Portable cords/extension cords - construction site

[stockexpert]

Just need some clarification for the following:

Building construction site - SO cord made up in 50' lengths with plug on one end/receptacle on the other (locking, 20A, 120VAC). Three of these cords were made up - connected end-to-end - to connect electrical equipment to nearest power source - 120VAC, 20A source.

questions: Does the term "extension cord" mean the same as "portable cord?"; 2) What section in the NEC specifically states allowed use of cords at a construction site?; 3) Does anything in OSHA, article/section, prohibit what is noted above?; 4) Assuming three cords noted above are correctly sized, cords are three conductor - H, N, G -, and have a GFI at the source, what safety issues would there be, if any?

Thanks and Happy Thanksgiving!

 

[Timbert]

1. I think portable cord is connected to portable equipment, where an extension cord (flexible cord set) is not.
2. The NEC doesn't specifically address construction sites but is generally applicable.
3. I don't know of a specific rule, but the general duty clause should cover this (i.e. daisy-chaining extension cords is a recognized hazard). I've also seen arguments following that extension cords need to be UL listed and daisy-chaining violates the UL listing.
4. The safety issue I see with daisy-chaining extension cords is that the size of the cord is usually based on length. Longer cord, bigger wire, this is to handle voltage drop. So, a fifty-foot cord is designed assuming it will be fifty feet from the receptacle to the load. By daisy-chaining the extension cords it is now 150 feet from receptacle to load. If you get a short at the load you now have three times the expected resistance in the wire (not to mention contact resistance), this will decrease the short circuit current causing a delay in the circuit breaker opening. These means excessive current flows in the wire for a longer period possibly damaging the wire or conceivably starting a fire.

A good way to look at this is when considering voltage drop and conductor resistance a 50' cord set should be #10 AWG; a 150' cord set should be #6 AWG. That means those three cord sets are undersized when you want to run 150 feet.

 

[Upnorth]

2. The NEC doesn't specifically address construction sites but is generally applicable.

NEC Article 590 Temporary Installations does, in fact, have several sections referring to use of flexible cords on construction sites, including use of SO (and other hard-service) cords as feeders or branch circuit cables, and cords and cables entering enclosures (via proper fittings) for connection to devices.

Yes, chaining multiple cords together may violate the UL listing for the "maximum length of general purpose extension cords" for that AWG, as well as OSHA 1910.303(b)(2), which is also NEC 110.3(B) ("...used in accordance with any instructions included in the listing or labeling").

However, where the electrician has "made up" his or her own general-purpose extension cords, by field modification of the listed components, the cordsets are not "UL" or otherwise "listed or labeled" at all. Field-assembled extension cord sets are allowed on a 20-A branch, using 16 AWG and larger, in NEC 240.5(B)(4) [Overcurrent] Protection of Flexible Cords..

A properly engineered "special" cord (e.g., 100 ft to a sub-panel) might actually meet code at any desired length, at least for temporary use, and the customer can use off-the-shelf, listed cords from there.