LUG SPACING FOR 1200 AMP BUS GUTTER

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YouCanCallMeAl

Member
Location
Guelph
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Product Developer - Sheet metal manufacturing
Hi everyone,
This is my first post here, so I appreciate any help or guidance you can offer.

I’m working on a 1200A bus gutter system under NEC standards, and I’m looking for some clarification regarding lug spacing requirements, if any are defined.

The setup includes:
  • A main lug connection with 3 x 600 MCM aluminum conductors per phase
  • 5 branch lugs, each with a single 250 MCM aluminum conductor

The voltage is 600V, and the system includes 3 phases and a neutral.

Does NEC specify a minimum spacing between lugs in a bus gutter, or is this more of a practical design consideration (e.g., for bending radius, heat dissipation, or accessibility)?

Any references to specific clauses or tables in the standard would be especially appreciated.

Thanks in advance!
 
No need to post again in another forum. As stated, it's not in the NEC, it could possibly be in a manufacturers listing and labeling info.
 
So, if it's not NEC it's not in UL or CSA because UL/CSA abide to NEC? Therefore it's a manufacturers spec? Couldn't find this spec in the manufacturers instructions.
 
YouCanCallMeAl said:
So, if it's not NEC it's not in UL or CSA because UL/CSA abide to NEC? Therefore it's a manufacturers spec? Couldn't find this spec in the manufacturers instructions.
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Sometimes it falls back to common sense.

There are products that allow phases to be a fraction of an inch from one another.

1752754998389.png
There are versions that will fit your application.
 
You need to be concerned with wire bending space at the lugs. This is addressed in the NEC and by UL
You need to provide appropriate voltage clearance through air and over surfaces. This can be found in UL and NEMA standards. Stand off insulator manufacturers may also be a source.
Also you need to consider the short circuit bracing rating which is impacted by bus bar layout and insulator spacing. Again manufacturers are probably the best source.
You could try https://www.copper.org/applications/electrical/busbar/
 
YouCanCallMeAl said:
So, if it's not NEC it's not in UL or CSA because UL/CSA abide to NEC? Therefore it's a manufacturers spec? Couldn't find this spec in the manufacturers instructions.
Click to expand...
That is not correct. While there is some interaction between UL and the NEC, they serve two totally different functions. UL writes and publishes product listing standards that specify how equipment is constructed. The NEC is just an installation standard, and the NEC does not care about the internal parts of listed equipment because that is covered by the product standard.
The closest that the NEC comes to answering you question is in 366.100(C), but product standards will provide much more detail and likely result in a smaller enclosure.
 
zbang said:
It helps to remember that the NEC is a fire-prevention code, not a safety code or engineering design manual; as Don said, they serve different functions.
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I don't agree. That is part of the purpose of the NEC, but it also includes protecting people from shock hazards. If that was not part of the purpose, we would not have any GFCI requirements as those devices are only to limit the duration of the shock hazard.
A) Practical Safeguarding.
The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity.
Click to expand...
 
YouCanCallMeAl said:
Hi everyone,
This is my first post here, so I appreciate any help or guidance you can offer.

I’m working on a 1200A bus gutter system under NEC standards, and I’m looking for some clarification regarding lug spacing requirements, if any are defined.

The setup includes:
  • A main lug connection with 3 x 600 MCM aluminum conductors per phase
  • 5 branch lugs, each with a single 250 MCM aluminum conductor

The voltage is 600V, and the system includes 3 phases and a neutral.

Does NEC specify a minimum spacing between lugs in a bus gutter, or is this more of a practical design consideration (e.g., for bending radius, heat dissipation, or accessibility)?

Any references to specific clauses or tables in the standard would be especially appreciated.

Thanks in advance!
Click to expand...
If your familiar with IEC 61439-6 and it covers what you make have a look at UL 857 its a similar standard. Some jurisdictions accept either one.
 
Thanks everyone for your input.

But I guess it would help if I explained the scenario. Here is an image the bus gutter. The main feed is 3x 600 mcm and there are 5 branches with 250 mcm per branch. I wondering if there is a minimum spacing between each lug. Right now this minimum spacing is driven by the conduit spacing which is 4.75".
1752781115849.png
 
YouCanCallMeAl said:
Thanks. I'll have a look at UL 857 since is it what is available to me.
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What you have is more similar to a switchboard, UL891, not what the industry calls busway, UL857.

I know of no standard for spacing between lugs as shown in your drawing. The NEC wire bending spacing is based on lugs to the enclosure for making field terminations, it is probably not a bad guide to follow if you can tolerate the space.
 
YouCanCallMeAl said:
Thanks everyone for your input.

But I guess it would help if I explained the scenario. Here is an image the bus gutter. The main feed is 3x 600 mcm and there are 5 branches with 250 mcm per branch. I wondering if there is a minimum spacing between each lug. Right now this minimum spacing is driven by the conduit spacing which is 4.75".
View attachment 2578719
Click to expand...
The only issue with lugs on the same phase is the space to install the lugs and conductors as there is no voltage difference.

Not sure I have ever seen lugs installed parallel to the bus.

Typically they would be perpendicular.

If it is my project, I would want to terminate the conductors in two hole compression lugs, which would require a much greater horizontal spacing of the bus. Even where the manufacturer has supplied single hole mechanical lugs, I remove them and install compression lugs, two hole if possible, but if there is no space, single hole.
 
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