Aluminum wire going to make a comeback?

[wmetfab]

I have a 200 A 3 phase sub panel fed with about 35m of alum. The wire needs to have di electric grease on the connections which need to be checked for tightness every couple years or so.
The problem is the coeficient of expansion, alum moves a lot compared to the copper, thats why it was so troublesome in residential wiring.
I am not an electrician.

 

[mickeyf]

I always tune in to these threads about a week late...

I thought it caused some fires due to not being as pliable as copper.

My impression was that because aluminum forms a surface oxide layer when exposed, and that oxide is at least partially an insulator, that unless the connections were made properly that extra resistance caused heat, and potentially fires.

For most of my life doing 'homeowner permit' wiring, I have understood that Aluminum was disallowed for diy'ers, but when I mentioned this to the Inspector when he check my recent workshop wiring, he said "That's old school", implying that it was now allowed. On my previous workshop (with which I had professional help) we ran aluminum teck from a new panel to the 100A shop panel. I don't recall the length, but it was a fair ways, and would have cost much more if copper had been used.

 

[BaitMaster]

I always tune in to these threads about a week late...


My impression was that because aluminum forms a surface oxide layer when exposed, and that oxide is at least partially an insulator, that unless the connections were made properly that extra resistance caused heat, and potentially fires.

For most of my life doing 'homeowner permit' wiring, I have understood that Aluminum was disallowed for diy'ers, but when I mentioned this to the Inspector when he check my recent workshop wiring, he said "That's old school", implying that it was now allowed. On my previous workshop (with which I had professional help) we ran aluminum teck from a new panel to the 100A shop panel. I don't recall the length, but it was a fair ways, and would have cost much more if copper had been used.

Aluminum armoured cable is type ACWU.

Teck cable is copper.

 

[slow-poke]

We live in a bungalow, it has a 400A service, 200 for the house and 200A was for the pool heater that is no more (pool removed). I picked up a new in the box 200A panel on Kijiji for $100 and had an electrician divert the old pool feed to the new 200A panel in the garage. The electrician used the aluminum version of the teck cable I guess ACWU. No shortage of power in the garage.

 

[Susquatch]

I always tune in to these threads about a week late...

My impression was that because aluminum forms a surface oxide layer when exposed, and that oxide is at least partially an insulator, that unless the connections were made properly that extra resistance caused heat, and potentially fires.

My recollection is that there were three issues. Your recollection is one of them. One of the others is the other one already mentioned.

But I recall a third that was related to termination material issues. Moisture in the air could cause corrosion as a result of dissimilar metals.

In all three cases, the result was high resistance leading to high temperatures and sometimes to fires.

 

[slow-poke]

I have a 200 A 3 phase sub panel fed with about 35m of alum. The wire needs to have di electric grease on the connections which need to be checked for tightness every couple years or so.
The problem is the coeficient of expansion, alum moves a lot compared to the copper, thats why it was so troublesome in residential wiring.
I am not an electrician.

This is an interesting comment, I recall hearing this many years ago. I'm pretty sure aluminum wire is used for the majority of service feeds from the utility to the main panel in our homes. I'm also guessing that these connections are rarely if ever inspected for tightness. Best guess is that the conductor is terminated in a lug, that minimizes creep because the conductor is surrounded by the lug it can't creep out from under the edges of the screw?

I watched the electrician install the short length of 4/0 aluminum between our old pool feed and new 200A panel in the garage. I don't recall him applying any sort of anti-oxidant to the terminations but I might have missed that. I do recall that he did not use a torque wrench, he just tightened really tight, seemed less than ideal for something that is supposed to be so critical.

Would like to hear from an actual electrician on this topic

 

[wmetfab]

Pokie, you are correct about the wire from the pole to most residential services. Industrial sites with big amperage mostly use the copper.
Those are the bolt on lugs used.
The dielectric should be applied to the cable and under the lug. Someone in another post mentioned corrosion thats what prevents it.
No one should be afraid to use the alum for sub feed panels.

 

[BaitMaster]

Anti oxidant compound is mandatory on all aluminum terminations. I failed an inspection last week because the apprentice forgot.

Torquing works great for copper terminations and should be done.
Aluminum it literally works best to tighten the ever loving **** out of it. They say you should use a torque wrench on aluminum too but they say some pretty stupid stuff.

That’s my experience at least. Aluminum you crank that thing till she don’t crank.

 

[Susquatch]

Would like to hear from an actual electrician on this topic

Not an electrician @slowpoke, but did serve on the electrical code review committee for a few years. Does an "opinionated" engineer count? LOL!

There are a few things about your lugs that are important.

First, they are typically used with BIG stranded conductors. The shape ensures that the entire conductor is constrained to the clamping area. The cable cannot "wiggle" loose and flatten with temperature cycling the way it could in a typical flat connector.

The metallurgy of those clamps is selected to minimize humidity induced galvanic corrosion at the interface between the two metals. But an antioxidant coating was also mandatory.

It is much easier to deform the cable in that connector to improve retaining and low resistance contact. They really should not be used for solid conductors (but sometimes are).

It was the general consensus that electricians and home owners do not (and will not) use torque wrenches to tighten connections. That's why the screws are usually big allen key lugs or hex head screws that will quite naturally get torqued "sufficiently". This is one place where too much doesn't really happen because the head will deform before the thread strips.