300.19 (A) Supporting Conductors in Vertical Raceways

[NTesla76]

In reading 300.19(A) and Table 300.19(A), I'm somewhat confused, especially after reading the Application example. If you are using 1/0 copper, do you need or not need support if not greater than 100'. I think this section and table could be worded a bit better. Any thoughts?

 

[Dennis Alwon]

Article 300.19-- first sentence

Conductors in vertical raceways shall be supported if the vertical rise exceeds the values in Table 300.19(A).

So 1/0 copper does not need support unless it is more than 100'

BTW, welcome to the forum

 

[NTesla76]

I guess my confusion comes in with the first sentence of the Application Example. "......if the vertical run is not greater than 100 feet, 300.19(A) requires one cable support near the top of the run."

 

[Dennis Alwon]

I guess my confusion comes in with the first sentence of the Application Example. "......if the vertical run is not greater than 100 feet, 300.19(A) requires one cable support near the top of the run."

Yes you do need the one near the top to keep the weight off the transition point but you don't need supports all the way down

One cable support shall be provided at the top of the vertical raceway or as close to the top as practical. Intermediate supports shall be provided as necessary to limit supported conductor lengths to not greater than those values specified in Table 300.19(A).

 

[NTesla76]

Ok, thanks. That clarifies things for me.

 

[gadfly56]

When supports are needed, what do you use?

 

[big john]

The quick and cheap solution are basket grips installed in an enclosure at the top of the run.

They make wedge grips that may be a bit harder to come by but they're more versatile in that you could also put them in conduit bodies instead of setting a pull box.

 

[infinity]

The quick and cheap solution are basket grips installed in an enclosure at the top of the run.

They make wedge grips that may be a bit harder to come by but they're more versatile in that you could also put them in conduit bodies instead of setting a pull box.

I've never seen one, what kind of wedge grip is designed for a conduit body?

 

[big john]

I've never seen one, what kind of wedge grip is designed for a conduit body?

They aren't specifically designed for conduit bodies, but since they fit in the ID of the conduit they can be installed at conduit bodies:

 

[infinity]

They aren't specifically designed for conduit bodies, but since they fit in the ID of the conduit they can be installed at conduit bodies:

Those are designed to be used with a support bushing where the interior is made of an insulating material so the wedging action is not forcing the conductor weight against a metal edge. I have never seen one of those chocks listed for use in a metal conduit body even though they may fit, are they listed as such?

 

[jusme123]

Those are designed to be used with a support bushing where the interior is made of an insulating material so the wedging action is not forcing the conductor weight against a metal edge. I have never seen one of those chocks listed for use in a metal conduit body even though they may fit, are they listed as such?

:happyno::happyno::happyno:

below is the insulated bushing that accompanies the wedge

 

[Carultch]

Yes you do need the one near the top to keep the weight off the transition point but you don't need supports all the way down

I asked about this rule before, and it didn't come up in the discussion that you need a support if the vertical rise is significantly less than what the table prescribes.
http://forums.mikeholt.com/showthread.php?t=173731

I don't read anything in the NEC's text, that says you need a support when the length is less than the table. Maybe I'm missing it. Intuition would tell you that when your vertical rise is just a few feet shy of the value the table prescribes, you'd probably want to have one anyway. Yet if your vertical rise is only 10 ft, you probably wouldn't even be thinking about this.

Conductors in vertical raceways shall be supported if the vertical rise exceeds the values in Table 300.19(A). One cable support shall be provided at the top of the vertical raceway or as close to the top as practical. Intermediate supports shall be provided as necessary to limit supported conductor lengths to not greater than those values specified in Table 300.19(A).

The order of the sentences gives me the impression that to require a support, first vertical rise must exceed the value in the table, and then you follow the remaining rules for how to locate the supports. So this would mean that if the table prescribes 100 ft, then a 99 ft rise wouldn't require any supports, a 100 ft on-the-dot rise would require 1 support, and a 105 ft rise would require 2 supports. Please correct me if I am wrong.

kwired gave an interesting case to think about, which makes perfect sense. If you are reducing the wire to fit the equipment in a much smaller factory terminal, the factory lugs probably cannot withstand the weight of the upsized cable, and therefore supports should be provided even when 300.19(A) doesn't require them, to anticipate this less common situation. Even though in the general case, as he stated:

equipment with terminals that accept 500kcmil likely have reasonable physical ability to handle the weight

.

 

[jusme123]

I asked about this rule before, and it didn't come up in the discussion that you need a support if the vertical rise is significantly less than what the table prescribes.
http://forums.mikeholt.com/showthread.php?t=173731

I don't read anything in the NEC's text, that says you need a support when the length is less than the table. Maybe I'm missing it. Intuition would tell you that when your vertical rise is just a few feet shy of the value the table prescribes, you'd probably want to have one anyway. Yet if your vertical rise is only 10 ft, you probably wouldn't even be thinking about this.



The order of the sentences gives me the impression that to require a support, first vertical rise must exceed the value in the table, and then you follow the remaining rules for how to locate the supports. So this would mean that if the table prescribes 100 ft, then a 99 ft rise wouldn't require any supports, a 100 ft on-the-dot rise would require 1 support, and a 105 ft rise would require 2 supports. Please correct me if I am wrong.

kwired gave an interesting case to think about, which makes perfect sense. If you are reducing the wire to fit the equipment in a much smaller factory terminal, the factory lugs probably cannot withstand the weight of the upsized cable, and therefore supports should be provided even when 300.19(A) doesn't require them, to anticipate this less common situation. Even though in the general case, as he stated: .

...termination points should not be used to support cable, period.

 

[Carultch]

...termination points should not be used to support cable, period.

So does that mean I need a cable support in a conduit for a 10 ft vertical rise?

 

[jusme123]

no, but conduit layout can be considered

 

[Carultch]

no, but conduit layout can be considered

Are you responding to me? Please explain what you mean.

Are you saying that if friction in a horizontal run at the top of the conduit can support the weight of the cable in the vertical rise (less than 300.19's distances), then no cable support is needed?

 

[RB1]

Carultech,

The way I read it there are two types of supports: A top support and an intermediate support. 150 foot run of 1/0 requires one top support and one intermediate support. 100 foot run requires one top support. 99 foot run requires no support.

 

[bullheimer]

so that bushing would have to double as a coupling yes?

 

[infinity]

so that bushing would have to double as a coupling yes?

If you're referring to post #11 then no. That "chock bushing" is just that a bushing.

 

[kwired]

...termination points should not be used to support cable, period.

Long vertical run - agreed.

shorter vertical run - it happens all the time with little issues, to small and large conductors.