Mark V Electrical Requirement

[BuckeyeDennis]

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]

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]

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]

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]

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]

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.

Capture.JPG (170.74 KiB) Viewed 37368 times

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?

[BuckeyeDennis]

Who thee asking?

Anyone who has relevant knowledge!

Methinks thee missed the point.

[BuckeyeDennis]

Who thee asking?

Anyone who has relevant knowledge!

Methinks thee missed the point.

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

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 ...