Dust Extraction System

[Mike.C]

Many of you are probably fed up of hearing that my dad installed a dust extraction system for me when i was working away from home.

This seems to be working very good, but we have now been told that this has not been installed properly (or the earthing part of it hasn't), and may be a fire hazard.

When he bought the parts, to save money, he got the metal ducting, metal blast gates, metal joiners, and metal hangers from one place and because they were far cheaper, he got the "plastic" Y sections from another store.

After seeking advice on installing the system he was told to connect one end of the metal ducting to a solid copper earthing pole, which was hammered into the ground outside the workshop, and from there to run earthing cable on the outside of the ducting all along its length, and when he came to each piece of plastic Y section, to use self tapping screws and jump each one, securing it on the other side.
When he came to each machine, he again had to secure a piece of earthing cable, and jump the Y section.

But now i have been told that this is all wrong and that it is the plastic that needs earthing and the metal parts should never be earthed, and that as it is now it is a hazard, and could cause a fire. He said that i would have to find away of earthing just the plastic Y sections themselves.
He also said that the earthing cable should be run inside the ducting and not on the outside, but surely in the end the dust would collect around the wire and cause a blockage?

Can anyone tell me if any of this is right, and if so what can i do to correct it?

Cheers

Mike

 

[CHJ]

Mike: If your metal ducting is already grounded (earthed) then any plastic (non conducting) components attached to it are also earthed as far as any static that might be generated in them by friction of passing wood debris is concerned.

Your galvanized metal trunking itself is very low resistance as far as any static potential is concerned and there should not be a need for a continuous copper core, just ensure the gaps are bridged (which is what you describe) with a bonding lead, that way any potential that may be generated across the in-line plastic component is dissipated before it can build enough potential to create a spark somewhere in the system.

Aircraft fuel lines full of fuel vapor, oxygen lines, etc. and subject to lightening strikes only have enforced bonding on the ends and across flexible couplings.

I think your system as described is already several factors better installed than most and there are literally thousands of home workshops around with 2-4 metres of 100mm plastic ducting in use every day with no bonding other than its connection each end to a 'hopefully' earthed machine.

 

[Shadowfax]

Mike
That is all rubbish! If it were true there would be fires in private workshops all over the country every day! Some schools of thought say that everything should be earthed - you can't ground plastic despite what some people say. Others say all the metal should be earthed. This is not a bad idea from the bonding point of view but it will do little to help with static which would be the cause of a fire.
Forget it would be my advice - I have never in 32 years in the fire world seen a dust explosion in a woodwork shop. At least not on the small scale that we work in. Industry scale might be a different matter but so is the speed of extraction in that case and static could be more of a problem.
I think a lot of this is based on scaremongering by people who do not fully understand what they are saying.
Cheers.

SF

 

[Mike.C]

Chas, SF,

Thats great to hear, at least now we know that we will not have redo it all again.

I really don't know why some people talk a load of rubbish, when as your posts clearly show he did not know what he was talking about.

Thanks for putting our minds to rest.

Cheers

Mike