brought in 120, bypassed existing xformer

[matlark]

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

 

[Jraef]

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

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.

 

[arion]

if the system is supplied from more than one source it must be clearly posted on the enclosure door and a safety interlock is required

 

[templdl]

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.

Good points.
We placed a yellow label prominently placed on the door that there was separate source power present.
In addition we included either an electrical interlock either included in th breaker/ MCP disconnect or on the handle operating mechanism which disconnects the external power source prior to opening the enclosure. The yellow signage also alerts the tech that there is an addition power source besides the expected 480v(?) Power to also be aware of power entering the enclosure from a separate source. Separate source wiring may be yellow instead of red or(?) but not necessarily.

 

[iwire]

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.

 

[Jraef]

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.

NFPA79, section 5.3

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

Now one can argue as to the enforceability of NFPA79 if you are not talking about "Industrial Machinery".

 

[iwire]

NFPA79, section 5.3




Now one can argue as to the enforceability of NFPA79 if you are not talking about "Industrial Machinery".

Thank you.

I do not see the OP saying it is a machine of any type.

 

[don_resqcapt19]

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.

 

[templdl]

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.
In my copy 16.1.3 includes the wire colors with yellow being used as an ungrounded control circuit that 'may' remain energized when the main disconnect is in the off position. Please note the word "may" and not "is."

 

[Besoeker]

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.

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.

We make some equipment that has both AC and DC inputs. We warn about this in instruction manuals - but who ever reads these.....:roll:
So we also fit warning and mandatory labels to the kit itself. They are mandatory in that they set out instructions that have to be followed rather being a dictate of any code or standard (as far as I'm aware).
I do it because I think it's the right thing to do.

"Before working on this equipment remove all supply voltages"

Unfortunately, one of our customers didn't. He left the 700Vdc supply on. And got severely fried. But he survived despite serious burns.
Personally, it upset me a great deal. I knew the guy well at both a personal and business level. And I felt a degree personal responsibility.
Could/should the labels have bigger? Should the instruction (my wording) have been stated more clearly?

The incident, they only one that I know of on our kit, was about twenty years ago. It still bothers me.

Whether it is code or otherwise, I think it should be incumbent on manufacturers/suppliers/installers to provide adequate and clear instructions and warnings.
That might have avoided Jraef's unpleasant experience. And possibly others who have been caught out.

But in cases like that of my old friend, possibly not. He was under pressure from production. It was late at night. Mistakes happen.

 

[Jraef]

Thank you.

I do not see the OP saying it is a machine of any type.

Right. That's why I said, it could be argued.

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.

Sure. But "Electricians" generally must follow the NEC and have to assume their work will be inspected by an AHJ, right?

Article 409 in the NFPA 70 (NEC) defines an "Industrial Control Panel", article 670 describes an "Industrial Machine". If what an electrician is working on fits either description, it can be interpreted that way by the AHJ. He can then require further adherence to NFPA 79, and/or NRTL listing if appropriate for the jurisdiction. The safe bet is to use NFPA 79 as a minimum design guide even if you do not need NRTL listing in your jurisdiction.

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.]

Can you do with out following non-binding codes? Yes. Can that then lead to a red tag and associated project delays? Yes, because remember, an AHJ can require anything he deems necessary, then YOU, as the electrician, must successfully argue your way out of it, at which time you generally piss off the AHJ and your life becomes a living hell. Been there, done that, got the T-shirt and the hat. For what you might save in NOT following these basic guidelines, it's not worth the risk in my opinion.

 

[don_resqcapt19]

Sure if you are working on the machine itself or its control panel, but there are lots of applications outside of that where it is common to have multiple power sources in a single enclosure.

One example is a starter bucket in an MCC. It is a common practice to have the control power transformer in the bucket provide the power for the starter itself, but in many cases there will be an external source of power on the aux contacts for feedback to the PLC or DCS.

 

[iwire]

Again I am not disagreeing with anyone that good design may well warent labeling dual supplies.

But that said, we still do not know what the equipment is that the OP is dealing with.

It could be as simple as a combination disconnect motor starter. Or part of an MCC or it could well be part of an industrial machine, we do not know.

Electricians deal with many things that have multiple supplies without marking, with out disconnects etc.

Multi-pole lighting contactors are a good example, we might have 16 circuits in one enclosure each with it's own breaker.


Here is a typical refrigeration rack I would work on, a factory made and listed piece of equipment that may have one, two, or more feeders and branch circuits supplying it. Notice that there is no disconnecting means at all on it. Many are not labeled as having multiple sources supplying it.

In the rack above I will often find a greater than 100 amp 480 volt feeder, a greater than 100 amp 208 volt feeder and a couple of 120 volt 20 amp branch circuits supplying it.


The thought that ECs must follow every possible standard if they are enforceable or not is pie in the sky thinking when ECs are often chosen on price.