Alu and Cu cables together 3

[maypot]

Hi,

Is there any problem to use four single core 500 mm^2 Cu cable and two single core 500 mm^2 Aluminium cable together on each phase of a distribution network ?
So long as the cables may withstand the load, I do not foresee any problem ?


Bob

 

[RRaghunath]

I too don't see any problem provided you take care if the termination with correctly placed bi-metal washers to prevent electrolytic corrosion related to joining of dissimilar metals.

Use of trefoil clamps along the cable runs and use of non-magnetic gland plates at either end are common requirements with single core cables irrespective of the type of conductor material.

raghunath_n00@rediffmail.com

 

[maypot]

Hi RRaghunath ,

Why non-magnetic cable glands ? Eddy current ?

Bob

 

[RRaghunath]

Bob,

You are right, it is to prevent circulation of eddy currents and resultant heating / loss.

raghunath_n00@rediffmail.com

 

[dpc]

If you mean you want to put copper and aluminum conductors in parallel on the same portion of a circuit, I don't think this is a good idea.

When cables of similar material are connected in parallel, the assumption is that the current will be equally divided among all the conductors because each segment has approximately the same impedance. If you use differing materials and/or sizes, this is no longer the case and I would be concerned that the current will divide unequally and you cannot be sure that one segment will not become overloaded.

This is NOT allowed by the National Electrical Code in the US, and I suspect this is the reason.

It would interesting to do some calculations....

 

[RRaghunath]

dpc,
Thanks, the possible overloading of aluminium cable or under utilisation of copper cables is an issue to be checked out. Thanks for reminding and a star to you.

raghunath_n00@rediffmail.com

 

[maypot]

Hi DPC ,

Thks. A very interesting point indeed .

Bob

 

[PowerfulStuff]

Another issue is different thermal coefficients for resistance. Whichever cable has the lower change in resistance with temperature will take even more current once the load increases.