MechMate CNC Router Forum

Go Back   MechMate CNC Router Forum > Electrical & Electronic > 70. Control Systems
Register Options Profile Last 1 | 3 | 7 Days Search Today's Posts Mark Forums Read

Reply
 
Thread Tools
  #1  
Old Wed 24 June 2009, 08:05
andyclarkecncuk
Just call me: andy
 
bristol
United Kingdom
Isolator switch ?

Hi, Well i have said before that my electrical skills are not too hot.
I am ordering some more parts for my control box. It will have a three phase supply as i intend to have a three phase spindle.
My question is does the door mounted isolator need to swith all three phases and the neutral or just the lives?
Would this be suitable rs 381-3893
Thanks Andy
Reply With Quote
  #2  
Old Wed 24 June 2009, 08:10
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Andy,
Your box does not have to be 3 phase for a spindle. You can get a VFD that will run on single phase electrical. The VFD does the electrical conversion to drive the spindle and also varies the frequency of the drive voltage to change the speed of the spindle.

Normally in electrical equipment you only switch the hot or live wires. The neutrals do not get switched.

Your last part number, what manufacturer is that? Do you have a link to a datasheet or website? Kind of hard to answer those type questions with no info.
Reply With Quote
  #3  
Old Wed 24 June 2009, 08:17
andyclarkecncuk
Just call me: andy
 
bristol
United Kingdom
Hi Heath, thanks for your reply.
http://uk.rs-online.com/web/search/s...hTerm=381-3893

So do you think i should wire it 240v or go with the three phase , most of my machines run on three phase so no problem to use either.
Thanks Andy
Reply With Quote
  #4  
Old Wed 24 June 2009, 08:29
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
If you already have three phase in your shop, I'd wire for three phase. If you use single phase, you draw more amperage and will need heavier wire. Also, viewed from the overall electrical supply perspective in your shop, the load from the spindle on a single phase will act to unbalance the phases in your shop. Not likely to be enough to be a problem, but always good to keep an eye out for.

I'm based in the U.S., and as Heath states, common practice here is to switch only the hot wires and not the neutral. Your electrical system in the U.K. is different, and thus common practise may vary as well. You may want to have a conversation with somebody local who is experienced in industrial electrical.
Reply With Quote
  #5  
Old Wed 24 June 2009, 10:13
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
A typical VFD, for a given physical size (and price), can power a bigger spindle if used on 3-phase as opposed to single phase. Or, if you have 3-phase supply, you could typically use a less expensive, smaller VFD for a given spindle.

Since you are in the UK, with strict electrical standards and many lawyers, I would suggest you consult a local expert. However, my personal choice is to switch the neutral together with the lives . . . one actuator handle, breaking all 4 poles together.

But, before looking at what's in the box, let's be sure you have "Earth Leakage" or "Residual Current" protection before the box. If you leave the neutral unswitched, and fiddle around in the box, touching neutral to earth/ground will trip the EarthLeakage/RCD . . . in our case that trips the whole building because we only have one earthleakage/RCD at the main distribution board. Hence my preference for switching the neutral with the lives.
Reply With Quote
  #6  
Old Wed 24 June 2009, 10:51
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Andy,
Your switch looks like a good match. It has 4 poles so you could switch the neutral as well, like Gerald suggested. If you have the three phase then that would be fine, I just meant if you did not have it already it was not needed.
Reply With Quote
  #7  
Old Wed 24 June 2009, 10:51
servant74
Just call me: Jack
 
Nashville (Tennessee)
United States of America
"Earth Leakage" or "Residual Current" protection

Is this what I have heard called "Ground Fault Circuit Protection" in the states?
Reply With Quote
  #8  
Old Wed 24 June 2009, 10:53
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Jack,
Yes the same thing. European and North American terms for electrical and electronic terms are sometimes very different.

http://en.wikipedia.org/wiki/Residual-current_device
Reply With Quote
  #9  
Old Wed 24 June 2009, 10:57
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Gerald,
Your RCD protection at the panel sounds like a pain in the behind. Does this trip lights as well? This sounds to me like it would not be a good thing to do. Machinery running, then bam, lights go out. I have never seen a building wired this way. Here individual circuits or perhaps individual receptacles will have the protection when needed. This way only the circuit that had the fault will trip off. Not the rest of the building.
Reply With Quote
  #10  
Old Wed 24 June 2009, 11:26
andyclarkecncuk
Just call me: andy
 
bristol
United Kingdom
Thanks Guys for the replys,
This whole electrical stuff has made my head feel like it is full of cotton wool!
Im also trying to order the parts for my power supply, i have the pk296ae-sg7.2 motors, gecko 203v and pmdx 122 bob and i have calculated that i will need a 345va torrid and 41vdc output. These are the items i am looking at.
http://uk.rs-online.com/web/search/s...duct&R=2238207
http://uk.rs-online.com/web/search/s...duct&R=6290192
http://uk.rs-online.com/web/search/s...duct&R=3819188
Are these going to be suitable? or should i go for a torrid with 500va and 2 x 30v?
Im sorry to be asking questions that have been asked time and time again, i will be getting an electriton to help me but i want to get it right as it is hard to get him here once let alone twice.
Thanks Andy
Reply With Quote
  #11  
Old Wed 24 June 2009, 11:29
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Lights are not required to be connected to RCD devices, but for many houses the RCD device and the "Main Switch" are one and the same device. Cheaply wired factories also just use a single RCD as the Main Switch - complies with all codes. They trip at 30mA fault current. But, I must add, that somehow we have few few incidents of false tripping. My factory has 2 RCD's for two circuits, both have lights on them. I re-wired Sean's new place with 4 RCD's (max of 2 MM's per RCD, and the kitchen toaster has its own). Factory kitchen toaster is the worst culprit for tripping our "earth leakages" - toast gets stuck, and a knife is stuck in the element area after switching off at the wall, but neutral gets shorted to ground and it trips.
Reply With Quote
  #12  
Old Wed 24 June 2009, 11:38
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Your RS selection is safe, except that the capacitor needs more capacitance. Try:

http://uk.rs-online.com/web/search/s...duct&R=0189793
Reply With Quote
  #13  
Old Wed 24 June 2009, 11:46
andyclarkecncuk
Just call me: andy
 
bristol
United Kingdom
Thanks Gerald
Reply With Quote
Reply

Register Options Profile Last 1 | 3 | 7 Days Search Today's Posts Mark Forums Read

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -6. The time now is 08:50.


Powered by vBulletin® Version 3.8.3
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.