Cablebus versus Busway

[ron]

Has anyone seen any disadvantages of using cablebus (NEC Article 370) versus feeder type Busway (NEC Article 368)? It will be for 480V, 5000A feeders.

 

[shamsdebout]

Ron,

I do not have any experience with this type of cable distribution medium.

Based on what I see this should be less expensive than a busway system. However it seems one would be able to access the cables easier with the cable bus system if they wanted to cause themselves or the electrical system harm.

 

[ron]

shamsdebout

Thanks for the information. This is a controlled environment and the cablebus will actually be run from one side of a room to the other, within the same room.

One item I have found is that the manufacturers catalogs show sizes and ampacities based on 90 degree terminations. The SWBDs that will be in / out in my application all have 75 degree termination requirements.

 

[petersonra]

if you are just running from one side of the room to another it seems unlikely that this will be less expensive than cable tray of some sort.

How does one attach a bus drop to a bunch of separate conductors in this kind of setup. just curious.

 

[ron]

if you are just running from one side of the room to another it seems unlikely that this will be less expensive than cable tray of some sort.

How does one attach a bus drop to a bunch of separate conductors in this kind of setup. just curious.

The conductors just drop in and terminate onto the lugs in the SWGR like as if they were conduit and wire.

Because of the ampacity, cable tray would require tremendous derating and additional copper, or giant tray avoiding conductor proximity.

 

[JoeStillman]

You have to use the 75? ampacity because of the lugs, but use the free-air (much higher) ampacity because it's cable bus.

 

[ron]

You have to use the 75? ampacity because of the lugs, but use the free-air (much higher) ampacity because it's cable bus.

Agreed, thx

 

[rcwilson]

Putting cables in tray not only has derating for ampacity but derating for unequal sharing of current between paralleled conductors due to the magnetic effects.
Imbalance can approach 20%. There may also be issues about short circuit bracing of the cable in the tray.

Cable bus suppliers use simulation programs to determine the best configuration of phase conductors in the cable bus. The cable bus uses support blocks to hold the cables for cooling and short circuit bracing.

Whether the installers connect it that way is another question. Electricians do not like weaving 1000 MCM conductors. On several jobs I have found boxes of the supports left over and had to force the contractors to take an outage and reinstall the cable supports that they thought were "excessive" at 12" spacing.

Cable bus is good if you are not sure of the bus duct dimensions and labor is not expensive. It takes time to assemble and terminate all those cables.
Terminations at switchgear may take more room than the bus duct's bolted connections.

 

[GoldDigger]

The conductors just drop in and terminate onto the lugs in the SWGR like as if they were conduit and wire.

Because of the ampacity, cable tray would require tremendous derating and additional copper, or giant tray avoiding conductor proximity.

I think the question was related to the equivalent of using bus plugs to connect a load at an intermediate point in a run of bus duct.
Apparently cable bus is not intended for this situation?

Sent from my XT1080 using Tapatalk

 

[ron]

I think the question was related to the equivalent of using bus plugs to connect a load at an intermediate point in a run of bus duct.
Apparently cable bus is not intended for this situation?

Sent from my XT1080 using Tapatalk

Cablebus is instead of feeder busway (not plug-in type).

 

[m sleem]

Cablebus is instead of feeder busway (not plug-in type).

I was in a project that needs the 8000a busway to be connected with a 5000a breaker, we allowed this size of the busway due to the voltage drop where we have to run 300m, due to the high cost of the busway larger than 4000a we decided to split into three parallel feeders connected to the 5000a breaker. So the busway beyond 4000a could be costly.

 

[kingpb]

Cable bus is essentially cable in tray, except it is an engineered design that reduces the number and size of conductors required to get the desired ampacity.

Verify with the switchgear manufacturer in regards to terminations but I believe the swbd will be limited to 75 degree design. Manufacturers are working on 90deg terminations so it pays to check and not just assume.

 

[ron]

Cable bus is essentially cable in tray, except it is an engineered design that reduces the number and size of conductors required to get the desired ampacity.

Verify with the switchgear manufacturer in regards to terminations but I believe the swbd will be limited to 75 degree design. Manufacturers are working on 90deg terminations so it pays to check and not just assume.

The standard design from the vendor was 90 deg terminations with a 40 deg ambient. When they derated for 75 deg terminations and a 30 deg ambient (similar to the standard ampacity tables in NEC), the quantity of conductors per phase were the same as their original design.