Solid vs. Stranded Conductor


Thread Starter


Can solid conductor wires be used for industrial lighting circuits that are supplied on industrial machinery?? I am always used to using THHN or MTW wires for conduit and panel wiring. What standards, if any, say when solid conductors are allowed?? I have only seen solid conductors used in residential wiring so far, never on industrial equipment.
> Can solid conductor wires be used for industrial lighting circuits that are supplied on industrial machinery??

Please refer also to IEC/EN 60204 (formerly also known as VDE 0113) Part 1 Chapter 9.
Basically it's a good practice to use *ONLY* flexible wires in industrial equipment. Massive conductors should only be used for power (not control) circuits connecting stationary "building-fixed" equipment without freely hanging cable and sections should be >= 1.5 mm2 (roughly AWG 16) although smaller sections are used too but tend to lead to fragile connections.
An exception concerns small signal cables using traditional massive copper wires with 0.6 or 0.8 mm diameter (not section, diameter), typically telephone cables used for field-wiring. Also patch panels wired using Wire-Wrap or TermiPoint technology use rigid wires.
Good minimal section for multiconductors cables for general Instrumentation & Control purposes is 0.75 mm2 flex (approx. AWG 18).
Inside usual factory-wired electrical cabinets only flexible conductors as well as massive Cu or Al busbars should be used. Exceptions are acceptable for some special proprietary cables but wiring must be done very carefully to avoid connection failures.

NFPA 79 Electrical Standard for Industrial Machinery Sec.14.3.3:
"The conductors to stationary lights used as an integral part of the machine shall be Type MTW, and the conductors within the fixtures shall be not smaller than No. 18 AWG."

Section 15 covers "Conductors" and the only place where solid conductors are allowed is 15.2.3:
"Solid conductors AWG 24-30 of soft-annealed copper shall be permitted for use within control enclosures where not subject to flexing."

David Baird
Senior Controls Engineer
(937)-223-4600 x1456 FAX (937) 226-1908
[email protected]

Solid wires, below a certain size, are allowed by the NEC code (310-3). However, if there is the slightest hint of vibration exposure, especially where even slight movement is normal, for eample, at motor controller or relay terminals, I wouldn't hesitate to recommend stranded.

In addition, many panel USA shops are adverse to using solid, but it is normal European practice.

Phil Corso, PE
(Boca Raton, FL)


Bouchard, James [CPCCA]

Stranded wiring is used to reduce the possibility of connections coming loose due to vibration. It is also used to make the wiring more flexible. It
is also easier to install compression lugs on stranded wire that on solid wire. And finally if you need to make connections with wire nuts it is
easier to do with stranded wire than with solid wire. As far as I know the electrical code does not have any limits on the type of wire used so it is really up to the end user to specify what suits him best. In our case we have specified stranded wire for all applications even offices and lighting to avoid possible problems. There is a slight premium for stranded wire in smaller sizes but if you put it in your specification at the beginning then there will be no problem.

James Bouchard


I don't remember what the NEC allows, but if it's a piece of machinery that vibrates much then you stand a good chance of the wires breaking,
loosening the connection, or rubbing through the insulation. I'd stick with stranded wire.

Paul Baker


Trevor Ousey

IMHO, avoid solid conductors as they become maintenance issue from breaking. A lot of panels I used to maintain, came wired in solid and we went through and changed it to stranded, actually
what we refer to as 'flex', 32 strands. I have not come across any standard, but some site standards will not allow the use of solid's.