300HP motor on Al Bussway

[SparkyRules]

I have a customer who has 300HP motors (335FLA and with Soft Start 600+ish start up amps) and the bussway is being put out the bid, the folks who are suggesting copper bussway are saying the Aluminum buss will not hold up under the starting current. I have been told all the jaws on the bussplugs are copper so the mix of metals could be an issue??? This is not a corrosive environment nor is it very hot. ( 85 F ish) The bussway is spec'd at 1000A 480V (600V). Has anyone had experience with AL buss VS copper bussway to support this claim? I thought 1000A = 1000A- Cu or Al ? Sure if the Al has to be replace then that mitigates any savings but if it hold up just as well, then the cost savings are justified.

 

[petersonra]

IMNSHO, they are talking out their backside.

 

[augie47]

IMNSHO, they are talking out their backside.

I agree.

I have nothing to substantiate my thoughts, but the only AL Buss problem I have experienced was with large welders.

 

[jim dungar]

Highly repetitive 'shock' type loads like welders, can have problems as the copper jaws and aluminum bus do not expand/contract at the same rate.
If your motor has inrush currents every 2-3secs, the copper bus people may have a case.
However, if your 300HP is like most motors, the jaws and bus will have the ability to reach steady state conditions between starts.

 

[ptonsparky]

FWIW we replaced the all the vertical buss in a MCC a couple years ago. All were AL and every bucket connection was pitted, some to the point of failure. (The reason we were there). Bucket stabs were CU. The MCC was also close to 40+ years old. Like I said, FWIW.

 

[Jraef]

I agree that the main potential issue is just the difference in expansion rates between the metals, and that unless the duty cycle is high, (which is highly unlikely unless the load only needed 100HP and the motor is over sized fir duty cycle) that will not be a problem for decades. If anything, Al bus may cool off more quickly after a high starting current event. Most buss is tin plated now, so the direct contact of dissimilar metals is not so much of an issue.

 

[SceneryDriver]

If anything, Al bus may cool off more quickly after a high starting current event.

Copper has almost twice the thermal conductivity of aluminum.

http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

Though I'm sure surface area of the AL bus VS the CU bus would have some bearing too. Interesting question to ponder.


SceneryDriver

 

[Fulthrotl]

I have a customer who has 300HP motors (335FLA and with Soft Start 600+ish start up amps) and the bussway is being put out the bid, the folks who are suggesting copper bussway are saying the Aluminum buss will not hold up under the starting current. I have been told all the jaws on the bussplugs are copper so the mix of metals could be an issue??? This is not a corrosive environment nor is it very hot. ( 85 F ish) The bussway is spec'd at 1000A 480V (600V). Has anyone had experience with AL buss VS copper bussway to support this claim? I thought 1000A = 1000A- Cu or Al ? Sure if the Al has to be replace then that mitigates any savings but if it hold up just as well, then the cost savings are justified.

as long as the buckets have clamps specifically designed to provide correct
contact pressure to the bus, and anti oxidant paste is used when plugging
in the buckets, i can't see a significant difference in the two as far as life
in service.

aluminum has a higher temperature coeffecient than copper, so it'll expand
slightly more than copper, but the springs on the clips can more than compensate
for that.

are the folks suggesting the copper busduct profiting from the sale of it?

i've installed both, but the last time i put in copper bus duct was 1982
at Hughes electro optical in el segundo. the price is pretty daunting.

even SCE at their LARS facility used 3,000 amp aluminum bus duct.