240v single phase secondary.

[GOZ]

Hello all.
I was looking over a new piece of equiptment we recieved at the facility i work at. I noticed a single phase control XFMR (480v single phase to 240v single phase) that had a phase on the secondary grounded. Should the grounded phase be color coded? What would be the purpose for the grounded phase?

 

[iwire]

If it is covered by the NEC the grounded conductor should be white.

The purpose is to provided a grounded 240 volt supply so if the ungrounded conductor goes to ground it will cause the over current devie to operate.

It also simplifies troubleshooting as you can take readings to any grounded point.

 

[kwired]

To have a grounded system on the secondary you have to ground something, if there is no neutral your only remaining choices are output 'A' or output 'B'. If there is a neutral, chances are very likely it is required to be the point that is grounded.

 

[templdl]

Hello all.
I was looking over a new piece of equiptment we recieved at the facility i work at. I noticed a single phase control XFMR (480v single phase to 240v single phase) that had a phase on the secondary grounded. Should the grounded phase be color coded? What would be the purpose for the grounded phase?

Is it UL listed? If so then the NEC has accepted as such in Art 110. The color coding, wire sizes, etc have been approved and listed by Ul. Should you suspect that the manufacturer has violated their UL listing bring it to the attention of UL.

 

[GOZ]

If it is covered by the NEC the grounded conductor should be white.

The purpose is to provided a grounded 240 volt supply so if the ungrounded conductor goes to ground it will cause the over current devie to operate.

It also simplifies troubleshooting as you can take readings to any grounded point.

White? Even for 240v? Could you give a Code # for reference. I'm having trouble finding it. I have always seen a phase grounded in three phase systems. Its a first for me with single phase.

Thanks.

 

[GOZ]

Is it UL listed? If so then the NEC has accepted as such in Art 110. The color coding, wire sizes, etc have been approved and listed by Ul. Should you suspect that the manufacturer has violated their UL listing bring it to the attention of UL.

Thats a good point I overlooked. I will check. Thanks.

 

[iwire]

White? Even for 240v? Could you give a Code # for reference. I'm having trouble finding it. I have always seen a phase grounded in three phase systems. Its a first for me with single phase.

Thanks.

Regardless of the voltage the NEC requires grounded conductors to be white.

200.6 Means of Identifying Grounded Conductors.

(A) Sizes 6 AWG or Smaller. An insulated grounded conductor
of 6 AWG or smaller shall be identified by one of
the following means:

(1) A continuous white outer finish.

(2) A continuous gray outer finish.

(3) Three continuous white stripes along the conductor?s
entire length on other than green insulation.

(4) Wires that have their outer covering finished to show a
white or gray color but have colored tracer threads in
the braid identifying the source of manufacture shall be
considered as meeting the provisions of this section.

(5) The grounded conductor of a mineral-insulated, metalsheathed
cable shall be identified at the time of installation
by distinctive marking at its terminations.

(6) A single-conductor, sunlight-resistant, outdoor-rated
cable used as a grounded conductor in photovoltaic
power systems, as permitted by 690.31, shall be identified
at the time of installation by distinctive white
marking at all terminations.

(7) Fixture wire shall comply with the requirements for
grounded conductor identification as specified in 402.8.

(8) For aerial cable, the identification shall be as above, or
by means of a ridge located on the exterior of the cable
so as to identify it.

(B) Sizes 4 AWG or Larger. An insulated grounded conductor
4 AWG or larger shall be identified by one of the
following means:

(1) A continuous white outer finish.

(2) A continuous gray outer finish

(3) Three continuous white stripes along its entire length
on other than green insulation.

(4) At the time of installation, by a distinctive white or gray
marking at its terminations. This marking shall encircle
the conductor or insulation.

(C) Flexible Cords. An insulated conductor that is intended
for use as a grounded conductor, where contained within a
flexible cord, shall be identified by a white or gray outer finish
or by methods permitted by 400.22.

That said I suspect the equipment is not covered by the NEC as has been suggested.

 

[templdl]

Thats a good point I overlooked. I will check. Thanks.

Also, besides the use of red you will also find the us of blue for DC and yellow for separate control if I remember correctly. But I have never been aware of white in any motor control wiring that I have worked with.
However their is NFPA 79 electrical standard for industrial machinery which does include wire color codes with white/gray for a grounded circuit conductor, green for grounded control circuits, etc. But NFPA 79 is not necessarily what UL listed as.

 

[Smart $]

Regardless of the voltage the NEC requires grounded conductors to be white.





That said I suspect the equipment is not covered by the NEC as has been suggested.

True... but field wiring is covered by NEC, unless supplied by manufacturer as part of the equipment.

 

[kwired]

White? Even for 240v? Could you give a Code # for reference. I'm having trouble finding it. I have always seen a phase grounded in three phase systems. Its a first for me with single phase.

Thanks.

See iwire's post for code reference.

Forget about what you call normal for a bit.

If you have a two wire system and want to ground the system you have only two choices of what to ground, and really have no difference dependent on which one you choose. Does not matter if the voltage between those two conductors is 24 volts, 120 volts, or even 600 volts. Same for a three phase three wire except there are three choices. Once a particular point is grounded, that is the "grounded conductor" of the system. White and grey are the primary colors accepted identification colors for grounded conductors, no matter what voltages there may be in the system.

 

[GoldDigger]

White and grey are the primary colors accepted identification colors for grounded conductors, no matter what voltages there may be in the system.

And if you need to distinguish the "system voltage" of this end-grounded 240 in building wiring, you could always do that with a choice of color for the hot conductor.

 

[GOZ]

Thank you everyone for the help.

 

[GOZ]

The power is feeding two 240v Freq drives for a set of DC servo motors. The drives have their own equipment grounds. I don't see where it is necessary to have a grounded phase. Should the power terminal on the drive be indicated as L1 and L2/N. I am currently pulling the specs of the drive to see if a "Neutral" is required. If it is not i will be removing the ground. I feel like i am over thinking this.

 

[kwired]

The power is feeding two 240v Freq drives for a set of DC servo motors. The drives have their own equipment grounds. I don't see where it is necessary to have a grounded phase. Should the power terminal on the drive be indicated as L1 and L2/N. I am currently pulling the specs of the drive to see if a "Neutral" is required. If it is not i will be removing the ground. I feel like i am over thinking this.

Freq drives are for AC motors, you probably just have DC motor drives.

What is meant by drive has its own ground? Is this drive a power source or just a power converter? Just because it has a grounding terminal doesn't mean it is a grounded source, it could be where you are to land the equipment grounding conductor from the input source.

A DC drive typically only rectifies incoming voltage and doesn't separately derive output power, therefore output does have potential to the input. An AC drive rectifies incoming AC to DC, then inverts it back into a simulated AC wave. The resulting output is more isolated from the source than what the output of a DC drive is.

I don't like to see the term ground a phase used here - you have a single phase source so there is only one phase but two leads. If there were a mid point in the supply winding and you had 120/240 I don't think you would have much confusion - you would ground the mid point and call it a neutral. You have a two wire source, there is no neutral to a two wire source. You can ground either end of the coil, and it is still same voltage to other end of coil. Whichever one is grounded it the one with a ground reference, it does not need overcurrent devices installed in that conductor. The other conductor is the "hot" in reference to "ground". You ground one of them and create a grounding system so that if the "hot" (which there just happens to be only one hot in this system) contacts something grounded it will result in high current flow and quick interruption by overcurrent devices. Exactly same reasons we ground one conductor of any other grounded system.

There are advantages of having an ungrounded system, but you generally need to have some kind of ground detection equipment to indicate there is a problem when using ungrounded systems, cause if you develop a second fault on another system conductor you will have high fault currents, and equipment will shut down when overcurrent devices open.

So for your installation you still need to ground a conductor of the system or you can possibly have an ungrounded system, but like I said the ungrounded system does have other requirements. If there is no critical process that needs to be shut down in an orderly fashion should there be a fault, the ungrounded system is usually not that desirable.

 

[Smart $]

The power is feeding two 240v Freq drives for a set of DC servo motors. The drives have their own equipment grounds. I don't see where it is necessary to have a grounded phase. Should the power terminal on the drive be indicated as L1 and L2/N. I am currently pulling the specs of the drive to see if a "Neutral" is required. If it is not i will be removing the ground. I feel like i am over thinking this.

In the OP you said this is a control transformer. If it powers drives, it is not a control transformer.

That doesn't matter regarding the grounding of one side of the transformer secondary. IMO, you should not remove the grounding. First, you will likely void any warranty. Additionally, with one side grounded, there may only be ocp on the other side... and if I'm not mistaken, ungrounded would require ocp on both sides (can't exactly recall why though).

I would only unground the secondary if there are related problems, and attempt to get manufacturer approval.

 

[kwired]

In the OP you said this is a control transformer. If it powers drives, it is not a control transformer.

That doesn't matter regarding the grounding of one side of the transformer secondary. IMO, you should not remove the grounding. First, you will likely void any warranty. Additionally, with one side grounded, there may only be ocp on the other side... and if I'm not mistaken, ungrounded would require ocp on both sides (can't exactly recall why though).

I would only unground the secondary if there are related problems, and attempt to get manufacturer approval.

I think he is just balking at something he is not really all that certain about. He needs to understand he must either ground this transformer secondary or install a proper ungrounded system with ground detection. The fact that it is two wire and 240 volts is what he is balking at, as he doesn't feel it is right - not used to seeing 240 volts between conductors without a 120 volt ground reference somewhere in there, problem is he needs to realize there is no possible way to ground this and not have 240 volts to ground, and that it is acceptable to do it that way. Same two wire secondary could be 120, 277, 480, or any other voltage and you would still connect it same way. Add a midpoint to the secondary and you now have a point that code says you must ground, no mid point take your pick, it is still full voltage to other conductor.

 

[GOZ]

To have a grounded system on the secondary you have to ground something, if there is no neutral your only remaining choices are output 'A' or output 'B'. If there is a neutral, chances are very likely it is required to be the point that is grounded.

Let me start over and let's go back to this quote and overlook everything else. Output 'A' is grounded in my case. I understand the need for grounding. That being said. The wire for output 'A' and output 'B' are black colored wires and a voltage of 240v.


As per Article 100 definition of a grounded conductor. The wire for output 'A' is grounded via the terminal on the XFMR. Making it a grounded conductor.


As per Article 200.6. The wire for output 'A' should NOT be black in color. Being a grounded conductor.
200.6 Means of Identifying Grounded Conductors.

(A) Sizes 6 AWG or Smaller. An insulated grounded conductor
of 6 AWG or smaller shall be identified by one of
the following means:

(1) A continuous white outer finish.

(2) A continuous gray outer finish.

(3) Three continuous white stripes along the conductor?s
entire length on other than green insulation.

(4) Wires that have their outer covering finished to show a
white or gray color but have colored tracer threads in
the braid identifying the source of manufacture shall be
considered as meeting the provisions of this section.

(5) The grounded conductor of a mineral-insulated, metalsheathed
cable shall be identified at the time of installation
by distinctive marking at its terminations.

(6) A single-conductor, sunlight-resistant, outdoor-rated
cable used as a grounded conductor in photovoltaic
power systems, as permitted by 690.31, shall be identified
at the time of installation by distinctive white
marking at all terminations.

(7) Fixture wire shall comply with the requirements for
grounded conductor identification as specified in 402.8.

(8) For aerial cable, the identification shall be as above, or
by means of a ridge located on the exterior of the cable
so as to identify it.

My concern is that if i change to a white conductor it will be mistaken as a 120v circuit later down the road.
Sorry for all the confusion and i hope this is simplifying my concern.

 

[Smart $]

...

My concern is that if i change to a white conductor it will be mistaken as a 120v circuit later down the road.
Sorry for all the confusion and i hope this is simplifying my concern.

Then use one of the alternatives... gray, for example. You will only have to do it for field wiring.

 

[GOZ]

Then use one of the alternatives... gray, for example. You will only have to do it for field wiring.

Why only field wiring? Does the code have an exception for this?

 

[Smart $]

Why only field wiring? Does the code have an exception for this?

Not specifically... I'm assuming this piece of equipment is manufactured and to a standard other than the NEC. Typically, the equipment is approved (sometimes not) as is by the AHJ. Thus the only wiring done under NEC is the field wiring (i.e. wiring between other associated pieces of equipment), unless it is a manufactured system with interconnection wiring furnished by the manufacturer as part of the system (see NFPA79, one of the other standards I mentioned at the start).