NEMA Config 125-250

[chris kennedy]

Why is it that looking at the NEMA charts 120V devices are rated 125V and 240V devices are rated 250V vet 120/208 devices are rated 120/208 and same for 277/480???

Thanks

 

[jumper]

UL testing. Look in white book, page 466,RTDV, under paragraph heading" ratings".

Cannot cut and paste at the moment.

https://www.ul.com/wp-content/uploa...ty&utm_campaign=codeauthoritieswhitebook

 

[Jraef]

Might be this:
On the 3 phase devices, they are more specific because there is an issue with the maximum potential to ground being 58% of the maximum line potential. It affects how the terminals are spaced, fault current withstand capability etc. So in other words if a device is rated 480/277V, it can ONLY be used on a grounded Wye system, you cannot use it on a 480 delta system where the line-ground potential would be 480V, not 277V. Same with the 208/120 devices; you cannot use them on 240V delta systems because the line-ground potential could be 240V, not 120V. So if they said "250V", you might assume you could use it on 240V delta and you can't.

 

[raider1]

UL testing. Look in white book, page 466,RTDV, under paragraph heading" ratings".

Cannot cut and paste at the moment.

https://www.ul.com/wp-content/uploa...ty&utm_campaign=codeauthoritieswhitebook

Derek,

You are correct,

Here is what the Guide Information page has to say in regards to rating of receptacles

Devices rated 250 V are tested on circuits involving a nominal potential to ground of 125 V. Devices having other voltage ratings are tested on circuits involving full rated potential to ground, except for multiphase rated devices, which are tested on circuits consistent with their voltage ratings (e.g., a 120/208 V, 3-phase device is tested on a circuit involving 120 V to ground).

Also UL has a new online version of the Whitebook called PRODUCTSPEC. You can more easily search for information by Installation code, product type or product category.

Chris