Hello John, The heat dissipation should be calculated from measurements, not from maximum ratings. It is most common for the input into the equipment to be -52.6 VDC as this is the standard float voltage in C.O.'s. It probably is not a big deal if you use -48 VDC, you will just have higher current. You must also subtract any power that is dissipated in OSP cables, and remote equipment such as phones, span powered remotes, etc. You must also add in any power that may be dissipated by the equipment that comes from other equipment on telecom or other types of ports. An example is an FXO card which sinks current from an FXS or other POTS line. Another example is sealing current, if your equipment "sinks" sealing current on an interface such as ISDN, DDS, T1, HDSL, etc., you need to add it to your equipment's heat dissipation. Remember that if you "source" sealing current or span power, you need to subtract the power sent to other equipment, it is dissipated elsewhere such as remotely or in the footprint of other equipment in the C.O.
POTS interfaces can be tricky though as the power dissipated in each interface can vary radically with its on-hook/off-hook state (almost 0 watts on-hook, and .5 to a couple watts off-hook). If you are testing FXO's, you also can have drastic differences if the POTS interface feeding it is a constant voltage (old step x step switch or older FXS) or a constant current (newer electronic switch, PBX, FXS's, etc.). Taking all the ports off-hook at the same time will give you a worst case scenario, but that is rarely representative of reality. Most customers can provide you with the CCS number that you need to use. The CCS number helps you determine the percentage of off hook/ringing/active POTS lines at any given time. We have seen typically that range to be 17% to 50%. We typically have the labs make the calculations at 17%, 50%, and 100%, this way the end customer can interpolate the heat dissipation based on typical loads. I believe all customers allow you to assume constant current switches, FXS's, PBX's now. For non-POTS interfaces and equipment the calculations are typically much easier as the wattage does not vary much with load. One technology to be careful of is ADSL though. It varies substantially with cable length and whether it is trained (sync'd) with a remote or not trained. Most other DSL's have the same or similar heat dissipation even if not sync'd. Good Luck, Jim Jim Wiese NEBS Project Manager/Compliance Engineer ADTRAN, INC. 901 Explorer Blvd. P.O. Box 140000 Huntsville, AL 35814-4000 256-963-8431 256-963-8250 fax jim.wi...@adtran.com -----Original Message----- From: John Loiselle [mailto:jloise...@integralaccess.com] Sent: Monday, October 14, 2002 8:48 AM To: nebs@world.std.com Subject: Equipment Area Heat Release Objective Hello, I am requesting information to help me obtain a better understanding of the requirements called out in GR-63, 4.1.4, R4-11, O4-12, O4-13, and Table 4-6. I have a "shelf" equipment configuration with the following Assumptions noted in the report: Rack depth (Rd) is 1 ft. Rack width (Rw) is 2.17ft. Maintenance aisle depth (Md) is 2.5 ft. Wiring aisle depth (Wd) is 2 ft. Height of equipment is 2ft. Maximum operating voltage (V) is 48VDC. Maximum operating current (A) is 23.4. My report states that I do not conform to O4-12. The calculated Heat Dissipation was 80W/ft2/ft (2790W/m2/m). Since more than half the current draw is derived from POTS (all phones being off hook at the same time), I am curious if the 23.4A is the correct number to use for this calculation. It appears that the heat would not be dissipated inside the enclosure but at the other end of the cable (phone?). When I see various TDM enclosures, they are physically smaller and the port density is greater. How are these enclosures allowed to fill a rack in one bay? Is there allowances taken for POTS configurations? Thanks. Regards, John Loiselle Regulatory Compliance Integral Access, Inc. ph (978) 367 7585
