B
bthielen
Guest
I have been trying to clarify the specific requirements for the use of supply power disconnects on industrial machinery and thought I'd ask the experts in this forum.
I work for a company that builds packaging machinery and my responsibilities center around modifications and rebuilds. Occasionally, I find that a modification to a machine requires enough additional equipment that the FLA of the machine will exceed the supply rating of the machine. When I approach our customer with this dilemma and suggest that the machine?s supply circuit will require upsizing, the cost and work involved causes issue. One solution that is often suggested is providing another power drop to supply power to the added components, which many times include servo drive systems. This is a concern for me because now there are multiple disconnect switches that must be opened in order to completely isolate the supply power to the machine for servicing.
NEC 2005
670.4 (B) indicates that a machine shall have a disconnecting means but it does not indicate if it must have only one.
NFPA79, 2002 Edition:
5.1 Indicates that ?where practicable?, the machine shall be connected to a single power supply circuit but it does not seem to forbid multiple supply circuits.
5.3.1.1 (1) does indicate that each power supply circuit must have a disconnecting means.
5.3.1.1.2 requires labeling the location of other disconnecting means.
5.3.1.2 seems to require some form of interlocking of the multiple supply circuits, in particular when it
comes to control circuits but I am not completely sure I understand this code.
This how I understand it. Multiple power supply circuits to an industrial machine are discouraged but acceptable. Each supply disconnect must be marked to identify the location of all other supply disconnect switches on the machine. Each disconnect must open all control voltage related to all equipment and components supplied by the disconnect.
Am I on the right track?
Bob
I work for a company that builds packaging machinery and my responsibilities center around modifications and rebuilds. Occasionally, I find that a modification to a machine requires enough additional equipment that the FLA of the machine will exceed the supply rating of the machine. When I approach our customer with this dilemma and suggest that the machine?s supply circuit will require upsizing, the cost and work involved causes issue. One solution that is often suggested is providing another power drop to supply power to the added components, which many times include servo drive systems. This is a concern for me because now there are multiple disconnect switches that must be opened in order to completely isolate the supply power to the machine for servicing.
NEC 2005
670.4 (B) indicates that a machine shall have a disconnecting means but it does not indicate if it must have only one.
NFPA79, 2002 Edition:
5.1 Indicates that ?where practicable?, the machine shall be connected to a single power supply circuit but it does not seem to forbid multiple supply circuits.
5.3.1.1 (1) does indicate that each power supply circuit must have a disconnecting means.
5.3.1.1.2 requires labeling the location of other disconnecting means.
5.3.1.2 seems to require some form of interlocking of the multiple supply circuits, in particular when it
comes to control circuits but I am not completely sure I understand this code.
This how I understand it. Multiple power supply circuits to an industrial machine are discouraged but acceptable. Each supply disconnect must be marked to identify the location of all other supply disconnect switches on the machine. Each disconnect must open all control voltage related to all equipment and components supplied by the disconnect.
Am I on the right track?
Bob
