Span powered means that a DC voltage and current are used to provide powering to a device at the customer end or to a mid span repeater. T1, E1, DDS, HDSL, and ISDN all have devices which are sometimes used by the Telcos to extend or terminate these services. These devices typically (but not always) are powered by the telco network. Non-span powered simply means that the loop is dry (no DC component) or has -48V DC provided from the central office for use as "sealing current" (this is typical for ISDN). In these cases, there are no repeaters or active terminating devices at the customer premise. Since ISDN basic rate in the US is a 2B1Q signal sent over 2 wires, the voltage is measured from tip to ring. The voltage is typically <-1 VDC from tip to ground, and -48 VDC from ring to ground. Voltages in the telco industry are almost always negative with respect to ground. This slows the corrosion process of the outside plant cabling, especially in areas with high ground currents. Bellcore GR-1089-CORE section 8 addresses this issue.
T1, E1, DDS and HDSL use 4 wires to transmit phantom/span powering or -48VDC sealing current. The voltage appears from the tip/ring pair to the tip1/ring1 pair. T1, E1 and DDS can also be dry. I believe that HDSL always has span powering or sealing current. Hopefully this answers your questions. Jim ---------- From: treg-approval To: treg Subject: RE: ISDN and T1 maximum voltage List-Post: [email protected] Date: Wednesday, September 18, 1996 1:18PM Jim - what does span and non-span mean? I know that in analog telephone, DC feed is across a twisted pair, and in ISDN, T1, they typically use phantom power across the center taps of tx, and rvc transformers which uses 2 twisted pair. Victor At 01:01 PM 9/18/96 PDT, you wrote: > >Try section 7 of Bellcore GR-1089-CORE. It allows as much as 200 VDC from >tip or ring to ground provided that the current when measured tip to ground >or ring to ground does not exceed 10 mA (Class A3). In reality, vendors of >central office ISDN typically generate -48VDC 10-20 mA DC for non-span >powered circuits, and <-140VDC <135mA DC for span powered circuits. T1 can >typically be dry (no DC voltage), -48VDC, or -130/+130 VDC with respect to >ground (repeater powering). I am sure there are multiple other schemes, but >this is what I am familiar with. > >Jim > ---------- >From: treg-approval >To: treg >Subject: ISDN and T1 maximum voltage >Date: Wednesday, September 18, 1996 9:06AM > > > >Subject: ISDN and T1 maximum voltage > > >Hello fellow TREG'ers, > >One of my colleagues asked me the following questions and I was unable to >provide an answer. I >would welcome any help from some one who knows. > >The question is what is the maximum voltage and current I can expect >to get out of a T1 or ISDN line. > >I know the power isn't very high normally, but how much can the max be? >I couldn't find an upper limit. References to the correct standards >would be nice. > >Thanks, > > >Dan Teninty P.E. >Senior Design Engineer >Product Safety >[email protected] >FLUKE Corporation >Everett, Washington >(206) 356-6035 >(206) 356-6490 fax > > > > > > >
