Beware of Poor Electrical Advice

[Dennis McCullen]

I just read some weekly e-tips from a Woodworking magazine /website and I'm quite disappointed in one of the tips offered. I wrote to the publisher, but do not expect a correction or feedback from them since they were not smart enough to avoid the subject matter to begin with. This particular tip concerned using a "smart strip" to start a router AND a shop vac at the same time. If you have not encountered this before, a "smart strip" looks like a standard power strip but there is a master outlet and a few "slave " outlets. Power is sent to the slave outlets when you turn on the device that is plugged into the master. Convenient for gear with a low amp draw not adding up to the total strip capacity of 15A.

In this "quick tip" there was no mention of Amp draw or checking your devices and adding them up to see if the strip was made to handle this. All the information should be readily available on the manufacturer's plate on the tools and also molded into the strip itself. The two "smart strips" that I checked on were both rated 15 Amps. This strip might work for some cases, but it seems likely that, in most cases, the 15A rating would be surpassed by the cumulative ratings of tool and shop vac. A p-c 690, for example, is shown to pull 11A and many shop vacs pull 10-12A. The amp draw would be 22A for these two devices going through a "smart strip" rated for 15A. I suggest this is not smart at all. Several scenarios are possible: at least one could easily burn the power strip you just paid $20 for, or you could simultaneously damage the motors on the shop vac and the router and realize ten times that dollar amount in loss. If you are lucky, the circuit breaker would trip first. Don't rely on luck when it comes to electricity!

I caution against piecemeal electrical advice for the "devil's in the details". All of the electrical information is readily available to you; you just need to be curious enough to find it. I use a convenience that works for me in my shop, but this may not work for many others. I plug my 1 hp dust collector into a remote-controlled outlet and clip the remote to a belt loop. I found a remote controlled outdoor outlet (think Christmas lights) with an Amp rating high enough to handle the dust collector amp draw but beware many such devices are only rated for half that! I have the outlet plugged into a different circuit than any of the stationary power tools so the 20A circuit rating is not surpassed with tool and vac both on. Additionally, I have read articles where some enterprising woodworkers use such a remote to flip a larger magnetic switch that can handle the amp draw of a large dust collector. That costs a few $$, but is a safe bet.

When I built the shop, I ran two different circuits into many of the 4-square boxes so that I have duplex outlets side-by-side powered by different circuits. The same end can be accomplished by running a short extension cord from a different circuit to the tool or the shop vac, whichever is easier. Just be sure the cord is rated to handle the amp draw and allow for amp drop if you use a long cord (not recommended). I keep a 15 ft. 12/3 cord handy for saws, as well as a couple of 15 ft. 14/3 cords for sanders, etc.

Again, everything is labeled, just use the information and your head (or calculator). Above all, be safe having fun!

[Frederick Skelly]

Thanks for the heads up and the advice Dennis!
Fred

[Matt Day]

I know you mentioned it but wouldn’t the “smart strip” breaker kick in before anything really goes wrong?

I’ve been using a power strip like that for years to power on my shop vac while using ROS’s and router table. I notice no change in power up (max amp draw) and have no breakers tripped.

I’m not concerned about it, though I appreciate your detailed explanation.

[Art Mann]

I believe I saw that same stupid tip. It was actually part of an email sent out by one of the woodworking magazines.

[Ole Anderson]

Not unusual to run a big vac and a router at the same time on the same circuit using one of those smart i-socket vacuum switches. I do it all the time. Probably running near the limit of the breaker. 10 amp vac + 10 amp router with a 20 amp panel breaker. Vac could be pulling full amps, but you rarely load a router heavily.

[Wade Lippman]

You are right of course, BUT...
There is a huge amount of slop on these things and you can routinely get away with things that aren't right. For instance; I bought a cottage that had a 23a water heater on #12 wire for 20 years without anything going wrong. I replaced it, but probably didn't have to.

[Bill Dufour]

Prbably has to do with less then 100% useage rules per NEC.
Bill

[Tony Leonard]

Well, I am not an electrician, but, I use a Bosch 1617 on a CNC router. I have it and all the CNC electronics running through a strip and that goes through a "box" I made with an amp meter. I have never seen it draw more than around 6A - even chugging through wood. A Kill-a-Watt device is a fun toy too - it can tell you exactly what is going on. At my old shop (garage), I always had whatever tool I was using and the shopvac on the same extension cord. Never had any issues. Never measured those.

Tony

This is without the router on...
381585

[Julie Moriarty]

As an electrician with 35 years field experience, I am always amazed when I see people asking for help from those who are not professionals. When I was a first year apprentice we were shown grisly pictures of electricians who, unfortunately, experienced what can happen when you're not ever vigilant. The pictures were intended to scare the hell out of us so we would never take safety for granted. We were also taught how electricity can kill you. Those things were ingrained in my mind forever.

Tips and tricks with electricity? :eek:

[John C Cox]

I understand the concern... Fuses, circuit breakers, and power strips are all there to protect the wiring inside your house from overheating and catching the house on fire... The circuit breaker isn't there to be the Killjoy fun stopper....

And heat buildup is a time/amps thing.. If you are running a 15 amp circuit at 14.8 amps for 6 hours straight - it may get pretty warm... The circuit breaker won't care, though...

And YES - if I was a magazine editor, I don't want to go on record for publishing bad advice that could burn somebody's house down... Not a smart move...

But the other end of this is you as the user seeing what your devices actually pull to verify you really are in the clear.. Most devices tend to pull very high loads at startup - so if the control unit sequences the starting of each thing by a few seconds - it won't whomp the system with a ton of amps all at once... The next thing is to understand your devices... Dust collectors and vacuums typically pull the highest load when the fan is running in free air - no bag, no housing, no hoses or ducts... Add all that junk back on and fan amps can go down quite a bit because the fan isn't moving much air.... Saws, sanders, and routers also typically pull pretty low loads until they are loaded up... And often we don't load them heavily because the quality of work goes down drastically...

Tony has a great suggestion here about using a current monitor to see what you actually are pulling... It may be a surprise..

[Bill Dufour]

When i took welding as a night class the welders had nice digital meters showing the amps as the arc was burning. Problem was they were led meters and showed zero when the arc was not in use. In use the welding helmet did not allow the user to read the numbers. It did allow class members to watch the numbers as other people worked.
Bill

[Martin Wasner]

As an electrician with 35 years field experience, I am always amazed when I see people asking for help from those who are not professionals.

I don't trust or touch wire. I'm way too stupid. Luckily I'm close friends with a commercial electrician, but if you don't know how too do something and there's solid potential for dying for your ignorance, hire someone else to do it.

Replace a cord end? No problem.
Screw around in a 100 amp 480v control box? No flipping way. I'll be riding the lightning.

[Art Mann]

Am I the only person who has tripped a breaker cutting rails and stiles and using a big shop vac on the same circuit at the same time? If I load up my big ancient Hitachi M12V to the max with a big bit, it is going to draw 14 or 15 amps. You can see that with a Kill-A-Watt device. The thing about breakers is they are slow devices. You can draw twice the rated current for a minute or more and they won't open up. That is a fact that is easily verified by looking at trip curves. Most of the time, a router won't be running at full rated load for more than 20 or 30 seconds while a vacuum is running. I still don't think it is a good idea.

[Julie Moriarty]

I don't trust or touch wire. I'm way too stupid. Luckily I'm close friends with a commercial electrician, but if you don't know how too do something and there's solid potential for dying for your ignorance, hire someone else to do it.

Replace a cord end? No problem.
Screw around in a 100 amp 480v control box? No flipping way. I'll be riding the lightning.

Of all the things I had to do during my career that made me really nervous, two things stand out. Changing out a 480V disconnect in live switchgear and hanging a transformer on a pole with 12kV inches from the top of my hardhat. Those two incidents caused my spacial awareness to go into overdrive and probably took some time off my life.

[Mike Cutler]

Dennis
My Fein vac works on the same principal. Any device plugged into the vacuum will start up the vacuum when it turned on. It's actually pretty common now a days.
I can use the Fein with my Festool TS75, My sanders,and smaller routers, but not my Festool OF2200. That combination pops the breaker.

"Newer" kitchen and dining room duplex receptacle strategy is kind of the same as your "two duplex receptacle strategy". You alternate the duplex receptacle circuits to not overload one circuit.
The Smart Strips appear to have a resettable breaker built into them, so it shouldn't get any more dangerous than a normal power strip.

[Josh Kocher]

While I don't disagree with the statement of the post.....

Like the above post... I routinely run a tool, router/saw/sander/etc through my vacuum on a same circuit. Usually 20 amp, but sometimes 15 amp if I don't want to unplug something else or it's more convenient.... no problem.

[Jason Roehl]

Of all the things I had to do during my career that made me really nervous, two things stand out. Changing out a 480V disconnect in live switchgear and hanging a transformer on a pole with 12kV inches from the top of my hardhat. Those two incidents caused my spacial awareness to go into overdrive and probably took some time off my life.

There are many things I would do related to electricity. What you just described is not one of them...without training, that is. I've done plenty of things "live"--replaced receptacles, switches, light fixtures. Just last week, for the first time, I had to swap out a dead circuit breaker in a 208V 3φ panel at work, and it was the kind screwed into the buss bar (I've pulled many in residences that just snap in).

My hat is off to the linemen/linewomen--they do some of the riskiest work electrically, and often in some of the worst weather conditions. Little mistakes don't just bite, they kill.

[Dennis McCullen]

I am happy to hear that so few have had problems with routers and shop vacs starting simultaneously and then working together. What about saws? Anyone risking their table or miter saw by vacuuming on the same 15 or 20A circuit? The one event that steered me toward caution was a circular saw purchase. I built my house some 37 years ago using a 2 hp circular saw. There was lots of old heart pine (hard lumber) used and the saw was dropped more than once. Still running but a bit loose and bent, the saw was replaced with a one rated at 2-1/4 hp. The first time I attempted to use the saw on a long extension cord (same one used extensively building the house), I burned the motor. Only then did I inspect the manu plate and find the amp draw was 2 amps higher. From then on, I always proceed on the side of caution.

Another tip that I read many years later and have only seen in print that one time, coiled cords have more voltage drop than cords laid out. This was when working as a "Safety Man", or professionally called EHS, environmental health and safety officer. The article referred to using a long cord when you only need a short one whereby lots of cord stays coiled. Supposedly, a magnetic field is invisibly at work robbing a little more of the voltage than if the cord was stretched out in linear fashion. If you are on the edge, it takes just a little more effort to unwind the cord. Again, caution has me using a heavy cord, and only of a length sufficient to do the job when the amp draw is high.

[Mike Cutler]

Dennis

Most folks don't really look at the load ratings of an extension cord, but they should. As length increases, voltage drop increases and current draw increases, for a given gauge. For any "tool of significance", a 12AWG good should be about the min. 14AWG if it's short. There is very little use for a 16AWG, or smaller, extension cord in the shop. I have a 10AWG 100' for working outside.

IN a coiled up extension cord, the AC voltage "appears" as induced "lines of flux" when coiled up. The induced lines of flux present themselves as "opposition to current flow", and will decrease the current/voltage. It would take a pretty significant coil for this to happen, and it would have to be wound fairly tight, but an extension reel could begin to present this effect. The bigger issue is heat dissipation. The coiled up extension cord cannot dissipate the heat and this also compromises it's ability to maintain rated current and voltage over it's length. It's for this reason that I do not use extension cord reels.

SouthWire has some excellent tables for stranded conductor capacities on their website, based on cord type. They're worth a look for any one that uses extension cords of any type.

[Martin Wasner]

What about saws? Anyone risking their table or miter saw by vacuuming on the same 15 or 20A circuit?

Unless I'm on a really short cord and nobody else is drawing on the same circuit, I usually have to bump the jobsite saw to get it spun up. Once running it's fine, but startup will snap a breaker pretty easily.

Good contractors drop a turtle wired into the panel and there's plenty of power to go around. Most give you an outlet next to the panel, one in the laundry room. That gets to be fun when ten cords are coming out of four holes.

[Carlos Alvarez]

While I don't disagree with the statement of the post.....

Like the above post... I routinely run a tool, router/saw/sander/etc through my vacuum on a same circuit. Usually 20 amp, but sometimes 15 amp if I don't want to unplug something else or it's more convenient.... no problem.

If they are low-powered tools, sure. But I absolutely cannot run my Shop-vac (most powerful model available) on the same branch as the miter (Hitachi 12" SCMS). I might get a light cut done before the breaker trips, but not two, and not a heavy cut.

The problem is that most people know absolutely nothing about electricity, motors, and such. They can't make educated choices. The writer had a good idea but also didn't know how to frame it for where it might be appropriate and where it is not. He doesn't know what he doesn't know.

[Kevin Beitz]

Not to get off topic but if you want to see some crazy electric go to Dominican Republic.

[Ole Anderson]

I get a kick out of those folks that will wire up 120 volt stuff but are intimidated by 240 volts. Implies to me a basic lack of understanding of simple electrical circuits and makes me wonder if they should be working on the 120 volt things. I have done enough remodel work to see what scary things folks do with wiring. I have a buddy that mentioned that he moved a light switch in a simple remodel. I asked if he put in a JB. He said he just wire nutted it behind the wall, but he taped it real good after. No amount of conversation could convince him to go back and do it right.

You don't have to be an electrician (I am not) to do simple wiring correctly, but it helps. If you are going to the internet to learn stuff, you need to know how to separate the wheat from the chaff.

[John K Jordan]

...I have a buddy that mentioned that he moved a light switch in a simple remodel. I asked if he put in a JB. He said he just wire nutted it behind the wall, but he taped it real good after. No amount of conversation could convince him to go back and do it right.


I ran into that in my own house, a timberframe built in '88, purchased in '03. I pulled out a built-in book case to move a wall and I knew I was going to have to reroute various switches and outlets to new junction boxes in the crawl space. What I didn't expect was a junction wire-nutted and taped above the bookcases. Now I wonder if I should pull out and inspect the other 14 book cases built into that room. (It was labeled "Library" on the construction plans.) I also found a trim nail through a romex cable but that's a different story.

JKJ

[Roy Petersen]

When we bought our house (old hewn beam, balloon frame, 1837-ish), we figured some things were going to be wonky. We weren't disappointed.
The bathroom wall had two flat plates on it, roughly head height. Odd. Opened one up, there was a bare wire behind it, and it was live. Same thing behind the other plate. Apparently they'd had a sale in the house and sold off the sconces that used to be there, and simply tucked live wires back in the hole and covered it.

Shut the power off, chased the wire, leading to the wall outlet in the next room. The wire was so old the insulation and fabric(!) covering crumbled to the touch, exposing bare wire. From there it hit another outlet, then a wall switch, then another outlet, split into three more....in all 16 outlets/switches on one 15a circuit covering 5 rooms up and down stairs. All with very dodgy wire, half or so with crumbling outlets...

Needless to say, we redid it all.

[Jim Dwight]

My most used setup in my shop is on my one 20A 120V tool circuit. I have an auto-on switch plugged with a heavy cord to the outlet. The shop vac, rated to draw 10A, is plugged into the switch location on the auto-on and a 15A breaker power strip plugged into the auto-on for the tools. My Ryobi BT3100 table saw, my Hitachi 12 inch CMS, my DeWalt tracksaw, and my smaller sanders and other tools get plugged into the power strip to trigger the vacuum. I move a 2.5 inch hose onto the dust deputy on the shop vac for the table saw or a Bosch 5 meter hose on the DD for the other tools.

The 20A breaker has never tripped. The 15A breaker on the power strip will trip if the table saw is on a hard cut. In theory, I have up to 25A of tools on the 20A circuit but the auto-on switch said it will work and it does. It works because the two tools do not start up at the same time. All these tools are universal motors which draw the most current when loaded at just less than stall torque. A shop vac should never be at stall torque, especially if it has a cyclone keeping junk out of it. Sanders should never be at stall torque but saws can.

I'm not sure I would want to use my setup all day in a full time woodworking shop. I am probably pulling less than 15A most of the time but even running at 75% of the circuit capacity will get the wires warm. I had an electrician run the the circuit to the first box and then I put in all the other boxes, wire, and outlets. So I know it is all 12 gauge wire and all 20A outlets. Properly grounded. It is also on a ground fault breaker because it is a shop in a garage. My house is old and I would not want to be doing this on my old circuits where I am unsure the wire size matches the breaker and all the outlets are correct for the breaker.

There are lots of things that count. Professionals are not infallable either. i am not an electrician but I am an engineer and I have a copy of the NEC and I look at it when I am unsure. Both builders I have worked with on this house were comfortable with me doing the finish electrical (and plumbing and carpentry). That included hooking up a heat pump. I don't like working in the panel but I can do it. I will work on 110V live but I prefer to just turn the circuit off. I've almost gotten the whole panel labeled now.

The thing that will kill you is even a small current across your chest. The problem with higher voltage is it will cause a higher current to flow with a given resistance. Your body is more of a resister than a conductor. To avoid the current across the chest I've heard of people working in a panel with only one hand. I do not work on a 220V circuit live. I know from experience that under normal circumstances 110V will not do anything other than make you wish you had turned the circuit off. I've only accidently gotten bit by 220V a few times and none in the last 20 years. It was enough different I am more careful with it. It's best to be careful with 110 too but I think taking chances becomes increasingly stupid when voltage increases.

[Andrew Seemann]

The thing that will kill you is even a small current across your chest. The problem with higher voltage is it will cause a higher current to flow with a given resistance. Your body is more of a resister than a conductor. To avoid the current across the chest I've heard of people working in a panel with only one hand. I do not work on a 220V circuit live. I know from experience that under normal circumstances 110V will not do anything other than make you wish you had turned the circuit off. I've only accidently gotten bit by 220V a few times and none in the last 20 years. It was enough different I am more careful with it. It's best to be careful with 110 too but I think taking chances becomes increasingly stupid when voltage increases.

It is difficult to get hit by 240V in residential work. You would need to contact both hot wires simultaneously. On a single phase 240V circuit, each hot is only 120V to ground, they are only 240V to each other. That said, other than hooking up the service drop to the wire going to the meter, there is no reason I can think of to work on a 240V circuit live in residential work.

I took 120V in one arm and out the other once. Had my knees not buckled and caused me to fall; I'm pretty sure it would have killed me.

[Julie Moriarty]

I was in my first class as an apprentice and right off the bat the instructor taught us how electricity can kill you. He even showed us some grisly photos to drive home the point. When I learned it only took between 0.1 and 0.2 amps to kill you, I was pretty surprised. It's at that amperage the heart goes into ventricular fibrillation. Of course the current has to pass through your heart - hand to hand, head to toe, etc - but if you "get caught up", where your muscles contract and you can't let go, better hope someone is nearby to knock you off.

While it is tough to get a 240V shock in a residence, 240V will give you a start of something shorts across it. My most memorable experience was not with 240V but with 277V. We were working an office remodel. The foreman, who had advanced beyond his capabilities, had gone around cutting wires in JBs without capping them. I was on a ladder sliding a 2x4 fluorescent troffer from one bay of the drop ceiling to another. The inside of my arm was resting on the grid. Suddenly the room started flashing (it was my vision, not the lights) and I felt burning on the inside of my arm. I knew the grid was grounded and that I was getting shocked made no sense. Then it stopped.

I looked around and right where my temple was, a cut wire stuck out of a JB. It was live 277. I got down off the ladder and released the charge my body had just absorbed onto the foreman. Now his eyes were lighting up. :rolleyes:

[Carlos Alvarez]

I got down off the ladder and released the charge my body had just absorbed onto the foreman.

The human body is not capable of absorbing a charge.

[Mike Henderson]

The human body is not capable of absorbing a charge.

I think she is talking metaphorically (or figuratively and not literally).

Mike

[Carlos Alvarez]

I think she is talking metaphorically (or figuratively and not literally).

Mike

My autistic self often misses those kinds of nuances. But I've also heard people make the claim seriously.

[Mike Henderson]

My autistic self often misses those kinds of nuances. But I've also heard people make the claim seriously.

I understand. I'm a very literal person, also. My wife makes fun of me because of it.

Mike

[Side comment: Julie spent her career as a union electrician working commercial and industrial jobs. She knows electricity, electric wiring and electric code pretty well.]

[Marshall Harrison]

Thanks Dennis.

[Curt Harms]

The human body is not capable of absorbing a charge.

Maybe it changes state and is released as .... harsh .... words;)

[Julie Moriarty]

The human body is not capable of absorbing a charge.
I'm pretty sure the foreman I gave that tongue lashing to that day would disagree. :rolleyes:

[Kevin Beitz]

I think he had a charge of anger...