spacing between uninsulated parts

[hacim23]

On the job I've typically heard 1/2 inch spacing between uninsulated parts up to 1000v. For the most part I haven't seen anything that close except for some ATS' that come equipped with lugs and the spacing between some of them is barely enough to get a finger between. The ATS has an arc shield that goes between phases but does not completely isolate everything. We have wrapped (fish-paper) around B phase just to be safe but I also know that we haven't on some of them and had no issues. Is this covered in the NEC or is there something more specific to an ATS? This example is 400A, 480V. Thanks.

 

[infinity]

Take a look at Table 408.56 Minimum Spacings Between Bare Metal Parts.

 

[Jraef]

The NEC only applies to field installation, not manufacturing. There are recommendations on spacings, but in reality if the unit passed its dielectric withstand and impulse tests with only 1/2" air gap, then it passed.

Here is perhaps the best paper I have seen on this issue. Note that this is even discussing MEDIUM voltage gear.
https://www.powellind.com/sites/dow...Bus Spacings in Metal-Enclosed Switchgear.pdf

 

[raider1]

The Standard that the product is built to will specify the Clearance and creepage distances for the components, terminal and other live parts.

For ATS' UL 1008 Standard For Safety For Transfer Switch Equipment has Tables that specify clearances based on voltage and location.

Chris

 

[petersonra]

Ul 508a requires 1 inch on feeders and 1/2 inch on branch circuits. Why the difference? Who knows?