Static and a melted CPC!

gerard · Jun 27, 2011

I have just noticed the insulation surrounding the earth going to 2 machines at work has melted close to the connection points of the machine. I don't know why this has happened but I do know there is alot of static built up on the machines due to the materials used in the conveyors. Would this static have caused the insulation to melt? How do you discharge the static from these machines if the earth is not doing this?

mayfair · Jun 27, 2011

stupid i know , but its not heat from the machine as you say its at the conection point. Not trying to be funny just a thought.

gerard · Jun 27, 2011

No, it's connected in the control panel and it's nowhere near hot enough to melt it. It melted to about 5" from the connection point.
I'm going with the static theory until i'm proven otherwise!

gerard · Jun 27, 2011

No, it's connected in the control panel and it's nowhere near hot enough to melt it. It melted to about 5" from the connection point.<br>I'm going with the static theory until i'm proven otherwise!

Knobhead · Jun 28, 2011

Do you have access to a DC clamp meter? It may give you some clue if it’s static. To be honest continuous static build up doesn’t normally give that high a current to do any damage. Multiple bonding points spring to mind if static I that bad a problem, it has to be done on coal and gas handling plants.

Another thought, as it’s burnt in one specific area has something hot been spilt on it?

gerard · Jun 28, 2011

Tony said:
Do you have access to a DC clamp meter? It may give you some clue if it’s static. To be honest continuous static build up doesn’t normally give that high a current to do any damage. Multiple bonding points spring to mind if static I that bad a problem, it has to be done on coal and gas handling plants.

I have a DC clamp meter - but what do I do with it?! When you say multiple bonding points, do you just mean I should earth a few more points of the machine?

silva.foxx · Jun 28, 2011

Although I don't believe it this to be the problem, I worked on a paper laminating machine, in a previous role, in which hydraulics were used to move the printing/gluing decks. A fault developed on a 110vac valve coil for one of the decks. The 110vac supply was 55-0-55v. The coil fault appeared on the -55 side of the coil supply which was via a 'neutral link' as opposed to a fuse terminal. The earth wire insulation melted all the way back to the Tx. Wow.

Any electric welding been done on these machines lately?

Is the connection soldered?

Is the connection tight?

Is the connection to 'bared' metal?

.

gerard · Jun 28, 2011

All connections are tight and are not soldered. There was some welding done, but not near the machine in question and not on the same circuit. Do you think welding carried out close to the machine would cause this? I am going to increase the size of the supply cable and therefore the earth connection. Any thoughts?!

Knobhead · Jun 28, 2011

Nice one Silva. Stray earth welding currents, should have remembered that one. I’ve had umpteen SWA’s and earths toasted by Muppet welders not earthing properly.

gerard · Jun 28, 2011

Thanks guys - so ye reckon it's stray welding currents? Sounds like a logic explanation. I will replace the damaged cable and see how it goes. If I have welding going on I will monitor it and see if it has any effect. I'm going to put that in the problem solved folder, for now.

Knobhead · Jun 28, 2011

You will find a welder will just plonk his earth return any where near the machine, not necessarily on it.

One company I worked for came up with a brilliant idea. All fixed welding sets had to have an earth wired from the welding return terminal. The welders thought this was great, they didn’t have to drag an earth return out because it was connected at the welding set and the via the plant cabling CPC’s. The idea lasted about a fortnight before I went around the plant welding sets cutting the permanent return earths off.

You think plumbers are morons? Welders are in a class of their own!