importance of internally grounding dust collection hose?

[groomden]

anyone have any deep thoughts on this? I did it, but mainly because it seems like cheap insurance against... something?

that's all.

dennis

[Northboy]

Originally Posted by groomden anyone have any deep thoughts on this? I did it, but mainly because it seems like cheap insurance against... something? that's all. dennis

Vacuum systems can build up a stunningly large static charge while being used. I have seen industrial vacuum trucks have lightening bolts of several inches fly off the hose to nearby metal objects. This object could also be you or your valuable electronics.It could also theoretically indiuce current into your steppers and cause problems or missed steps or trigger false limits etc.

Northboy

[eloid]

remember to ground one end only ie to earth... other end should fastened down but floating not tied to chasy gnd... other wise you just made a big ground loop... and that nothing but problems down the road.

[CarveOne]

The small "lightning bolt" discharge can also be the igniter for a large dust explosion if there is a lot of dust in the air. Professional woodworking shops usually pay a lot of attention to this possibility.

CarveOne

[groomden]

Originally Posted by eloid remember to ground one end only ie to earth... other end should fastened down but floating not tied to chasy gnd... other wise you just made a big ground loop... and that nothing but problems down the road.

i have one end of the copper wire attached to the blower housing. Is it okay if the other end (by the cnc bit) is attached to my dust hood housing, which will be mdf board?

thanks,
dennis

[eloid]

as long as it is not touch or making contact with the bit or router.... I would make a insulated fixed plastic termination lug at the end keeping 4-5 inch away from any moving part or router bits... this way it will never be suck up or have the chance of wrapping it self up in the spindle.

[BobF]

Dust explosions are real and can cause serious damage.
We recently had a tragedy here. I live in Savannah GA and a little over 1 year ago, the Imperial Sugar refinery here had a tragic explosion. It was blamed on a sugar dust explosion.
Do what you can to prevent a dust explosion. Sawdust is just as explosive as sugar dust.

[Realmseeker]

I'm planning on using a shop vac for my suction system,
I know its small but it is what I have for now,

Would a small 6-8 galleon shop vac,
or even the bigger ones need to have a grounding wire?
its not large,
but the principle seems to be the same,
and i've seen a large coffee tins worth of dust blow,
and even that is a scary sight

[Al_The_Man]

There is a great deal of misconception regarding the difference between grounding, ground loops and bonding.
For example, say you had a dust collection hose that was constructed of non-metallic material.
If you were to place a conductor the length of the hose and ground one end at the machine ground point in order to discharge static build up for example, if the other end (gantry, router etc) were not bonded to the machine ground and/or a static charge or other AC induced voltage were to build up, this could cause a spark or discharge to occur to the conductor.
If a bonding conductor is used, this ensures that no difference in potential occurs between different parts of the machine.
All metallic parts of the machine should be connected by a suitable bonding conductor to the central Earth ground point.
Bonding actually decreases the chance of ground loops by attempting to ensure there is no potential between one part of the machine and another.
The exception is the likes of shielded cables where it is imperative that no current flows by chance in the shield, due to the sensitive nature of the cable contents.
Al.

[stevespo]

Al, I think I understand what you are saying. I have a central dust collection system with metal ductwork. If I tie everything together (bonding), there is no difference in potential.

First question - Should some part of the ductwork be tied to (earth) ground, or is having a grounded motor attached to the housing enough?

Second question - I am using shielded cables for my limit switches, but I occasionally get false signals. I'm going to clean up my wiring and keep them away from the AC and DC motor wiring. Where should the shielding terminate? Should it be grounded to (earth) ground, or AC ground, or ?

Thanks,

Steve

[Al_The_Man]

AC (supply) ground and Earth ground are normally the same thing.
The shields should normally terminate at a central ground point, This includes the service ground.
Any motor should also have an earth ground conductor run to it, rather than rely on any metal frame it is attached to.
It would not hurt to wire a bonding strap to the metal duct work.
Al.