208/120 panel used as 480 panel

[wirenutjim]

I recently encountered an installation in which a 208/120 v panel was being fed with and used for, 480/277v loads in an industrial machine shop. As it was done some time before I began my work, I am unsure who the blooming idiot was that installed it! The question I have: What are the consequences of such an installation? Could it blow? Melt-down? My guesstimate is that is has been this way for about 5 years. And yes, I replaced the panel.

 

[charlie b]

The voltage rating of any item is based on the ability of that item?s insulation system to prevent leakage current from the energized parts to the outside world. If you hit an item with a voltage level that exceeds its rating, it creates a danger of leakage current, insulation breakdown, and eventually a fault. And yes, that could be explosive, and it could cause serious injury (or worse) to anyone standing nearby at the inopportune moment.

The people who work in this area should consider themselves lucky. This was a disaster waiting for its moment to announce itself to the world. You did them all a great favor by replacing that ticking time bomb.

Welcome to the Forum.

 

[480sparky]

I recently encountered an installation in which a 208/120 v panel was being fed with and used for, 480/277v loads in an industrial machine shop. As it was done some time before I began my work, I am unsure who the blooming idiot was that installed it! The question I have: What are the consequences of such an installation? Could it blow? Melt-down? My guesstimate is that is has been this way for about 5 years.

Whoever installed that whould be flogged, hung, dragged and quartered.

And yes, I replaced the panel.

And you get a big "Atta-boy!"

Too bad you couldn't have taken a photo of it and used it in our informal "Spot the Violation" contest.

 

[tom baker]

Charlie said it well. In a fault on the load side, the breakers won't be able to interrupt the fault current and will explode.

 

[weressl]

Charlie said it well. In a fault on the load side, the breakers won't be able to interrupt the fault current and will explode.

You can't say that with certainty. All depends on the available fault.

 

[realolman]

Not to suggest for one minute that it's Ok to use a 120 /208 for 277/ 480... but is there really that much difference in materials or spacing for the two panels?

 

[LawnGuyLandSparky]

Too bad you couldn't have taken a photo of it and used it in our informal "Spot the Violation" contest.

Yea, I would have posted "some moron taped B-O-Y colors on a 208v feeder!"

 

[davidr43229]

Charlie said it well. In a fault on the load side, the breakers won't be able to interrupt the fault current and will explode

Anytime that you take a component and use it beyond its "tested parameters", damage will occur. To what degree of damage, depends on many issues.
If I was a betting man, I would put my money on Charlie, knowing UL489.
Just my $.02

 

[charlie b]

Not wanting to take credit for someone else?s contribution, let me clarify that my point had to do with a failure taking place within the panel. That failure could be caused by an inadequate insulation system, given that the panel would be supplied with a voltage beyond its rating.

It was Tom who mentioned the ratings of the breakers. If you have a higher voltage supply, it is going to be able to supply a higher fault current to an otherwise identical system. It becomes a question, then, as to whether the breakers installed in the 120/208V panel are rated to handle the fault current that a 480/277V power source can supply. If they are not adequately rated, if they are subjected to a fault beyond their rating, then their metal contacts might melt and fuse together, permanently preventing them from opening, and thus allowing the fault current to continue flowing.

Laszlo correctly pointed out that we don?t know enough to say for certain whether the breakers installed in this particular panel would have been able to handle the fault current to which they could have been subjected.

 

[realolman]

Not wanting to take credit for someone else?s contribution, let me clarify that my point had to do with a failure taking place within the panel. That failure could be caused by an inadequate insulation system, given that the panel would be supplied with a voltage beyond its rating.

.

Again, not suggesting that the lower rated panel is an adequate substitution for the higher rated one, but strictly from an insulation standpoint, what would be the differences between the two?

 

[charlie b]

Again, not suggesting that the lower rated panel is an adequate substitution for the higher rated one, but strictly from an insulation standpoint, what would be the differences between the two?

I don't happen to know. Perhaps there is a manufacturer's representative on this Forum who could shed some light on this question.

I was speaking from "first principles," starting with the basis for voltage ratings. The manufacturer of a 480V panel will guarantee that it will withstand 480 volts, with no breakdown of any portion of its insulation system. The manufacturer of a 208 volt panel will not give that same guarantee (i.e., that it will withstand 480 volts).

 

[480sparky]

The manufacturer of a 208 volt panel will not give that same guarantee (i.e., that it will withstand 480 volts).

If there ever was a problem (explosion, fire, etc.), the insurance company would have a field day if they found out this panel had been installed that way. I'm sure that one would end up being one of their favorite 'war stories'.

 

[LarryFine]

Again, not suggesting that the lower rated panel is an adequate substitution for the higher rated one, but strictly from an insulation standpoint, what would be the differences between the two?

Probably in the spacing of conductive parts by air gap size and/or thickness of insulative materials.

 

[kid_stevens]

I just looked at Square D panels a 208 and a 480 rating and the only difference was the Main breaker.

 

[jim dungar]

Again, not suggesting that the lower rated panel is an adequate substitution for the higher rated one, but strictly from an insulation standpoint, what would be the differences between the two?

Actually there are other factors besides just static insulation. The first that comes to mind is the clearance/insulation required for venting the gasses created in during current interruption especially if they are vented towards the panel busbars rather than towards the breaker lugs.

 

[haskindm]

The fact is that we do not know what, if any, differences there are between a 480/277 panel and a 120/208 panel. They may be identical with only the labels being different. The fact is that they have only been labeled or tested for the voltage for which they are labeled. They may work fine at the higher voltage, but in the event that something fails the manufacturer will be entirely without blame since they were not installed according to the label. The installer would have all of the liability.

 

[ZZZ]

I believe the arcing of the higher voltage would be greater than the distance, opening speed, and arc chute design could handle when the breaker tried to open under a fault condition. This would cause a failure of the breaker of unknown degree, depending on impedence and feeder overcurrent protection upstream.

 

[kid_stevens]

480 Volts won't significantly ARC over any more than 208/240. The atmosphere would have to be well over 90% humidity to produce an arc over at those low voltages. The arc range difference in an arc welder is null from 40V AC to well over 400V AC. It still takes a strike of metal to metal to produce the arc. 400V AC at 300 amps still does not jump and arc it takes contact to produce the arc and current to sustain it.

The arc gases can not sustain an Arc over condition as the conductive properties of the gas components are scattered by the Arc shock wave to a point they cease to conduct.

The shock you get and hear in the winter time is caused by 3000V for feeling and 5000V to hear it.

I worked for an electronic testing company in California years ago. We tested for arcs to the cases of power supplies for instruments and telecomm. It takes a lot of voltage or a very small gap. A case with 480 input had an arcing problem at high humidity . The case had .015 clearance from Phase leg C to the housing and when Humidity went over 90% we gat an arc sometimes. A piece of treated paper stopped the arc. So the 3/16s of plastic behind the buss bar in a panel would easily stop Arc over.

SquareD lists a QOB (bolt on 480 breaker) But only 1 in the QO line. All the QO line is 240 or less. The arc clearance is greater in the 480 and up breaker so the arc at high currents can be broken. An Arc Welder with 400V 300A output won't arc more than 3/16s of an inch in very good conditions.

 

[DaveTap]

Again, not suggesting that the lower rated panel is an adequate substitution for the higher rated one, but strictly from an insulation standpoint, what would be the differences between the two?

I think if you compare any manufacturers 208v equipment to their 480v you'll see more spacing and thicker insulation in the 480V to compensate for the higher voltage potential.
(Not saying it would be okay use a 480V panel for 208V but I think it would be much safer than the other way around.)

 

[Jraef]

I think the answer is; we just don't know, but it COULD have lead to a disaster and it was not worth taking the chance.

Most panelboard manufacturers do NOT make two different classes of bus systems, so they will make only the higher class, which is perfectly fine to use on a lower voltage. The real difference is in the breakers, as has been discussed already. There ARE significant differences in the breaker construction and for this reason, sometimes the manufacturer will install physical barriers in a panelboard to prevent the installation of lower voltage rated breakers into one LABELED for a higher voltage, i.e. the interior will not fit, clips that will not stab in etc..

The reason is, the destructive part of a fault as far as the circuit breaker goes is fault ENERGY, not just fault current. At a higher voltage then, the energy in a fault of equal current is drastically higher. Let's say for instance that you have a breaker with a "slash" rating, i.e. 480/277V. This means that you CANNOT use that breaker on a 480V 3 wire service, it has not passed the necessary tests at full line voltage because if there is a grounded fault, the voltage could be 480V, not 277V. In other words, by displaying the "slash" rating, it means that to pass the UL489 tests it relied upon the fact that there would never be a ground fault in excess of 277V, which limits the amount of fault energy in the circuit even if the current is the same.

Now apply this principal to the above situation. We don't know, but it is possible that the breakers were only rated for 240V max. Since the panel was originally labeled for 208V 4 wire, it would not have been a problem to use breakers like that, there would have been no physical barrier to prevent installing them. So when the dufus changed the service to 480V, he was overcoming any safeguards that would have been in place. It is possible that there was no problem because the breakers were rated for 480V anyway, again we just don't know.

You were right to change it out.