Can aluminum conductors be used for instrumentation wiring?

[bobwd40]

Im currently in a situation where our prefabricated copper twisted shielded pair (18awg) instrumentation cables are coming up short. Coincidentally, we were able to find a spool of aluminum twisted shielded pair cable (also 18awg). Is there any reason why we can't (or shouldn't) use this instead? We are using the instrumentation cables to carry 4-20mA and 0-10V signals.

 

[BobB]

I would not use it at all. Aluminum usually requires bi-metal lugs to stop the corrosive effects of 2 different metals coming together. And then there are issues of gases and moisture possibly getting into the cable and corroding it. It also hardens and breaks very easily if there is vibration/movement.
Gave away using aluminum years ago.

 

[dogleg43]

Do they even make it in aluminum?
Use it only if you'll be able to be paid to replace it again in a few years.

Bend a small pieces of aluminum wire just a few times and it will break. That's why it's no longer legal in most places to use in house wiring. Too many fires.

 

[Bullzi]

Stay away from that. I didn't even know they made aluminum Insturment wire!! Most likely it has been sitting on you Distibutor's shelf for a long time and they are trying to unload it.

 

[James Mcquade]

Sorry, but that won't work the way you wan.

#1 you are creating a thermocouple at the joint.
#2 the physical characteristics of aluminum and copper will create a problem in itself. that's like saying that an apple is an orange.

regards,
james

 

[cleeton]

Are you sure it's aluminum, I would be surprised to find twisted shielded pair aluminum. Might be tinned copper conductors?

 

[Bit_Bucket_07]

Are you sure it's aluminum, I would be surprised to find twisted shielded pair aluminum. Might be tinned copper conductors?

I agree. I've never heard of aluminum instrumentation cable, and can't imagine a legitimate reason for making such a cable. Perhaps the OP assumed that the shiny silver color of the conductors implied aluminum when it is really just tinned copper, which isn't unusual in shielded cable.

 

[tragically1969]

Sorry, but that won't work the way you wan.

#1 you are creating a thermocouple at the joint.
#2 the physical characteristics of aluminum and copper will create a problem in itself. that's like saying that an apple is an orange.

regards,
james

Joining copper to Aluminium to copper busbars is common practice in the power industry so apples and oranges is not a good analogy, using the right connection type and technology is however important.

 

[James Mcquade]

tragically1969,

I agree, but the op stated it was an analog circuit.
james

 

[jraef]

Are you sure it's aluminum, I would be surprised to find twisted shielded pair aluminum. Might be tinned copper conductors?

+1.

I have never seen Aluminum instrumentation cable, too many problems.

Get a magnifying glass and cut one of the wires, then look carefully at the fresh cut end. You will likely see a copper core. Tin plating is done to aid in resistance to some types of corrosive gasses, especially H2S. H2S attacks bare copper and it causes silver to "grow whiskers", either of which can be big problems in sensitive instrumentation circuits. The tin plating will not cause you any concern if you don't need it though.