CU vs AL

[Ingenieur]

Is this not just as easy as referencing something like RSMeans? Does anyone have that data to share?

I usually use the neca manual for elec estimating, means for other stuff
but you need current prices for Cu and Al
I have yet to find a scenario where Cu is cheaper, it's usually ~25% more

 

[Besoeker]

I usually use the neca manual for elec estimating, means for other stuff
but you need current prices for Cu and Al
I have yet to find a scenario where Cu is cheaper, it's usually ~25% more

So why is it almost never used in UK or (m)any of the other countries I've had the pleasure to visit?
They are global commodities after all.
That still puzzles me.

 

[Tony S]

So why is it almost never used in UK or (m)any of the other countries I've had the pleasure to visit?
They are global commodities after all.
That still puzzles me.

I’ve installed a fair number of MV/LV transformers here in the UK. The LV tails have been about 50/50 Al/Cu depending on cost.

This may sound strange but I preferred 600mm² 4 sector Al to 500mm² Cu.

 

[mbrooke]

Is it easier from a handling standpoint?

 

[Tony S]

Is it easier from a handling standpoint?

Not really, terminating 600mm² Al needs a hydraulic crimp head that requires some form of lifting gear to get it in to place.

4 sector Al cable is extruded as solid ¼ sections it then bound in to a single core cable so that it is virtually a solid bar. Once you get used to bending it in to shape it’s easy to dress to the terminations.

 

[mbrooke]

Sounds neat.

What makes AL preferred though?

 

[Tony S]

Sounds neat.

What makes AL preferred though?

Martin, The engineer’s preference is down to cost. My preference is down to aesthetics, if it looks right it is right.

A while ago I posted a link on MH showing the effects of magnetic repulsion under transformer fault conditions. Aluminium 4 sector has a far better resilience under fault conditions.

 

[mbrooke]

Martin, The engineer’s preference is down to cost. My preference is down to aesthetics, if it looks right it is right.

A while ago I posted a link on MH showing the effects of magnetic repulsion under transformer fault conditions. Aluminium 4 sector has a far better resilience under fault conditions.

Then AL would be the best choice.

I know that round cores are better at withstanding short circuit forces, or at least thats what I have heard.

 

[Besoeker]

I’ve installed a fair number of MV/LV transformers here in the UK. The LV tails have been about 50/50 Al/Cu depending on cost.

This may sound strange but I preferred 600mm² 4 sector Al to 500mm² Cu.

Have you ever seen control panel wiring in Al?

 

[jumper]

Have you ever seen control panel wiring in Al?

Bes, I believe we talking about larger conductors here.

In the US a common breakpoint between when to use AL or CU is around 100A, possibly 200A for some.

While smaller AL conductors are often used, many only use CU only below those size loads.

 

[Besoeker]

Bes, I believe we talking about larger conductors here.

But if the argument works for larger conductors why wouldn't it work for smaller conductors?
We have designed, manufactured, installed, and commissioned drives up to 6650kW. Other than heatsinks, no Al used either internally or externally that I recall. Other than the multiples of 10kA rectifiers.

So the why remains.

 

[jumper]

But if the argument works for larger conductors why wouldn't it work for smaller conductors?
We have designed, manufactured, installed, and commissioned drives up to 6650kW. Other than heatsinks, no Al used either internally or externally that I recall. Other than the multiples of 10kA rectifiers.

So the why remains.

Reverse question:

Since AL works for smaller conductors, #12 and larger, and is cheaper, why do you not use it?

 

[Besoeker]

Reverse question:

Since AL works for smaller conductors, #12 and larger, and is cheaper, why do you not use it?

That's what I'm trying to fathom out. The why.

 

[publicgood]

That's what I'm trying to fathom out. The why.

The substitution of AL for CU at larger feeder sizes comes with it the proper precautions due to the greater expansion and contraction of AL, which loosens terminations. Common examples:

1. Aluminum alloy conductors shall be compact stranded conductors.
2. Aluminum conductors shall terminate on a compression lug or compression adapter.
3. Oxide-inhibiting joint compound must be applied on the aluminum conductor during termination.

Using AL for branch circuits may be done if the cost difference is there, but it typically is not done. Branch circuit conductors have higher likelihood of casual changes over time purposely loosening and tightening - precautions are often forgot. Forgetting has high arc flash hazard concerns. Furthermore, most mechanical equipment is listed based on CU terminations (due to the vibrating nature is my guess); thus, motor branch circuits are especially CU.

 

[kwired]

But if the argument works for larger conductors why wouldn't it work for smaller conductors?
We have designed, manufactured, installed, and commissioned drives up to 6650kW. Other than heatsinks, no Al used either internally or externally that I recall. Other than the multiples of 10kA rectifiers.

So the why remains.

As mentioned some have a low end of 100 or 200 amps and below that all they use is copper. My suppliers have as small as 6AWG aluminum conductors in stock. I use 4AWG aluminum frequently but seldom use 6 AWG, mostly for long underground feeds. Quite often such feeds would only use 10 or 12 AWG copper if it were a short run.

In 60's and 70's there was quite a bit of 10 and 12 AWG aluminum solid conductor used for power wiring - we then found out it wasn't the best option for this application, thermal expansion at terminations was a problem with this application.

 

[electrofelon]

The substitution of AL for CU at larger feeder sizes comes with it the proper precautions due to the greater expansion and contraction of AL, which loosens terminations. Common examples:

1. Aluminum alloy conductors shall be compact stranded conductors.
2. Aluminum conductors shall terminate on a compression lug or compression adapter.
3. Oxide-inhibiting joint compound must be applied on the aluminum conductor during termination.

Using AL for branch circuits may be done if the cost difference is there, but it typically is not done. Branch circuit conductors have higher likelihood of casual changes over time purposely loosening and tightening - precautions are often forgot. Forgetting has high arc flash hazard concerns. Furthermore, most mechanical equipment is listed based on CU terminations (due to the vibrating nature is my guess); thus, motor branch circuits are especially CU.

I disagree with your #3. There is no such requirement in the code, nor from the wire manufacturers. That being said, I do use it most of the time.

 

[kwired]

I disagree with your #3. There is no such requirement in the code, nor from the wire manufacturers. That being said, I do use it most of the time.

I will add - for the aluminum alloys that have been NEC required for quite some time now.

 

[mstrlucky74]

I usually use the neca manual for elec estimating, means for other stuff
but you need current prices for Cu and Al
I have yet to find a scenario where Cu is cheaper, it's usually ~25% more

It's more expensive in the scenario I posted. Whether it needs to be upsized as much as the engineer specified is another issue.