Want to move to all 208V for server racks

Thu Dec 2 18:47:38 UTC 2010

>>> Err, I meant "skip the neutral wire". It's still grounded. And there are normally significantly more covers over the panel than this, there were a dozen screws I had to remove to expose all of this. :)
>>>
>>> This is a much smaller scale panel though, not far up from a typical home system. The more current you start talking about, the more isolated everything becomes until you wouldn't even be able to see the bus bars like in this one.
>>
>> are "Residual-current device" (Fi in German) are common in us?
>> I use for servers "Residual-current device" and circuit breaker integrated in one device; but I try to use the more expensive pulse tolerant ones.
>
> They're called "Ground Fault Interruptors" here, or GFI/GFCI.
>
> They're extremely common built into wall power outlets, and GFI outlets are required in wet areas (kitchens, bathrooms, hot tubs, outdoors, etc). Most wall outlets with GFIs built into them have a "daisy chain" system where one outlet in the kitchen has the circuitry and the Test/Reset buttons, and it protects all non-GFI downstream outlets from it. Downstream outlets usually have a sticker on them saying "GFI Protected" which is a hint that if the outlet stops working, check other outlets in the room to see if one of them tripped. Newer versions have a light that comes on to indicate when they've been tripped, which is handy for non-technical people to figure out what happened more easily.
>
> You can get breakers with GFIs built into them(called GFCIs), but they're favored less than putting them at the outlet. I haven't seen any datacenters using them, but I haven't looked that closely. An electrician I talked to once about it felt that the panel mounted variety were designed to be less sensitive/slower reacting due to much longer wire lengths, but I'm not sure if that's just urban legend, experience with a single product or fact.

in europe GFIs are always needed for prection and by law.
to avoid the cascading effects the GFCIs are better.
break current ranges from 10mA (bath) up to 300mA; for servers I use the 
30mA with pulse protection (internal delay) to avoid the server 
powersupply capacitor loading GFCIs "flip".

Kind regards,
 	Ingo Flaschberger