Al to Cu

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Alwayslearningelec

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NJ
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Estimator
Someone at my job told me that there is Al Compressed cable out there that can be used as the size as Cu for the same ampacity. Has anyone heard of this? I thought you always had to increase wire size if switching from Cu to Al. Thanks
 
The "compact strand" type of conductor construction was introduced by the aluminum conductor manufacturers to permit the use, in many cases, of the same size raceway for the same ampacity as copper conductors. The strands are not round and there is no space between them like you find in conductors made up of round strands. This permits an increase in the cross sectional area of the conductor and a reduced physical diameter.
 
don_resqcapt19 said:
The "compact strand" type of conductor construction was introduced by the aluminum conductor manufacturers to permit the use, in many cases, of the same size raceway for the same ampacity as copper conductors. The strands are not round and there is no space between them like you find in conductors made up of round strands. This permits an increase in the cross sectional area of the conductor and a reduced physical diameter.
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I have heard of and used reduced diameter compact conductors (CU and AL), but I do not see any where in the NEC where it would be allowed to size them the same size as copper conductors for a given load as asked in the OP?

A 100 amp load will still require a #3 copper, or a #1 Aluminum at 75? terminations? have I missed somthing?
 
hurk27 said:
I have heard of and used reduced diameter compact conductors (CU and AL), but I do not see any where in the NEC where it would be allowed to size them the same size as copper conductors for a given load as asked in the OP?

A 100 amp load will still require a #3 copper, or a #1 Aluminum at 75? terminations? have I missed somthing?
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So the AL cable the other poster refers to still need to be "up sized"?
 
don_resqcapt19 said:
The "compact strand" type of conductor construction was introduced by the aluminum conductor manufacturers to permit the use, in many cases, of the same size raceway for the same ampacity as copper conductors. The strands are not round and there is no space between them like you find in conductors made up of round strands. This permits an increase in the cross sectional area of the conductor and a reduced physical diameter.
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Ahhh...so same size raceway/conduit but still nedd to increase conductors?
 
hurk27 said:
..............have I missed somthing?
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....The conductivity of aluminium does not change due to its compact size and so its current carrying capacity does not change.......
 
Take a look at Chapter 9 Table 5A.

It gives dimensions of compact conductors, and according to title there apparently is compact copper conductors also.

You still calculate ampacity according to 310. If your calculations require use of a 2/0 conductor and you want to use compact you still use 2/0. If using compact conductors your raceway fill will be different than it is for non compact conductors, and you may be able to use a smaller raceway in some cases.
 
kwired said:
Take a look at Chapter 9 Table 5A.

It gives dimensions of compact conductors, and according to title there apparently is compact copper conductors also.

You still calculate ampacity according to 310. If your calculations require use of a 2/0 conductor and you want to use compact you still use 2/0. If using compact conductors your raceway fill will be different than it is for non compact conductors, and you may be able to use a smaller raceway in some cases.
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Thanks, looking now at the table. So my question is. I guess there are "non-compact and compact conductors....??? What are most commonly used and why not use compact if it could decrease raceway size?
 
horsegoer said:
Thanks, looking now at the table. So my question is. I guess there are "non-compact and compact conductors....??? What are most commonly used and why not use compact if it could decrease raceway size?
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The non compact are the ones listed in Table 5 that you are probably used to using almost all the time. You may have installed compact aluminum and not even realized it was different. Most of the aluminum the supply houses have around here is compact conductors. Some USE may be the exception but otherwise most of it is compact. I have never seen compact copper, but the title of the table suggests there is some out there.
 
kwired said:
The non compact are the ones listed in Table 5 that you are probably used to using almost all the time. You may have installed compact aluminum and not even realized it was different. Most of the aluminum the supply houses have around here is compact conductors. Some USE may be the exception but otherwise most of it is compact. I have never seen compact copper, but the title of the table suggests there is some out there.
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Thanks!!!!
 
T.M.Haja Sahib said:
....The conductivity of aluminium does not change due to its compact size and so its current carrying capacity does not change.......
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Moreover, the effective area for current capacity calculation does not change;only the apparent overall size reduces.......
 
"Compact" aluminium or copper conductors have a smaller external diameter than conventional wires, this is achieved by shaped wire strands that give less wasted space between the strands.

If code requires that #4 be used, then at least #4 must be used, BUT compact #4 will have a reduced external diameter and may permit smaller conduits.

In practice I have my doubts as to the usefulness of such conductors. They tend to be less flexible than conventional wire and therefore potentialy problematic to pull into conduits.
Code may permit of smaller conduit, but that does not mean that it is a good idea in practice.

Also I would expect that these wires would run slightly hotter if heavily loaded.
A "compact" #4 and a conventional #4 would have the same resistance and therefore the same losses in watts per foot.
However the reduced diameter, and therefore reduced surface area of the compact wire means that it must get slightly hotter with same watts per foot losses.
 
broadgage said:
Also I would expect that these wires would run slightly hotter if heavily loaded.
A "compact" #4 and a conventional #4 would have the same resistance and therefore the same losses in watts per foot.
However the reduced diameter, and therefore reduced surface area of the compact wire means that it must get slightly hotter with same watts per foot losses.
Click to expand...

Luckily the NEC allowable ampacity tables are not built like a switch watch and have a lot of leeway built in to them. :cool:


As far as conduit sizes, I rarely use the smallest conduit I can, but having the availability of compact conductors for re-use of existing conduits is an option worth keeping in the back of our mind.:)
 
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