Re: Could a telephone line damage a modem ?
- From: Jim <me2@xxxxxxxxxxx>
- Date: Mon, 03 Oct 2005 14:11:34 +0100
Peter Crosland wrote:
Before one can learn why modems are damaged and how to avoid damage, first, one must establish some well proven principles.
Electricity means a complete circuit. That means electricity must first have an incoming and outgoing path through each device in a circuit. Myths would have you believe a surge enters on phone line, damages a modem, then stops. Reality - first a transient forms a complete circuit through that modem. Only later does something in that circuit fail.
An excellent exposition that is most welcome. I have printed it off for future reference. Thank you!
Peter Crosland
Another reference at "old faithful" http://web.ukonline.co.uk/freshwater/lightng.htm
According to this, the GPO stopped installing lightning protection on subscriber premises because it was cheaper to replace damaged equipment. Of course, in those days the terminal belonged to them, whereas now it's the customer who literally "takes the hit".
I don't know if BT will actually install an earth wire on request, but there is an earth terminal on their side of the Master Socket. The link above recommends wiring this to a suitable earth point and uprating the discharge tube, but not many customers would be up to this and it would be against BT regs. anyway.
Most commercial lightning protection is designed for multi-line business installations rather than single lines. This item might provide decent protection. It would cost more than a few modems, but maybe less than the cost of frequent replacement:
Keison Products Plug-in protectors for telephone lines
http://www.keison.co.uk/acatalog/Catalogue_Index_Plug_in_protectors_for_telephone_lines_5.html
This DIY version carries a health warning! Do not view if easily shocked. :)
http://www.satcure.co.uk/tech/phonesurge.htm
.
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