Spacing between Phases in Equipment

[ron]

Existing panelboard, in which the contractor want to replace single mechanical lugs ( http://www.ilsco.com/e2wShoppingCat...k=2100001183:3100012178:3100012221:3100012923 ) with stacking type http://www.ilsco.com/e2wShoppingCat...k=2100001183:3100012178:3100012221:3100012939 .

Would someone know if there is a NEMA rule of thumb with required clearance needed between phases at 480V and then from phase to ground (277V)? I'm guessing an inch or two, but could find any reference material.

 

[petersonra]

Existing panelboard, in which the contractor want to replace single mechanical lugs ( http://www.ilsco.com/e2wShoppingCat...k=2100001183:3100012178:3100012221:3100012923 ) with stacking type http://www.ilsco.com/e2wShoppingCat...k=2100001183:3100012178:3100012221:3100012939 .

Would someone know if there is a NEMA rule of thumb with required clearance needed between phases at 480V and then from phase to ground (277V)? I'm guessing an inch or two, but could find any reference material.

UL508a requires an inch for feeders and half an inch for branch circuits if they are not insulated. We usually insulate them with heat shrink so it is never an issue.

 

[ron]

UL508a requires an inch for feeders and half an inch for branch circuits if they are not insulated. We usually insulate them with heat shrink so it is never an issue.

Thanks.

I will suspect that those are consistently applied to other items like panelboards and switchboards. UL508a is for control panels

 

[Jraef]

Thanks.

I will suspect that those are consistently applied to other items like panelboards and switchboards. UL508a is for control panels

Officially, there is no standard that would apply actually. There is no equivalent to UL508A that allows you to construct a panelboard in a shop or the field. The ANSI standards for switchboards and panelboards apply to factory assemblies, which include testing to ensure dielectric isolation; 2200V for 1 minute on systems 635VAC and below. If a 1/2 of separation works for that, it passes (but FYI, it does not work). However UL1558, again for FACTORY assemblies, requires 1" of air gap, 2" of surface creepage distance on 600V gear. So basically it matches the UL508A requirements.

Still, what you are planning to do is not something the equipment was designed for, which means you are on your own. Using the UL1558 or 508A standard however is your best option, we know that works.

 

[qcroanoke]

Would 408.56 2008 NEC apply?