Mark V Electrical Requirement

[DLB]

IIRC the NEC requires any branch circuit with excessive distance from breaker to load be wired with oversized wire. So I discount the 100 ft internal wiring point.

As I understand this it is in the form of a recommendation, as opposed to a requirement, that branch circuits wiring should be sized for a voltage drop up to 3%, or a total of 5% to include feeder circuits. Assuming 120 VAC at the breaker, a 15 Amp circuit, I get maximum resistance of 0.24 Ohms for a branch circuit. Wire length is two times circuit length. At 2.525 Ohms per 1000 feet, 14 AWG gives me a circuit length of ~47.5 feet. 12 AWG is much better at 1.588 Ohms per 1000 feet, a circuit distance max of ~75 feet. 10 AWG (0.9989 Ohms per 1000 feet) yields will get me 120 feet.

Large homes are pretty common these days, I would expect 15 amp branch circuits for outlet receptacles to commonly exceed 120 feet and therefore either contain at least one leg of 8 AWG or not meet the 3% recommendation. (I don't know if you can legally mix wire gauges in a branch circuit, I have read of inspectors failing that approach.) My home has a three car garage with the breaker panel is an outside corner. 47.5 feet barely gets me to the house so 14 AWG is essentially useless in my case. I am reasonably certain that most of the 15 and 20 Amp branch circuits in my own home do not meet the 3% Voltage drop recommendation. If I consulted my manual for an extension cord that I could throw out the window of my laundry room and run my conventional SS headstock I might have a serious problem.

- David

[BuckeyeDennis]

Thanks David, that definitely sheds more light on the subject.

Running the numbers on my planned 15A manual-machine bus, at 15A I get a 2.9% to 3.9% branch-circuit voltage drop at the far end of the 50' series-connected multi-outlet extension cord, depending on whether I use the rated maximum initial contact resistance (10 milliOhms) or maximum long-term contact resistance (30 milliOhms) for each plug/receptacle blade connection. The 50' 6AWG feeder voltage drop is 1.9% at 50 amps. So it appears that the branch circuit design should meet those NEC recommendations unless the plug connections degrade. Even then, it would be darned close.

Since your post gave me some good search terms, I Googled the NEC requirements, and found this article by Mike Holt. It corroborates everything you said.

[HopefulSSer]

I've already purchased the multi-outlet cords, but haven't installed them yet. Can you think of any reason why I should not?

Personally, one concern I'd have given the quality of some goods being sold on Amazon these days is: does it meet its claimed ratings?

[BuckeyeDennis]

I've already purchased the multi-outlet cords, but haven't installed them yet. Can you think of any reason why I should not?

Personally, one concern I'd have given the quality of some goods being sold on Amazon these days is: does it meet its claimed ratings?

The mechanical build quality seems very good, and it's UL listed. But you still make a good point. I should probably do some physical voltage-drop testing under load. I have a couple of 1500W portable ceramic heaters that would make good 12.5A test loads.

[DLB]

Getting back to the Shopsmith headstock... I think that Shopsmith got it almost right when, as of PowerPro Gen 2, they decided to provide overcurrent protection (OCP) in the headstock where it belongs. Reading the note from Jim, it seems to me that they should have added OCP when they went to the Emerson motor as a preferred solution as opposed to changing the manual to mandate external 15 Amp overcurrent protection. If I felt a change was warranted in my shop I would add an in-line fuse or push button circuit breaker to the hot line in the conventional headstock to meet the intent so that I could continue to run on 20 Amp circuits. One of several good reasons for this is that I cannot typically tell if an outlet receptacle has 15 or 20 Amp OCP. The NEMA 5-15R receptacle is commonly used on both 15 and 20 Amp circuits.

I say almost right because in the case of the PowerPro the headstock is dual voltage by design. As someone here (RFGuy IIRC) pointed out that for US 230/240 Volt it is standard that both legs should have OCP. The PowerPro should have two fuses or circuit breakers so that I can use it in whatever 230/240 outlets I have available without downgrading them specifically for the PowerPro.

- David

[JPG]

Guess I have been leading a 'charmed" life for the past 60+ years. 230v 20A branch circuits and no motor failure yet.

Although using lesser rated receptacles is common practice, I prefer using 20A receptacles on 20A branch circuits. The difference is the blade orientation on the hot blade. The receptacles are designed to accept either 15A or 20A plugs and that gives them a different appearance..

[DLB]

Guess I have been leading a 'charmed" life for the past 60+ years. 230v 20A branch circuits and no motor failure yet.

From the more modern (after introduction of Emerson 115V motors evidently) manual: "Do not use the Mark V on any circuit rated higher than 15 amps, 250 volts, unless fused to 10 amps maximum." And: "...Have a qualified electrician install the 15 amp 250-volt circuit fused to 10 amps and have him recommend a compatible plug for the power cord. So this idea of the facility OCP protecting the motor is not unique to the the 115V version. This manual is from around '89 I believe. My early 80's manual that reflects the 'more is better' approach to power like the OP described doesn't have 230V version power requirements to compare.

Interestingly, for both the 115V and 230V versions, the '89 manual asserts that the motor "develops more than 1-1/2 hp in use." The older manual makes no such claim.

- David

[JPG]

But then my motor was made by A O Smith.

So Emerson is what is unique.

I think appliance located OCP makes more sense.

[RFGuy]

I see there has been a good discussion during my absence. Some random points I will make that hopefully will add to the discussion. IF NOT, then I apologize in advance. I brought up the worst case because it is there where trouble often lies. Also where a lot of rules get written to mitigate it. Hence things like the NEC and fire safety codes, etc. exist. First, UL listing....I take this one seriously because my 1st co-op job was working at a company where I did A LOT of testing to ensure their products would pass UL when we sent them out to them for testing. Even back then (decades ago), competitors were creating fake UL and CE labels to put on their copycat products. Most companies are powerless to stop these imitation products and it is unfortunately a fact of life today. So, just because that Amazon product says UL listed or has the CE mark means NOTHING. You can try to mitigate risk by buying a major brand, but there are copycat products unfortunately so caveat emptor. Now for a personal anecdote about UL listing. My inlaws bought my wife and I, a lighted angel to put atop our Christmas tree many years ago. It was UL listed, or rather I should say it had a UL listing sticker on it. One day we started to smell something burning and found it partially melted on the Christmas tree. Upon inspection, I found nothing obviously wrong with it and it worked trouble free for quite some time before this incident, but suddenly one day it just started to melt. Into the trash it went. Now, with regard to some Amazon extension cord like that I would have concerns regarding is it truly UL listed? Another thing to consider...I hope this isn't new information for anyone here, but 12AWG stranded is NOT the same as 12AWG solid. So, putting 12AWG solid in conduit between junction boxes on the wall of the basement is superior to stringing a multi receptacle 12AWG extension cord because solid wire can carry more current than stranded wire. Also I can guarantee that THHN wire has a much higher temp rating than anything in any extension cord. I am sure for the vast majority of Shopsmith owners, they will have no issues with their Mark V (assuming it is good to begin with), using it as intended in their shop with a 12' or less extension cord. It is on the periphery where problems seep in, which is why Shopsmith has that recommendation. Another personal story to try to make a point here. As a child, we didn't have much back then because not much existed that you could plug into a receptacle. Our television burned up. Now, my Dad was an Electrician at that time and after some troubleshooting came to the conclusion that the problem was NOT anything inside of our house. He had to argue with the power company and argue and argue until finally they installed monitoring equipment on the power line feeding our home. Remember computers were NOT ubiquitous back then so this was a big deal to get a recording monitor as I am sure these would have been very expensive. When they came back to remove the recording device and analyze it they found out that the voltage was varying wildly to our house because there was a floating neutral at the transformer on the power pole near our home. They fixed it and the problem was solved. What is the message I am trying to emphasize here??? ALWAYS challenge assumptions. I have had this lesson many times in my life and it was emphasized for me in my engineering career. IF I make a false assumption in discussions on this forum, then I beg you to point it out and we can discuss. This is what I have been doing on this thread, i.e. challenging assumptions. You can't always assume the ideal case and you can't assume a lossless branch circuit feeder. For most threads on this forum, it is about the average Shopsmith user and the average shop, etc. so mainstream advice is fine. IMHO, this thread is different, because it IS about the worst case, the extreme case that this requirement from Shopsmith originated - which is the center of the OP's question on this thread. Hence, I tried to point that out on this thread and again I implore all of you to always challenge assumptions. You will be surprised what you learn when you do this.

Another thing to point out is that line voltage fluctuates with neighborhood load. I have a continuous voltage monitor in my house and with reasonably the same load in my house and NO change in that particular branch circuit load, I witness about a 5V change over time to the voltage supplied to my house. I have witnessed this swing within a single day but it also varies seasonally. I live in a large city and we have quite the variation in load demand for the generating stations here because of the massive HVAC demand in the daytime of summer. Fortunately, I am on the high side, 125V becomes 120V at my house. What if you are on the low side and 115V becomes 110V? Then you are running that Mark V on an extension cord in your shop and you lose another 5% of line voltage due to extension cord + branch feeder circuit? Are you still within the motor manufacturer's rating then? Oh, right most of us have ancient Mark V's whose motors were built when the national electrical standard was 110V, NOT 120V as it is today. So, you have plenty of buffer margin to keep that induction motor happy!!! Good thing the standards changed and they moved the line supply up for your benefit!!!

[SteveMaryland]

I use about a 75 ft extension cord on my Shopsmith because it's outside and I don't have an exterior outlet. Guess I'm living dangerously...

I don't want to start a brou-ha-ha with this but I thought that stranded wire was supposed to carry more current than the equivalent-area solid wire. I thought that a current-conducting material carried most of electron movement at the surface, where the electrons were "freer" to move than those in the interior. And I read this:

"A changing electrical current (AC) experiences the skin-effect where the electricity flows more easily in the surface layers. The higher the frequency the thinner the surface layer that is usable in a wire. At normal household AC (50/60hz) the skin depth is about 8-10mm but at microwave frequencies the depth of the metal that the current flows in is about the same as a wavelength of visible light".

"The individual strands have to be insulated from each other for the skin effect to apply to each individually."

"There is an effect with AC electricity that the current mostly flows near the surface of the conductor. A number of thinner wires have more area-near-the-surface and so a larger effective cross section area than a single thick one. At the 50/60Hz frequencies used by AC transmission this only affects wires more than a cm thick."

So it sounds like stranded vs solid may be a wash for 60 hz AC?