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Current leakage om CNC

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Dave Halford25/08/2019 17:11:12
438 forum posts
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Posted by Vasantha Abey on 25/08/2019 04:22:50:

You need to fix an Earth wire to the body of your cnc, then at the end have a piece of flat metal like copper with a rubber sponge pasted to the bottom and wet the sponge with a bit of salt water.

this will allow the charges to go to the earth. This is because you have the machine on wheels is the problem. You can also change the rubber wheels to steel wheels that can solve the problem.

This is part of the connection used in the electric chair only it has to be a natural sponge as rubber does not conduct to well. What you might call a single use connection. !!!!!

fizzy25/08/2019 18:01:58
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1601 forum posts
106 photos

I am indeed using an extension lead, two infact albeit only 4 ft long each. I will test as advised but go away tomorrow for a week so lack of response on my part will ensue, at least for a week. Lots to ponder and plan whilst away, thanks again.

Johnboy2526/08/2019 09:58:24
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211 forum posts
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Old mart - there are recommended RCD for these applications - I don’t know specifics and are not confident to advise. I’m just aware of this problem. I’ll,try to do some trawling/research on the subject as I’m sure I’ll be asked about again sooner or later.!🤔

John 🙂

fizzy12/09/2019 14:15:14
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1601 forum posts
106 photos

Update! I tested the wall socket as advised and all is as should be so I tested the spindle motor - 4 pins, 3 of which were 120v, same as the frame measured. I had a spare motor so swapped it in and ran it up. Now 70v between table and earth. Dissconnect spindle motor and 40v between earth and table. Tested resistance from plug earth to table and no reading at all. I tested wherever I could and got the same no reading. Tested continuity and nothing....now my mate set this up for me so ive never been near the wiring but on investigation I see that the cnc has a TWO pin plug. My question is, woild fitting an earth strap to everything and connecting it into the extension cable (checked that and all good) allow the current to escape or is there a fundemental problem with my machine? Many thanks

Ian P12/09/2019 14:18:34
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2144 forum posts
89 photos

Answer to last part of your question is yes.

Ian P

John Haine12/09/2019 14:20:47
2591 forum posts
133 photos

It isn't earthed. It should be. Ideally, if the cable that has a 2 pin plug has an earth wire, change the plug to a normal one and connect the earth.. If not, change the cable. Can you post a photo of the cable and the plugs (on each end, if it's that type of cable)?

Ian P12/09/2019 14:21:34
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I'm sure I and others may have already asked, but what are you measuring with and what two points are you actually touching the probes on?

Table of machine is one I can understand but what are you calling earth?

Ian P

Ian P12/09/2019 14:25:52
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2144 forum posts
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Unless the machine is manufactured to double insulated standards (unlikely for a machine tool) than there should be low resistance wiring between the machine frame and the earth pin of the plug,

Full stop, that's it, nothing else matters.

Ian P

fizzy12/09/2019 14:31:45
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1601 forum posts
106 photos

Im using the earth of the 240v socket - there is no earth pin of the plug, hence my concern.

Stuart Bridger12/09/2019 14:34:21
336 forum posts
17 photos

This a a downright dangerous and potentially lethal situation,

Two pin plugs are designed for double insulated equipment, where there are two independent functional levels of insulation that prevent contact with anything that could come into contact with live components. One of these is typically a plastic case. The fact that a machine tool has exposed metal means that it can never meet this criteria.

It needs to be properly earthed, end of....

Edited By Stuart Bridger on 12/09/2019 14:57:34

Ian P12/09/2019 14:46:27
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2144 forum posts
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I agree with Stuart absolutely.

How has this thread become so long before we find out the machine has a two pin plug, also how do you put a 2 pin plug in a normal 13A socket?

Ian P

JasonB12/09/2019 15:46:23
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16018 forum posts
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Post a photo of the 2-pin plug.

Some do have an earth but not a pin such as this if you are running it via some sort of adaptor the earth may not be making contact.

 

Edited By JasonB on 12/09/2019 16:07:40

fizzy12/09/2019 16:11:51
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1601 forum posts
106 photos

nope, defo no earth. I will be adding chassis earths and converting to twin and earth 3 pin plug.

Ian P12/09/2019 16:58:23
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2144 forum posts
89 photos

Please Fizzy put us out of our misery and explain how a two pin plug was fitted in the first place.

If this was a machine you bought then for the sake of safely potential buyers others should be alerted.

Ian P

JasonB12/09/2019 17:31:03
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16018 forum posts
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Here you go Ian, from another post. China via Germany hence what looks like a german 2 pin earthed plug like I posted photo of.

Fizzy if this is being used for business then check it has proper CE and testing as your insurance will probably be void if it or you go bang

Edited By JasonB on 12/09/2019 17:31:36

Edited By JasonB on 12/09/2019 17:34:12

john fletcher 112/09/2019 17:40:32
524 forum posts

OK about bonding and earthing, but where is the electrical leakage originating from, that needs eliminating. Testing with a simple continuity tester is not good enough, PAT testing we go a long way to proving the earthing is effective or now as it known as the CPC circuit protective conductor.

Ian P12/09/2019 17:43:46
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2144 forum posts
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With failing memory I dont recall seeing any links or references in this thread to the actual machine, regardless though, the German supplier should have supplied the correct cable for the destination country.

Ian P

Mike Poole12/09/2019 17:51:39
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2041 forum posts
47 photos

Some of the travel adaptors on the market make no provision for the earth connection, much equipment does not use an earth but it is essential to connect it if required. One of the most dangerous things around is a 2 core extension cable intended for double insulated garden equipment. At an event in our village someone turned up with a 2 core extension to supply the stage back line and PA for a band, lucky I was there and vetoed this cable.

Mike

JasonB12/09/2019 17:53:42
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16018 forum posts
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It was another thread, your memory is OK.

E-bay photo shows it with the typical power lead socket you see used on computers so could just plug one of those in and see if the earth is connected. But as John says pluging into mains with leakage may just trip something and should be properly tested.

fizzy12/09/2019 19:17:20
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1601 forum posts
106 photos

Ian - it was bought off ebay from China, not a great starting point I know but there are a lot of them used in the UK and apart from me being electrocuted how they make them for the money they charge is anyones guess. Ive now earthed it and it shows varying but very low volts and almost zero amps so its going in the right direction. Nothing tripped and ours is a new house. My mate forced the two pin plug into a uk 3 pin socket - I never even saw it or gave it a thought until you kind lot prompted the questioning so big thanks to one and all.

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