OT: Ungrounded system

Not a PLC question, but I know that we've got some pretty smart folks around here.

I ran into an ungrounded conveyor system here at the plant. I had no idea that this practice was still in effect in the '90's (1990's, not 1890's), so I really didn't believe it until I saw it with my own eyes.

I was under the impression that these systems were outlawed in the '70's, how in the heck did it end up here?!?

I'm fond of some if not almost a bunch of our electricians, and would not necessarily like to see them get hurt. If for nothing else, than to avoid the paperwork.

So I would like to ground it. That would require removing the fuses on the neutral side and bonding the neutral with the ground at the transformer.

Can anyone think of a "gotcha" that might be lurking there if we decide to do this?


Thnaks!

Neutral does not have to be grounded.
and the neutral should be gaurded for overcurrent (normally it will switch down all fases)
grounding should be done on the chassis not on the wires.

shooter said:

Neutral does not have to be grounded.
and the neutral should be gaurded for overcurrent (normally it will switch down all fases)
grounding should be done on the chassis not on the wires.

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It turns out that it is still legal here in the states (although I wouldn't advise it).

http://www.csanyigroup.com/grounded-or-ungrounded-systems

As an old electrician from a previous life, I take a dim view of ungrounded systems.


Here we bond the neutral to the ground on the secondary side of the isolation transformer. And never protect the neutral by fusing it. Well, almost never. Gas pumps are one exception IIRC.

If fact, this is the only case of an ungrounded system that I am aware of here at the plant. And we have a PLC system or two (more like a couple thousand )

It might be a Paint shop thing (since these chains run through the booths), but we never did this in General Assembly, Polymers, VIS, Body, Steel, or Powertrain (I should know, I've worked them all... )


BTW, how are things in the old country? (I'm Dutch as well)

Are you talking about power wiring or control wiring? Is there an isolation transformer and what is the secondary voltage?

DickDV said:

Are you talking about power wiring or control wiring? Is there an isolation transformer and what is the secondary voltage?

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Just some of the control wiring. Not all of it.

Yes there are isolation transformers (three!) on this beast, and some of the control wiring is isolated, some not. Some neutrals fused, some not. It has to be because the chain runs through the booth.

I'll have to take a peek at the motor section and see if they are grounded. I would normally expect them to be grounded, but after recent developments, I'm not so sure.

There is no point grounding the neutral of a 24VAC isolation transformer - you lose your isolation. Same with the 24VDC output from a switch mode. I do frown upon ungrounded medium voltage though. I never ground the neutral or negative on isolated control circuits though otherwise the isolation is lost.

BobB said:

There is no point grounding the neutral of a 24VAC isolation transformer - you lose your isolation. Same with the 24VDC output from a switch mode. I do frown upon ungrounded medium voltage though. I never ground the neutral or negative on isolated control circuits though otherwise the isolation is lost.

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Oh, sorry. This is 120VAC. I should have mentioned that.

shooter said:

Neutral does not have to be grounded.
and the neutral should be gaurded for overcurrent (normally it will switch down all fases)
grounding should be done on the chassis not on the wires.

Click to expand...

Shooter
We are talking about an installation in USA. You are wrong on several points re USA and wiring to comply with USA Nat'l Electric Code.

What is commonly called neutral is termed the grounded conductor in NEC.
The neutral is almost never fused or switched with exception of overloads in motor control circuitsn (here in USA)

How you guys do it over there I do not know and will not try to apply USA standards to what you guys do.

Since he is talking 120 single phase he will be required to bond his neutral at the service entrance (or at a stepdown transformer) to the ground electrode system. There are some exceptions in the NEC that should be carefully reviewed to ensure they are not applicable to his system.

Dan Bentler

I'm certainly not an NEC expert but 120VAC control circuits without any ground reference are not uncommon and I doubt are in violation of the NEC. They tend to appear in critical applications like hospitals and power houses where a single ground would not take the control system down. Now, this is for control only, no power outlets.

While I certainly prefer control circuits whether 120, 48, or 24VAC to be grounded on one side, I understand the need for fault tolerant controls in some situations.

With regard to the original poster's conveyors, it doesn't sound like he's got any kind of critical application. Just sounds like a patchwork mess. I wish him luck in sorting it out!

The older Chrysler transmission plant in Kokomo IN (KTP) list specifically in their plant specification that power supplied to machinery is ungrounded (due to a failed soil study I was told) and that new machinery designs shall accommodate it. Company that I started working for about ten years ago found out the hard way that they should not have ignored it - couple of fried larger Ultra3Ks.

That is not true at their other two neighboring plants, ITP1 & ITP2.

The older Chrysler transmission plant in Kokomo IN (KTP) list specifically in their plant specification that power supplied to machinery is ungrounded (due to a failed soil study I was told)..

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The soil excuse is as pure BS as I have seen in awhile. The usual case is that old plants were fed with transformer secondary ungrounded delta power, difficult to hard-ground without creating other problems.

Secondary delta systems were frequently installed in the days when human life was cheap, and keeping the plant running was more important than getting a few people electrocuted. Many of the old automotive plants were built or modified during WWII to produce military equipment such as tanks, jeeps, trucks, and artillery. I have worked in some of those old plants built in wartime, speciallly the old ammunition plants. The secondary-delta ungrounded transformers were a Defense Department standard, the Army thinking being that was more important to keep the plant running and making munitions, than to have a safe worker environment - the right way, the wrong way, and the Army way!

These old ungrounded delta systems should be outlawed and forcibly replaced, or shut down- owner's choice.

I couldn't have said it better myself, Lancie1. But, unfortunately, new buildings are still being built with floating delta systems. Ford Motor Co. standard spec is for all new construction to still be floating delta. I've even seen new construction commercial buildings wired that way.

Ford Motor Co. standard spec is for all new construction to still be floating delta.

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What are they thinking? How can they possibly justify this? Sooner or later, no matter how good the maintenance department, a second phase of the ungrounded delta gets shorted, with catastrophic results. It is much safer, and cheaper, to have the main breaker trip when the first phase goes to ground.

On the machinery side, it forces isolation - we know that when we quote and price it accordingly. As far as maintenance crews, they're getting it right (they install new equipment all the time) - only once or twice in 30 years have I experienced any issues at any plant.

In my view, the worst part of floating delta power is that there is no control of the network to ground voltage. In one Ford plant, we were loosing VFD's so we put a recorder on the network to ground. In one day we saw 800VAC to ground and later 700VDC to ground.

What's to keep it from being 4160VAC to ground or maybe just 1200VAC to ground. In any case, the standard-issue CAT III 1000V meter is not adequate for personal protection.

Or, as commonly occurs, one phase goes to ground leaving the other two phases 480V to ground. It is a well-known fact that many dusts that will not ionize at 277V will at 480V. That means that you can LockOut-TagOut and the two high phases can ionize the dust around the disconnect blades and cause the load side conductors to float up to 480V. That happened to me some years ago and, since the load was a DC drive with rectifiers, I got 700VDC from arm to arm across my chest. I'm lucky to have survived. Yes, it was locked out and tagged out! I should have ground strapped all three load side conductors. I do now!