Is PVC drainpipe safe for ducting if I have it grounded, or should I go to the extra expense and use metal tubing?
The main reason why PVC pipe is not recommended is the buildup of static electricity and the high risk of explosion.
With a metal dust collection piping system, static electrically won't develop. Elbows and other various fittings are properly designed for conveying dust. The diversity of fittings and accessories will enable you to meet design requirements.
When we create a duct system, the interior should be as obstruction-free as possible. A copper wire will snag chips and curls. In addition, many extraction systems are abrasive, such as the conveying of hardwood chips. This material will wear the copper wire.
While removing the plastic (prior to a metal install) on a Monday after a non-working weekend, I noticed that the pipe still held a charge from the previous Friday's work. As a precaution I put on light duty rubber gloves. I got zapped right through the gloves by the static discharge from a length of pipe connected to the planer, which had been working hard the previous week. A few minutes later I picked up a piece of pipe that had also been connected to the planer and watched as a large spark arced from the pipe to my chest. These shocks were not life-threatening, as the discharge was mostly voltage with little amperage. That said, they made me painfully aware of the potential for static build-up.
You may get away with a plastic system for years, but some day when you are collecting large quantities of fine dust through your new wide-belt sander, disaster may strike. I'd never consider using anything but metal pipe for dust collection.
Though dust related explosions may not be an every day occurrence, they are not rare and the use of plastic pipe in a system that generates large amounts of fine flammable dust/particles is asking for a disaster.
Iíve seen first-hand evidence of what static discharge in dust collection systems can do. Practically speaking, it cannot be eliminated in plastic systems. When it discharges, it can ignite the dust in the system with explosive force. Iíve also spoken with experts in all phases of woodworking plant management and dust collection system design. They all condemn the use of plastic pipe and fittings for transport or collection of wood dust.
I have personally experienced the dramatic effects of static discharge in pvc systems. I also have very reliable information of a dust system explosion, caused by static discharge, that caused a devastating fire in a commercial woodworking shop.
Frankly, I just donít understand the zealous defense of pvc pipe dust systems. Itís potentially dangerous, and itís only marginally cheaper and easier to install than standard metal pipe and fittings. Iím going to use pvc for plumbing and metal for dust system construction.
Comment from contributor A:
One of the biggest reasons that I will not have a PVC duct system is that I always jump when the static zaps me. The last thing I want when my hand is near a spinning cutter is a zap that may cause me to jump right into the cutter.
Once I started reading all the adverse effects of the PVC in relation to static electricity I began to worry. As a test, I drilled the PVC pipe every 12" and screwed a 3/4" stainless sheet metal screw into the pipe and extending about 1/2' into the flow area. Each of these screws were then wired together and tied to the nearest electrical box for ground.
I haven't had any zaps while working with the system since. Again my shop is only 14 x 20 with 4 inputs to the 2hp system. Most of the collection is large particles from the table saw, router, combination saw and lathe. I use it to vacuum the floor as well.