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Mark V Electrical Requirement

BuckeyeDennis

GG0452 wrote I feel that the 25 feet of 12 gauge extension is more than adequate for several reasons. 1. SS recommends 12 gauge wire for a 50 foot extension cord. 2. I ran my Mark v for 40 years using a 50 foot 14 gauge extension cord without any problems. 3. The cord is exposed, lies on the floor, and can be monitored for overheating. The only issue, as i see it, is start up time and that does not seem to be a problem. Heck, my house vacuum runs on 18 gauge wire and get hot every time the vacuum is used. BTW when is first got my Mark V i ran it on a 15 amp fused circuit. That was a pain and why i had a breaker box installed and the 30 amp 10 gauge wire circuit for the SS (and i think at the time local code was 20 amp circuit on 14 gauge wire and now it is 15 amps).

I agree that 25 feet of 12 AWG cord should work fine. The resistance of 12AWG copper wire is 0.0017 Ohms/foot. The electricity will have to travel 50' round-trip in your 25' cord, so the total series resistance of the wire is 50 * .0017 = 0.085 Ohms. Assuming a 13.2 Amp continuous rated current for your Mark V motor, the voltage drop across the additional wire is 13.2 * 0.085 = 1.1V. Not a problem.

At the 54V startup surge current that I measured on my own Mark V, the voltage drop across the extension cord would still be only 54A * 0.085 Ohms = 4.6V. Even factoring in the 30 milliohm rated maximum contact resistance of Nema 5-15 plugs and receptacles, the worst-case voltage drop during the startup surge is 54 * (0.085 + 0.030) = 6.21V, or roughly 5% of the nominal line voltage. Again, not a problem -- that's well within specs for an induction motor.

RFGuy

BuckeyeDennis wrote I agree that 25 feet of 12 AWG cord should work fine. The resistance of 12AWG copper wire is 0.0017 Ohms/foot. The electricity will have to travel 50' round-trip in your 25' cord, so the total series resistance of the wire is 50 * .0017 = 0.085 Ohms. Assuming a 13.2 Amp continuous rated current for your Mark V motor, the voltage drop across the additional wire is 13.2 * 0.085 = 1.1V. Not a problem.

At the 54V startup surge current that I measured on my own Mark V, the voltage drop across the extension cord would still be only 54A * 0.085 Ohms = 4.6V. Even factoring in the 30 milliohm rated maximum contact resistance of Nema 5-15 plugs and receptacles, the worst-case voltage drop during the startup surge is 54 * (0.085 + 0.030) = 6.21V, or roughly 5% of the nominal line voltage. Again, not a problem -- that's well within specs for an induction motor.

Dennis,

I gotta disagree with you on this one. What is often forgotten is the feeder length, i.e. how long is the wire pull from the breaker in the service panel or subpanel to the receptacle the extension cord is plugged into. If you are living in one of those new tiny houses (<400 sq. ft.) then great, but if not, even a modest sized home likely has at least 75' to 100' (one way) of wire connecting breaker to receptacle - depending on where your shop is located relative to the panel. You need to talk about IR drop and startup surge under actual real world conditions which means including the house wiring + extension cord. This is precisely why short extension cords, typically 9' long, are sold for things like window air conditioners, etc. These are usually marked "appliance extension cord" on them indicating their purpose. It is NOT prudent to use a 25' extension cord on common appliances like refrigerators or window air conditioners. Also to Russ's point regarding fire safety and factoring in this extra wire loss, I would really discourage against ANY excess wiring in the loop. However, anyone that does this in choosing to use a long extension cord, it is your Mark V and it is your house. I just hope your homeowner's insurance policy is paid up...just in case.

BuckeyeDennis

RFGuy wrote
BuckeyeDennis wrote I agree that 25 feet of 12 AWG cord should work fine. The resistance of 12AWG copper wire is 0.0017 Ohms/foot. The electricity will have to travel 50' round-trip in your 25' cord, so the total series resistance of the wire is 50 * .0017 = 0.085 Ohms. Assuming a 13.2 Amp continuous rated current for your Mark V motor, the voltage drop across the additional wire is 13.2 * 0.085 = 1.1V. Not a problem.

At the 54V startup surge current that I measured on my own Mark V, the voltage drop across the extension cord would still be only 54A * 0.085 Ohms = 4.6V. Even factoring in the 30 milliohm rated maximum contact resistance of Nema 5-15 plugs and receptacles, the worst-case voltage drop during the startup surge is 54 * (0.085 + 0.030) = 6.21V, or roughly 5% of the nominal line voltage. Again, not a problem -- that's well within specs for an induction motor.
Dennis,

I gotta disagree with you on this one. What is often forgotten is the feeder length, i.e. how long is the wire pull from the breaker in the service panel or subpanel to the receptacle the extension cord is plugged into. If you are living in one of those new tiny houses (<400 sq. ft.) then great, but if not, even a modest sized home likely has at least 75' to 100' (one way) of wire connecting breaker to receptacle - depending on where your shop is located relative to the panel. You need to talk about IR drop and startup surge under actual real world conditions which means including the house wiring + extension cord. This is precisely why short extension cords, typically 9' long, are sold for things like window air conditioners, etc. These are usually marked "appliance extension cord" on them indicating their purpose. It is NOT prudent to use a 25' extension cord on common appliances like refrigerators or window air conditioners. Also to Russ's point regarding fire safety and factoring in this extra wire loss, I would really discourage against ANY excess wiring in the loop. However, anyone that does this in choosing to use a long extension cord, it is your Mark V and it is your house. I just hope your homeowner's insurance policy is paid up...just in case.

My workshop is in my basement. But for the sake of argument, let’s suppose that it was in my garage.

My builder installed two 20A outlets in the garage wall that is shared with the house (which is immediately adjacent to the load center /breaker panel), but no outlets on the other garage walls. Now let’s suppose that I need to locate my Shopsmith on the far side of the garage, opposite from the 20A outlets, near the garage doors. Aside from the 30 mOhm contact resistances of an extra Edison plug & jack, how exactly would running a 12AWG extension cord compromise the machine’s electrical supply, in comparison with running a hard-wired 12AWG branch through the garage perimeter walls to a nearby location?

RFGuy

BuckeyeDennis wrote My workshop is in my basement. But for the sake of argument, let’s suppose that it was in my garage.

My builder installed two 20A outlets in the garage wall that is shared with the house (which is immediately adjacent to the load center /breaker panel), but no outlets on the other garage walls. Now let’s suppose that I need to locate my Shopsmith on the far side of the garage, opposite from the 20A outlets, near the garage doors. Aside from the 30 mOhm contact resistances of an extra Edison plug & jack, how exactly would running a 12AWG extension cord compromise the machine’s electrical supply, in comparison with running a hard-wired 12AWG branch through the garage perimeter walls to a nearby location?

Dennis,

I think you missed my point. You have been assuming that the reference plane is the receptacle...which means you are assuming that the house wiring is ideal and lossless, but that is NOT the case. You are assuming 120V nominal at the receptacle and that may not be the case given the significant current draw of a Mark V over the internal house wiring. This actually goes to the point of Shopsmith's recommendation and why they are pushing this because of their motor manufacturer hoping to avoid unnecessary warranty claims. Every house and/or shop is different. In the best case, the panel/subpanel is in the garage/shop and it is a short run of EMT (or in the wall) to a junction box where the Mark V plugs into. Let's say between the wiring from breaker to junction box and the Mark V power cord itself it is only 20ft. In the moderate case, I am positing that there could be 100ft. of wiring to consider. In the worst case, well it really is difficult to pin down. Some nitwit could have wired their shed shop on their property themselves with 14AWG and let's say for argument's sake it is 1000ft. from panel. My point is there are actual use cases where the deviation from nominal line voltage can be over 10% exceeding every known induction motor rating that I know of. Then there is startup to consider as well. IF someone wants to potentially shorten the life of their Mark V motor by using an unnecessary extension cord, then by all means go ahead. There are lots of warnings out there already from firefighters and industry groups urging people to limit extension cord use and/or only use them for temporary use cases. They are NOT recommended for major appliances (Mark V qualifies as this due to high current draw). Of course, if you know the exact line voltage under load, and its time variation, at your shop receptacle AND you want to use an extension cord, go right ahead. I just hope they have done the calculations first and know what they are doing. That is all.

JPG

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.

1000 ft is absurd.

Now the concern re improperly sized wire (diy electrical work) is very valid.

The major culprit here is startup current surge(a temporary hopefully short term event).

Also the typical extension cords the fire departments so abhor are 18 AWG.

RFGuy

JPG wrote 1000 ft is absurd.

Yeah, about as absurd as someone calling a 25ft extension cord "short", but I digress. Checking out of this thread...

BuckeyeDennis

RFGuy wrote
I think you missed my point.

I don't believe that I did -- I merely thought that you were being overly broad in your recommendations against using "long" extension cords. Can we agree that total supply-voltage drop is the real issue here?

I agree completely with you that the fixed house wiring causes part of the total voltage drop, and the extension cord contributes another part. But a blanket recommendation against "long" extension cords may preclude someone from using one in a situation where it solves a real machine-supply challenge, without causing either excessive voltage drop or additional safety concerns.

I'll use my own basement shop as a case in point. I recently installed a new subpanel in it, connected it to the main load center using a pre-existing 6AWG feeder cable, and protected that feeder with a 50A breaker. (I'll pull a new 100A feeder in the future, but 50A will suffice in the short term.) I plan to run a single new 12 AWG branch circult from the subpanel to supply a number of manually-operated woodworking machines that draw 15A or less, including my Mark V. It's a one-man shop, so only one of these machines will be powered on at any given time. I plan to set up that new branch circuit as a "bus" that supplies all those machines, and install a 15A breaker as external motor overload protection (for the reasons discussed previously). Any machine that could be operating independently (CNC router, air compressor, dust collector, etc.) is already powered from separate branch circuits.

The dozen or so "small" manually-operated machines in question are all positioned around the periphery of my workshop, where it's convenient to plug them into wall receptacles. But it would be a huge PITA to install a bunch of new branch receptacles. While pondering that, I ran across some 25-foot,12AWG heavy-duty multiple-outlet extension cords on Amazon. They have a receptacle about every four feet, and each receptacle has a pair of mounting-screw lugs molded in.

My current plan is to mount a single duplex receptacle for that new "bus" circuit very near the subpanel, but strategically located so that one of the 25' multi-outlet cords can serve all the small manually-operated machines on one side of the duplex receptacle, and two of them in series can serve the ones the other side of the receptacle. Thus the longest total wire run is less than 60' (from the subpanel) of 12 AWG wire. The individual outlets will each be screwed to either the tops of the walls or to ceiling joists, high up where the risk of mechanical damage is exceedingly remote. This setup will give me outlets about every four feet around the entire perimeter of my shop, maximizing flexibility in machine positioning. It's less expensive, and far less labor intensive, than installing discrete recepticles in the conventional manner, and the cords are UL certified.

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

JPG

Who thee asking? :D

BuckeyeDennis

JPG wrote Who thee asking? :D

Anyone who has relevant knowledge!

Methinks thee missed the point. ;)

BuckeyeDennis

BuckeyeDennis wrote
JPG wrote Who thee asking? :D
Anyone who has relevant knowledge!

Methinks thee missed the point. ;)

Dang, Red, did you edit my actual post?! :confused:

But to your point, I did indeed miss the point. As a matter of fact, I missed a few entire posts, including the last one by RFGuy. On my system, when I click the "First unread post" link at the top of the page, it will sometimes take me to the first post of a new page of a thread, even if there are a couple of unread posts at the bottom of the previous page. I try to remember to check for that, but this time I forgot to, and it bit me.

Or maybe you and RFGuy both posted whie I was writing my long post about my basement shop wiring. But the system normally warns me when that happens ...

DLB

JPG wrote 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

BuckeyeDennis wrote 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

HopefulSSer wrote
BuckeyeDennis wrote 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

JPG wrote 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!!! :D

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?

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