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Ground loop with external POE device

Hi All,
Consider mounting a camera outside a building on a metal pole as displayed in the pic below. Is there a safety issue here with the ground? It shows the ethernet surge protector grounded at the pole, and assuming that is shielded cable going back to the building, it will be bonded to the building ground. Does this introduce a ground loop and possible safety issue? I have been comparing it to installing an outdoor outlet on the side of a detached shed. I don’t believe code would allow for a ground rod to be driven at the shed and connect to the ground wire?  Thanks


Capture.JPG


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Re: Ground loop with external POE device


@bob_m10 wrote:

... the cam uses a plastic rj45  (non shielded) jack so I don't think (could be wrong) it would make any difference in terms of ESD. 


FTP and metal ends have no termination on the camera then so of no value there.  Using FTP with metal ends in between two ETH-SP is questionable as the thin drain wire could try to carry high current from potential differences.  The foil drain is not meant to equalize ground potential differences, just to drain electrostatic potential that may be generated by wind, etc.

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Re: Ground loop with external POE device

[ Edited ]

This isn't perfect; you can choose how much to do.

Those surge protectors will drain ESD and surges

from distant lightning strikes to ground, but only if

there is a decent ground of course. It's not best to

use the ac mains ground for surge grounding, but

for ESD alone, it's common.

 

If you live in a lightning-prone area or need to follow

specific building codes, you might want to put in

those lightning rods. Without them--or some other

earth ground--ETH-SP has less value. If you aren't

concerned about lightning, any ground is better

than none, I suppose.

 

While linking the two ETH-SP grounds via a separate

conductor is proper practice--and required for towers,

for example--I wouldn't bother with that for a short pole.

If the pole is as high as the building.....   Dave


> HQ in Seacoast region New Hampshire U.S.A.
> Ubiquiti Certified Trainer [UCT] for:
     UBWA [AirMax] / UEWA [UniFi] / UBRSS [routers]
UBNT.NH@gmail.com

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Re: Ground loop with external POE device

If the ground at the entrance is shared with AC mains and is poor then ground current and potential could be present at the pole.  The code intent for entrance protection (grounding) is to save lives (and buildings), not to save electronics.

 

Lightning protection for electronics involves bonding all points to maintain as much as possible, the same potential to reduce current through the devices.  Motorola R56 Guideline is a good reference to follow but usually prohibitively expensive for you average residential install.

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Re: Ground loop with external POE device

 


@LLigetfa wrote:

If the ground at the entrance is shared with AC mains and is poor then ground current and potential could be present at the pole.  The code intent for entrance protection (grounding) is to save lives (and buildings), not to save electronics.

 

Lightning protection for electronics involves bonding all points to maintain as much as possible, the same potential to reduce current through the devices.  Motorola R56 Guideline is a good reference to follow but usually prohibitively expensive for you average residential install.


Thanks for the info.  Curious, when running STP inside the building,  would you only want a connection to ground at one end, presumably at the switch rather than the switch and wall jack?  Reading all sorts of confilicting recommendations on the Internet.    

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Re: Ground loop with external POE device

The foil drain wire has to be terminated at both ends to be effective.  One would not normally have a surge protector on indoor devices but having everything well bonded where there is already a natural grounding point still makes sense.  Most Ubiquiti kit (excluding switches and outdoor radios with external antenna) are electrically isolated through the case and very few even have a ground lug.

 

A while back, there was an edge case where 24V passive PoE through FTP with terminated drain wire could create an undesirable loop between the PoE negative and the foil drain.  AF/AT power through the same switch was fine and Ubiquiti supplied Instant AF converters to those affected.  Again, that was an edge case and not the norm.

 

I have for decades, designed network cable plants for large industrial complexes where disparate grounds are often the case.  Bonding is not always possible nor practical and in those cases I would normally use fibre optic cable for electrical isolation.

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Re: Ground loop with external POE device

I would avoid using shielded cable from the building

surge protector to the router/switch. That ETH-SP

provides the necessary ground for ESD grounding

of the radio. Using two ETH-SP as shown will

provide extra ESD protection, but they are not

'lightning arrestors'.   Dave


> HQ in Seacoast region New Hampshire U.S.A.
> Ubiquiti Certified Trainer [UCT] for:
     UBWA [AirMax] / UEWA [UniFi] / UBRSS [routers]
UBNT.NH@gmail.com
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Re: Ground loop with external POE device

[ Edited ]

@Dave-D wrote:

I would avoid using shielded cable from the building

surge protector to the router/switch. That ETH-SP

provides the necessary ground for ESD grounding

of the radio. Using two ETH-SP as shown will

provide extra ESD protection, but they are not

'lightning arrestors'.   Dave


Thanks Dave, makes sense.  In my actual case,  I would like to install a poe cam (Ring Stick up Cam) on the outside of my home and want to make sure I do this correctly. I planned on using a Cat 6 utp patch cable from the camera through PVC conduit inside to my basement and immediately connect to the ETH-SP. I would bound the ETH-SP to a nearby outlet. From the ETH-SP I will run utp back to my poe switch 8 as you suggested.  I thought about using a Cat 6 shielded cable from the cam to the ETH-SP but they are stiff and the cam uses a plastic rj45  (non shielded) jack so I don't think (could be wrong) it would make any difference in terms of ESD. 

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Re: Ground loop with external POE device

[ Edited ]

For the camera to have any ESD protection and for

the ETH-SP to have full valuel, the cable from the

camera to the first ETH-SP and from the first ETH-SP to

the second one must both be shielded [FTP} outdoor

rated cable--either CAT5e or CAT6--with compatible

shielded connectors. That shield is what creates

a ground. If your camera has no shielded jack, it

may not even be rated for full outdoor use, and

unless it has a ground lug, this may not do much.

 

ETH-SP does have some benefit because it bypasses

surges on the data lines--which can be produced by

distant lightning discharges.

 

Also, standard codes usually mandate that any ground

on a cable must be outside the building--usually at the

point of cable entry. Its ground should go directly down

to a ground rod--never to an ac receptacle or the like.

Follow the graphic here:

   https://dl.ubnt.com/datasheets/ETH-SP/Ethernet_Surge_Protector_DS.pdf

 

Dave


> HQ in Seacoast region New Hampshire U.S.A.
> Ubiquiti Certified Trainer [UCT] for:
     UBWA [AirMax] / UEWA [UniFi] / UBRSS [routers]
UBNT.NH@gmail.com
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Re: Ground loop with external POE device


@bob_m10 wrote:

... the cam uses a plastic rj45  (non shielded) jack so I don't think (could be wrong) it would make any difference in terms of ESD. 


FTP and metal ends have no termination on the camera then so of no value there.  Using FTP with metal ends in between two ETH-SP is questionable as the thin drain wire could try to carry high current from potential differences.  The foil drain is not meant to equalize ground potential differences, just to drain electrostatic potential that may be generated by wind, etc.

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Re: Ground loop with external POE device


@Dave-D wrote:

 

Also, standard codes usually mandate that any ground

on a cable must be outside the building--usually at the

point of cable entry. Its ground should go directly down

to a ground rod--never to an ac receptacle or the like.

Follow the graphic here:

   https://dl.ubnt.com/datasheets/ETH-SP/Ethernet_Surge_Protector_DS.pdf

 

Dave


Hi Dave,

 

That all makes sense, but in reality are folks driving 8' grounds rods for every camera they mount on outside their home? I suppose if you enter your home near where cable and telco enter you can tie into the same ground but impractical if your camera is on the opposite side of the house.   I  understand there is a right and wrong way but curious how many folks are following the code here. 

 

That battery operated Arlo is looking better and better.  Man Happy  Appreciate your insight.  Bob

 

 

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Re: Ground loop with external POE device


@LLigetfa wrote:

@bob_m10 wrote:

... the cam uses a plastic rj45  (non shielded) jack so I don't think (could be wrong) it would make any difference in terms of ESD. 


Using FTP with metal ends in between two ETH-SP is questionable as the thin drain wire could try to carry high current from potential differences.  The foil drain is not meant to equalize ground potential differences, just to drain electrostatic potential that may be generated by wind, etc.


So this is interesting, are you saying you would not use FTP with metal ends between two ETH-SP because of the possibility of high current transfer over the shield?

 

 

 

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Re: Ground loop with external POE device


@Dave-D wrote:

Also, standard codes usually mandate that any ground

on a cable must be outside the building--usually at the

point of cable entry. Its ground should go directly down

to a ground rod--never to an ac receptacle or the like.


I question the accuracy of this.  First off, code says:

"For each communications circuit, you must install a listed primary protector as close as practicable to the point of entrance [800.90(B)]."

It can be inside the envelope.

 

As for a separate ground rod, ideally they should all be bonded with #6 wire.  Section 800.100 does however allow for #14 wire.

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Re: Ground loop with external POE device


@bob_m10 wrote:

So this is interesting, are you saying you would not use FTP with metal ends between two ETH-SP because of the possibility of high current transfer over the shield?


Correct.  The two grounding points should be bonded with at least #14 wire and ideally #6 wire.

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Re: Ground loop with external POE device

[ Edited ]

This isn't perfect; you can choose how much to do.

Those surge protectors will drain ESD and surges

from distant lightning strikes to ground, but only if

there is a decent ground of course. It's not best to

use the ac mains ground for surge grounding, but

for ESD alone, it's common.

 

If you live in a lightning-prone area or need to follow

specific building codes, you might want to put in

those lightning rods. Without them--or some other

earth ground--ETH-SP has less value. If you aren't

concerned about lightning, any ground is better

than none, I suppose.

 

While linking the two ETH-SP grounds via a separate

conductor is proper practice--and required for towers,

for example--I wouldn't bother with that for a short pole.

If the pole is as high as the building.....   Dave


> HQ in Seacoast region New Hampshire U.S.A.
> Ubiquiti Certified Trainer [UCT] for:
     UBWA [AirMax] / UEWA [UniFi] / UBRSS [routers]
UBNT.NH@gmail.com
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Re: Ground loop with external POE device

thanks to you both for interesting information.  

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Re: Ground loop with external POE device

You're welcome--I hope more than 'interesting'.

 

Feel free to mark posts you found helpful as your

'solutions'   Dave


> HQ in Seacoast region New Hampshire U.S.A.
> Ubiquiti Certified Trainer [UCT] for:
     UBWA [AirMax] / UEWA [UniFi] / UBRSS [routers]
UBNT.NH@gmail.com
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