1、364-5-551IEC:1994-9NOTES1-Attention should be given to the size of individual loads as a proportion of the capacity of the generat-ing set and to motor starting currents.2 Attention should be given to the power factor specified for protective devices in the installation.3The installation of a genera
2、ting set within an existing building or installation may change the conditionsof external influence for the installation(see IEC 364-3-32),for example by the introduction of movingparts,parts at high temperature or by the presence of noxious gases,etc.551.3 Protection against both direct and Indirec
3、t contactAdditional requirements for extra-low voltage(ELV)systems which provide protectionagainst both direct and indirect contact and where the installation is supplied from morethan one source.551.3.1 Where a SELV of PELV system may be supplied by more than one source,therequirements of 411.1.2 o
4、f IEC 364-4-41 shall apply to each source.Where one or more ofthe sources is earthed,the requirements of 411.1.3 and 411.1.5 of IEC 364-4-41 for PELVsystems shall apply.If one or more of the sources does not meet the requirements of 411.1.2 of IEC 364-4-41,the system shall be treated as a FELV syste
5、m and the requirements of 411.3 of IEC 364-4-41shall apply.551.3.2 Where it is necessary to maintain the supply to an extra-low voltage systemfollowing the loss of one or more sources of supply,each source of supply or combinationof sources of supply which can operate independently of other sources
6、or combinationsshall be capable of supplying the intended load of the extra-low voltage system.Provisions shall be made so that the loss of low-voltage supply to an extra-low voltagesource does not lead to danger or damage for other extra-low voltage equipment.NOTE-Such precautions may be necessary
7、in supplies for safety services(see IEC 364-3-35).551.4 Protection against indirect contactProtection against indirect contact shall be provided for the installation in respect of eachsource of supply or combination of sources of supply which can operate independently ofother sources or combinations
8、 of sources.551.4.1 Protection by automatic disconnection of supplyProtection by automatic disconnection of supply shall be provided in accordance withsection 413.1 of IEC 364-4-41,except as modified for particular cases by 551.4.2,551.4.3or 551.4.4.551.4.2 Additional requirements for installations
9、where the generating set providesa switched alternative to the public supply(stand-by systems)Protection by automatic disconnection of supply shall not rely upon the connection to theearthed point of the public supply system when the generator is operating as a switchedalternative to a TN system.A suitable earth electrode shall be provided.
