Chad

Grounding through the TP??

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Chad   

Need some electrical help....  Am using a TP-60 with an ePMP 1000 AP on a tower. We are seeing what looks like some odd grounding issues and I can't narrow down the problem.  When I power the AP from our switch and the AP is in the TP horn, it blows a fuse. If I pull the radio from the TP adapter, it does not blow the fuse.  

The radio does not have a grounding lug on it. The Ethernet has a drain wire that is crimped to the connector at the radio and the switch.  Is it possible for the Ethernet connector to hit ground on the top of the tower through the horn? The horn is obviously attached to the tower standoff. Is there an electrical or metal connection between anything on the Ethernet port and the mounting bracket on the side of the horn? It does not appear so but I can't see inside...

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JT   

Chad - only conductive material touching the radio on antenna side are the connectors - you can see them inside the TP adaptor. What is inside ePMP1000, I can only judge - black box in this case. The Horn is completely conductive (metal).  Without knowing more details we can not help here. E.g. what switch are you using and how is it grounded? Or shoot me PM and we can follow up.

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Chad   

Using a Netonix DC powered switch. When we power an ePMP 1000 radio naked (not in the TP), it powers fine. If we install it in the TP adapter which is twisted onto the horn, as soon as we power the radio, it blows the 48v fuse in the switch. 

We have a dedicated #4 green ground wire coming up the tower for the switch and two ePMP 2000 radios (the 1000 in question had no ground lug). 

I'm trying to figure out where my ground issue is. Is the ePMP can connect to tower ground through the TP, that helps narrow down the path. 

Edited by Chad

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JT   

Not sure about how ePMP1000 vs ePMP2000 construction / wiring / grounding. ePMP1000s coax ground connects to the tower once twistport is locked. Not sure how it is at ePMP, but example UBNT radios have negative from power connected to coax ground. Assuming it is similar here, than you create loop by connecting the radio to the antenna. So one issue can be that you have two different grounds - one on antenna (= tower itself) and another on the switch (via separate #4 green wired up the tower). By connecting the radio to the antenna, you get two different grounds into loop. Now why it blows the fuse, that is not typical symptom, but the truth is I am not an engineer :). I would also check the grounding, those 48V.. -48V telco could also cause problems in some cases.

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Chad, testing the radio in the TP when it is not attached to the tower might tell you something.  If it still trips the breaker when the radio is in the TP and the TP is not attached to the tower, there may be something else wrong.

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Chad   

Took a volt meter up the tower. Can not find any electrical continuity between the Ethernet port (or shielding) to tower ground through the TP. Which is what I would suspect. I'm still trouble shooting where my ground short is happening - or which piece of hardware up there is failing.

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Jan_RFe   

Chad, which model of the switch are you using? Also, please tell me if input voltage at switch is -48VDC (negative 48VDC)?

Thanks, Jan.

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Chad   

This has been resolved but not sure why.  I think the initial problem was related to a new FM station that did some bad grounding. I wish I could say what made it go away but I can't. Which means it will probably come back...

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Jan_RFe   

Chad, thanks for coming back with above info :) if you will find out the cause or resolution, please put it here :) 

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