400 AMP BUS - COPPER TO ALUMINUM

[elecsup1]

OUR FACILITY ORDERED A 10' LENGTH OF 400 AMP 3 PHASE GE BUS W/ALUMINUM CONDUCTORS (REFURBISHED). WE RECEIVED THE BUS SECTION WITH COPPER CONDUCTORS AND THE ASSURANCE THAT INSTALLING IT BETWEEN TWO ALUMINUM SECTIONS WOULD NOT BE A PROBLEM. THE MASTER ELECTRICIAN WE HAVE LINED UP TO DO THE WORK FEELS THERE WILL BE PROBLEMS DOWN THE ROAD AND HE IS NOT COMFORTABLE WITH PERFORMING THE WORK. DOES SOMEONE HAVE EXPERIENCE WITH THIS AND CAN YOU OFFER ADVICE?

 

[charlie tuna]

Re: 400 AMP BUS - COPPER TO ALUMINUM

we had the same situation---and installed adaptor sections with copper buses between them and have had no problems...

 

[hurk27]

Re: 400 AMP BUS - COPPER TO ALUMINUM

I would make sure that the connections are coated well with a anti-corrosion compound like No-Lox.
I have seen to many failures from dissimilar metal connections.

 

[charlie tuna]

Re: 400 AMP BUS - COPPER TO ALUMINUM

i am a firm believer in knolox---but the adaptor sections had aluminum on one end and copper on the other. of course the copper bus was about half the size of the aluminum. this is in a 55 story building and has basically four bus ducts running throughout the building--4000a-3000a and 2000a. the aluminum has that armorclad insulation. we have had five failures in this building--twenty years old. all but one of the failures were from water entering the bus, one failure was due to an un-torqued joint. no knolox is used in the installation --- i think since it is a conductor of electricity and such close clearances within the bus---knolox might cause a problem??? i would check with the factory before using!

 

[brian john]

Re: 400 AMP BUS - COPPER TO ALUMINUM

I was informed in the past that aluminum is nickle plated and corrosion is not the major problem. My question was at high loads with cycling what about different expansion and contractions.

 

[Ed MacLaren]

Re: 400 AMP BUS - COPPER TO ALUMINUM

at high loads with cycling what about different expansion and contractions.

When an aluminum lug is fastened to a copper or alumunum bus, or two aluminum buses are joined, using steel fasteners, a "Bellville" spring washer should be used to prevent the connection loosening due to "cold flow".

Ed

 

[charlie tuna]

Re: 400 AMP BUS - COPPER TO ALUMINUM

the problem with knolox in bus duct is the extream close clearances between phases---this armorclad g.e. bus's insulation is tuff stuff! in the past we made some bus jumpers and needed to remove the insulation--it required grinders to reach the aluminum! for this reason they can lay this insulated phase on top of another insulated phase! no problem---heat---cold -- etc.. but think of the vertical joint where the insulation stops--very close clearances between phases. now we are going to coat the joint with a material that might run down and conduct across phases. the factory doesn't ask for it -- and i haven't seen failures in joints that were properly torqued during insulation. i have found plenty of un-torqued joints--some with the guy's innitials on them! another problem to keep an eye on---westinghouse bus duct has a sheet metal plate that holds the torque nut in place while you torque it--guess what---this keeper plate sometimes strips out before the torque is attained and never reaches proper torque requireements! my $.02

 

[hurk27]

Re: 400 AMP BUS - COPPER TO ALUMINUM

I have to retract my info on the No-Lox as I was thinking that these buss ducts had more space between the buss's, and had a barrier between them like an old Square D power buss that ran through a plant that I worked at, and had places for disconnects to pull power from.
The spring torque washer is the best way.

 

[charlie]

Re: 400 AMP BUS - COPPER TO ALUMINUM

Something to keep in mind is the new Al. alloys that do not need an inhibiting compound. Unless the manufacturer calls for an inhibiting compound to be used, it is not needed.