Maybe there's no contradiction here. I could see how wrapping a non conducive pipe with wire could keep a spark from reaching you since the spark would hit the conductor since it's likely closer.
Contributor
Maybe there's no contradiction here. I could see how wrapping a non conducive pipe with wire could keep a spark from reaching you since the spark would hit the conductor since it's likely closer.
Bob C
Member
If you sheath the entire pvc pipe with grounded metal screen or spiral wrap a grounded wire many times around the duct, closely spaced (1/2"??) you can prevent or reduce the chances of personal shock in that area only.
Corporate memory seems to have faded! Everyone needs to Google "Dr. Rod Cole, static." He is/was an MIT physicist (and woodworker) who wrote probably the best article about these topics - both the difficulty of grounding PVC for personal comfort and the myth of static induced duct fires.
I used to know a few people at Wood when I was writing articles and submitting tips (I also knew the tips editor) but all are gone. I exchanged emails with Bob Hunter, the Tools Editor a few years back after the IBOX and Lock Miter Master came out. My suggestion is just to write an email to their editorial staff at woodmail@woodmagazine.com and/or to the shop tips address: shoptips@woodmagazine.com I suspect they are already getting blasted about this one.
I also found the article on ducting to be lacking- they do not define "thin wall" PVC- there is a lot of bad info out there on the right (best) PVC pipe and where to get it. ASTM 2729 "thin wall," also called "thin wall S&D," "solid perf" and a few other names is the right stuff. Big box stores often carry it in 4" but typically the only place to get it in 6" is from specialty plumbing, irrigation, and landscape design suppliers). The blue/green stuff, SDR35 (ASTM D3034), also called S&D has the same OD as ASTM 2729 (so can use the same fittings) but has a thicker wall, is heavier, and has a smaller ID. Fittings for ASTM 2729 are found in the drainage/irrigation section of big box stores, NOT the plumbing section. Lowes carries 6" fittings but doesn't carry 6" ASTM 2729 pipe- go figure. Fittings for ASTM 2729 may be marked with any of these: ASTM 3034, ASTM 3035, etc. They sometimes also carry the correct fittings made from styrene plastic instead of PVC.
Last edited by Alan Schaffter; 01-27-2017 at 12:42 AM.
Member
A hundred peer-reviewed articles saying the same thing will not change a person's mind if they have personal experience to the contrary.
BTW Alan, that is the article Andy linked to earlier.
Of all the laws Brandolini's may be the most universally true.
Deep thought for the day:
Your bandsaw weighs more when you leave the spring compressed instead of relieving the tension.
Member
I was sourcing a motor and starter to outfit my shop. I was trimming a lake house at the time and my client's neighbor was a manager for a company in Broken Arrow that sold motors and starters. He told me of a story about a plant that was using PVC ducting. As he was walking through the plant with their current system running, he steppe over a 10" pipe and got zapped in the nuts and they had a ground wire running along the side of the pipe. He implored that I do NOT use PVC. I'm currently using PVC but it's all over head or behind machinery along a wall. He said it hit him so hard he was down for about 10 minutes. Funny story, but not funny getting nut zapped.
My funny story - the flex hose drop to the planer builds up quite a bit of static when the chips are flying. At a foot, it will pull your arm hair. I was explaining (in Layman) to my helper about the static and to watch out for getting popped. I ran my arm up the pipe and showed him. Then I got cocky and stuck my tongue out about a foot from it. We still laugh about it a year later. He saw a visible spark hit the end of my tongue and then he saw me jump about 14 feet. I'm laughing right now remembering it.
-Lud
Moderator
I have about 50 feet of 4" pvc in my shop for my DC system. When it was first installed there was considerable static charge inside and outside the pipe. Initially I would get a mild shock if I tried to touch the pipes. Getting your arm near the pipes would raise all the hairs on your arm toward the pipe. After a few months (I don't use my shop every day) of running dust through the pipe the static charge disappeared. If I go out to the shop now there is no charge inside or outside the pipe and none gets generated even when running the planer or belt sander for long periods of time. There are no grounding wires inside or outside of my duct work. The hairs on your arms don't even wiggle if you get your arm near the pipe.
Lee Schierer
USNA '71
Go Navy!
My advice, comments and suggestions are free, but it costs money to run the site. If you found something of value here please give a little something back by becoming a contributor! Please Contribute
I love these threads, they always remind me I made the right decision by going with steel duct.
BTW, static issues will fluctuate with humidity.
And grounding a wire reinforced flex hose is easy:
Last edited by Ole Anderson; 01-27-2017 at 10:34 AM.
NOW you tell me...
Moderator
As has been stated, the wire can help in very localized areas of the PVC. If there is a wire located in a spot where a human is bound to contact, then odds are good it'll help. In fact, if the human contacts the wire first, even better.
However, over time as dust collects on the ouside of the pipe, guess what? The dust does the same thing. Most people who complain about the static just installed new, clean pipe. The act of particles (air, wood chips, dust, etc.) moving is what causes the build of of static electricity on the inside of the pipe. The same thing can happen to the outside of the pipe (mostly from air). As all the pipes in my shop got dirty, the static build up on them was not to be found because the dust had displaced any area where it could build up.
Member
25000V will jump 1.5 inches in air.. I'd like to see how many volts a 36 inch arch would be haha.Originally Posted by Larry Edgerton
Contributor
Here's a chart on the relative potential of different materials rubbing together. Note wood and ABS are fairly close together, while PVC is way down the list which would seem to make it a far worse choice in this application. If there's really any real risk to begin with.
https://www.trifield.com/content/tribo-electric-series/
Member
I have PVC pipe and had a similar experience as Lee Schierer. Initially, I could make the hairs on my arm stand up when getting near the pipe. Over time I stopped noticing the effect.
The only place I ever noticed a spark was on the end of a long section of flexible spiral pipe. I guess the long coil of wire must be like the coils in a generator. I could see a spark about 1/8" long on my bandsaw. It made a tic-tic sound about 2-3 times per second. I was able to bend the wire so it touched the grounded frame of the bandsaw and never had any static issues.
Steve
Member
Static is a big ta'doo (sp?) about nothing. As has been said, static effect in PVC subsides quickly. And, if you never have a need to touch your duct or blast gates (autogates), all the better.
6" PVC (ASTM 2729 S&D) was so much easier to handle, install, and seal, and so much cheaper! When I built my latest set-up over 13 years ago, a 6" ASTM D3034 S&D wye ran around $14 while a comparable 6" metal wye went for between $26 - $34 (some outfits were evidently selling gold ones because they were asking $45!) Though the price spread wasn't as large PVC pipe was cheaper as well. A quick check indicates there is still a considerable price spread between metal and PVC fittings today.
Knowing what I know now after over 15 years in use (two different shops and setups), I would choose PVC all over again in a heartbeat!
Member
Alan,
I'm installing a 6" PVC DC system now. You mentioned sealing. The friction fit seems pretty good. Do I need to seal? If so, with what? I was even thinking about skipping the screw to hold the joints together.
I sure appreciate all the advice you provide on here!
Most of the joints in my system are simply friction fit. I reinforced a couple of joints with the aluminum duct sealing tape. If I need to reconfigure those parts, I can slit the tape with a knife to separate the joint.
Lee Schierer
USNA '71
Go Navy!
My advice, comments and suggestions are free, but it costs money to run the site. If you found something of value here please give a little something back by becoming a contributor! Please Contribute
Member
Different fittings will fit differently. Some friction fit joints may still leak. I think sealing them is worth the small amount of effort required. While the impact may not be great and hard to measure, sealing reduces the chance of leaks that can cause turbulence (which increases SP), reduce CFM, and it will make your ducts quieter. You won't notice the change in sound, however, if the DC is nearby (mine is located in a garage below my shop).
All you need is a tiny bead of 100% silicone caulk applied to the outside. Don't use latex, "siliconized" latex, or other types of caulk, it is a pain to remove. 100% silicone rubs of easily with your fingers.
Moderator
In certain spots, I needed to secure fittings with a short screw or two. Like Alan, I just smeared silicone around the outside of the fitting/pipe joint to seal it. This makes it easier to remove in the future...which I've needed to do.
Posting Permissions
Reply With Quote
