48VDC power system and Article 250
- Thread starter Dennis P
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Got a feeling I designed this plant as there are very few 10,000 amp plants in the USA. Wouldn't be a former Worldcom now Verizon would it?Dennis P said:
To answer your question, there is no requirement for the bus to be grounded. What you probably have is a 2/0 running above the Rectifiers and Battery Distribution Frames line up and each frame tapped to the overhead 2/0 with a 1/0 to each individual frame.
Here is the deal with the bus. More than likely you have anywhere from 6 to 14 strings of 48 VDC battery strings rated at 2000 AH per string. Each battery string is connected to the overhead buss via multiple 500 MCM cables without any over current protection devices designed as not to have more than ? volt drop at the full rated current (tons and tons of copper). What I am driving at here is the fault current potential on the battery buss and BDF?s is astronomical with 6 to 14 strings of batteries and 16,000 amps of rectifiers, all without any OCPD on the charge and load side of the bus; there is no grounding conductor that could clear a fault. In reality if there is a fault, what ever causes the fault will be the fuse when it is vaporized.
Now you may ask how a telco gets away with this, simple read 90.2(4). Further only authorized personnel are allowed in the area.
You bet it is a grounded system. All 48 VDC systems I have ever worked on or designed have the positive return buss grounded. It is the industry standard practice for 48, 24, and 12 VDC battery plants.acrwc10 said:
Otherwise you would have to fuse both polarities with GFD circuits. You do hear of some of these once in a while but it is rare and very expensive to implement.
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