Installing busduct or cablebus for padmounted transformer

[rotmgbetter]

MP Husky and Superior are competitors. Competition is good. They are similar, although Superior will do custom stuff.
You might be able to get a custom opening on the side of a pad mount transformer, but I do not suggest top due to potential rain intrusion.
Short runs are not likely worth it unless the smaller profile is helpful.

In your experience, when does it become worth it if I can get the free air rating? 20 feet? 50 feet? 100 feet? 200 feet?

 

[Elect117]

In your experience, when does it become worth it if I can get the free air rating? 20 feet? 50 feet? 100 feet? 200 feet?

A free air rating doesn't really exist. It is almost unusable with the way existing equipment is made and tested. Switchgear and terminations will require you to rate at 75°C. UL product code AALZ is what you would be looking at.

But your conductor ampacity can use the 90°C rating as long as the splices take place outside and you can go from like 10 runs to 8 runs then back to 10 runs. The small reduction in wire then results in increases in failure points, voltage drop and labor hours. It really only make sense in a few applications.

 

[rotmgbetter]

A free air rating doesn't really exist. It is almost unusable with the way existing equipment is made and tested. Switchgear and terminations will require you to rate at 75°C. UL product code AALZ is what you would be looking at.

But your conductor ampacity can use the 90°C rating as long as the splices take place outside and you can go from like 10 runs to 8 runs then back to 10 runs. The small reduction in wire then results in increases in failure points, voltage drop and labor hours. It really only make sense in a few applications.

So in this scenario, for shorter runs, there is little cost savings? If I use presure contact switches instead of breaker style switches, does that change? Sounds like for me the short run from the transformer to switch might as well be standard conduit and then potentially use cablebus for the interior. I don't know if paying for the custom flanges and stuff are worth it for the service conductors.

 

[Elect117]

So in this scenario, for shorter runs, there is little cost savings? If I use presure contact switches instead of breaker style switches, does that change? Sounds like for me the short run from the transformer to switch might as well be standard conduit and then potentially use cablebus for the interior. I don't know if paying for the custom flanges and stuff are worth it for the service conductors.

There is nothing that I am aware of that is rated to 90°C (for switchgear, breakers, etc.) or the free air ampacity ratings in those tables.

In my experience, cable tray and cable trench with no free air rating is the easiest if the building already exists.

If this is new construction, conduit into the building since you can get that done before the footing and walls are poured.

Attached photo is not my work or design. Just an example of cable tray. I am standing on the tray cover at the transformer. Everything is de-energized. Cables are secured with sunlight and weather resistant zip ties at a regular interval.

d / placed.

 

[rotmgbetter]

There is nothing that I am aware of that is rated to 90°C (for switchgear, breakers, etc.) or the free air ampacity ratings in those tables.

In my experience, cable tray and cable trench with no free air rating is the easiest if the building already exists.

If this is new construction, conduit into the building since you can get that done before the footing and walls are poured.

Attached photo is not my work or design. Just an example of cable tray. I am standing on the tray cover at the transformer. Everything is de-energized. Cables are secured with sunlight and weather resistant zip ties at a regular interval.

View attachment 2575324d / placed.

Good to know.

Maybe using a cable tray and following the arrange as triangle (or square) rule is probably the best idea for us. How would you handle it if your installation needs more than 30 conductors?

 

[ron]

Using free air ratings or 90 deg ratings, as mentioned by Elect117, are almost unusable other than very special scenarios in 110.14.

The photo shown in Elect117's post is bundled conductors on cable tray. Similar concept as cablebus, but less "Engineered" as it is field assembled without the conductor saddles of cablebus. I'm not a fan of bundled conductors on cable tray unless the securement is cable cleats tested to IEC 61914. Wire ties are not a tested product to comply with 392.20(C), but the intent is similar for non-paralleled circuits.

 

[rotmgbetter]

Representative at superior bus told me that to his knowledge, pressure contact switch terminals are suitable for free air ampacity at the 75 degrees C but all breaker style switches are not. Does anyone know anything about this?

 

[jim dungar]

Representative at superior bus told me that to his knowledge, pressure contact switch terminals are suitable for free air ampacity at the 75 degrees C but all breaker style switches are not. Does anyone know anything about this?

There is no UL Listed breaker, fused switch, panel, MCC, or switchboard that allows connection above 75C
However some ANSI rated drawout rated switchgear may have high ratings, partly do to the size of its enclosure.
Free air ampacities may not be applicable when entering most enclosed equipment/ UL listings are based on heat dissipation, through the enclosure ventilation and the heatsink effect of the conductors/

In today's environment of electrical safety, like NFPA70E, and NEC requirements for arc reduction methods, I would definitely be looking at breakers rather than bolted pressure switches.

 

[Elect117]

Good to know.

Maybe using a cable tray and following the arrange as triangle (or square) rule is probably the best idea for us. How would you handle it if your installation needs more than 30 conductors?

Get a cable tray wide enough? lol I don't know. I will leave the specifics up to you, your contractor, the engineer, etc. I am just tossing ideas that can work.

Using free air ratings or 90 deg ratings, as mentioned by Elect117, are almost unusable other than very special scenarios in 110.14.

The photo shown in Elect117's post is bundled conductors on cable tray. Similar concept as cablebus, but less "Engineered" as it is field assembled without the conductor saddles of cablebus. I'm not a fan of bundled conductors on cable tray unless the securement is cable cleats tested to IEC 61914. Wire ties are not a tested product to comply with 392.20(C), but the intent is similar for non-paralleled circuits.

Good points.

Representative at superior bus told me that to his knowledge, pressure contact switch terminals are suitable for free air ampacity at the 75 degrees C but all breaker style switches are not. Does anyone know anything about this?

I would ask what ampacity and temperature they are tested and listed at. From my understanding the wire, terminals, the internal components, bus, etc. are all tested to meet the ampacity they are labeled at and the temperature at which they can handle that ampacity. AALZ goes into more detail on the 60°C and 75°C differences and labeling. There is no such label, to my understanding, that is tested at the free air ampacity for a single landed conductor terminating. Not to mention the components being capable of meeting the 90°C temperature needed to reach that ampacity (310.16) for a single conductor's termination/connection.