Would it be safe to assume that a 1200 Amp 480v/277 Y 3r Fused Service Disconnect Switch Fused at 900 amps would relieve you of the GFI requirement of 1000 amps and above?
230.95 Ground-Fault Protection of Equipment. Groundfault
protection of equipment shall be provided for solidly
grounded wye electric services of more than 150 volts to
ground but not exceeding 600 volts phase-to-phase for each
service disconnect rated 1000 amperes or more. The
grounded conductor for the solidly grounded wye system
shall be connected directly to ground through a grounding
electrode system, as specified in 250.50, without inserting
any resistor or impedance device.
The rating of the service disconnect shall be considered
to be the rating of the largest fuse that can be installed or
the highest continuous current trip setting for which the
actual overcurrent device installed in a circuit breaker is
rated or can be adjusted.
Install an enclosed circuit breaker in series, and include the GFI protection on it? :lol:. . . just out of curiousity, how does one provide GF protection on a fuse?
It is never safe to assume anything. In this case, it would be a particularly poor assumption. The beginning of the second paragraph of 230.95 says that the rating of a fused service disconnecting means is the highest size fuse that can be installed. So your installation would exceed the 1000 amp threshold, even though you used 900 amp fuses.
Install an enclosed circuit breaker in series, and include the GFI protection on it? :lol:
I have been taught it is because an arcing ground fault is not sustainable (does not restrike after zero crossing) on a 208/120Y system, but it is on a 480/277Y system. The arcing fault can produce enough heat to melt the switch gear down without tripping the OCPD unless it has GFP....
why are 208/120 systems excluded?
not if it is a service.
beat me to it. but if it is just a feeder, it would seem to be ok.
just out of curiousity, how does one provide GF protection on a fuse?
I have been taught it is because an arcing ground fault is not sustainable (does not restrike after zero crossing) on a 208/120Y system, but it is on a 480/277Y system. The arcing fault can produce enough heat to melt the switch gear down without tripping the OCPD unless it has GFP.
From the part that I can access, it appears to be talking about 277 volt arcing faults, and I agree that those re-strike, and that is the very reason for the ground fault protection rule, but I was trying to say that the 120 arcing ground faults do not re-strike and that is why GFP is not required on 208/120Y systems.Recent studies from IEEE suggest otherwise
http://ieeexplore.ieee.org/xpl/logi...iel5/28/4503404/04503412.pdf?arnumber=4503412
That engineer needs to get a lesson on "Charlie's Rule." The code says what it says, not what anyone (engineers included) thinks it says. The actual text is quoted in post 3 above, and it clearly says, "1000 amps or more."The Engineer rejected the submittals indicating that the rule applied to "Above" 1000 amps.
I have to agree with you. But you need to get the engineer to wake up to the fact that your original submittal correctly included the GFI feature.But once the Temp Generator gets taken off line, I dont see any way around not having to replace the Fused Disconnect. The 900a Fuse Option came up but evidently the clause in the code rule would not allow this either.
From the part that I can access, it appears to be talking about 277 volt arcing faults, and I agree that those re-strike, and that is the very reason for the ground fault protection rule, but I was trying to say that the 120 arcing ground faults do not re-strike and that is why GFP is not required on 208/120Y systems.
Recent studies from IEEE suggest otherwise
http://ieeexplore.ieee.org/xpl/logi...iel5/28/4503404/04503412.pdf?arnumber=4503412
Zog -
This was published in 1977. Did I miss something about how recent this is? A lot of my work concerns Arc flash. I'm definitely interested if there is new data.
ice
I don't have any access to the entire study. It does not appear to be available to me without cost.You need to read the entire study, this was done to conduct research specifically on 208/120V systems to settle that arguement from IEEE 1584 ommiting 208/120 systems from arc flash analysis requirements, which was then removed from 70E after this research showed sustainable arcing faults to ground on 208/120V systems.
... If there really is the possibility of an "acring burndown" on a 208/120Y system like there is for a 480/277Y system, why does the code only require GFP protection for the 480/277Y system?
So installing a 1200 amp main lug only switchboard and dividing up the feeders to not exceed 1000 amps (staying 6 switches or less) is ok? I guess as long as it would be physically impossible to put anything 1000 amps or larger in it?
...
just out of curiousity, how does one provide GF protection on a fuse?