The enclosure must be clearly labeled as having a Foreign Source of power, and I believe NFPA79 is going to require that those conductors be yellow, plus when the door is opened, ALL sources of power are disconnected. They can do it via aux contacts on the main disconnect device.Hello,
A subcontractor bypassed the control transformer (480:120) that was in an existing control enclosure and brought in 120 from somewhere. I know the potential dangers of doing this but does it violate any codes?
Thanks
Good points.The enclosure must be clearly labeled as having a Foreign Source of power, and I believe NFPA79 is going to require that those conductors be yellow, plus when the door is opened, ALL sources of power are disconnected. They can do it via aux contacts on the main disconnect device.
But are they back-feeding the existing transformer too? That's really dangerous. The only time I've ever been shocked with 480V (probably less, but it was Delta), was in exactly that situation. I opened a main breaker on a control panel, but a foreign 120V source was connected, it back fed the CPT and made 480V on the load side of the main breaker, which I made contact with.
NFPA79, section 5.3I work on a lot modern, of listed equipment that requires two feeds and has no marking about two feeds and have no interlocks.
While I don't disagree with the good intentions of the posters above me I sure would like to see some code cites to back their positions.
5.3 Supply Circuit Disconnecting (Isolating) Means.
5.3.1 General. The following general requirements apply to
5.3.2 through 5.3.5.
5.3.1.1 A supply circuit disconnecting means shall be provided
for the following:
(1) Each incoming supply circuit to a machine
(2) The supply circuit to a feeder system using collector wires,
collector bars, slip-ring assemblies, or flexible cable systems
(reeled, festooned) to a machine or a number of machines
(3) Each on-board power source (e.g., generator)
5.3.1.1.1 Each disconnecting means required by 5.3.1.1 shall
be legibly marked to indicate its purpose.
5.3.1.1.2 Where a machine is supplied by more than one supply
circuit, a marking shall be installed at each supply circuit
disconnect location denoting the location of all other supply
circuit disconnects.
5.3.1.2 The supply circuit disconnecting means shall disconnect
(isolate) the electrical equipment of the machine, including
all control circuits, from the supply circuit when required
(e.g., for work on the machine, including the electrical equipment).
Circuits that are not required to be disconnected by the
supply circuit disconnecting means shall comply with 5.3.5.
5.3.5 Excepted Circuits.
5.3.5.1 The following circuits shall not be required to be disconnected
by the main supply circuit disconnecting means:
(1) Lighting circuits for lighting needed during maintenance
or repair
(2) Attachment plugs and receptacles (plug and socket outlets)
for the exclusive connection of repair or maintenance tools
and equipment (e.g., hand drills, test equipment)
(3) Under voltage protection circuits that are only used for
automatic tripping in the event of supply circuit failure
(4) Circuits supplying equipment that are required to remain
energized for satisfactory operation [e.g., temperature controlled
measuring devices, product (work in progress)
heaters, program storage devices
NFPA79, section 5.3
Now one can argue as to the enforceability of NFPA79 if you are not talking about "Industrial Machinery".
What is the scope of that document? It would be my opinion, that in general, NFPA 79 would not apply to work done by electricians.NFPA79, section 5.3
Now one can argue as to the enforceability of NFPA79 if you are not talking about "Industrial Machinery".
Yes, I looked in my old 1997 copy of NFPA 79 and overlooked it but went back and looked again and sure enough they had it in 7.3 at that time.NFPA79, section 5.3
Now one can argue as to the enforceability of NFPA79 if you are not talking about "Industrial Machinery".
I understand your point about markings. If there are no mandatory requirements label equipment as having more than one feed and no such label is fitted then no rules are contravened.I work on a lot modern, of listed equipment that requires two feeds and has no marking about two feeds and have no interlocks.
While I don't disagree with the good intentions of the posters above me I sure would like to see some code cites to back their positions.
Right. That's why I said, it could be argued.Thank you.
I do not see the OP saying it is a machine of any type.
Sure. But "Electricians" generally must follow the NEC and have to assume their work will be inspected by an AHJ, right?What is the scope of that document? It would be my opinion, that in general, NFPA 79 would not apply to work done by electricians.
I. General
409.1 Scope. This article covers industrial control panels
intended for general use and operating at 600 volts or less.
Informational Note: UL 508A-2001, Standard for Industrial
Control Panels, is a safety standard for industrial control
panels.
409.2 Definitions.
Control Circuit. The circuit of a control apparatus or system
that carries the electric signals directing the performance
of the controller but does not carry the main power
current.
Industrial Control Panel. An assembly of two or more
components consisting of one of the following:
(1) Power circuit components only, such as motor controllers,
overload relays, fused disconnect switches, and
circuit breakers
(2) Control circuit components only, such as pushbuttons,
pilot lights, selector switches, timers, switches, control
relays
(3) A combination of power and control circuit components
These components, with associated wiring and terminals,
are mounted on or contained within an enclosure or mounted
on a subpanel. The industrial control panel does not include
the controlled equipment.
670.2 Definition.
Industrial Machinery (Machine). A power-driven machine
(or a group of machines working together in a coordinated
manner), not portable by hand while working, that is used to
process material by cutting; forming; pressure; electrical,
thermal, or optical techniques; lamination; or a combination
of these processes. It can include associated equipment
used to transfer material or tooling, including fixtures, to
assemble/disassemble, to inspect or test, or to package.
[The associated electrical equipment, including the logic
controller(s) and associated software or logic together with
the machine actuators and sensors, are considered as part of
the industrial machine.]