IEC 60950-21:2002 pdf download

IEC 60950-21:2002 pdf download.lnformation technology equipment-safety – Part 21: Remote power feeding.
4 General requirements
4.1 Power from a telecommunication network (see also 1.4.11 of IEC 60950-1)
RFT CIRCUITS normally exceed the limit in 2.3.1 b) of IEC 60950-1 and also exceed 15 VA.
See 4.7.2 of IEC 60950-1 regarding the possible need for a FIRE ENCLOSURE.
4.2 Access to energized parts (see also 2.1.1.1 of IEC 60950-1)
The equipment shall be so constructed that, in OPERATOR ACCESS AREAS, there is adequate protection against contact with bare parts of RFT CIRCUITS.
These requirements apply for all positions of the equipment when it is wired and operated as in normal use.
Protection shall be achieved by insulation or by guarding or by the use of interlocks. Compliance is checked as given in 2.1.1.1 of IEC 60950-1.
4.3 Protection in service access areas (see also 2.1.2 of IEC 60950-1)
In a SERVICE ACCESS AREA, bare parts of RFT CIRCUITS shall be located or guarded so that accidental shorting to SELV CIRCUITS or to TNV CIRCUITS, for example, by TOOLS or test probes used by SERVICE PERSONS, is unlikely.
Bare parts of RFT CIRCUITS that involve an energy hazard shall be located or guarded so that unintentional bridging by conductive materials that might be present is unlikely during service operations involving other parts of the equipment.
Any guards required for compliance with 4.3 shall be easily removable and replaceable if removal is necessary for servicing.
Compliance is checked by inspection and measurement. In deciding whether or not unintentional contact is likely, account is taken of the way a SERVICE PERSON needs to gain access past, or near to, the bare parts in order to service other parts.
4.4 Protection in restricted access locations (see also 2.1.3 of IEC 60950-1)
For equipment to be installed in a RESTRICTED ACCESS LOCATION, the requirements for
OPERATOR ACCESS AREAS apply, except that contact is permitted with the bare parts of an RFT
CIRCUIT by the test finger shown in Figure 2A of IEC 60950-1 (see 2.1.1.1 of IEC 60950-1);
however, such parts shall be so located or guarded that unintentional contact is unlikely.
Compliance is checked by inspection and measurement. In deciding whether or not unintentional contact is likely, account is taken of the need to gain access past, or near to, the bare parts.
4.5 Interconnection of equipment
4.5.1 General requirements (see also 3.5.1 of IEC 60950-1)
Interconnection circuits shall be selected to provide continued conformance to the requirements of Clause 6 for RFT CIRCUITS, after making connections.
NOTE It is permitted for an INTERCONNECTING CABLE to contain more than one type of CIRCUIT (for example, SELV, LIMITED CURRENT, TNV, ELV, RFT, or HAZARDOUS VOLTAGE) provided that they are separated as required by IEC 60950-1 and this standard.
4.5.2 Interconnection between RFT circuits (see also 3.5.2 of IEC 60950-1)
RFT-C CIRCUITS in the supply equipment shall be connected only to RFT-C CIRCUITS in other equipment.
RFT-V CIRCUITS in the supply equipment shall be connected only to RFT-V CIRCUITS in other equipment.
For compliance, see 6.4 e).
5 Connection to telecommunication networks
An RFT CIRCUIT is permitted to be directly connected to a TELECOMMUNICATION NETWORK.
6 Remote power feeding
Access to the conductors of the REMOTE FEEDING TELECOMMUNICATION CIRCUIT is restricted to SERVICE PERSONS.
NOTE Clause 6 covers power feeding to remote equipment at voltages in excess of the voltage limits for TNV CIRCUITS. There are two types of circuits as follows:
— RFT-C CIRCUITS provide for safety by limiting the current to 60 mA d.c. and are presently used in Europe;
— RFT-V CIRCUITS provide for safety by limiting the voltage to 200 V d.c. and currents to the same limits as in 6.3 of IEC 60950-1, and are presently used in North America,
See Annex A.
6.1 RFT-C circuit limits
NOTE Unless the current limits in 6.1.1, 6.1.2 and 6.1.3 are inherently met, the RFT-C CIRCUIT should have a monitoring and control device (for example, a balance control), that operates in such a way as to maintain the required current limits.