The floor sander left this at a job site. It's pretty safe by flooring company standards. :roll: It's a 30 amp dryer cord with a 20 amp/250 volt twistlock. They actually wired the twistlock correctly and used black and red for hot and green wire for the ground. I guess they never have to worry about the breaker tripping.
Bonus: can you spot something else that's wrong with this setup?
Bob Badger Construction & Maintenance Electrician Massachusetts
One thing that comes to mind is typical range cords are listed for Domestic Range use only and even though they fit a 50 amp receptacle the wire inside them is not rated for 50 amps. In this case the load from the Sander won't exceed the ampacity of the cable. I appreciate that these guys go into someone's house with little or no hope of finding a correct rated outlet for their sander and resort to this. It is infinitely better than the guys who pull the cover off the panel and connect direct to a breaker in the panel. In a perfect world a cord adaptor would be available with an o/c device rated for the sander.
#125130 - 03/16/0708:18 PMRe: The floor sander left this at a job site.
It's missing the battery jumper cable clips to clamp on the panel busbars? A few years ago I saw one clipped to the line side of the main fuses for a 5-story building that shared the pig with half the block. Yikes!
#125131 - 03/16/0711:08 PMRe: The floor sander left this at a job site.
...even though they fit a 50 amp receptacle the wire inside them is not rated for 50 amps.
I don't know about that. The last time I looked at a NEMA 14-50 range cord, the hots were 6 awg, the neutral was 8 awg, and the ground was 10 awg. Table 400.5 states the ampacity of 6 awg(whatever type of cord other than TPT, TST, HPD, HPN, etc, etc.) as 45A for Column A (more than 2 conductors) and 55A for Column B (2 conductors). Since a floor sander uses only 2 conductors, it doesn't matter that the cord came from the factory with 3. I wouldn't nitpick. I'd just give that floor sander guy a medal for being the first floor sander I've ever known to actually bother to try to do things right, instead of reflexively reaching for the %^$#&^% alligator clips when there is already a range or dryer outlet available!
Besides, the nameplate current of a 5hp motor is 28A according to Table 430.148. That means there is nothing wrong with using it on a 30A circuit, as long is it is not a continuous load (and isn't the continuous load rule waived under Article 527 (temporary wiring)?
An example of where the standard range cord would be inappropriate at 50A would be for an RV, since the full neutral ampacity is needed. (Never mind that a 6' long range cord would not be of much benefit as an RV extension cord!)
#125132 - 03/16/0711:23 PMRe: The floor sander left this at a job site.
OK, my mistake, it's a dryer cord, so all the conductors are 10 awg. So, I repeat, has anyone ever seen a floor sander that was over 5hp?
Can we assume that the floor sander contains running overload protective devices? I've never actually studied one that closely, but these things are manufactured by businesses that have to worry about product liability, and I assume their product is listed, so let's say yes.
That leaves branch-circuit short-circuit and ground-fault protection. Table 430.52 says that for an instantaneous-trip breaker (realistically the norm in any residence nowadays), the maximum percentage of full-load current is 800%. 800%*28A>50A. Did I do that right? Article 430 is probably the trickiest article in the NEC, I don't use it all that much, it's late on a Friday night, and I've had a few brews. Even if I'm wrong, I have to give credit to the floor sander guy for at least trying to get it right.
#125133 - 03/17/0712:27 PMRe: The floor sander left this at a job site.
Some things are most definitely easier here... the Hummel is made in Germany (by the way, Hummel means bumblebee) and here those things plug into a 230V 16A Schuko receptacle available in almost every place (only some real old places only have 10A fuses).
#125135 - 03/17/0709:57 PMRe: The floor sander left this at a job site.