White or Black

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bthielen

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I have a situation I would like some opinions about.

A few years ago we designed and sold a machine that included a single phase 480vac - 240vac transformer used to supply a series of servo motor drives. The original design was for the 240v secondary power to be left ungrounded. As a result the wire colors were to be black.

At some point after the machine was installed, one leg of the 240v secondary was grounded. I do not know if this was done by end-user personnel or our own service personnel nor do I know why it was designed ungrounded then later grounded.

Here's my dilemma. I am now in the process of designing additional servo drives into the system using the same 240v secondary power supply. When the leg of the secondary was grounded, the newly grounded conductors were left black and therefore do not correctly identify the grounded conductor as grounded.

As part of my installation instructions for my new design, I believe I have a responsibility to order the existing grounded conductors replaced or at least marked with white tape or something to indicate that they are grounded. I do not believe the NEC would require the wire to be replaced if marked as grounded. The additional grounded conductors that will be added by my design will be ordered white.

Is this an appropriate action?

Edit: Incidentally, the ungrounded secondary conductor was originally designed and remains red. Don't think this matters but thought I'd add it.

Bob

[ December 27, 2005, 02:52 PM: Message edited by: bthielen ]
 
Re: White or Black

Tecnically, they can only be marked with a white finish if they are #4 AWG or larger or the conductors are apart of a cable assembly.
 
Re: White or Black

Looks like I may have misunderstood the code requirements.

I assume that since the one conductor is grounded it is required to be white, gray, or natural (whatever natural is).

Bryan, am I understanding you correctly that marking a wire white is not an acceptable alternative except for 8ga or larger therefore, the only correct action is to replace the wires that are smaller than 8ga? Most are 12ga on the load side of the branch circuit fuses and these then would require replacement to comply with code?

Bob
 
Re: White or Black

Why can't the secondary grounding be removed and labled as ungrounded if need be?

Roger
 
Re: White or Black

bthielen wrote: At some point after the machine was installed, one leg of the 240v secondary was grounded. I do not know if this was done by end-user personnel or our own service personnel nor do I know why it was designed ungrounded then later grounded.

Some ungrounded, mission-critical apps are designed without OCD's in favor of supervised, ground-fault alarms.

These ground-fault alarms are immediately repaired to prevent the next fault burning down the house.

Sounds like you're not shure why this system was grounded, or how its protected now?

Me thinks, without proving compliance with grounded-system protection and conductors, as Bryan points out, its a liability time bomb if your equipment is implicated in the rubble.
 
Re: White or Black

Actually if the componets and wiring are inside or part of a machine, the NEC may not be applicable anyways.

Roger

[ December 27, 2005, 06:00 PM: Message edited by: roger ]
 
Re: White or Black

Without further detail of this installation, it is hard to say, but I agree with Roger that this may not be part of the NEC. It may be within NFPA 79, or other standards, such as a UL standard.
 
Re: White or Black

You may be correct that this is not an NEC issue but a NFPA79 issue because it is part of a machine. NFPA79 14.2 (2002) does specify that a grounded current-carrying conductor be identified by a white or gray wire. There are other deviations such as WHT/BLU, WHT/YEL, etc. but they all include white.

As far as the grounding of the secondary, my experience with our current servo systems is somewhat limited and I was not involved with the troubleshooting processes that we as a company have been through. It is now suggested that perhaps the reason for grounding one leg of the secondary was to provide a common reference for the servo drives between the drive supply power and the drive processor power. Leaving the 240v supply power floating while using grounded 120v supply for the drive processors may have been causing some problems internal to the drive. I do not know this for certain.

My question now is: since this single-phase 240v system has been changed from an ungrounded to a grounded system, is there a reasonable way to properly identify the grounded current-carrying conductors short of replacing all of the affected conductors? Secondly, do I as a designer have a responsibility to order these changes? There are 11 servo drives being supplied by this one transformer so replacing the conductors is not a small task. Perhaps I am just making a mountain out of a mole hill?

Bob
 
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