Bus Drop Wiring

[Rotato]

Started at a new factory not to long ago. Trying to get educated on Buss Drops. Specifically wiring methods from bus drop through plugs to a machine. Machinery is meant to be semi-permanent (interchangeable eventually). They're using bus drop cable and bus drop clamps at the ceiling. Just not sure about using plugs for feeders to semi-permanent machinery and how your supposed to enter the machinery with bus drop cable. Is a cord grip enough or are there specific cord grips for this type of installation?

Last place I worked at used conduit everywhere.

Where can I find the relevant codes for these types of installations in the NFPA 70 or NFPA 79.

 

[retirede]

Start with NEC 368.56.

 

[Rotato]

That hit the spot. Thank you.

 

[garbo]

The company that I worked out back in the 1980's improperly just ran 12/4 cord drops from buss duct switches & 1900 boxes with a Romex connector mounted on the cover to supply 480 to what they considered semi permanent machines ( might move one once every ten years to rebuild it ). All cords had twist lock cord connectors. I tried to tell them they were doing it wrong and was labeled a trouble maker. Only told the facility Forman my concerns. OSHA spent days writing up violations. We had to get rid of twist lock plugs on machines except for a few that were on wheel. I used long steel elbows thru side of 1900 ceiling boxes and Klems cord grips. Any machine on wheels I also installed Klems grip cable drops that I installed a spring on it and attached it a piece of unistrut. All 6 electricians each got over a hundred hours of overtime fixing OSHA violations.

 

[Rotato]

So reading 368.56(B)(4). What does the code consider "Strain Relief Cable Grip"? I couldn't find it in the definitions. I am assuming it means only grips that have that braiding on the outside that squeeze the cable as its pulled. Or does it include other grips too?

 

[retirede]

So reading 368.56(B)(4). What does the code consider "Strain Relief Cable Grip"? I couldn't find it in the definitions. I am assuming it means only grips that have that braiding on the outside that squeeze the cable as its pulled. Or does it include other grips too?

I never thought about before, but manufacturers call some cable compression gland fittings “strain relief” so I’d think they would be acceptable.

If the equipment is normally fixed while in use, I’d be fine with a compression gland. If it gets moved around a lot, the braided grip is probably a better choice.

 

[garbo]

I never thought about before, but manufacturers call some cable compression gland fittings “strain relief” so I’d think they would be acceptable.

If the equipment is normally fixed while in use, I’d be fine with a compression gland. If it gets moved around a lot, the braided grip is probably a better choice.

I would never use so cord cord connectors with a rubber donut that marked strain relief on drops higher then 10' off the floor or heavy cable. Several times I had to drop 30' of 6/4 cord and and used a Klems cable grip on a heavy spring attached to unistrut then a short loop of cable thru an approved non strain relief cord connector.

 

[MTW]

This is what I a;ways used on bus drops. With this style beam clamp, the hanger spring fits nicely hooked in the two bottom rod holes.

https://www.hubbell.com/wiringdevice-kellems/en/products/electrical-electronic/wirecablehose-management/wire-mesh-grips/strain-relief-grips/c/2198698

Sky-Tie - Bus Drop Cable Clamp

www.adalet.com

https://www.eaton.com/us/en-us/skuPage.B751-J4-3%7B%7D8ZN.html

 

[retirede]

I would never use so cord cord connectors with a rubber donut that marked strain relief on drops higher then 10' off the floor or heavy cable. Several times I had to drop 30' of 6/4 cord and and used a Klems cable grip on a heavy spring attached to unistrut then a short loop of cable thru an approved non strain relief cord connector.

In the OP’s case, the end is attached to a stationary machine. I think compression style would be fine on the bottom end. If it were a pendant, I’d agree with you.

 

[jes25]

What I'd like to figure out is the ampacity of bus drop. It's not a recognized cord in Table 400.4 or 400.5. The conductors inside don't have any markings either so I don't see how you would apply Table 310.16

 

[MTW]

What I'd like to figure out is the ampacity of bus drop.

Industrial Flexible SPEC 45030

cabletechsupport.southwire.com

 

[jes25]

Interesting. They 'based' the ampacity per 310.
16. But as far as I can tell, the NEC gives no guidance on the ampacity of this stuff. It's not a cable per 400.. t's not a conductor per 310. Nor is it a wiring method like NM, AC, MC, TC etc. it just a cable permitted to run from busways

 

[jes25]

This company based their ampacities on 400.5

 

[MTW]

They are based on different temperatures, look in the page specifications for each brand. 60, 75, 90C which one are you using?
The Royal brand (Southwire) specifies TW insulation, page is dated 2024 based on 2023 NEC

The Carol brand specifies PVC insulation, dry location 60C I don't see a date on that attachment.

 

[MTW]

368.56 Branches from Busways. Branches from busways shall
he permitted to be made in accordance with 368.56(A), (B),
and (C). You will find bus drop cable mentioned there.

 

[jes25]

They are based on different temperatures, look in the page specifications for each brand. 60, 75, 90C which one are you using?

Both cables are rated at 60c. I suspect they all are?

The Royal brand (Southwire) specifies TW

Thanks for noticing that it specifies TW. That gives me a place to go in 310.16.

Do you find it odd, perhaps misleading, that Southwire's product is rated at 60c, but they only list 75c and 90c columns in the spec sheet for that 60c product?

 

[jes25]

368.56 Branches from Busways. Branches from busways shall
he permitted to be made in accordance with 368.56(A), (B),
and (C). You will find bus drop cable mentioned there.

I know, but it doesn't reference ampacity at all.

 

[MTW]

Both cables are rated at 60c. I suspect they all are?

Thanks for noticing that it specifies TW. That gives me a place to go in 310.16.

Do you find it odd, perhaps misleading, that Southwire's product is rated at 60c, but they only list 75c and 90c columns in the spec sheet for that 60c product?

I don't know what temp rating or ampacity your looking for or size, I normally size it based on 60C for sizes #10 and under, but if you want to find out more specifics a call might be in order to your supplier. I doubt that Southwire would list ampacity values for their cable @75 and 90C if their cable was not suitable for that. Their 60C rating is shown for outdoor use according to the page I linked to above. To dig any deeper you would likely have to look up their UL listing #, likely would be much easier to contact them and have them send you what your looking for. The 60C would be a conservative number to use, if you needed more than that I would request it directly from your supplier. Just because there is not a direct listing in the NEC doesn't mean that there is not a UL rating for the particular cable your interested in. Just would take a bit more work to find out about a specific application.

Here is another vendor example that is showing a 75C rating for a #12 cable but lists the amacity @ 20A, which equates to the 60C rating. Different brands may be listed and constructed differently.

12/3 Bus Drop Cable | 12 AWG, 3 Conductor Bus Drop Cable

12/3 Bus Drop Portable Cord has three bare copper conductors with a Thermoplastic/Nylon insulation and PVC jacket. Submit an RFQ for 12/3 Bus Drop Cable!

www.awcwire.com

 

[jes25]

Thanks for your responses. I don't have a particular install in mind here.

I guess the answer to the question is to contact the manufacturer/ UL since the NEC doesn't say how to calculate it's ampacity.

 

[Elect117]

Thanks for your responses. I don't have a particular install in mind here.

I guess the answer to the question is to contact the manufacturer/ UL since the NEC doesn't say how to calculate it's ampacity.

You can use 110.14(C). Basically, if the cord is a conductor size (AWG or KCMIL) of 100A and less you can use the 60°C rating in table 310.15. If it is more than 100A you can use the 75°C.

I had someone try and tell me that southwire's ampacity was the one they used for cable trench runs of a special 2000V cord. They REALLY wanted to use the higher ampacity southwire had on their sheet, but unfortunately that is not how UL or the NEC handles it. There is more information in UL white book AALZ section.