Cam-lok Panel (bus bar questions)

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overkill94

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Just did an inspection on some cam-lok panels - basically a power distribution unit for when they want to do load bank testing. It's rated at 416 Volts, 4000 Amps, 3-Phase and uses copper busing in the panel. A few questions:1. They come across with two 8" x 1/4" bus bars per phase but then split that between two sets of two 5" x 1/4" bus bars split between the cam-lok connectors (13 of them rated 400 Amps each). They claim that each pair of 5" x 1/4" bus bars are good for 3,000 Amps but according to Table 23 in UL 891 it's only 1,000 Amps per square inch which would be 2,500 Amps and thus unable to handle the 2,800 Amps maximum that the part with 7 connectors would be rated for.2. The bolts connecting the connectors to the bus bars do not have any threads showing after the nut. I've always been told you need at least two full threads showing but can't find a code reference supporting that. Is this just a general engineering practice or is it stated somewhere?3. Is there a UL standard dealing with this sort of installation? I used the basic principles for bus bars from UL 891 but this isn't really a switchboard. UL 1640 - Portable Power-Distribution Equipment is the closest I could find but this is definitely permanently installed.Thanks!
 
Hopefully it works better this time.

Just did an inspection on some cam-lok panels - basically a power distribution unit for when they want to do load bank testing. It's rated at 416 Volts, 4000 Amps, 3-Phase and uses copper busing in the panel. A few questions:

1. They come across with two 8" x 1/4" bus bars per phase but then split that between two sets of two 5" x 1/4" bus bars split between the cam-lok connectors (13 of them rated 400 Amps each). They claim that each pair of 5" x 1/4" bus bars are good for 3,000 Amps but according to Table 23 in UL 891 it's only 1,000 Amps per square inch which would be 2,500 Amps and thus unable to handle the 2,800 Amps maximum that the part with 7 connectors would be rated for.

2. The bolts connecting the connectors to the bus bars do not have any threads showing after the nut. I've always been told you need at least two full threads showing but can't find a code reference supporting that. Is this just a general engineering practice or is it stated somewhere?

3. Is there a UL standard dealing with this sort of installation? I used the basic principles for bus bars from UL 891 but this isn't really a switchboard. UL 1640 - Portable Power-Distribution Equipment is the closest I could find but this is definitely permanently installed.

Thanks!
 
overkill94 said:
Just did an inspection on some cam-lok panels - basically a power distribution unit for when they want to do load bank testing. It's rated at 416 Volts, 4000 Amps, 3-Phase and uses copper busing in the panel. A few questions:1. They come across with two 8" x 1/4" bus bars per phase but then split that between two sets of two 5" x 1/4" bus bars split between the cam-lok connectors (13 of them rated 400 Amps each). They claim that each pair of 5" x 1/4" bus bars are good for 3,000 Amps but according to Table 23 in UL 891 it's only 1,000 Amps per square inch which would be 2,500 Amps and thus unable to handle the 2,800 Amps maximum that the part with 7 connectors would be rated for.2. The bolts connecting the connectors to the bus bars do not have any threads showing after the nut. I've always been told you need at least two full threads showing but can't find a code reference supporting that. Is this just a general engineering practice or is it stated somewhere?3. Is there a UL standard dealing with this sort of installation? I used the basic principles for bus bars from UL 891 but this isn't really a switchboard. UL 1640 - Portable Power-Distribution Equipment is the closest I could find but this is definitely permanently installed.Thanks!
Click to expand...

Off the top of my head, I'm not sure what standard this should be listed to, but I know there are listed products available for this application as this is becoming a fairly routine for load banking and such.
So I guess my first question is this a field built assembly or a factory built assembly and if so, is it listed?
 
texie said:
Off the top of my head, I'm not sure what standard this should be listed to, but I know there are listed products available for this application as this is becoming a fairly routine for load banking and such.
So I guess my first question is this a field built assembly or a factory built assembly and if so, is it listed?
Click to expand...

Yeah, we installed one on a building we did for the NYPD. Building was 12 ft wide and the switch was probably 6 ft wide. I think it was a 1200 amp rating. And it was listed.
I would look for a listing first and if it is listed, I wouldn't and couldn't say anything more.
And if it isn't.... well, you know what to do.
 
overkill94 said:
Hopefully it works better this time.

Just did an inspection on some cam-lok panels - basically a power distribution unit for when they want to do load bank testing. It's rated at 416 Volts, 4000 Amps, 3-Phase and uses copper busing in the panel. A few questions:

1. They come across with two 8" x 1/4" bus bars per phase but then split that between two sets of two 5" x 1/4" bus bars split between the cam-lok connectors (13 of them rated 400 Amps each). They claim that each pair of 5" x 1/4" bus bars are good for 3,000 Amps but according to Table 23 in UL 891 it's only 1,000 Amps per square inch which would be 2,500 Amps and thus unable to handle the 2,800 Amps maximum that the part with 7 connectors would be rated for.

2. The bolts connecting the connectors to the bus bars do not have any threads showing after the nut. I've always been told you need at least two full threads showing but can't find a code reference supporting that. Is this just a general engineering practice or is it stated somewhere?

3. Is there a UL standard dealing with this sort of installation? I used the basic principles for bus bars from UL 891 but this isn't really a switchboard. UL 1640 - Portable Power-Distribution Equipment is the closest I could find but this is definitely permanently installed.

Thanks!
Click to expand...

Thoughts:
1. Are there engineering calcs somewhere that might explain why the copper buss might appear to be undersized? Perhaps there was thought given to a lower duty cycle? Perhaps someone buggered the math?

2. As long as all the threads in the nut are engaged, there is no strength or electrical advantage to having bolt threads protrude beyond the nut. Specs often call for several threads showing simply for ease of visual inspection.

3. I can't speak to the UL listing or standards issue.


SceneryDriver
 
It is not uncommon to feed the power to a bus bar into the middle of the bus bar somewhere. That way effectively you get twice the ampacity as if it had been fed from the end.

You could feed 2000A into a 1000A rated bus bar and have 1000A go in each direction and not overload the bus bar because there is no place on the bus bar where there is more than 1000A of current.
 
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SceneryDriver said:
Thoughts:
1. Are there engineering calcs somewhere that might explain why the copper buss might appear to be undersized? Perhaps there was thought given to a lower duty cycle? Perhaps someone buggered the math?

2. As long as all the threads in the nut are engaged, there is no strength or electrical advantage to having bolt threads protrude beyond the nut. Specs often call for several threads showing simply for ease of visual inspection.

3. I can't speak to the UL listing or standards issue.


SceneryDriver
Click to expand...

Thanks SD.

1. They sent me a table with different temperature rises but it does not seem to come from any UL standard so I told them it is not valid.

2. Thanks, I think the building specs will make them change it, but unless it's in the code then I won't call them out for it.

3. Oh well, I'll just use the NEC and UL 891
 
If the assembly is not UL listed, or required to be UL listed, arbitrarily applying a UL listing standard to the busbar ampacity is not a valid argument in my opinion. UL891 is going to be based on temperature rise expected to prevent an internal enclosure temperature not to exceed 40C in a 25C ambient environment (IIRC) based on minimum air space volume around units that is also dictated in the UL spec. So arbitrarily assigning that to something that is not a UL891 Switchboard is not supportable. If you do not have OCPD devices inside of this box that are calibrated for 40C max ambient, why worry about maintaining that?

Also, even if there are OCPD devices inside, air flow and distribution arrangement makes a difference as well. For example in an UL845 MCC arrangement, where the bus bars are in a separated / segregated air space, I can get up to 1600A/sq. in. and still pass the UL845 heat rise testing. So that makes your 2 ea 5" x 1/4" bars good for 4000A (in theory). Basic UL845 MCC design tends to be min. 800A/sq. in., but even then, you would be at 2000A, so a center feed in a 4000A rated system would be fine.
 
Jraef said:
If the assembly is not UL listed, or required to be UL listed, arbitrarily applying a UL listing standard to the busbar ampacity is not a valid argument in my opinion. UL891 is going to be based on temperature rise expected to prevent an internal enclosure temperature not to exceed 40C in a 25C ambient environment (IIRC) based on minimum air space volume around units that is also dictated in the UL spec. So arbitrarily assigning that to something that is not a UL891 Switchboard is not supportable. If you do not have OCPD devices inside of this box that are calibrated for 40C max ambient, why worry about maintaining that?

Also, even if there are OCPD devices inside, air flow and distribution arrangement makes a difference as well. For example in an UL845 MCC arrangement, where the bus bars are in a separated / segregated air space, I can get up to 1600A/sq. in. and still pass the UL845 heat rise testing. So that makes your 2 ea 5" x 1/4" bars good for 4000A (in theory). Basic UL845 MCC design tends to be min. 800A/sq. in., but even then, you would be at 2000A, so a center feed in a 4000A rated system would be fine.
Click to expand...

Thanks for the response.

If UL891 wouldn't be valid, what standard would you use for this installation?
 
overkill94 said:
Thanks for the response.

If UL891 wouldn't be valid, what standard would you use for this installation?
Click to expand...

You cannot pick and choose parts of standards. The standard as a whole has to be followed.

If you decided to select UL891 as your standard you would need to follow all of the standard, not just what it says about bus bar ampacity.

My opinion is that the closest standard would be UL508a. UL engineers have told us that if it has wires in it and does not come directly under some other standard UL508a is probably appropriate.

However, once again, I would suggest that the totality of UL508a would need to be applied, not just a tiny piece of it.

I am not even know that Camlok connectors are in the UL508a list of acceptable components.
 
petersonra said:
You cannot pick and choose parts of standards. The standard as a whole has to be followed.

If you decided to select UL891 as your standard you would need to follow all of the standard, not just what it says about bus bar ampacity.

My opinion is that the closest standard would be UL508a. UL engineers have told us that if it has wires in it and does not come directly under some other standard UL508a is probably appropriate.

However, once again, I would suggest that the totality of UL508a would need to be applied, not just a tiny piece of it.

I am not even know that Camlok connectors are in the UL508a list of acceptable components.
Click to expand...
Bus bars are often problematic for UL508A, unless they are pre-fab systems that have been UL listed or at least recognized. That may be the way to go however.
 
petersonra said:
It is not uncommon to feed the power to a bus bar into the middle of the bus bar somewhere. That way effectively you get twice the ampacity as if it had been fed from the end.

You could feed 2000A into a 1000A rated bus bar and have 1000A go in each direction and not overload the bus bar because there is no place on the bus bar where there is more than 1000A of current.
Click to expand...

i'm not getting this.... if you have 2K amps available, it'a available everywhere on the
bus, in the event of a short circuit.

using the same theory, i could take a 40 amp circuit, and tie two number 12 wires
onto it, if there were only 20 amp loads on the end of those #12's.
 
Fulthrotl said:
i'm not getting this.... if you have 2K amps available, it'a available everywhere on the
bus, in the event of a short circuit.
Click to expand...
in the event of a short circuit the available short circuit current is available on the bus at any point. the ampacity of the bus bar has nothing whatsoever to do with the available SCC.

Fulthrotl said:
using the same theory, i could take a 40 amp circuit, and tie two number 12 wires
onto it, if there were only 20 amp loads on the end of those #12's.
Click to expand...

they would be taps and you would have to follow the tap rules.

paralleled conductors are not taps. the OP appears to be talking about a paralleled conductor situation.

IME, bus bars that are listed are listed for center feeding at twice the ampacity of what the ampacity is when end fed.
 
overkill94 said:
So the panel manufacturer's response is that they used the bus bar manufacturer's information as their guideline - http://www.husseycopper.com/production/products/bar/

It seems that the 50 degrees C table matches up with the UL 891 table but they're trying to say the 65 degrees C column can be applied to this situation. Anyone know if their interpretation is correct?
Click to expand...

The Camlok connectors are rated for an ambient temperature of -40 to 105 deg C. I have not been able to find a termination temperature rating though but it seems reasonable that if the connector is rated to 105 degree C the termination is as well.

They are probably thinking that at 40 deg C ambient plus a 65 deg C rise they are good with the 105 deg C rating.

It is a supportable argument, at least superficially.

The bus bars don't appear to be listed or recognized and it seems unlikely to me that the assembly is listed with this combination. But, you never know.
 
petersonra said:
The Camlok connectors are rated for an ambient temperature of -40 to 105 deg C. I have not been able to find a termination temperature rating though but it seems reasonable that if the connector is rated to 105 degree C the termination is as well.

They are probably thinking that at 40 deg C ambient plus a 65 deg C rise they are good with the 105 deg C rating.

It is a supportable argument, at least superficially.

The bus bars don't appear to be listed or recognized and it seems unlikely to me that the assembly is listed with this combination. But, you never know.
Click to expand...

Thanks Bob.

I may have found a more applicable standard in UL 857 - Busways and it basically has the same ampacity table as UL 891. Unless the bus bar manufacturer's table has been evaluated by UL or any other standard, I don't think it's relevant.
 
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