Modifying 480V Switchgear Bus

[kingpb]

Client is asking to convert 4000A non-seg bus from transformer to swgr with cable. Due to the number of cables in parallel, we think there is going to be a connection issue. We contacted the switchgear manufacturer and are not getting good response. Client wants to move forward with the project and leave the manufacturer out of it, but we say we cannot sign/seal drawings without their input because we are not manufacturer's and don't want to be responsible for the modifications.

Questions: Would Contractors be willing to make bus modifications without manufacturers input; client seems to think that's what they did on another project. What about signing and sealing?

 

[wsbeih]

Client is asking to convert 4000A non-seg bus from transformer to swgr with cable. Due to the number of cables in parallel, we think there is going to be a connection issue. We contacted the switchgear manufacturer and are not getting good response. Client wants to move forward with the project and leave the manufacturer out of it, but we say we cannot sign/seal drawings without their input because we are not manufacturer's and don't want to be responsible for the modifications.

Questions: Would Contractors be willing to make bus modifications without manufacturers input; client seems to think that's what they did on another project. What about signing and sealing?

I agree with your reasoning. Not sure if the contractor is willing to do these changes, especially if it would result in warranties liabilities, etc..
Also, you I want to consult with transformer manufacturer for the termination of cables instead of bus. Not sure what type of transformer you are using, but typically I see there is Air terminal chamber for Cables termination, and throat connection for bus duct.

 

[NYSolar]

Have had UL come out and aprove modifications done before. Is that what your looking for?

 

[don_resqcapt19]

I would expect that you could get a bus to cable transition box that would work with the switchgear. This would not have to be from the gear manufacturer as there are a number of 3rd party suppliers that can supply a listed transition box for this purpose.

I recently installed cable bus to replace bus duct and the cable bus manufacturer supplied transition boxes for both the switchgear and the transformer where they were necessary. In a number of cases the existing transformer and gear were suitable for the number of cables I was installing, but the largest circuit I did was 3,200 amps.

 

[TrueRMS]

I would expect that you could get a bus to cable transition box that would work with the switchgear. This would not have to be from the gear manufacturer as there are a number of 3rd party suppliers that can supply a listed transition box for this purpose.

I recently installed cable bus to replace bus duct and the cable bus manufacturer supplied transition boxes for both the switchgear and the transformer where they were necessary. In a number of cases the existing transformer and gear were suitable for the number of cables I was installing, but the largest circuit I did was 3,200 amps.

At the plant for bus transitions and extensions we use 777 or locomotive cable. Its expensive but has a very high ampacity.

 

[Jraef]

I would expect that you could get a bus to cable transition box that would work with the switchgear. This would not have to be from the gear manufacturer as there are a number of 3rd party suppliers that can supply a listed transition box for this purpose.

I recently installed cable bus to replace bus duct and the cable bus manufacturer supplied transition boxes for both the switchgear and the transformer where they were necessary. In a number of cases the existing transformer and gear were suitable for the number of cables I was installing, but the largest circuit I did was 3,200 amps.

I agree. If the gear has been installed for a while, warranty is likely a moot point now and UL is generally irrelevant after the fact. The problem you are going to have however will be, as mentioned, that there are no "wire bending space" requirements for direct bus connections but there will be for cable. So it's unlikely that there is adequate room in the incoming switchgear section for this, as well as in the transformer termination cabinet. But aftermarket transition boxes can be fabricated by any number of local or national fabricators.

Just out of curiosity though, WHY would they want to do this? Direct bus connections are generally superior to cable connections, less things to go wrong, less heat issues etc.

 

[TrueRMS]

Client is asking to convert 4000A non-seg bus from transformer to swgr with cable. Due to the number of cables in parallel, we think there is going to be a connection issue. We contacted the switchgear manufacturer and are not getting good response. Client wants to move forward with the project and leave the manufacturer out of it, but we say we cannot sign/seal drawings without their input because we are not manufacturer's and don't want to be responsible for the modifications.

Questions: Would Contractors be willing to make bus modifications without manufacturers input; client seems to think that's what they did on another project. What about signing and sealing?

My mistake 777 is the size of the locomotive cable and has the ampacity of 910 amps in a conduit with 3 current carrying conductors or less at 90 degC

 

[don_resqcapt19]

...
Just out of curiosity though, WHY would they want to do this? Direct bus connections are generally superior to cable connections, less things to go wrong, less heat issues etc.

In my case, the busway was from the transformer outside to the gear inside. Even though the busway was rated for wet locations, they had a number of failures at multiple plants from water getting into the bus. Their design choice is to replace all outside busway with cable bus and any new installations of that type will use cable bus.

 

[don_resqcapt19]

My mistake 777 is the size of the locomotive cable and has the ampacity of 910 amps in a conduit with 3 current carrying conductors or less at 90 degC

What section of the NEC lets you use that cable at that ampacity?

 

[TrueRMS]

What section of the NEC lets you use that cable at that ampacity?

Southwire OEM Division manufacturing spec sheet​

* (1) Ampacities based on 90°C Conductor and 30°C Ambient temperature based on Table 310.16 in the
National Electrical Code
® for not more than three current-carrying conductors in raceway, cable or earth.
(2) Ampacities based on single-conductor in free air, in accordance with National Electrical Code
® Table 310.17.
** Actual shipping weight may vary.
http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheetOEM71

 

[don_resqcapt19]

Southwire OEM Division manufacturing spec sheet​

* (1) Ampacities based on 90°C Conductor and 30°C Ambient temperature based on Table 310.16 in the
National Electrical Code
® for not more than three current-carrying conductors in raceway, cable or earth.
(2) Ampacities based on single-conductor in free air, in accordance with National Electrical Code
® Table 310.17.
** Actual shipping weight may vary.
http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheetOEM71

There appears to be a misprint in that document...the ampacity of the 777 is way out of line to the high side as compared to the other sizes. If you look at the other sizes and compare them to the NEC, you will find that they match very well with the next smaller and larger size of conductors shown in the table.
I would expect that the correct ampacity for the 777 kcmil is about 545 amps for 3 or less conductors in a raceway at 90°.

 

[TrueRMS]

In my case, the busway was from the transformer outside to the gear inside. Even though the busway was rated for wet locations, they had a number of failures at multiple plants from water getting into the bus. Their design choice is to replace all outside busway with cable bus and any new installations of that type will use cable bus.

Exactly right we have had multiple failures with wet location bus duct and changed them to cable. Mostly at cooling towers.

 

[templdl]

In my case, the busway was from the transformer outside to the gear inside. Even though the busway was rated for wet locations, they had a number of failures at multiple plants from water getting into the bus. Their design choice is to replace all outside busway with cable bus and any new installations of that type will use cable bus.

The way that I would approach this is to evaluated the response from the swgr mfr. Sometime the response is correct and one runs into the there is the risk of getting an answer that you don't want to hear or an answer from and individual that doesn't have a clue as to how to help you solve your problem, someone who may not want to make the effort to help you.
Personally I would question their response. If I were to have gotten the call I would have pulled the drawings if they were still available and evaluated as to how I could you a transition section from my swgr bus to the cable bus that your customer would like to use. Not cheap but consider it would be custom.
The other choice would be to commission an engineering service who has the expertise to do a design and build that transition section for you according the industry standards, (NEMA?) An original factory built ransition section the is powder coated and built is a listed facility would be benificial..
Regardless, I think you should be able to get the job done.
In not knowing how much your customer(manufacturer?) is depending upon the reliability of this power source I would guess that they want the bussed connection upgraded because of the cost of loss of production. It is obvious that the realize that a reliable power souce will provide a significant payback. If it is benificial you may relate the cost of the upgrade to what the would be saving because of loss of production. But from what I can tell unless the cost is stupidly high, cost isn't a big factor, your customer just wants you to resolve their problem. You're their hero. Get 'er done. You probably will have a customer for life.

 

[TrueRMS]

There appears to be a misprint in that document...the ampacity of the 777 is way out of line to the high side as compared to the other sizes. If you look at the other sizes and compare them to the NEC, you will find that they match very well with the next smaller and larger size of conductors shown in the table.
I would expect that the correct ampacity for the 777 kcmil is about 545 amps for 3 or less conductors in a raceway at 90°.

The lowest amacity I have seen is 904.

http://www.cmewire.com/catalog/sec18-DLO/DLO-Cu-01-AMP.pdf
hhttp://www.electrowire.com/wp-content/uploads/2011/09/1KV-DLO.
http://www.electrowire.com/wp-content/uploads/2011/09/1KV-DLO.pd

 

[don_resqcapt19]

The lowest amacity I have seen is 904.

http://www.cmewire.com/catalog/sec18-DLO/DLO-Cu-01-AMP.pdf
hhttp://www.electrowire.com/wp-content/uploads/2011/09/1KV-DLO.
http://www.electrowire.com/wp-content/uploads/2011/09/1KV-DLO.pd

Only one of those would open for, me but it was a "free air" ampacity and is consistent with the 90°C 750 kcmil and 800 kcmil "free air ampacities found in Table 310.15(B)(17).

The original table you posted was for conduit and I stand by my statement that it is a misprint.

 

[kingpb]

In my case, the busway was from the transformer outside to the gear inside. Even though the busway was rated for wet locations, they had a number of failures at multiple plants from water getting into the bus. Their design choice is to replace all outside busway with cable bus and any new installations of that type will use cable bus.

That is exactly what's going on here. I swear if you were in my location I'd say you were our client.

Definitely will check on the cable; may be a good alternative. We tried to get manufacturer involved and the client is balking. We think there is bad blood there, so we are going to a third party OEM custom builder to go out and take measurements and come up with an engineered design. My gut tells me not enough clearance and a transition box will be required.

 

[templdl]

That is exactly what's going on here. I swear if you were in my location I'd say you were our client.

Definitely will check on the cable; may be a good alternative. We tried to get manufacturer involved and the client is balking. We think there is bad blood there, so we are going to a third party OEM custom builder to go out and take measurements and come up with an engineered design. My gut tells me not enough clearance and a transition box will be required.

The existing gear must have a bus duct throat. If it is out the end remove the throat and by adding a NEMA3R air terminal chamber (ATC) of suitable size, assuming this is outdoor gear, putting bus extensions on the existing bus with pads on the ends of sufficient size with NEMA hole drilling patterns to bolt the cable to should get the job done.

 

[templdl]

That is exactly what's going on here. I swear if you were in my location I'd say you were our client.

Definitely will check on the cable; may be a good alternative. We tried to get manufacturer involved and the client is balking. We think there is bad blood there, so we are going to a third party OEM custom builder to go out and take measurements and come up with an engineered design. My gut tells me not enough clearance and a transition box will be required.

The gear must have a bus duct throat (BDT). If it comes out of the end of the gear remove it and add an air terminal chamber (ATC) extending the bus with suitable pads with NEMA hole drilling patterns to terminate the cable to. If the bus exits in a disaster place the modification may be a bit more complex.