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3 phase workshop wiring

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3 phase workshop wiring

Postby wallace » 05 Jan 2016, 18:50

I am in the process of planning a rewire of my 3 phase wiring in my workshop. At the moment it is daisy chained and done with cheap 16amp sockets. I plan on having a distribution board with mcbs for each machine going to isolators. Everything will be ran in conduit. My question today is does each machine have to have its own earth cable or can there be a 'communal' that each machine can be linked to?
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Re: 3 phase workshop wiring

Postby 9fingers » 05 Jan 2016, 20:26

Your distribution board should have an earth busbar and so I would run an earth wire along with each three phase run down the conduit. You might want to run a neutral as well for future proofing the installation if later machines might need the neutral for control circuits/lighting etc.

hth

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Re: 3 phase workshop wiring

Postby wallace » 05 Jan 2016, 21:00

Thanks Bob
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Re: 3 phase workshop wiring

Postby wallace » 07 Jan 2016, 16:14

I got myself what looks to be a decent board which has a good mix of B and C breakers.

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I have been shopping around for 4mm cable and so popped into my local CEF, normally I find them expensive but I just thought I'd try them. The guy quoted me £31.20 for 100m of 4mm single core. I went home and did a bit more searching for prices. After some research this seems to be a cracking price so I duly went back and ordered 3 reels and a reel of earth. the guy who quoted me was not there so I just told this other chap. He looked a bit puzzled and went into the back room to check with the boss I presume. I think I must of got the super doper trade price instead of the joe public price. :D
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Re: 3 phase workshop wiring

Postby 9fingers » 07 Jan 2016, 16:35

That is a pretty good price Mark. If your invoice quotes the % discount or the terms you were given, keep it for next time to prove the rate you are "entitled" to!!

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Re: 3 phase workshop wiring

Postby Robert » 07 Jan 2016, 16:44

That looks very similar to the board we had in our factory.

Most of our machines were wired with SWA cable. much easier than conduit and compared to plastic conduit tougher too.

Have fun pulling all those wires.
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Re: 3 phase workshop wiring

Postby Jimmy Mack » 26 Mar 2016, 10:30

+1 for running the extra core as Bob says, really usefully. Like Rob, We also run (black) wall clipped, swa ... to isolated switches then the machines are on flexible, clear coated SWA cable (I forget the name) on commando plugs. It makes things more easy to move about (especially when you've got to stick the planner out the door for long runs), PLUS if you move workshop you can take the cables with you. The conduit runs are professional and tidy but a bit more of a fiddle and permanent.

Looking forward to seeing pics of the board wire up,... have one to do myself at some point and want to avoid making a rats nest before I get it commissioned.

Jim

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Re: 3 phase workshop wiring

Postby wallace » 14 Apr 2016, 16:42

I have finally nearly finished extending my workshop, and having a good clearout. I bought a load of old isolators and switches last year. They were a bit crusty so they got a spin on the wire wheel. Mmm shiny. I ran some trunking around the shop, I hope its big enough to house the amount of wire that's going to be in it.

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I have a few Invicta 'Bill' ones which looked good once cleaned up. I plan on having my RAS, high precision drill, nipper saw and a wadkin mitre saw all in a row. I have a really nice LM borer drill which I am undecided if I will keep it.

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Re: 3 phase workshop wiring

Postby wallace » 17 Apr 2016, 18:51

I have this monster starter which I would like to use on my flat belt planer. I forgot to take a pic of the inside but its of similar vintage to a lot of my wadkin starters 40's/50's. I think it must have been used for a big motor because of the starting procedure. What do people think?

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Re: 3 phase workshop wiring

Postby 9fingers » 17 Apr 2016, 20:07

Curious that one! I've seen similar manual starters with three positions. Off , run and start.
But at the moment I can't think of how to define three states needed with only two positions.

is it three phase or single and what are the voltage rating on the plates of motors that use that system?
I'd expect them to possibly be 700/440 vac

The name Leonard (or more correctly Ward Leonard) is more associated with the speed control of DC motor especially as used in lifts before electronic controllers became feasible.

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Re: 3 phase workshop wiring

Postby RogerS » 17 Apr 2016, 22:06

Piqued my curiosity and did a bit of Googling and came across this article.
Fewer Smart things. More smart people.
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Re: 3 phase workshop wiring

Postby Robert » 17 Apr 2016, 22:24

So is this thing not a manual star-delta starter?
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Re: 3 phase workshop wiring

Postby 9fingers » 17 Apr 2016, 22:35

Yes this is the AC version of the original ward leonard DC system.

The original system consisted of some sort of prime mover typically an ac motor running at constant speed. This drives a dc generator the output of which drives a dc motor.

The clever bit is that the field coils of the dc generator can have a variable current flowing which affects the speed of the final dc motor. Also the currents in the field coil is much much lower than that needed to power the motor. So we have a small current controlling a much bigger one.
This can be thought of as an amplifier - the core of almost any control system ie a little effort can control a large effort.

I too have been searching and yet to find anything about a Leonard Starter. Almost certainly the same man but so far no luck on my part.
I do have some older text books which I will start on next week.

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Re: 3 phase workshop wiring

Postby 9fingers » 17 Apr 2016, 22:44

Robert wrote:So is this thing not a manual star-delta starter?


Well it could be but for the instructions which say to turn off, return the switch to A, which was the position to start the motor.

This is why I asked about the motor voltages.
For a traditional star delta starter, the motor is would for about 700 volts in star mode but onlyrun from 440 during starting, this gives about 1/3 power, drawing reduced current naturally. Once up to speed, it is switched to delta where the winding rating of 440v is run from 440v and so develops full power.
Star delta switch enables big motors >5hp to be started without drawing huge currents.

Not that "normal" three phase motors ( under about 5hp) tend to be 440v when operated in star. When such a motor is wired in delta, it must them be run from 240v three phase ( as produced by most modern inverters)

Note the ratio between the two voltages is always sq root 3 when converting between star (higher v) and delta (lower v)

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Re: 3 phase workshop wiring

Postby Robert » 18 Apr 2016, 09:53

I read it as position A does not latch so returning the lever to A but not keeping hold of it = off.

I did 3 phase theory at ONC and I do remember a fair bit of it. Unlike transmission line theory during HNC electrical and electronic engineering which I've completely forgotten.
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Re: 3 phase workshop wiring

Postby 9fingers » 18 Apr 2016, 10:07

Robert wrote:I read it as position A does not latch so returning the lever to A but not keeping hold of it = off.

I did 3 phase theory at ONC and I do remember a fair bit of it. Unlike transmission line theory during HNC electrical and electronic engineering which I've completely forgotten.



Yes it may well be there is some sort of spring return position between A & B that is the off condition.
Like several topics taught on modular courses, I found transmission line theory just too theoretical and at the time there was no attempt to tie it into practical application so it slipped from my memory too.

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Re: 3 phase workshop wiring

Postby Rod » 18 Apr 2016, 17:22

As part of my Civil Engineering degree course we studied Chemical, Mechanical and Electrical Engineering in the first year - forgotten most of it after 50yrs
Though my notes and some text books are still in the loft!

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Re: 3 phase workshop wiring

Postby wallace » 18 Apr 2016, 17:39

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Re: 3 phase workshop wiring

Postby 9fingers » 18 Apr 2016, 17:47

Looks like a simple star delta and not really worthy of Mr Leonard who provided much cleverer things! :lol:

Mark. Make sure that you only use this with motors that are designed for star delta starting eg those marked 700/400 volts.

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Re: 3 phase workshop wiring

Postby wallace » 18 Apr 2016, 20:33

So a false alarm on something differant :D I was hoping to use it on this brooks motor, I think its just 400v. I will see if I can find something with a bit character.

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Re: 3 phase workshop wiring

Postby Robert » 18 Apr 2016, 22:24

9fingers wrote:Looks like a simple star delta and not really worthy of Mr Leonard who provided much cleverer things! :lol:

Mark. Make sure that you only use this with motors that are designed for star delta starting eg those marked 700/400 volts.

Bob


Bob - just for my curiosity... why would the motor be 700V rated? In delta the windings see 415V but in star only 240V. Where does 700 come in to it?

If you wanted full power in star then I can see 700V being needed.
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Re: 3 phase workshop wiring

Postby 9fingers » 18 Apr 2016, 22:35

700 volts ( = approx 400 x root3) is not needed, but would be the natural voltage for full power for a motor that is designed for 400v when in delta.

During starting, the windings are in star but only getting 1/root3 of the voltage and as power is proportional to V squared, the power during starting is about 1/3rd of the normal rated power.

Does that help?

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Re: 3 phase workshop wiring

Postby Robert » 18 Apr 2016, 22:53

not really unless you meant to say full power in star :)

In delta each winding sees 415V. connect those same windings in star to 415v and each winding sees 415/1.73 = 240V with the middle of the star effectively being Neutral but not connected of course. And yes it will be at fractional power for a gentle start run up.

So I'm still not seeing why you need to consider 415 x 1.73 for a motor rating.
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Re: 3 phase workshop wiring

Postby kirkpoore1 » 19 Apr 2016, 02:52

Huh.

I was going to guess that it was a starting compensator, which was an early 1900's soft start device for high horsepower electric motors. Here's an old owwm.org post on the topic:

Reason for one ?? Need was brought about by the
general lack of sufficient capacity of early
distribution systems to start "across the lne " a
large motor on a machine with a high inertia.
The compensator was an early "Soft Start", in
that the first step from the off position was to
manually insert either a transformer or some
value of resistance to ease the starting surge
and limit the inrush current during the period
when the motor was essentially stalled. After the
machine was moving and coming slowly up to speed,
the operating lever on the compensator was moved
to "Run" and full voltage was applied to the
motor.. Later this manual switching was made more
automatic, through the provision of push buttons
and a step timer. If the price is reasonable and
you have a limited electrical service in your
shop,, then consider it's purchase,,, HOWEVER, if
you have to change the motor because of you not
having the right power available for the old
motor (like , you don't have three phase.) then
forget it you don't need it.
More questions ??


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Re: 3 phase workshop wiring

Postby 9fingers » 19 Apr 2016, 09:42

9fingers wrote:700 volts ( = approx 400 x root3) is not needed, but would be the natural voltage for full power for a motor that is designed for 400v when in delta.

During starting, the windings are in star but only getting 1/root3 of the voltage and as power is proportional to V squared, the power during starting is about 1/3rd of the normal rated power.

Does that help?

Bob


"not really unless you meant to say full power in star :)"

I rather thought I had?

In my experience motor plates state the voltages/current for the design power of the motor and hence one intended for use with a) Star Delta starting and b) on standard UK/EU 400v ish 3 phase would be marked as 400 ish/700 ish.
400 ish being between 380 and 440v and corresponding 700 ish being 660 to 760

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