ADSL modem power connector

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furpile

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Hi. I am trying to set up a 12v DC ups for my modem. What is the purpose for the network cable to pass through the power adapter? Is this for lightning protection?

Will the modem be safe without the network cable going through the adapter?
 
Yes it is for surge protection.

It is difficult to say, but you can use it without the power connector plugged in as usually there are MOVs in there which would work with it off. What modem do you have?
 
Wasabee! said:
Yes it is for surge protection.

It is difficult to say, but you can use it without the power connector plugged in as usually there are MOVs in there which would work with it off. What modem do you have?
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It's the standard Telkom Netgear N300 modem.
 
It's probably worth leaving the phone line to run through the power brick, even if you are not using it (so long as it is plugged in to the wall), so that any surges on the phone line can get diverted to the mains ground, and not destroy your modem.
 
RoganDawes said:
It's probably worth leaving the phone line to run through the power brick, even if you are not using it (so long as it is plugged in to the wall), so that any surges on the phone line can get diverted to the mains ground, and not destroy your modem.
Click to expand...

What type of surges do you get on the phone line? Mainly lightning or what? I have seen many installation guides for different modems and many do not have this on the power adapter. I am trying to run the modem off a 12V DC UPS, so I won't be using the power adapter anymore. Our phone lines are underground so lightning is not an issue.
 
Yes, lightning surges. Keep in mind that the surge can be induced in the wiring by a strike some distance away, so if the lines are overhead at any point, it may be better to be safe than sorry.

From http://www.netshieldsa.com/briefs/Surge%20protection.pdf

More common is the induced surge on a buried cable. In one test, lightning-induced
voltages caused by strokes in ground flashes at distances of about 5 km were
measured at both ends of an unenergized power distribution line.
Click to expand...
 
RoganDawes said:
Yes, lightning surges. Keep in mind that the surge can be induced in the wiring by a strike some distance away, so if the lines are overhead at any point, it may be better to be safe than sorry.

From http://www.netshieldsa.com/briefs/Surge%20protection.pdf
Click to expand...

OK thanks. Our entire town's power lines are underground, haven't seen any overhead lines anywhere close to us. might leave the power adapter plugged in just for the network cable, and hopefully there isn't any lightning during load shedding :)
 
Well, it is only the live that is disconnected during load shedding, the earth goes directly to your building ground, and should always be connected.

The example mentioned a surge measured in a buried power cable (that happened to be disconnected at both ends), but there is nothing to suggest that it cannot happen with a buried phone line either. It is just a metal conductor, after all. I quoted that to show that the fact that it was buried was irrelevant, you could still get a current induced in it, which could destroy your modem.
 
RoganDawes said:
... but there is nothing to suggest that it cannot happen with a buried phone line either.
Click to expand...
Happened a couple of years back in our area and PE's not noted for lightning strikes, lightning hit a double storey and damaged a Telkom underground feeder. Took the cable guys a few weeks to sort out as there were no manholes along the 500m stretch of road, grass verges and driveways were a mess while they were busy.
 
MickZA said:
Happened a couple of years back in our area and PE's not noted for lightning strikes, lightning hit a double storey and damaged a Telkom underground feeder. Took the cable guys a few weeks to sort out as there were no manholes along the 500m stretch of road, grass verges and driveways were a mess while they were busy.
Click to expand...

Good to know my paranoia is not misplaced :-)
 
RoganDawes said:
Well, it is only the live that is disconnected during load shedding, the earth goes directly to your building ground, and should always be connected.

The example mentioned a surge measured in a buried power cable (that happened to be disconnected at both ends), but there is nothing to suggest that it cannot happen with a buried phone line either. It is just a metal conductor, after all. I quoted that to show that the fact that it was buried was irrelevant, you could still get a current induced in it, which could destroy your modem.
Click to expand...

But will the switching of the overload protection still work with live off? I read your link, hence why I said I will then still leave the phone line plugged into the power adapter. Thanks for your input.
 
furpile said:
But will the switching of the overload protection still work with live off? I read your link, hence why I said I will then still leave the phone line plugged into the power adapter. Thanks for your input.
Click to expand...

The protection is usually passive and does not require power.
 
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