300SS Problems

Hard to explain this weird issue I’m having.

If I use a surge supressor (300SS) during an installation of a 900MHz SM, the system fails to work. The computer, router, or switch fail to see the SM.

This isn’t the case with every installation though. I’ve tried various things to see if I was doing something wrong. They surge boxes are properly grounded, etc. I’ve looked at configurations on the SM for any clues, called technical support (but was referred to my local electrician).

I’m up for any ideas on what could be causing this. I’ve compared installations sites that are successful with the 300SS with the installation sites that have failed.

All I have to do is simply bypass the 300SS and everything works. It’s like the unit is constantly being triggered by a surge or something…so I figured I’d test out ground stakes and bypass other means of grounding. That was unsuccessful… So I have a box of a few hundred 300SS sitting here. Along with some other surge supressors from a different vendor. I ran an ethernet tester against the 300SS and a different vendor surge supressor. Other vendor comes up pinned straight thru. Motorola 300SS comes up 123xx6xx. 45, 78 crossed.

If anyone has any clues as to what I could try to do, or what I’m doing incorrectly, it would be extremely appreciated. I’m failing to install at this point due to this problem, which is a big setback.



I had the same problem with a customer. Customer worked fine so I grounded and retested and no service. After several 300’s I just started swapping circuit boards. Each time going thru the 300 I had no service. Bypassing it with a coupler solved the problem. Eventually, after a partner came with me it miraclously started worked as intended (grounded).

Moto tech support only suggested that the house had grounding problems. The customer has worked well since but it was very frustrating.

The last 4 client installations with the 300SS have gone without problem.

I guess it’s a hit & miss. Nothing was done differently. Who knows at this point…

Did a few installs yesterday…50% success rate with the 300SS. Going to do some extensive testing in the office today to hopefully find out why this is happening to me.

Very frustrating. :evil:

We had a tower site like that, When we hooked up the ground to the 300SS the link stoped working, we found that it was a noisey ground in the building causeing all the problems. Perhaps it’s the same thing at your end. Just an idea.

The building ground is indeed the problem. The resistance to ground at the outlet, and the resistance to ground on your newly installed SS is different. The only solution is for the customer to have their ground system corrected by an electrician.

This poses a bit of a dilemma, doesn’t it?

If you don’t use the SS due to a customers poor ground, you are opening up the potential for the radio to take a spike either induced onto the cable or back up through the customer’s computer or router. If a fire starts because you did not use an SS, a good attorney could find a way to make you liable.

So you tell the customer they need anywhere between several hundred and several thousand dollars worth of work to correct the problem with the grounding system. Like that’s going to happen.

So what do you do?

Depending on your local code, the customer may be able to have an electrician add or replace a ground to the outlet that the PC, radio, and router are connected to. Ideally this would be the same ground point as the SS.

Contact Moto and ask this question: What is the acceptable variance of the resistance from ground to outlet and from ground to SS. I am guessing the number is pretty small like .2 ohms. You can try using a circuit tester to check the outlet, but I don’t think they are sensitive enough to detect anything lower than about one ohm.

Find a good electrician to partner with. Tell them your situation, that you might need a single outlet grounded from time to time, and ask how you can test the outlet to determine if it needs to be corrected. This way when it needs to be done you have a resource for your customer so they don’t have to call around.

Some links that might help you:
http://www.mikeholt.com/code_forum/arch … 57170.html
http://www.acmehowto.com/howto/homemain … unding.php

I am fortunate in that we live in an area where lightning in general is pretty rare, and ground strikes are extremely rare. I think that If I did, I would push back on the customer to fix the grounding rather than open myself up for liability.

NOTE: The above information is for informational purposes. Before doing any electrical work, consult the NEC as well as your local Electrical Code, and have any and all work performed by a licensed, insure, and bonded Electrical Contractor.

i would have thought that local utilities are responsible for the ground rod since they bring the power to the building. is the ground rod the contractors job?

I’m referring to the ground from the outlet to the house ground which may be a rod, (or less likeley in a high lightning strike area it’s bonded to the neutral and grounded somewhere further up the grid.)

Most likely the ground to the house’s service panel is OK. It’s the connections from the service panel or sub panels to the outlets that tend to oxidize and increase resistance. Less that 2 ohms is still safe-ish, but may be too high compared to your new .15 ohm ground for your SS.

So, if the ground from the outlet to the house’s service ground is flaky and is causing your SS to not work, it needs to be corrected. That should not be your problem.

Thank you very much Jerry. I’m going to look into this further and consult a local electrician that I happen to know well. Maybe he will come out with me to a problem location and help me determine if the grounding is improper.

I’ll keep you updated on my findings as soon as I get some time.

Thanks again to everyone responding,



That sounds feasible but our power supplies don’t have ground lugs on them so how can it reference ground when there isn’t one? I’ve been thinking pretty heavily about this and just trying to get some things straight.

The Power supply is ACPS110-03A.

I’m just confused by if it were to be because of grounding then why would if I didn’t use a SS and just coupled, it worked…and if I used an SS it didn’t work.

Is there some spike or something of that nature that is causing the SS to do what it’s doing?

I’ve got power to the radio with a bad SS, it’s just that ethernet isn’t working, as power is.

I’ve contacted a friend at our local electric company and am awaiting a response.

Thanks again Jerry,


Even if the router is ungrounded as most are, it still has a ground reference provided by the neutral which is bonded to Earth somewhere up the supply line - it could be at the service panel, or a transformer up the street.

But, the issue is not the radio power supply as we are only concerned with the data pins 1, 2, 3, 6. The power supply does not touch those pins, they are passed through from the radio to the computer or router.

Take a look at this:

As you can see, the surge suppressor directly affects the data pins. Therefore it stands to reason that the Ethernet jack in the computer that is plugged into the wall would have a ground reference that is different from the ground reference provided to the radio by the SS.

This difference in ground potential is a ground loop, In Audio it reveals as hum or white noise and in video it reveals as rolling lines or “hum bars”. With the very small voltages on the Ethernet Data it reveals as no link.

Most Electricians will have never even heard of such a thing unless they have installed data center, medical, scientific, studio, or broadcast power systems.

It occurred to me that you might be able to test this by temporarily jumping a piece of #10 wire from a metal screw on the case of the PC or the screw on the cover plate of the outlet to to your SS ground lug. This should pull the ground references for the PC and the SS to the same point.

Ok, it’s alive again. Sorry, but I figured I’d let you know what I discovered today.

Typical install for me.

40’ TV Antenna through basement up a level to the computer center.

Cables tested OK.

No ethernet connection on computer again! This time I decided to run a test. I took a 100’ ethernet cable and ran it from the 300SS to the radio at the top of the TV antenna…it worked grounded!

So, I sat there dumbfounded. I have no idea why the original cable does not work. It passes ethernet testers & is terminated properly.

Decided to cut & run another ethernet line through same path original cable was installed. The new one worked! d’oh!!

I am really lost at why I’m having such great issues with this.

I tested the old cable with a coupler (bypassing 300SS) and it worked. Left it alone for awhile to determine if there were ether. errors; none!

Figured I’d update on my neverending problems.

I grounded the SS to the subpanel in the basement, btw.