Don't kill the moderator. Please note who messages originate from within
the message. When non-members (or non-listed email addresses) post to
treg I have to manually approve them and this results in them being
branded with my email address. While I'd love to take the credit for well
thought out treg postings it is more appropriate that the actual authors
receive the accolades (or blame).
Jon D. Curtis, PE
Curtis-Straus LLC [email protected]
One-Stop Laboratory for EMC, Product Safety and Telecom
527 Great Road voice (508) 486-8880
Littleton, MA 01460 fax (508) 486-8828
http://world.std.com/~csweb
On Fri, 13 Dec 1996, Doug McKean wrote:
> Jon D Curtis wrote:
>
> > Doug:
> > At least in Spain, public switching telephonic network works with 48 V =
> > dc but the ringing signal could reach 75 V ac (hazardous voltage =
> > according to LVD). In fact, if you catch both poles of a telephone line =
> > during the ringing process, you will suffer that voltage. So for that =
> > reason, LVD applies.
>
> Gee, I hate to disagree with you Jon.
>
> I'm not supporting the argument I'm presenting. It was used
> by a former boss to a great extent. More like a little
> knowledge is a bad thing, especially when marketing gets a
> hold of something like this. It was a battle.
>
> The ring signal of which you speak is in what I've known
> as the 'local loop' between [I believe] a Class 5 office
> [last in line before the subscriber] and the subscriber on
> the analog line. The ring signal is handled *sometimes*
> [because I'm not 100% sure] by a *channel bank*. There are
> analog and digital channel banks. Some that I'm familiar
> with control the interface between the T1 line and the
> ring voltages out to the subscriber. A T1 line by spec
> cannot handle the ring voltage.
>
> Now, if your product is a T1 IMUX device or a DCS device
> *behind* a channel bank, that is to say not on the
> subscriber side of the channel bank, the IMUX or DCS device
> handles only 48vdc power [and sometimes 24vdc] and the
> T1 signal levels.
>
> Now for Europe, substitute the above use of T1 with E1,
> remove the Bell term "Class 5 office", and the scenerio
> is very much the same. I would appreciate any corrections
> here.
>
> So the voltages handled by this E1 device are:
>
> a power supply of 48vdc and
>
> the signals as defined in G.703
>
> There are no voltages anywhere near the 75vdc lower
> limit of the LVD as defined in 73/23/EEC, Article 1.
>
> So, the conclusion could be any telco device powered
> by 48vdc and only handling E1 signalling is NOT
> covered by the LVD - 73/23/EEC.
>
> This same argument was used by my former boss to try
> circumventing UL testing, i.e. 48vdc being in the SELV
> and NOT a hazzard.
>
> I got him nailed on both T1 and E1 devices by pointing
> out that safety testing of a device is not solely dependent
> upon normal use voltages. It is used to test the device
> for overcurrent overtemp overvoltage abnormals, ground
> currents ... conditions for safe operation attested by an
> independent third party.
>
> Comments.
>
> ************************************************************
> ------------------------------------------------------------
> The comments and opinions stated herein are mine alone,
> and do not reflect those of my employer.
> ------------------------------------------------------------
> ************************************************************
>
