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Check my 480v 3 ph plan please

Cannonmn

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Jun 25, 2016
We've recently bought some used 480v/3 ph machine tools and a fork battery charger and will soon power them up. Here's the diagram on the transformer that we'll feed backwards and get our 480 from the primary. We take 208v. 3 ph from a 100 amp breaker in the main breaker box, the transformer is the only load on that breaker.
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I want to make sure I'm interpreting the 7 transformer terminals correctly. I think X0 is where I connect ground both from the panel and to my loads, is that correct? I got that impression just due to the process of elimination, that's the only terminal that's not obviously one of the hots for each phase. I'd like verification that X0 is where ground wires go.

Panel breaker to transformer is via 2 gauge stranded copper, ground wire is no. 6 stranded copper. Transformer output to loads is 4-wire, 8 gauge, goes to the fused disconnect panel here.

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Our initial loads plugged into the outlets shown will be a large forklift battery charger and a 2 hp pedestal grinder which we don't need to run simultaneously.

I have no experience with 480v. And I noticed on the transformer diagram what appears to be delta primary and wye secondary. I know power to motors is normally from a delta circuit. Am I keeping my wyes and deltas in their proper places with the way I'm hooking this up?
 
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Cant address the system without a circuit diagram and access to local electrical code. Your best bet is to have a local electrician with industrial experience (NOT residential) vet your project. It's wort a box of beer or a jug of the man's favorite potation.

Seems to me you also need a "Fed From (insert panel and breaker number)" label on the panel disconnect which should be prominently labeled "240 Volts" Also I don't think you're allowed multiple circuits from a single breaker, One breaker per transformer is my understanding but I could be wrong. Check with NEC and local code. I think any conduit, J box, and buss duct conveying 480 volt has to be labeled every so many feet to distinguish it from 240. I also think you need a strain relief hasp near ever receptacle to attach your cords to so no mechanical strain comes on the connector.

Look closely at your receptacles. Are they NEMA rated or 480 volt 30 Amp three phase four wire with ground?

Anyway, don't trust us. Most of us are electrical dumb-asses; some are very plausible dumb-asses.

480 Volts aint noting to mess with. Repeating: get your project vetted by a local licensed electrician with industrial experience.
 
It is always good to have an industrial electrician at least look it over. Some places may want to know who the responsible electrician is, and may not accept you.

You ARE allowed multi outlet branch circuits under article 210, at up to 50A, and above that in industrial settings where qualified people are servicing the equipment.

Your circuits are not supplying only motor loads (one load is a charger), so you do not have to deal with section 430 per 210.1

Yes, splice points, connections, terminations, etc need to be identified by voltage, including phase information for each ungrounded wire.

because you have a delta transformer being used as the secondary, which has no neutral, you will need to choose one conductor to be the grounded conductor, and it should not be fused in any of the locations.

That grounded conductor is a "separately derived" system, which needs to be bonded to a new equipment grounding conductor, and a new local ground connection made to water pipe, building steel, etc, See article 250.30 of the NEC.

That XO is not to be grounded, because it would be a second ground not at the service box, which is forbidden. That is because you are using the secondary as a primary. if you WERE using it as a secondary, then it would be the neutral and would be bonded to ground as a separately derived system.

This stuff is why a good industrial electrician should do, or at least check over, the system.
 
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You need to get an electrician to help. There are specific rules for transformers and for reverse feeding, your assumption that X0 is for ground is incorrect. There are two grounds - frame ground and secondary (now your 480). In most jurisdictions you are going to have to ground the secondary and with that transformer it means "corner grounding". These need to be bonded (wire size, location etc) as per code. Be prepared to bond to building frame, local ground rod etc. Your local electrician will have to fill in the blanks to get a permit. Also, unless your transformer is TP rated (energy code) it's installation may be prohibited. The market is full of older transformers that could not be reinstalled after tenant improvements.

Permit... sound like it's for a business. Do it right and get a Permit. If you don't and someone gets hurt or worse, crap will fall out of the sky on you.
 
Thanks, all sounds like good, straight info., I've seen some of the "arc flash" videos and sure don't want anything like that, and I want everything to be grounded per code. Still curious about that X0 terminal, not a ground but then is it the neutral or what?
 
AND one more little tidbit that my friend Chuck, an industrial electrician friend told me years ago. 240 volts will hurt you and might kill you, but 480 volts will just kill you. I've never forgotten that.
 
That transformer is NOT designed to provide a neutral for the load, since you are driving it backward.

There is no obviously correct place to connect the 480 volt neutral.

It was designed to BE a DELTA LOAD without using the neutral.

If there is ever any 277 volt load in any of the circuits, you have a PROBLEM.

480 Volts, get an industrial electrician
 
Thanks, all sounds like good, straight info., I've seen some of the "arc flash" videos and sure don't want anything like that, and I want everything to be grounded per code. Still curious about that X0 terminal, not a ground but then is it the neutral or what?

It is the secondary neutral point when driven 480->208/120. 208 phase to phase, 120v phase to neutral.
 
That transformer is NOT designed to provide a neutral for the load, since you are driving it backward.

There is no obviously correct place to connect the 480 volt neutral.

It was designed to BE a DELTA LOAD without using the neutral.

You have to corner ground it. Not standard anymore, but can be done, still allowed.

If there is ever any 277 volt load in any of the circuits, you have a PROBLEM.

480 Volts, get an industrial electrician

Correct, a 277 load has no place to connect in that system.
 
That transformer is NOT designed to provide a neutral for the load, since you are driving it backward.

There is no obviously correct place to connect the 480 volt neutral.

It was designed to BE a DELTA LOAD without using the neutral.

If there is ever any 277 volt load in any of the circuits, you have a PROBLEM.

480 Volts, get an industrial electrician


Thanks, looking for that electrician, if anyone has personal experience with a reliable one in Washington DC general area let me know. Now I'm starting to see the issue with ground here, I guess I was thinking one would simply continue the ground from the main panel onto the transformer's box, then connect the ground wire from the 480 v. Disconnect panel (those blue boxes) to the transformer's steel box. But although that would ground the transformer box in case of a problem inside of it, with respect to the 208v. Panel supply, the transformer box ground has no electrical circuit connection to the "new" 480 volt system. If that's correct, it took a while for the reasoning to sink in. Thus the need to establish a corner ground, for example.
 
That transformer is NOT designed to provide a neutral for the load, since you are driving it backward.

There is no obviously correct place to connect the 480 volt neutral.

It was designed to BE a DELTA LOAD without using the neutral.

If there is ever any 277 volt load in any of the circuits, you have a PROBLEM.

480 Volts, get an industrial electrician

Thanks again. My one direct question re your post is this: I don't anticipate any need for 277 volts, all my machines are either 120/1, 208/3, or 480/3. Are you saying the 277v. Deficiency will show up as some other problem, or is it a non-problem since I won't need 277v?

I now have a local, very experienced commercial electrician who has installed hundreds of 480v. Systems both using panel-supplied 480v. And transformer-provided juice. He won't use term "industrial electrician" since there is so little heavy industry in this area. He listened to what I need done and asked me to call GE customer support to find out if this particular transformer, given where taps are etc., is considered by GE to be usable for our intended purpose. That determination was a bit time-consuming and he'd rather not run up the clock on me just doing phone research I could do, and I appreciated that. He has great faith in the GE c.s. Group. I Called the GE c.s. Line and the rep asked about 80 questions from the xformer s/n to addresses, biz info, etc., then said a member of their c.s. Team would call me back, but 7 hours later that hadn't happened.

Meanwhile I read over GE's online instructions on this type xformer http://apps.geindustrial.com/publib...nstallation and Instruction|475A667AAP001|PDF

And there's no warning not to reverse-feed it, but it does say the influx current at startup might be 10x what it would be with normal feeding. I'll give GE a couple more days then call again. I'm not going to rush anything with the deadly 480v.
 
Here's an interesting discussion on reverse-feeding transformers complete with a list of FAQ.

REVERSING A TRANSFORMER FOR STEP-UP

I'm gradually educating myself with stuff like this but will leave the ultimate hook-up design to my "industrial electrician."

I've now read in a few sources how and why the startup current in the "in" side of a reversed xformer will be very high and you need a breaker with a high-settable feature to compensate. I bought an ordinary 100A. Breaker to supply 208v. From panel to xformer, so it probably won't work.

That may be another reason to just cut my losses and start over with a xformer designed for 208-480 boost. My electrician prefers to work with a boost xformer anyway; said it would be simpler.

However, again just for my own education, I want to fully understand this last post on pp. 2 of above-linked thread, which btw gives me name of the electrician who seems to have a lot of experience with Step-up jobs, plus he's local if he's still around:

"Re: REVERSING A TRANSFORMER FOR STEP-UP
I always buy the right transformer for the job at hand. I prefer to have a delta primary with a wye secondary that permits grounding of the XO/Neutral/grounded conductor. Step up, step down I buy delta/wye

The major problem I see with a delta grounded secondary is. Other electricians will freak out when they find "C" phase at "0" volts to ground and "A" and "B" phases at 480 VAC to ground and no 277 VAC for lighting.

For testing purposes, such as deriving the proper voltage on the output of a UPS set for a foreign voltage ( testing UPS's and Generators in embassies) I have utilized two transformers stepping voltage up and down adjusting taps as necessary to achieve a voltage my load banks operate accurately at. I also have to feed the fans from a different source as these UPS's/generators are normally 50hz.
Brian John
Leesburg, VA"
 
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Judging by the wads of duct tape on the operating handles for tingle protection, looks like it was operated previously from an ungrounded delta output winding.

Capacitive coupling leakage from connected equipment, can be very uncomfortable even when there is no direct fault leakage, when operated ungrounded.

A fault condition on connected equipment to an ungrounded winding can be a lot more than uncomfortable.
 
Judging by the wads of duct tape on the operating handles for tingle protection, looks like it was operated previously from an ungrounded delta output winding.

Capacitive coupling leakage from connected equipment, can be very uncomfortable even when there is no direct fault leakage, when operated ungrounded.

A fault condition on connected equipment to an ungrounded winding can be a lot more than uncomfortable.

Thanks for the insights. Dont know rsn for the duct tape, I'll look soon to see if any more clues on that juice manifold; it is all steel construction and certainly sat on a concrete floor, but ihni on resistance of concrete with respect to whether any stray voltages on those handles would have taken a path to the concrete or to people. If earth ground wasn't connected to the subsystem I guess we can't assume stray voltage would have any reason to go there?

Hard to imagine that any factory of any size today would defy OSHA and all the other regulators by operating an ungrounded 480 v. System, would think workers getting tickled that way would drop a dime pretty quick if bosses didn't get it fixed. I say this to pull out any recent horror stories anyone has on this.

Reading up on corner grounds, that seems a very common practice to use the B phase of transformer output as ground for the system. Can you see any reason that wouldn't work for the transformer whose schematic is pictured? We have no need for 277 v.

No I haven't decided to do this myself, I have an experienced electrician who will set it up, but I want to learn as much as I can now. As mentioned in a recent post, I'm helping him research the transformer's adaptability to supplying a 480/3 subsystem in our shop which now has only 208/3 and 120/1. The one issue I've found so far is that backfeeding it will have a 12x input current spike at startup, perhaps requiring a special breaker, cost of which I don't yet know.
 
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The inrush problem, if it actually exists, may be solved by a breaker intended for mercury lamp lighting. Square D has them, others may, so if your box is Square D you may be OK.

The magnetizing surge is short, one or two cycles, and may not be an issue. Or it may. Depends on the transformer. Max size Variac units have been a problem for that in labs I have worked in.
 
Isolation transformer corner grounding and building grounding electrode bonding.

Regarding the overcurrent transformer protection and breaker size allowed, considering your reverse connected inrush current.

The code has differing overecurrent protection requirements depending on if you have primary only protection or primary and secondary protection. The setup you described only qualifies as primary protection. Primary only protection requires you to protect the transformer input at 125% or less.

If you had primary and secondary protection your allowed to go up to 250%. This would be good for your high inrush current for the reverse connected transformer. But because you don't have a single overcurrent device on the output side, your not allowed to use the 250% limit.

30KVA @ 208V = 83A, 83A x 1.25 = 104A, so the maximum breaker you can use is 100A
30KVA @ 208V = 83A, 83A x 2.50 = 207A, if you had a single overcurrent device on the load side of the transformer.

Load side overcurrent requirements.
30KVA @ 480V = 36A, 36A x 1.25 = 45A, can be rounded up to 50A for the next standard size.

The 100A input breaker may trip at turn on, or it may hold. It won't be consistent. The inrush surge will depend on where in the sine wave where it was last de-energized and where it was at the instant of being re-energized. The magnetic material in the core stores a charge. If the charges match at the instant of energization, the inrush is low. If the charges are at opposite points of the sine wave, the inrush is very large.

If you added another breaker or fused disconnect on the output of the transformer, then you could increase the size of the input breaker. This would allow for the high inrush currents when the magnetic memory doesn't line up with the line wave.

As to the grounding. You need either a connection to the building structural steel or the main water service entrance pipe to properly ground the transformer output. You could also use the existing service entrance connection point where these existing ground wires are terminated. A ground rod locally does not qualify for the required grounding electrode, for a separately derived system (isolation transformer).

The transformer you have will need to be corner grounded, using the delta winding as the output. Its the only way you can ground it. There are no other connection points provided on the output winding.

In regards to the duct tape on the disconnect handles. I have seen this before, normally associated with sanding machines. When the supply system is not properly bonded as shown above, even with ground wires run to the equipment, huge static charges can build up on the ungrounded system and have no means to be properly dissipated to mother earth. When they reach upwards of 10's of thousands of volts, they jump the gaps they can find, to reach mother earth. These built up static charges can give you a hell of a poke when you touch any equipment on the machine or the supply system. In a woodworking environment or other combustibles it can start fires readily. Dust collection systems are especially prone. Lots of fine combustible particulate combined with lots of airflow and a nice blue static spark discharge, results in a quick system burndown inside the duck work and dust collector hopper.

I have seen it in action. The operators will coat every part of the machine they have to touch for operation, in duct tape, in order to try and avoid getting a massive static poke. If not found and corrected in time it usually results in a fire. So the grounding encompasses more than just worrying about the 480V fault current issue.

Properly corner grounding the system and connecting to the building grounding electrode system in the proper manner will mitigate these problems. Corner grounding is pretty rare today and many electricians do not understand how to properly implement the proper connections. There should not be any fuses in the grounded leg. Meaning your disconnects should only contain 2 fuses each. The grounded leg should have dummy fuses installed in the clips, and the grounded leg should be bonded to each disconnect enclosure. If you have a look in them I doubt you will find this implemented properly, hence the duct tape workaround.

Make sure you find a sparky that knows how to properly deal with a corner grounded system and how to properly bond it to the building grounding electrode system. If not properly implemented, you will have problems, sooner or later.

SAF Ω
 
Thanks, good info, will pass on to the electrician.

" If you have a look in them I doubt you will find this implemented properly, hence the duct tape workaround."

The blue 4-disconnect juice manifold came from a factory with 480/3 "on the wall" and isn't related to that transformer or backfeeding. Not sure I made that clear.

It'll be easy for us to put protection on xformer output to up our legal current capacity, I think we have collected 6 or 7 slightly used 3 phase, 600v fused disconnects besides the blue ones, in anticipation of setting this up.
 
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AND one more little tidbit that my friend Chuck, an industrial electrician friend told me years ago. 240 volts will hurt you and might kill you, but 480 volts will just kill you. I've never forgotten that.
He's wrong.....I've been shocked by 480 volts before...it hurt like hell but I'm still here. Current kills more so than voltage....people have survived 2,000 volt shocks. 115 volts can kill as the current is often about the right amount to stop a heart muscle.

Still, no doubt 480 volts could kill you, so best to be cautious around any AC voltage over 30 or so.
 
He's wrong.....I've been shocked by 480 volts before...it hurt like hell but I'm still here. Current kills more so than voltage....people have survived 2,000 volt shocks. 115 volts can kill as the current is often about the right amount to stop a heart muscle.

Still, no doubt 480 volts could kill you, so best to be cautious around any AC voltage over 30 or so.

Many times in my short Navy career I was required to watch the training film "115 volts, Your Deadly Shipmate." There was 440 all around ships too but way more sailors were knocked off by 115v.
 
He's wrong.....I've been shocked by 480 volts before...it hurt like hell but I'm still here. Current kills more so than voltage....people have survived 2,000 volt shocks. 115 volts can kill as the current is often about the right amount to stop a heart muscle.

Still, no doubt 480 volts could kill you, so best to be cautious around any AC voltage over 30 or so.
Not just the heart muscle... ALL muscles. More than a few stories about people who get connected between a power tool or trouble light with a bad ground and the grounded structure they are working on, who simply CANNOT MOVE to free themselves. Higher voltages tend to cause involuntary muscle spasms that at least get you disconnected, before you fall from the ladder, scaffold, whatever.

Dennis
 








 
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