relation to the pd between just two conductors, regardless of what sort of supply they derive from - so, to my mind, a "2-wire load" can never be anything other than a 'single phase' load.

Kind Regards, John

 

[bernardgreen]

I recall an electric boiler that produced high temperature hot water under several bar pressure for heating plastic extrusion machines. This had several immersion heater elements ( 9 ? ) which were connected variously between two phases. The number of elements powered could be changed by the control system to maintain the correct temperature in the extruder.

 

[JohnW2]

I recall an electric boiler that produced high temperature hot water under several bar pressure for heating plastic extrusion machines. This had several immersion heater elements ( 9 ? ) which were connected variously between two phases. The number of elements powered could be changed by the control system to maintain the correct temperature in the extruder.

Fair enough, but I think you might agree that it's extremely rare to see separate single 'single phase' (2-wire) loads connected between phases of a 3-phase supply.

In any event, what you describe is (at least when all elements are being used) somewhat of a semantic issue, since if three (or more) elements were within the same housing, with three conductors coming out of the housing, I think we would all happily call it a "3-phase load", wouldn't we?

Kind Regards, John

 

[bernardgreen]

I maybe wrong in memory but I am sure the elements each had two terminals to allow for various combinations. Most important this allowed for disconnection of a failed element ( earth leakage ) without having to shut down the boiler and interrupt production.

 

[JohnW2]

I maybe wrong in memory but I am sure the elements each had two terminals to allow for various combinations. Most important this allowed for disconnection of a failed element ( earth leakage ) without having to shut down the boiler and interrupt production.

Yes, I realise that was what you were suggesting but, as I said, it's almost semantic, because if three or more elements had been in the same housing, which had three terminals (with whatever arrangement of elements there was within), I don't think anyone would describe the situation as anything other than '3-phase' - particularly given that, in the absence of a 'neutral', each of the 'bits' of the load was inevitably connected between two phases.

Let's face it, once could probably turn the argument on its head in an attempt to argue that, say, a 3-phase motor was three separate single-phase loads (each having its own winding, or part of a winding, in the motor)!

Kind Regards, John

 

[bernardgreen]

(each having its own winding, or part of a winding, in the motor)!

but in almost all motors the three windings are interactive with each other via the magnetic structure of the motor. If one phase is disconnected from the motor then the currents in the other two phases are affected.

 

[JohnW2]

but in almost all motors the three windings are interactive with each other via the magnetic structure of the motor. If one phase is disconnected from the motor then the currents in the other two phases are affected.

Very true, but, as I hope you realised, I didn't intend that to be a serious suggestion. - I was merely indicating the manner in which some people might try to argue.

Anyway, that's obviously different from the situation in which the three (or more) '2 terminal' things are (as with heating elements) totally separate and non-interactive - in which case I struggle to see how they can be regarded as anything other than 'single phase'. As I said, 'phase' doesn't have any meaning with regard to the pd between two points (such as the terminals of a 2-wire' load).

Kind Regards, John

 

[SUNRAY]

... so, to my mind, a "2-wire load" can never be anything other than a 'single phase' load.

Kind Regards, John

... As I said, 'phase' doesn't have any meaning with regard to the pd between two points (such as the terminals of a 2-wire' load).

Kind Regards, John

Yes I agree too. And on that basis I'm sure you'll agree this is a single phase load:

Despite the fact the socket it's plugged into (represented by the red line)is this: