Industrial Machines Supply Wiring Method Conduit vs SOOW Cable


This Machine shop has several older mills and lathes some 480v 3Ø & 240v 3Ø. No E-Stops, guards pretty much 1930' or but still working machines.
In evaluation to upgrade these unit, the supply wiring method has become the debate.
Previously all were connected soow cable w/ twist lock plugs and receptacles to the safety sw.

The only method I recall for permanent installation is Conduit either supported overhead or anchored to the floor with a cover to prevent tripping hazards unless the machine is movable for cleaning.

Is the soow cable w/ twist lock plugs permitted, or is this only for a temporary connection.

As if the operator is finished using the equipment and removes the plug like on a welding machine.

Can someone provide the article in NFPA 79 or 70 or if this is a OSHA requirement.

Thank you,


Senior Member
North Georgia mountains
Owner/electrical contractor
At least they are using SO cord, the plant I’m at today, used a motor guy that does mostly well pumps. Pump wire strewn everywhere! LOL! Slowly getting rid of it. Most of the machines here are from the thirties too, but the plant is about 30 years old.


in regards to
NEC 370.20(A)2
374.20 Size of Conductors. No conductor larger than 1/ 0 AWG shall be installed, except by special permission.
Article 370 Cellular Metal Floor Raceways
This facility is concrete floor connection conductors are only for 50A

368.56 B
in this facility a drop from the ceiling would exceed the 6' of 368.56(B)(2)
however if the connection to the wall receptacle doesn't exceed 6' would this been seen as within the

I have found in
29 CFR 1910.305 – Wiring methods
Question 5: Under what conditions might the use of flexible power cords as permanent wiring be an acceptable/permissible use of flexible wiring?

Response: In accordance with §1910.305(g)(1)(iv)(A), unless specifically permitted otherwise in section §1910.305(g)(1)(ii), the use of flexible cords and cables is prohibited as a substitute for the fixed wiring of a structure. Section 1910.305(g)(1)(ii)(A) through (L) provides ways in which flexible cords and cables may be used; and section §1910.305 (g)(1)(iv)(A) through (F) provides ways flexible cords may not be used

Appliances where the fastening means and mechanical connections are designed to permit removal for maintenance and repair;

so if the intent to move for maintenance, would this apply as an exception allowing the flexible cable along with a cable cover.

Thank you,


Senior Member
SE Michigan
I think you need to read that code section again, a little more carefully. There is no bus drop cable length limitation of 6'. The 6' length limitation is for the horizontal portion of the cable from the last means of approved support (bus plug). The cable must be properly supported directly above the drop location, with the proper strain relief and tension take up device. In this post I gave the links to the approved support devices. Use conduit for the horizontal portion of the run to remain less than 6', and the bus drop cable and hardware for the vertical drop to the equipment. It's generally easier and cheaper to use conduit for horizontal extensions, than to use cable and sky-ty support devices every 6'.

368.56 Branches from Busways.
(B) Cord and Cable Assemblies. Suitable cord and cable
assemblies identified for extra-hard usage or hard usage and
listed bus drop cable shall be permitted as branches from
busways for the connection of portable equipment or the
connection of stationary equipment to facilitate their interchange
in accordance with 400.10 and 400.12 and the following
( 1) The cord or cable shall be attached to the building by an
approved means.

(2) The length of the cord or cable from a busway plug-in
device to a suitable tension take-up support device shall
not exceed 1.8 m (6ft)
(3) The cord and cable shall be installed as a vertical riser
from the tension take-up support device to the equipment

( 4) Strain relief cable grips shall be provided for the cord or
cable at the busway plug-in device and equipment terminations
Take a look at the photos I posted in the other thread above. All of the drops are directly below a transition box, from pipe to bus drop cable and a tension take up device mounted to the structure and strain relief chord connectors on each end of the cable. I have used this method for years in many plants and have never gotten negative feedback from AHJ or customers. It's many times more durable than some hard pipe dangling down 20 or 30' from a roof truss. But it requires the proper execution of installation and materials.

The method is from the busway article, and others have asked about that being suitable for other circuit supply sources. The same article allows branches from bus plugs with conduit extensions, I see little difference if the conduit and box extension is fed from a bus plug-in device or extended from a local panelboard or loadcenter. The method and materials are designed and approved for the purpose, aerial circuit drops to machinery placed out in the middle of the plant floor.



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Ok yes correct, let me rephrase they have (2) machines both about 10' - 12' away from the wall. the ceiling is approx. 25' 35' to the peak. no Buss in this facility. They are not planning to do anything like this.

here is how one of the machines is connected, and the second machine is planned to be the same.

main LV panel 60A 3Ø breaker is wired to a 240v 60A 3Ø safety switch, that is wired to a 30A twist lock receptacle.
machine fused disconnect interlock is wired with soow cable (20'-25') with twist lock plug. The cable is just laying on the floor, no protection.

for a fixed location is this installation allowable. According to §1910.305(g)(1)(iv)(A) this is only for temporary installation, and that would require a protective cover.

for a fixed machine in this scenario, the thought was that only conduit w/ support could run up and over to the wall and hard wired to the disconnect
or could a conduit secured to the floor with a cover to prevent a trip hazard run to the wall and hard wired to the disconnect.

I thought the soow cable could only be used for temporary installation.


Senior Member
SE Michigan
For a circuit 10 to 12' from the wall, I would be using rigid conduit overhead supported from the wall and the machine, depending on the actual site conditions. Without seeing the machine and site conditions, it is hard to advise. Is there hilo traffic in the area? Is the machine capable of having a support attached to it, to support one end of the conduit run?

I would never accept the liability of stringing a 3 phase extension chord on the floor, protected or not. It's just not smart, and a code violation. I would cut the floor and install a rigid conduit before I would leave a chord laying there. It's just too much liability to accept if something happens down the road. I would tell the customer to move it closer to the wall or do it one of the approved methods or walk away from the liability.

If you submitted a photo of the conditions at the site, you might be able to get better suggestions. But I would personally, never install a chord on the floor, that's just wrong and leaves you liable.


EC, Westchester, New York NEC: 2014
Hawthorne, New York NEC: 2014
If you submitted a photo of the conditions at the site, you might be able to get better suggestions.


I did a shop once with several old Bridgeport J head milling machines and several lathes. Ceiling trusses were about 12'. I installed a 1900 box with a twist lock receptacle above each machine. SO cord up from the control on the machine to a twist lock plug. Cord was hung with a Kellams grip or what @MTW shows in post #5 above. Plug acts as the disconnect.



I have gotten them to consider the support, cost was as always the hold up.

Had a meeting to discuss issues identified in NFPA79 so installing E-Stops at a minimum is a start.

Supports bolted to the machines and going overhead to the wall beams will be the method. Installing a small cable tray will allow for other connections including shop air.

These machines are needing a lot of upgrades, the E-Stop is first and then fixing or installing door interlocks.

Can you provide the code article of violation.

Thank you for your help