ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades What is the meaning of "R-S-T" in 3-phase system?

I'm trying to find the reason the 3 phases are named "R-S-T" in a unit from Taiwan. Is it just something someone came up with like "A-B-C" or could it be an acronym for something?
I've found that it's used in various places like Sweden and Korea. But Google doesn't come up with much else. Pointing me to the appropriate standard(s) would be super.
Thanks much.
Paul

It is not an acronym.

There are many different numbering schemes.
On motor contactors, manufacturers in the US usually labeled their incoming connections as L1, L2, L3. And then they will use T1, T2, T3 as the load terminals. In other parts of the world, terminals were labeled R, S, T and U, V, W.

A common current practice is the dual numbering scheme of L1/1, L2/3, L3/5 and T1/2, T2/4, and T3/6

So which is it?

R=L1, S=L2, T=L3, U=T1, V=T2, and W=T3?

Or

R=T1, S=T2, T=T3, U=L1, V=L2, and W=L3?

RST is the incoming supply, UVW and XYZ are the motor connections.

See here: TOS lathe - manual Y Delta start switch

I remember looking through a catalog when I was a kid and seeing RST on a European phase-rotation tester and wondering what, if anything, the letters meant.

Other letters can be found to identify phases. Here in the U.K., for example, we often used RYB for red/yellow/blue, the standard phase colors (well, until recently!).

Thanks Paul for the explanation. I did run across the U.K. "RYB" earlier in my search but didn't pick up on the red/yellow/blue linkage. I think the colors used sometimes here in the states are like red/blue/black. This of course confuses the Black/Red of DC power systems. Oh well.
My solutions will be to have our friends in Taiwan do some text editing. Thanks again for your input.

I was once told XYZ are generator terminals, UVW are motor terminals (the other set of terminals are usually U1, V1, W1) and RST are terminals of a receptacle and other stuff in/ on the walls.

The motor designations have stuck, receptacles, panels and everyting else now have the standardized L1, L2 and L3 all across Europe.

Phase colors way back were black, red and blue too! That is if there was no ground wire. In that case the phases would have been black, blue and grey. Unless there was a neutral... then the phases were black, blue and black.

Guess why that color scheme was abandoned in the 1960s...

Side note: in reality at least in Austria all those colors were hardly ever used. Conduit wiring mostly had all 3 phases the same color, for example 3 blue wires and a red one for the ground.

Sounds like the guy who dreamed that up had spent a little too much time at an Austrian beer festival!

Thanks Pauluk for putting in that link.

We discussed that topic already not too long ago.

R,S,T is now superseaded with L1, L2, L3 or A, B, C or R, Y, B in the South pacific.

All the new stuff here in NZ is Red,White,Blue.
Although there is a LOT of older stuff that uses the older type colour scheme.
We have been told to use the Yellow heatshrink up first before getting into the White stuff.
Darn bean counters!!

Weird that -- In Britain we changed the B phase from white to yellow in the mid 1960s, while in N.Z. you've just done the reverse!

How long before you guys go for the new brown/black/gray?

Ducks for cover.....

Hope not. Pauluk

Happy with the colours we have in NZ.
They are sensible colours.

Especially black which is a Neutral conductor here.

I'd say that depends on the point of view

Attached are two pics from common phase sequence meters used in our POCO area.

The RST marking is clearly visible.

Regards
Raymond


Kyoritsu Ø seq.


Densokki Ø seq.

What's on the end of them wires Ray?.
Probes or clamps?.
My Seaward Phase sequence tester uses probes, but I have seen a lot with alligator clips on them.

Here it is:

Mike, at the end of the Densokki are alligator clips.
The Kyoritsu 8031 has removable screw on insulated alligator clips, otherwise probes.

I have seen the one you use as well by other contractors in the field.

The Toptronic T855 becomes also more popular, as well as probes, clips it has fused leads, which adds to additional safety.