NEC related issues within a rack/panel

hrc · Mar 15, 2004

Lets say we have an equipment rack, and inside this rack we have a bunch of equipment (ethernet/fiber switches, etc), each requiring AC power. So within this rack is a primary power dist unit, and mulitple secondary units. Think of the secondary units being smart power strip where the outlets can be controlled via rs232.

The primary unit takes in a 3phase power (208Y) and gives 3 legs of 120VAC, each being sent thru a breaker then on to the secondary power strips. So technically we have a bunch of mini branch circuits.

So looking thru the NEC codebook, the majority of the articles deal solely with wiring in a dwelling, or wiring feeding to an equipment rack but doesnt't directly talk to wiring INSIDE the rack. So if we have a 20A circuit breaker on the primary distribution panel inside the rack, where it is rated for 100% load, then a 20A IEC recepticle where the secondary power strip then uses a 20A cable and plug to tie into that, does each of the items need to be derated 80%? Or does this ONLY apply to the main branch feeding the primary power unit in the rack. I tend to think that anything inside the rack does not require any derating.

Comments please?

jraef · Mar 15, 2004

In general, the NEC speaks to the installation of equipment and the building wiring systems. The internal construction and wiring of the equipment itself is usually left to a NRTL (Nationally Recognized Testing Lab), typified by UL for instance. Once an inspector sees a NRTL label for the entire assembly, they rarely go beyond that other than to see if you modified it. If you do not have a NRTL label on the entire system, many inspectors will default the internal construction to the NEC rules for building wiring, which may lead to trouble.

Typically, derating is not necessary on conductors and protective devices within an enclosed piece of equipment. That is why you will often find smaller conductors inside of a device than you would use to hook it up.

With all that said, ultimately the final authority is the inspector who sees it!

"Venditori de oleum-vipera non vigere excordis populi"

busbar · Mar 15, 2004

jraef sized it up well. One aside—IEC320 connectors have several ratings, but the most common 10-ampere pattern is listed with two temperature ratings… ‘C13/C14’ 70°C versus ‘C15/C16’ 120°C Limited description at

http://www.encyclopedia4u.com/i/iec-connector.html

panelman · Mar 15, 2004

don't the "hot" ones have an extra key groove in the base?

busbar · Mar 15, 2004

Looks like it. From the link, C15 cord will fit the C14 receptacle, but the C13 will not fit the C16.

panelman · Mar 16, 2004

Thought so....hot ones for kettles, cold ones for computers

According to my book they are available in 6, 10, 16 and 20A versions which all look identical

hrc · Mar 16, 2004

So this begs a question. For those who have put things thru certification for NRTL, do the 20A rated cords and recepticles have to be derated down to 16A?

ScottyUK · Mar 16, 2004

Panelman,

I think the 6A and 10A IEC320 cords are pretty much identical physically. The 16A version is visibly bigger, but has a similar appearance to the 6A and 10A types. I've not encountered a 20A type (yet).

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