Phone and electrical share a box??

Reply

  #1  
Old 01-05-03, 06:29 AM
E
exeter_acres
Visiting Guest
Posts: n/a
Phone and electrical share a box??

Just curious... in the kitchen could a phone line and a 20amp GFCI outlet share the same receptical box (plastic) or would there be interference....
Or shoule they be in their own boxes?

Thanks
Curtis
 
Sponsored Links
  #2  
Old 01-05-03, 08:19 AM
J
Member
Join Date: Sep 2000
Location: United States
Posts: 18,497
Received 0 Votes on 0 Posts
It's not allowed by code for safety reasons. And it's a bad idea for the interference reasons you mention. How much interference would depend on how much current flows through the electrical wire, how much and how often the current flow changes, what kind of phone wire you are using (bell wire/cat3/cat5/cat5e/cat6), and what kind of signals (voice/fax/modem/DSL) you are sending.

Bottom line: don't.
 
  #3  
Old 01-05-03, 05:22 PM
B
brickeyee
Visiting Guest
Posts: n/a
Boxes with dividers to create two boxes are available.
 
  #4  
Old 01-05-03, 05:39 PM
R
RayII
Visiting Guest
Posts: n/a
Not a good idea to have phone lines in the vicinity of conduit. I worked for an electrical company for years, and we never even ran a phone line through the same hole as romex for rough ins. If we could avoid it, we also didn't run phone line down the same stud as romex.

The reason is simple. Moving power creates a magnetic field that causes a degradation of the flow in DC lines. As for safety, I am not too sure about that. I can't think of anything that would make it unsafe, but I would avoid it altogether.
 
  #5  
Old 01-06-03, 09:34 AM
B
brickeyee
Visiting Guest
Posts: n/a
"degradation of the flow in DC lines"
Never heard EMI (electro magnetic interferance) called a degradation of the flow. It causes coupling of the 60 Hz into the phone line. The phone system has a lot of filtering to try and eliminate this. If you couple it in the house wiring then only the phone itself is reducing the noise. The twisting of the phone wires used in modern wiring goes a long way to reducing this problem. Most of the interferance that gets through is caused by switching transients. Every switch causes an arc when operated and creates EMI. The joke about noise from 'DC to daylight' is really there with an arc. In the phone handset you may hear it as a click. If the only place where the phone and power where close was in a divided box not much will couple. Probably about the same as putting two boxes side by side. Cat5 and other communication wires should be kept away from the power if you want to get high speed signals through them. But again it is not the 60 Hz that causes the problem, but the transients from switching.
 
  #6  
Old 01-07-03, 02:58 AM
P
Phonetek
Visiting Guest
Posts: n/a
Wiring telephone side by side to electric is not the best idea in the world. Granted it will not cause your telephone line not to work but your performance will be degraded. You WILL hear a hum on your line however. Sheilded twisted pair cable would help eliminate this but not 100%. Especially if you are using a line for a modem your asking for latency problems and slower connections. God only knows dial up connections can be slow enough due to the variety of other issues such as distance from the Central Office and such. If you absolutely are dead set on running your electric and telephone to the same box you can do it but why ask for problems? Putting a jack in its own box just a few inches away will go a long way towards not degrading the quality. Hope this helps!
 
  #7  
Old 01-07-03, 04:48 AM
R
RickJ6956
Visiting Guest
Posts: n/a
Although phone lines have some DC voltage, the signal itself is AC. Interference from a nearby electrical line can cause all kinds of problems with the AC portion of the phone line. Inductance can add "stray" voltage to the phone line and EM interference can adversely affect the sound quality. Inductance is mostly caused by parallel runs of electrical and phone. Induced voltage can cause phase cancellations of the audio signal. The main culprits for EMI are the brushes in electric motors. They add noise. Although not as common, Radio Frequency (RF) interference may also result from the induced voltage's phase differential. In effect, it can turn your telco line into an antenna.

It's really not a good idea to run high voltage and low voltage lines together.

Telco twisted-pair lines offer "common-mode rejection," meaning that any signal that hits the "in-phase" side of the pair will also hit the "out-of-phase" side. Any interference that is common to both sides will cancel out. It's very effective to a point, but that point may be crossed in extreme conditions such as parallel runs with electrical wires.

Phone lines should always cross electrical lines at right angles, and should be kept well away from transformers and fluorescent ballasts.
 
  #8  
Old 01-07-03, 06:23 PM
P
Phonetek
Visiting Guest
Posts: n/a
Telephone lines are -48 volts DC (talk battery)
5.1 volts DC (While talking)
96 volts AC (when ringing)

These are typical readings on a POTS line that I tend to see. They can vary depending on the equipment originating from and terminating to, also with the quality of the pair.
 
  #9  
Old 01-08-03, 04:33 AM
M
Member
Join Date: Dec 2000
Posts: 510
Received 0 Votes on 0 Posts
The actual signal of interest (the voice signal) is an AC signal with content up to 4 kHz. The voltage of this signal can be quite low compared to the DC on-hook/off-hook voltages and the AC ring voltage. The interference is with these low-level audio signals, not with the higher DC voltages. It does not take much interference to affect the voice signal; since modems encode data into the voice signal, they are particularly susceptable to such interference.

FYI, the purpose of the -48V is to provide power for your telephone (it can vary quite a lot - I believe it is -48V at the central office, but can drop quite a bit over a few miles of wire - this is why the voltage is lower when the receiver is picked up and the phone is drawing current). The 96V AC triggers the ringer in your phone (remember old phones with electromechanical ringers?).
 
  #10  
Old 01-08-03, 07:16 AM
R
RickJ6956
Visiting Guest
Posts: n/a
Phonetek,
I should have been more detailed in my dismissal of the DC portion of the circuit. The DC voltage is not as susceptible to interference as is the AC signal.

As I recall, the AC voice signal is .775 volts RMS at 600 ohms. It doesn't take much to cause interference.
 
  #11  
Old 01-08-03, 06:44 PM
P
Phonetek
Visiting Guest
Posts: n/a
Actually Mike the -48 volts should not drop provided the pair and equipment is good. If that does drop due to distance this is why they use load coils to amplify it again. If you find that your talk batter voltage is lower than -44 you either have a problem or will. Maybe people will not be able to hear you when you talk or the other way around. Talk battery is the first thing that I measure when I go on a trouble, then check Ohms, AC and the others. Chances are if the talk batter is low the others are out of whack as well. Most of the time it is either a bad pair, bad channel card in the CO or CEV or a loose but not open connection or unbalanced pair. Usually the unbalanced pair you will most of the time get a nice blasting of AM radio and the background as it acts like an antenna.
 
Reply
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: