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thims
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RB960PGS Grounding

Sun Dec 12, 2021 6:01 pm

Since I have no access to the real hardware now but want to purchase one... Does anyone know if the hEX PoE provides some kind of grounding terminal? I'd like all the cAPs to be powered over PoE and since the (shielded) cable will be outdoor, the grounding is obviously required. Hence, the RB960PGS must be grounded. I'm aware of PowerBox Pro but since hEX is going to be installed indoors, I don't want to pay extra. I'm also aware of the ability to use the grounded PoE injector but I'd like to use the ordinary power supply.
 
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Re: RB960PGS Grounding

Sun Dec 12, 2021 6:06 pm

This post might help clarify stuff.

Either grounding through poe cable or grounding separate.
Not both.
Last post has an interesting link to read.

viewtopic.php?t=180885
 
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Re: RB960PGS Grounding

Sun Dec 12, 2021 6:53 pm

Does anyone know if the hEX PoE provides some kind of grounding terminal?

It doesn't. (Just looked at one.)

However, you may well not need it. Whether you do still need it depends on what actual problem you're trying to solve.

If you're hoping a little 24-gauge ground lug will arrest lighting, for instance, you're dreaming. No, my friend, that's called a fusible link at such energies. Fortunately, it should vaporize before it can start a carpet fire. :)

If I had to put WAPs outdoors, I'd find a way to get local power for them and run fiber to them instead, giving much better lighting protection. You still have to take care of surge protection for the local power connection, and you should budget for replacing the most exposed WAPs when they "take a hit for the team," but these are endpoint problems. I think that's a better tradeoff than providing electrically-conductive paths back into the network core, where we keep the largest concentration of expensive devices and the people that run them.

But that's me.
 
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Re: RB960PGS Grounding

Sun Dec 12, 2021 7:34 pm

If I had to put WAPs outdoors
This is not the problem I'm trying to solve. Say, there are two houses and I just want to place hEX in one house and cAP in another one. The connection is to be done with shielded CAT5e (buried about 0.5 meters underground). I'm just trying to avoid the lightning problems since there are trees around there. Actually, I just want the shielded cable to be grounded.
Last edited by thims on Sun Dec 12, 2021 7:41 pm, edited 1 time in total.
 
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Re: RB960PGS Grounding

Sun Dec 12, 2021 7:40 pm

Last post has an interesting link to read.
viewtopic.php?t=180885
Unfortunately, it describes these cases only:
● The shielded run is between two buildings that are on their own AC mains (meters), or have two or more different subpanels that are separately earth grounded.
● The shielded run is inside the same building that has multiple AC subpanels (a great example is a factory), and these subpanels are using different grounds.
● The shielded run goes to a WiFi AP or camera outside, and there is a lightning protector involved that uses its own ground point. Then that same run is grounded yet again to the AC ground inside your house/building.

It looks like none of these are mine. In my case I have hEX PoE in one building and the cAP in another connected with CAT5e shielded outdoor cable only to hEX. This i why I want to ground the hEX device.

If you're hoping a little 24-gauge ground lug will arrest lighting, for instance, you're dreaming.
This makes sence.
 
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Re: RB960PGS Grounding

Sun Dec 12, 2021 7:53 pm

Actually, I just want the shielded cable to be grounded.
It looks like I'm stupid and this is the answer ;) Do I just need to ground the cable's shield separately on either side and that's it?
 
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Re: RB960PGS Grounding

Sun Dec 12, 2021 8:16 pm

there are two houses and I just want to place hEX in one house and cAP in another one.

All right, in that case what's most likely to happen is that one circuit in one house is hit — never mind how — and the resulting surge couples through that cable to another circuit in the other house. The cable itself and the conduit are extremely unlikely to be the direct-hit path, being too close to the ground even where they come up to go through the walls.

So I'd still go with fiber.

That rules out the cAP, but I don't see anything else I like that does have fiber on the MikroTik side. The RB2011UiAS-2HnD-IN is too old tech-wise, and the RB4011iGS+5HacQ2HnD-IN is ridiculously overpowered. If I had $250 to spend on wireless equipment in the second house, I'd slice off $49-69 for a hEX or RB260 class fiber switch and put the rest into a mesh system from another company. That gets you RouterOS power with solid consumer-grade WiFi.

I just want the shielded cable to be grounded.

That's what the EE.SE answer is trying to get across: the Ethernet magnetics mean you don't need grounding if the isolation level suffices for your use cases.

There's a metal shield around the ports on the hEX PoE, and I was hoping it was electrically connected to the DC barrel plug's outer "ground" connector, allowing the wall wart to be this ground path you're wanting, assuming the Cat-5e cable shield (STP) is connected to it, but alas, it isn't so. (Just measured it.)

The SFP cage is so-connected, oddly enough.

Do I just need to ground the cable's shield separately on either side and that's it?

If my shield test above showed that it was already done, it would be redundant, but instead what it shows is that by doing so you're connecting two different "grounds", which can be dangerous.

So no, don't do that!
 
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Re: RB960PGS Grounding

Sun Dec 12, 2021 8:33 pm

So no, don't do that!
Thank you so much for all the answers!

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