Conduit Sizing for Aluminum Conductors

[fandi]

Hello All,
My understanding is the NEC Annex C is a sample (not a code thing) for conduit sizing. These tables treat (600V or less) copper and aluminum conductors the same way. Please correct me if I'm wrong. Thanks.

 

[tkb]

The physical size of copper and aluminum conductors are the same for a given gauge and insulation.
I think you are confusing conduit fill with ampacity.

 

[fandi]

The physical size of copper and aluminum conductors are the same for a given gauge and insulation.
I think you are confusing conduit fill with ampacity.

Tim, I know the ampacity is different given the same size. That's why Table 310.15(B)(16) has copper and aluminum columns. I just don't see Annex C tables talks about copper/aluminum but now I know they're the same physical size. Thanks for your reply.

 

[iwire]

Well there are compact AL conductors and they are smaller than copper conductors of the same gauge.

 

[tkb]

I hear there are compact copper conductors also, but I have never seen them.

 

[Tony S]

I hear there are compact copper conductors also, but I have never seen them.

They are a pig to work with, compacting work hardens the copper.

 

[Smart $]

They are a pig to work with, compacting work hardens the copper.

For those that have no first-hand or eyewitness experience, pigs are exceptionally hard to work with. Damn things are just outright pig-headed. :happyyes::lol:

 

[Tony S]

Like pigs, they go where they want not where you want. It’s awful stuff to work with.

 

[Carultch]

Hello All,
My understanding is the NEC Annex C is a sample (not a code thing) for conduit sizing. These tables treat (600V or less) copper and aluminum conductors the same way. Please correct me if I'm wrong. Thanks.

Given the same insulation specification and the same geometry of the strand pattern, and the same gauge/KCMIL size, both copper and aluminum have the same outer diameter, and thus you can use the same data to size conduits for both kinds of conductors.

Bear in mind that the tables for wire outer diameter are overestimates of what you will actually get in practice. This is sort of an upper limit common across the industry of conductors of that specification. Actual manufacturer values usually are slightly less. It caught me by surprise when I review others' designs, and see fill examples that are just slightly over the fill limit. I'm all set to call them out on it, and then I see the datasheet for the exact manufacturer of the wire, and it fits.

 

[Carultch]

They are a pig to work with, compacting work hardens the copper.

Is compact aluminum a different story? Perhaps something to do with the mechanical material properties, that work differently than copper?

I'm noticing some examples (XHHW-2, PV Wire) where the aluminum conductor in that product family that comes standard is significantly thinner than its copper counterpart. Then I look at the diagram, and it is a compact conductor.

I always thought that compact conductors were a premium product over standard circular strand wire.

 

[Smart $]

... I always thought that compact conductors were a premium product over standard circular strand wire.

Not really a premium product, though I believe it has a slightly higher fabrication cost coupled with a substantially lower market demand.

 

[iwire]

We work with a fair amount of aluminum SER and it commonly has compact conductors.

 

[don_resqcapt19]

...
I always thought that compact conductors were a premium product over standard circular strand wire.

The original compact conductors were brought into the marker by the aluminum conductor manufacturers. The idea is that, in many cases, the same size conduit can be used for a given ampacity as you would use for standard copper conductors.

It improves the economics of using aluminum over copper even more, if you don't have to increase the conduit size for the same ampacity.

 

[electrofelon]

Hello All,
My understanding is the NEC Annex C is a sample (not a code thing) for conduit sizing. These tables treat (600V or less) copper and aluminum conductors the same way. Please correct me if I'm wrong. Thanks.

To summarize, I think in practice you will find that aluminum is compact stranded, and copper is not. I personally have never seen them any other way. Note the tables have a chart for compact conductors, iIRC those have the"A" suffix. Take a look.

 

[Julius Right]

From my experience, as cable manufacturer, no overall diameter could be guaranteed:weeping:. Once, I had to answer to a very angry customer which used the cable diameter from our catalogue in order to order cable glands.
Now, as an electrical installation designer, I never take more than 25% filling factor for a conduit.