fmtjfw
Senior Member
- Location
- Fairmont, WV, USA
I'm looking for constructive criticism on the following, and if you think it is merited, support in the form of comments from you on 12-147. Thanks, Jim Williams
4 Comment:
646.2 Definitions.
Premises Transformer. A transformer that is fed by premises wiring.
Service Entrance Transformer. A transformer that feeds the service equipment.
646.8 Field Wiring Compartments. .A field-wiring compartment in which service or feeder branch circuit connections are to be made shall be readily accessible.:
(1) Permit the connection of the supply wires after the MDC is installed;
(2) Permit the connection to be introduced and connected easily; and
(3) Be located so that the connections may be readily inspected after the MDC is installed
646.9 Flexible Power Cable.
(A) Flexible cable shall be permitted to be used for connections between enclosures of a MDC system. Flexible cords or cables shall not be used for connection to the branch circuit or electrical service. the external (not from another MDC) power feed.
646.11 Premises Transformers. Premise transformers installed in the MDC area shall be of the dry type or type filled with a noncombustible dielectric medium.
646.12 Service Entrance Transformers. Service entrance transformers shall not be permitted in an MDC.
646.19 General.
Exception: The depth of the workspace shall not be required to comply with Table 110.267(A)(1) if the equipment is marked with a warning sign which shall meet the requirements in 110.26 and shall read as follows:
?WARNING? and ?De-energize Equipment before Servicing? or the equivalent.
646.20 Working Space for ITE.
(A) The working space depth in front of ITE where any live parts that may be exposed during routine servicing operate at not greater than 30 volts rms, 42 volts peak, or 60 volts dc; with a fault current less than 200 Amperes shall not be required to comply with 646.19.
(B) Any areas of ITE that require servicing of parts that are greater than 30 volts rms, 42 volts peak, or 60 volts dc; or with a fault current of 200 Amperes or more shall comply with the workspace requirements of 646.19.
5 Statement of Problem and Substantiation.
646.8 Typos delete extra period, delete the colon following shall. I believe the size of these MDCs is such that they will be fed from feeders or services. I believe that ? internally ? they will have branch circuit OCPDs.
646.9 I believe the size of these MDCs is such that they will be fed from feeders or services. I believe that ? internally ? they will have branch circuit OCPDs.
646.2, 646.11, & 646.12: The premises and service entrance transformers are new, undefined terms.
646.19 <except>: The note refers to a non-existing paragraph. The standard way of defining labels and signs should be used. I have serious doubts that such a warning label will be heeded in the high pressure 24/365 environment these MDCs are used in. This is a serious safety issue.
646.20: The ?safe? voltages in this section should also and safe amperages. I have no direct information about safe amperages but I have worked on ITE that had low voltage high amperage uninsulated bus bars. Because of the increased efficiencies of DC distribution and reduced cooling requirements, I believe it will be come more prevalent in the future. See, for example:
http://hightech.lbl.gov/documents/data_centers/CEC-TB-40.pdf
4 Comment:
646.2 Definitions.
Premises Transformer. A transformer that is fed by premises wiring.
Service Entrance Transformer. A transformer that feeds the service equipment.
646.8 Field Wiring Compartments. .A field-wiring compartment in which service or feeder branch circuit connections are to be made shall be readily accessible.:
(1) Permit the connection of the supply wires after the MDC is installed;
(2) Permit the connection to be introduced and connected easily; and
(3) Be located so that the connections may be readily inspected after the MDC is installed
646.9 Flexible Power Cable.
(A) Flexible cable shall be permitted to be used for connections between enclosures of a MDC system. Flexible cords or cables shall not be used for connection to the branch circuit or electrical service. the external (not from another MDC) power feed.
646.11 Premises Transformers. Premise transformers installed in the MDC area shall be of the dry type or type filled with a noncombustible dielectric medium.
646.12 Service Entrance Transformers. Service entrance transformers shall not be permitted in an MDC.
646.19 General.
Exception: The depth of the workspace shall not be required to comply with Table 110.267(A)(1) if the equipment is marked with a warning sign which shall meet the requirements in 110.26 and shall read as follows:
?WARNING? and ?De-energize Equipment before Servicing? or the equivalent.
646.20 Working Space for ITE.
(A) The working space depth in front of ITE where any live parts that may be exposed during routine servicing operate at not greater than 30 volts rms, 42 volts peak, or 60 volts dc; with a fault current less than 200 Amperes shall not be required to comply with 646.19.
(B) Any areas of ITE that require servicing of parts that are greater than 30 volts rms, 42 volts peak, or 60 volts dc; or with a fault current of 200 Amperes or more shall comply with the workspace requirements of 646.19.
5 Statement of Problem and Substantiation.
646.8 Typos delete extra period, delete the colon following shall. I believe the size of these MDCs is such that they will be fed from feeders or services. I believe that ? internally ? they will have branch circuit OCPDs.
646.9 I believe the size of these MDCs is such that they will be fed from feeders or services. I believe that ? internally ? they will have branch circuit OCPDs.
646.2, 646.11, & 646.12: The premises and service entrance transformers are new, undefined terms.
646.19 <except>: The note refers to a non-existing paragraph. The standard way of defining labels and signs should be used. I have serious doubts that such a warning label will be heeded in the high pressure 24/365 environment these MDCs are used in. This is a serious safety issue.
646.20: The ?safe? voltages in this section should also and safe amperages. I have no direct information about safe amperages but I have worked on ITE that had low voltage high amperage uninsulated bus bars. Because of the increased efficiencies of DC distribution and reduced cooling requirements, I believe it will be come more prevalent in the future. See, for example:
http://hightech.lbl.gov/documents/data_centers/CEC-TB-40.pdf