Ground ring as effective fault current path

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synchro said:
Not that it matters for this discussion, but the positive 48VDC "return" conductor would be grounded and the hot lead would be -48VDC.
That being said, I've seen documents describing floating DC feeds to RRUs that have separate surge/lighting protection devices on the positive and negative conductors. So it might be wise to confirm that the +48VDC return conductor is bonded to the cabinet ground bar in your situation.
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That's true for the phone equipment but everything else on cell towers is negative ground.
 
ActionDave said:
That's true for the phone equipment but everything else on cell towers is negative ground.
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According to the following paper from a company that makes power supplies for feeding RRUs, on pg. 5 they say:
"The power delivery system at our example cell site is depicted in Figure 2. Grid ac power is rectified and regulated to a nominal 48 VDC (actually, -48 VDC, but polarity has been omitted here), then fed to one or more strings of backup batteries and to the trunk cables leading to the radio equipment at the tower top."

 
synchro said:
Not that it matters for this discussion, but the positive 48VDC "return" conductor would be grounded and the hot lead would be -48VDC.
That being said, I've seen documents describing floating DC feeds to RRUs that have separate surge/lighting protection devices on the positive and negative conductors. So it might be wise to confirm that the +48VDC return conductor is bonded to the cabinet ground bar in your situation.
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Correct +48vdc terminal bar in cabinet is grounded to ground ring and -48vdc has single pole breaker. Had it backwards

This one has surge/lightning protection in cabinet however its after the breakers load side and when cables enter to the cabinet from tower. So it is grounded and has surge/lighting protection
 
What if dc system was not grounded , float 250.4(b)(4) still requires effective ground fault current path. How can one provide the path for tower back to cabinet? Their would be no GEC from cabinet positive +48 vdc to ground ring.
 
hhsting said:
What if dc system was not grounded , float 250.4(b)(4) still requires effective ground fault current path. How can one provide the path for tower back to cabinet?
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Install an equipment grounding conductor between the cabinet and the tower.

(How many times do I have to say it?)
 
jaggedben said:
Install an equipment grounding conductor between the cabinet and the tower.

(How many times do I have to say it?)
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Right 2 wire dc system less than 60vdc which has + and - wires and is not required by code to be even grounded needs to have equipment grounding conductor between cabinet and tower? Don’t follow. Have EGC which connects to what + or - terminal and may then still current flow thru enclosure back to - or + terminal
 
hhsting said:
Right 2 wire dc system less than 60vdc which has + and - wires and is not required by code to be even grounded needs to have equipment grounding conductor between cabinet and tower? Don’t follow. Have EGC which connects to what + or - terminal and may then still current flow thru enclosure back to - or + terminal
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The code requires the EGC, period. Always. No matter the type of system. 250.4(A) or (B), take your pick.
 
synchro said:
According to the following paper from a company that makes power supplies for feeding RRUs, on pg. 5 they say:
"The power delivery system at our example cell site is depicted in Figure 2. Grid ac power is rectified and regulated to a nominal 48 VDC (actually, -48 VDC, but polarity has been omitted here), then fed to one or more strings of backup batteries and to the trunk cables leading to the radio equipment at the tower top."

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So there is some new equipment out there that I haven't been around yet. I wonder how all this will shake out. I still trust that the design of a cell site is such that anything that needs to be bonded is.
 
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