Clearance between exposed conductors inside a panel

[CaptKarnage]

When putting together an electrical panel for US 240V residential use (in this case a generator transfer switch), what is the required separation between hot and ground and hot and neutral?

I can't find this in NEC (I guess not in scope) but something has to determine what is acceptable. Obviously you can't have a short across them, and you need to maintain some distance between them in case of overvoltage / arcing. Is there any US regulation or body (e.g. UL) that uses IEC 61439 in this case, or is there a comparable US standard to guide in building the panel?

 

[LarryFine]

If you mean insulated conductors, none. What parts are you asking about? Can you post an example pic?

 

[CaptKarnage]

These are uninsulated conductors. Bus bars, terminal blocks, etc. I found the applicable standard: UL 1008. In particular, Table 3 is a summary of requirements. That is specific for transfer switches, though. Answers my question for this panel today but not sure yet for the larger question of any panel. I'd have to think they are similar.

 

[Jraef]

The NEC is not (generally) for building equipment, it is for installing equipment.

Standards for manufacturing are typically covered in ANSI and UL.

For example, table 10.1 in UL-508A (for building control panels) is a very comprehensive list of all of the rules. It is not in the least bit simplistic by the way. There are different rules for L-L, L-G, terminal-to-terminal, live-to enclosure walls, overt an air gap, across the surface, etc.

 

[ggunn]

I knew a guy who field modified a 480/277V panel to accept three sets of input conductors; it had been built with single lugs. When he was done I can only guess that there was maybe 1/8" clearance between one set of hot lugs and one of the internal rails of the enclosure on the cold day when he did the work. Then things warmed up; you can guess what happened.

 

[Carultch]

These are uninsulated conductors. Bus bars, terminal blocks, etc. I found the applicable standard: UL 1008. In particular, Table 3 is a summary of requirements. That is specific for transfer switches, though. Answers my question for this panel today but not sure yet for the larger question of any panel. I'd have to think they are similar.

The reason there need to be standards for distance between exposed conductive parts, is that air has limitations as an insulator. It is a great electrical insulator as long as it can remain in the gaseous state. Apply too many Volts per meter of electric field to the air, and it ionizes into the plasma state, forming an arc fault.