gate intercom makes hum on phone line

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acrwc10

acrwc10

Master Code Professional
Location
CA
Occupation
Building inspector
I am at a house that has an intercom at the gate that works through the phone system there is a constant hum on the phone line as long as the intercom is conected to the system. The company that did the original install has tried 1) running a new phone line to the gate over the ground to by pass the buried line. 2) they put a ground rod at the gate, this made no sense to me because the collums at the gate are large concrete pillars that make a solid earth ground connetion. 3)they changed the system from "Gate King" to a completely different brand. None of this did anything to help and the home owner is fed up with this to the point that they are just living with it. I said I would take a look at it on Tue. to see if I could figure it out. My thought is it maybe poor grounding on the phone side that back feeds into the gate when when connected. Any suggestions would be helpful''''''''Just not that it hums because it dosen't know the words""""
 
I'd say make it one ground, and a good connection at that. Sounds like that or one of two other things, mixed improper sevices in circuits, or an open short in a wire... (probably from the outside service to gate, AKA landscaper-guilty) Sounds like your a candiate for that Ideal tone -fault finder
 
I'd double check to make sure the phone system is bonded to the electrical GES at the house.

Beyond that...
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The entrance bridge might have taken a hit. I'd try replacing the entrance bridge. That usually cures it.

Just happened to think... did this ever work? If it never worked, I might suspect the cable between the entrance bridge and the call box. I might even swap out to a spare pair in that cable at both ends, in case there's a compromised pair. That cable might even have an open sheath, which would be pretty bad. Can you lift that cable at both ends and megger it out at 250 volts?
 
mdshunk said:
The entrance bridge might have taken a hit. I'd try replacing the entrance bridge. That usually cures it.

Just happened to think... did this ever work? If it never worked, I might suspect the cable between the entrance bridge and the call box.
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The intercom never worked without causing the hum on the phone line.
They did try running a completely new cat-5 cable across the yard to bypass the original cable and it still hums.
the fact that they replaced the controls at the gate makes me think it is external to the intercom/gate.
When you say "entrance bridge" are you talking about the phone company to customer bridge or something else ? We call the phone box that connects utility to customer the "SNI" or service network interface.
 
You could try removing the thing and walking it over to the SNI and connecting it directly. You could try disconnecting the power supply and feeding it from an alternative source (make sure to shut off the original supply circuit at the panel).
 
mdshunk said:
The entrance bridge I was talking about is the little surge suppressor most of these call boxes have for you to hook the end of your phone like to right before you terminate to the home's phone line.


For more hum troubleshooting help, check page 41 and beyond in this PDF:
http://www.dkaccess.com/English/Telephone_Entry/1812-065-M-3-07.pdf

Then look at this:
http://www.dkaccess.com/English/Telephone_Entry/1830-160-A-12-06.pdf
Click to expand...


That is alot of very useful info. I can see right off that some of the instrutions for installation were ignored by the installer. such as wire type for phoneline needing to be direct burial rated.

I'll let you know what eles I find.
 
The HUM is a result of an unbalance on a balnced system. In other words something is grounded that should not be. Look to see if there are any cable protectors like carbon blocks, gast Tubes ect connected to the talk pair and lift them out of the circuit temporarely.
 
acrwc10 said:
... Any suggestions would be helpful''''''''Just not that it hums because it dosen't know the words""""
Click to expand...
Yeah, forgot to mention the manual ...:rolleyes:
 
This whole problem is because somebody didn't know what they were doing and shouldn't have been doing it. I hear no mention of the "phone system" in the house or how the gate phone is connected to it. Lets hear about it- what is it and how does the gate phone connect to it.

-Hal
 
sentex system

sentex system

The "Door king" system was changed to a "syntex system" , I read through the manual for the Door king since that is what was installed originally. One of the first things it says in the installation instructions is " if the phone line between the gate and the house is underground in conduit use burial rated line." and it specifies using Twisted pair. Seems reasonable to me. I guess the guys who installed it didn't think it important, They used regular alarm wire "Shielded" although the shielding is not grounded to anything. I haven't gotten to far into trouble shooting it as I had many other things higher on the list.
I am going back tomorrow and will post some pictures of how it is run. It ain't pretty.
 
So this is one of the issues. three #12ccc ,blk,red,blu,for the lights on the collums in the same 3/4'' pvc with the cable type "E184061 (UL) CM or CL3 device" this cable is carrying 12 volt on one pair, the input phone line on the second pair ,and the output phone line one the third pair. the round trip for the phone line to and from the gate is about 550' to 600' . Most of the PVC is just under the serface of the ground.




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Is that cable they're using for phone even twisted? Could be as simple as that, if not twisted, might be induction.

That UL file number comes back to a hydromassage bathtub by Plastic Creations, so I think maybe you have a type-o there.
 
acrwc10 said:
"this cable is carrying 12 volt on one pair, the input phone line on the second pair ,and the output phone line one the third pair"
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As has already been mentioned the phone lines should be twisted pair. Also, the 12 volt should not be sharing the same cable as the communications. The length of the run also exacerbates the problem.
 
Last edited:
NOT Twisted

NOT Twisted

mdshunk said:
Is that cable they're using for phone even twisted? Could be as simple as that, if not twisted, might be induction.

That UL file number comes back to a hydromassage bathtub by Plastic Creations, so I think maybe you have a type-o there.
Click to expand...


No type-o that is right. If you look very close you should be able to read it right off the cable.

And yes it is not twisted pair on the phone line. And yes it is in the same cable as the power to the unit.

Me thinks the guy that put this in is not up to speed:rolleyes:
 
ike5547 said:
As has already been mentioned the phone lines should be twisted pair. Also, the 12 volt should not be sharing the same cable as the communications. The length of the run also exacerbates the problem.
Click to expand...

Phone lines should be on twisted pair, but it doesn't matter that much. Nor is putting 12vac on another pair going to do- remember the old princess phones? The AC dial lights were powered over the second pair. Length? My house phone is 35kft from the CO, it doesn't hum at all (but it does know the words).

What will cause massive hum on a phone line is a ground on the line (as mentioned previously, phones are balanced lines). Any ground any where. If the entry system is unintentionally connecting one lead of the real phone line to earth, that will unbalance the whole line and you get hum. (You can try this at home :D.) Simple check- pull all the connections from phone line to anything and try it with an old-style phone (one with a transformer in it, not an electronic thing). If it still hums, look for another ground on the line.
 
No doubt that this installation is using standard alarm or control-grade shielded cable. The pairs are not separately twisted and proximity to 120 volts AC WILL induce hum into them. In addition, the cable's shields aren't properly grounded or bonded together, so they are serving absolutely no purpose.

Lastly, these cables are not rated for underground installation. I challenge anyone to deny the fact that the conduits aren't completely filled with water at some point along the runs, if not the entire length. Let's see......Indoor-rated cable immersed in water. I'm sure that the cable has some degree of water penetration as well. That's more than likely causing the imbalance hum due to capacitance created by the water surrounding the conductors.

All three of these conditions are the cause for the problem being described. The only proper way to perform an installation like this is to use the proper cable (PE86 or better), the appropriate protectors and sheath bonding clamps.
 
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