TNV 1才是属于SELV
引用第20楼xuming0120于2011-05-12 12:06发表的:
TNV 1才是属于SELV
这位同学，纠正一下，TNV1不一定是SELV，好好的看一下950里面的Table 1A.
TNV-1不是SELV，只是正常情况下的电压不会超过SELV的限值
看来这个问题无解啊，不过大家倾向分为三类设备，我也有底气跟领导理论了，哈哈
版主啊看在我提出了这样一个好问题的份上 强烈建议给威望！！！
参考PAG clause 2.10.2-3 Working voltages in TNV circuits
If the equipment generates a ringing signal and the circuit connects to a Telecommunication
Network, the working voltage should be measured in accordance with sub-clause 2.10.4 and
Annex M.3.1 to determine maximum peak, rms and/or dc values.
If the equipment is intended for connection to a U.S./Canadian Telecommunication Network and
receives incoming analog telecommunication signals (e.g., from a Central Office), the following
maximum working voltages (TNV-3) should be assumed for purposes of determining required
clearances, creepage distances and electric strength test values:
a. peak: 200 V
b. rms: 120 V
c. d.c.: 60 V
176 PAG 60950-1 JULY 15, 2008
If the equipment is intended for connection to a European Telecommunication Network, consult
with IEC TR 62102, Technical Report on Electrical Safety Classification of interfaces for
equipment to be connected to information and communications technology networks.
The peak and rms values are used for clearance and electric strength determinations, and the
d.c. value is used for creepage distance.
RATIONALE:
Annex M (normative) describes maximum voltage levels associated with Telecommunication
Signals that comply with FCC Part 68. The maximum peak value specified is 200 V referenced
to earth. Since working voltages typically are measured to earth, this value should be considered
the maximum peak value in the U.S. and Canada.
Although Annex M does not contain a corresponding rms value, 120 V rms is an approximation
of a composite 56.5 V dc and 300 Vp-p signal. Sub-clause 2.3.5 uses 120 V rms to simulate
externally generated operating voltages. Therefore this value should be used for investigation to
this Standard. Also, sub-clause 2.10.4 indicates that cadenced ringing signals in TNV circuits
shall not be taken into account for determining creepage distances, thus a 60 Vd.c. value may
be used.
根据class III equipment定义的条款
1.2.4.3 CLASS III EQUIPMENT: equipment in which protection against electric shock relies upon
supply from SELV CIRCUITS and in which HAZARDOUS VOLTAGES are not generated
NOTE For CLASS III EQUIPMENT, although there is no requirement for protection against electric shock, all other requirements of the standard apply.
我认为应属TNV-3的设备也应属CLASS III，因为其只是接受来自上游的Ring singal，不是自己内部产生。
欢迎拍砖
引用第24楼包子于2011-05-17 22:24发表的:
参考PAG clause 2.10.2-3 Working voltages in TNV circuits
If the equipment generates a ringing signal and the circuit connects to a Telecommunication
Network, the working voltage should be measured in accordance with sub-clause 2.10.4 and
Annex M.3.1 to determine maximum peak, rms and/or dc values.
If the equipment is intended for connection to a U.S./Canadian Telecommunication Network and
.......
TNV-3是正常工作的电压超过了SELV，怎么可能是SELV供电呢？
直接接电话线的电话机应该是不分类的，不是class I, 不是class II, 也不是class III
标准也没有说IT产品一定要属于其中一种吧？
没有带ADAPTER的电话机，如果使用TNV-3端口，可以不分类。也就是说不属于CLASS I, II 和 III的任意一种。带了ADAPTER供电就跟适配器来分类。
不用判断属于几类！
我认为 电话机定义为三类产品最合适.没见过电话机打回字标签的.现在有好多产品都很难定义为哪一类产品,比如照相机,电池供电,虽然照相机是低电压供电,但是在使用闪光灯的时候,聚集的电压会很大远远超过安全电压.
郁闷 被十五天了
