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- John Montrose
May 2, 2006, 2:49 pm
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Dear All,
With the recent, ongoing thread on inverters, could I chip in and ask
a couple of questions concerning three phase wiring please?
1. If wiring up a 4-pin three phase plug/socket, is there an analogous
mnemonic to a 240v plug (bLue, left, bRown, right, etc.)? The
conductor wires out of my converter are black, blue and brown; the
socket is marked L1, L2, L3. At the moment, I have it wired
alphabetically (i.e. black-L1)
2. On said set-up, how (if at all) can I connect a transformer
[440--12v] to power the machine light? As received, the machine had
the live of the light connected to one of the phase wires, and a
separate (black) neutral (?) wire. As I understand it, this would
require three phases plus neutral (5-pin plug) and send 240v into the
light. Can I just connect the transformer across any two of the phase
wires?
A tip I recently read: when wiring a plug, make the earth wire longer
than the others. If the cable pulls out, the earth is the last to 'let
go'.
Thanks for any tips.
With the recent, ongoing thread on inverters, could I chip in and ask
a couple of questions concerning three phase wiring please?
1. If wiring up a 4-pin three phase plug/socket, is there an analogous
mnemonic to a 240v plug (bLue, left, bRown, right, etc.)? The
conductor wires out of my converter are black, blue and brown; the
socket is marked L1, L2, L3. At the moment, I have it wired
alphabetically (i.e. black-L1)
2. On said set-up, how (if at all) can I connect a transformer
[440--12v] to power the machine light? As received, the machine had
the live of the light connected to one of the phase wires, and a
separate (black) neutral (?) wire. As I understand it, this would
require three phases plus neutral (5-pin plug) and send 240v into the
light. Can I just connect the transformer across any two of the phase
wires?
A tip I recently read: when wiring a plug, make the earth wire longer
than the others. If the cable pulls out, the earth is the last to 'let
go'.
Thanks for any tips.
Re: Three phase wiring questions
Doesn't matter as you often have to swop phases over to get the
machine to run the right way.
If it is a 440 - 12v transformer than yes any two phases to the
transformer and 12v out.
--
Regards,
John Stevenson
Nottingham, England.
Visit the new Model Engineering adverts page at:-
http://www.homeworkshop.org.uk /
Re: Three phase wiring questions
John Stevenson Wrote:
Note that EACH of the 3 power leads is a hot lead. Each will have a
voltage compared to ground. So use care when dealing with this
stuff...
This aspect is similar to the way 110/220 systems are set up in the US.
It can sort of be looked at as 220 1 phase center-tapped to ground for
the 110. (Its relatively normal to see the ground and the "common"
wires joined to a single buss-bar in the breaker box...)
Yes, its a good idea to have the ground wire be slightly longer if
there's any chance of the wires being strained. It certainly can't do
any harm and it just might prevent a fire or save a life. Be
reasonable about the extra length.. 1 inch is probably plenty and adds
negligible resistance. (all wire has SOME resistance)
--
fhhuber506771
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Re: Three phase wiring questions
Just for clarification, the US system you refer to is NOT similar to the
three phase system used to power motors. The most common US domestic supply
is 110V-0-110V i.e. a single phase secondary with a centre tap, socket
outlets are wired across 0-110V and heavy appliances across the full 220V.
The two phases, if you wish to look at it that way, are 120 degrees apart
and thus useless for generating a rotating magnetic field in an induction
motor, in a three phase system they are 120 degrees apart so can generate a
rotating field. Note some states are 115V or 120V instead of 110V.
For completeness, the alternative US domestic supply that is becoming common
is to supply each apartment in a building with two phases and the neutral
from a three phase 4 wire system at 120V phase to neutral, each apartment
having a different pair of phases to balancing the load. The heavy
appliances have to be 208V for this system.
Greg
Re: Three phase wiring questions
The original question was on UK sourced three phase supplies and
bringing the crappy US electrical system into it not only clouds the
issue it's not even relevant.
However they managed to get a man on the moon when they can't get
three wires across 48 states beats me.
I'm sure Capricorn One was for real.
--
Regards,
John Stevenson
Nottingham, England.
Visit the new Model Engineering adverts page at:-
http://www.homeworkshop.org.uk /
Re: Three phase wiring questions
Under the old scheme we had:-
L1=Red
L2=Yellow
L3=Blue
Neutral=Black
Under the lethal new French scheme we have:-
L1=Brown
L2=Black
L3=Grey
Neutral=Blue
If you mix the old and the new colours anywhere it is recommended that the
cores on both cables are marked L1, L2, L3, N with ferrules, if possible, or
tape If you can't afford ferrules. You must also put a label on the cover of
the junction pointing out that both colour schemes are in use.
Labels are available from electrical suppliers. e.g.:-
http://www.tlc-direct.co.uk/Main_Index/Cable_Accessories_Index/Cable_Colour_Labels/index.html
Don't know if the likes of B&Q do them, they bloody well should.
As John indicates, you have an evens chance of having to swap things over the
first time you wire up a motor, but If you change things round so that the
phase rotation of the cable cores is correct after the first connection then
you should have a more predictable set up in the future.
Mark Rand
RTFM
Re: Three phase wiring questions
I would like to point out one VERY important item in your original
posting, you stated that the
the machine light was connected to one of the live phases and a
seperate Black (?) neutral cable so the machine must have originally
had a 5 wire connection.
Unless I am mistaken, your machine light is a 230v single phase unit
and as such MUST NOT be connected across two of you three 400v phases -
it can only be connected to a 230v supply, i.e. a phase and neutral.
You will need a 5 pin 400v plug or have a seperate fused single phase
230v feed to your machine light.
Hope this helps.
Best regards
Dave
Re: Three phase wiring questions
That's what I thought, hence the first thing I did was to disconnect
the light completely and remove the extra wire.
My original question was if it was possible to connect a 440-12
_transformer_ across the phase wires. As I understand it, mains
voltage machine lights are not a good idea: my lathe has a 12v light;
the surface grinder a 50v one. Presumably, it is absolutely imperative
that the transformer is an isolating one.
Thanks to everyone who responded to this question. Yet again, ukrme
does what google can't.
Re: Three phase wiring questions
Thanks for your concern. I appreciate your efforts to steer me on the
correct path. Be assured, though, that the _only_ place the neutral
was connected related to the light. The main control box (for want of
a better expression) contains four connections mounted on, and
insulated from, a rail; three brown and one yellow. As bought, all
earth connections went via one of the rail mounting screws: the yellow
connector which should be the earth was being (wrongly) used for the
neutral to the worklight.
Thanks once again for your input.
Re: Three phase wiring questions
Actually... The US power system works fine... thanks... and you can ge
a rotating magnetic field on a single phase... otherwise my 110 vol
2-wire fan with a squirrel cage rotor wouldn't work.
The aspect I pointed out as being similar really is similar... We ge
110 by going to ground, where you get your 220 or 240 off of your 44
3-phase by going to ground.
We have several differnt power systems over here... 110, 220, 408, 440
4160... and use each as is appropriate for the load.
As for Capricorn One being real... impossible. My Father was one o
the Flight Surgeons who examined the astronauts after 2 of the moo
missions. It is more likely for Queen Elizabeth to be a black man i
drag than for that movie to have anything to do with reality
--
fhhuber50677
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Re: Three phase wiring questions
Did I say it didn't ?
Yes of course there are several types of single phase motor. The fact
remains that the US 110-0-110 supply is fundamentally different to a 3 phase
supply, the 180 degrees between the two phase will not, on it's own,
generate a rotating field but the three phase 120 degree supply will, and it
is exactly this fact that drives the three phase motors used on machine
tools.
Greg
Re: Three phase wiring questions
take any 3-phase AC motor with a squirrel cage rotor...
Clip one input power lead.
Turn it on (best to remove the workload... you have severely reduce
the power output it can give without overheating)
It will run.
Now... if the single phase AC can't produce a rotating magnetic fiel
without playing games... why will the 3-phase motor even turn when yo
only apply power to one phase?
The sine wave AC input inherantly rotates the magnetic field. 1 phase
2 phase 3 phase .... 90 phases if you wanted to make such a system
--
fhhuber50677
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Re: Three phase wiring questions
fhhuber506771 Wrote:
The single phase AC field can be looked at as two counter-rotatin
fields.
The torque produced from both combined with the rotor at rest cancels
The motor won't start.
The starter windings produce a slightly larger field rotating in on
direction, and the motor begins to run.
( Or you can manually spin the motor in one direction or the other)
Due to the shape of the torque-slip curve, once it is running in on
direction the torque produced by the field rotating in the opposit
direction becomes very small,
while the torque produced from the field rotating in the same directio
increases.
Pat MacKenzi
--
pmackenzi
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