Sheet metal shop coil line apparatus transformer questions

[hhsting]

Is the forum worthy of a response? Did they tell you to leave it ungrounded as shown in their print, and call it NRTL listed?

Or did they tell you they shipped the wrong transformer and connection drawing? Curious minds would like to know...

Sorry it took this long for them to get back but yes I certainly asked the letter signed from Iowa precision. Guess what they are now going to change transformer from delta to delta To delta to wye step up. So they are telling me 208V delta to 480V wye secondary grounded. You all are correct! Wow what knowledgeable people here

However now the design engineer PE of this project not Iowa Precision said all the items would be NRTL listed but provided no certification of it? Also the PE of this project still says transformer is not premise wiring system.

 

[hhsting]

It appears pretty simple to me, but I've encounter this situation many times. Customer acquires a machine built for a voltage other that what they have. They want to use a transformer they have , or buy a used one for cheap, and connect it in reverse. I've seen many do it. They don't realize that the output coil is nearly always a delta coil, and there is no simple way to ground it, other than corner ground it, or leave it ungrounded. Neither do they realize what the implications are of leaving it ungrounded and floating or corner grounding it. From a safety aspect or equipment operational problems or damage that may result from doing so.

A lot of equipment today built as standard, doesn't play nice with an ungrounded or corner grounded supply. Most new equipment with any electronic requires a grounded wye supply to be reliable. Codes and listings aside, if I'm going to do it and accept the liability and support for the equipment, I want it done right. No mater what the buyer, salesman, line assembler, engineer or inspector thinks. I understand the difference and make it proper or I walk.

It seems clear in this case that the vendor selling the equipment, supplied the wrong transformer, and doesn't understand the difference. The machine builder clearly built the thing for a 480V grounded wye, and the machine dealer cobbled on the wrong type transformer to make the sale. And the customers contractor doesn't understand either.

The codes and standards are not a how to manual or a design manual and should not be used as a substitute for knowledge about the system engineering and design. Nor should they be used as a workaround, to get past inspectors, engineers or designers that aren't fully up to speed with the situation at hand.

This job needs the correct transformer, bonded and grounded properly, and that can't happen with what the vendor supplied. Simple.

Would you say since you saw this many times the correct transformer be separately derived or not for the application?

 

[MTW]

A delta to wye transformer is a separately derived system, there are no physical electrical connections between primary and secondary coils, only magnetic ones to transfer power.

As to the engineer... he didn't understand the problem in the first instance, correct? Drew up the prints with the wrong transformer type, specified an ungrounded system, with no ground fault monitoring as required by the code? And you needed to go over his head, to get the correct transformer supplied? Seems pretty clear to me that he is out of his league on this one. Everyone has to learn sometime, when encountering new applications, it's best to not learn them by trial and error if at all possible.

Did he supply a new print for the installing field electricians and the customer, showing how to properly bond and ground the new separately derived source? If the field installers don't do that part correctly, then the correct transformer and equipment would likely have the same problems as the incorrect delta output transformer.

Equipment or premises wiring? If the transformer was attached to the equipment, and prewired and tested buy the equipment builder with the equipment, then I would consider it part of the equipment and its listing. On the other hand if it it was supplied separately, untested with the equipment, and it is the installers responsibility to size the required overcurrent protection and wiring types and sizes, then I would consider it part of the premise wiring to supply a new load.

If you needed the listing of the new transformer, get the manufacture and model # from them and look up the listing on the manufacturer's site.

 

[winnie]

Would you say since you saw this many times the correct transformer be separately derived or not for the application?

IMHO the correct transformer for this sort of unit will have a solidly grounded wye output.

This could either be a delta:wye transformer which is an SDS, or this could be a three phase balanced autotransformer supplied by an upstream wye system. The latter approach is not an SDS. The critical feature IMHO is the balanced, neutral grounded supply, not the SDS status.

Jon

 

[hhsting]

A delta to wye transformer is a separately derived system, there are no physical electrical connections between primary and secondary coils, only magnetic ones to transfer power.

As to the engineer... he didn't understand the problem in the first instance, correct? Drew up the prints with the wrong transformer type, specified an ungrounded system, with no ground fault monitoring as required by the code? And you needed to go over his head, to get the correct transformer supplied? Seems pretty clear to me that he is out of his league on this one. Everyone has to learn sometime, when encountering new applications, it's best to not learn them by trial and error if at all possible.

Did he supply a new print for the installing field electricians and the customer, showing how to properly bond and ground the new separately derived source? If the field installers don't do that part correctly, then the correct transformer and equipment would likely have the same problems as the incorrect delta output transformer.

Equipment or premises wiring? If the transformer was attached to the equipment, and prewired and tested buy the equipment builder with the equipment, then I would consider it part of the equipment and its listing. On the other hand if it it was supplied separately, untested with the equipment, and it is the installers responsibility to size the required overcurrent protection and wiring types and sizes, then I would consider it part of the premise wiring to supply a new load.

If you needed the listing of the new transformer, get the manufacture and model # from them and look up the listing on the manufacturer's site.

The PE who stamped and sign is renovating building and includes room for shop which has coil machine and transformer. PE is saying transformer provided by the builder is not separately derived and is not part of premise wiring.

The builders of the equipments are mastek which is part of Iowa precision. They are the ones who are revising transformer and didn’t know or installed it incorrect

PE and builders of equipment two different.

Attached is what was submitted by builder revised. As you can see looks like separately derived transformer delta to wye grounded and secondary cables provided by the builder based on cut sheet to the cabinet. It does Not look like auto transformer or non SDS. However no equipment grounding conductor secondary side is shown also I imagine GEC would at least have to be shown by the PE in his plans? Not sure about all the above

View attachment file.pdf

 

[augie47]

As drawn it is an SDS and it shows a secondary ground.
It would seem this would satisfy your task as plans review. Let you inspector & the electrical contractor work out the specifics.

 

[MTW]

To sum things up, it's slowly moving towards the correct direction. You managed to get somebody to realize that the wrong type output transformer was specified, for the load at hand. Two competing engineering views and a offshore conglomerate management company, leaving it up to the plan reviewer to sort out the design deficiencies or suitabilities. Then a difference of opinions on what is premise wiring and what is separately derived....in other words, who is on the hook if things go poorly.

I come at it from a different perspective, what does the equipment need to function safely, properly and reliably, does it meet the code requirements, does it meet the local inspectors requirement, and does the job relieve me of excess liability when it's said and done. Augie has my vote. The local inspector will have the final say, not the competing engineers, installing contractor or the plan reviewer. And if it goes badly the customer will have something to say about it as well.

My view is that the revised transformer connection print is partially correct, but still has deficiencies and omissions. I think at this point the forum has answered your original question about the transformer originally specified and whether it need to be grounded or not. It is not the job of the forum members to do the engineering review for someone else's job, unless they willingly choose to do so. They are not the ones who get paid to take that responsibility. What each party decides is up to them. The forum is here to share knowledge and experience, not to perform someone else's engineering task responsibilities.

These are the things I see as incomplete or undocumented with the design as shown.

The grounding and bonding requirements of the transformer, and the requirements of the load equipment, were the reason the transformer choice was incorrect it the first place.

The transformer secondary needs to provide for short circuit currents, bonding to the grounding electrode system of the building, and provide an equipment grounding conductor to the machine. The VFD drives in the machine will need the equipment grounding conductor, as you surmised, not only for fault currents, but to provide a symmetrical ground reference for the surge suppression devices (MOV) inside the drives and a common point for dissipation of common mode currents which all VFD drives produce. Without this important pathway, properly connected, the VFD drives are likely to have short lives and be problematic in operation. The drawing also lacks a bonding connection for the case and core. It may be left up to the inspector to know and catch these things, if the installer fails to know what to do and why.

The last issue is the connection and protection of the transformer itself. There is nothing shown for the primary protection of the transformer or a main disconnect. The breakers shown on the secondary side may or may not be adequate, based on the choice of the primary overcurrent protection chosen. The transformer output is rated at 36A continuous but the beakers protecting it add up to 55A. There are tap rule requirements for distance and overcurrent protection as well as sizing of conductors, from the secondary. All of these choices as well as the physical layout and location of each item will affect if these things meet the code or machine listing requirements.

If these things were left up to the installing contractor to decide, then you have a part of the premise wiring system, and subject to the code.
If these things were specified, provided, located and prewired by the machine builder, then it would fall under the machine listing.
Your stuck somewhere in the middle as the plan reviewer, between multiple opposing viewpoints and responsibilities. When you add in the contractor and inspector the opinion may change yet again. This is why it's best to spell it out on a print, so every one involved can be on the same page.

Hope that helps.

 

[hhsting]

Wanted to update you in regarding this post my case. So I contacted the machine manufacturer myself who told me that they ship the machine and transformer separately. All wiring, grounding and bonding transformer has to be per local AHJ code and they are not responsible. All primary and secondary cables, overcurrent protections per local AHJ and they are not responsible. They apologize to me that wrong transformer was installed and now they are shipping correct transformer delta to wye grounded. The transformer they are shipping is not autotransformer. The transformer they are shipping is separately derived. Got it in writing from the machine manufacturer. Please note above is for my case only

That settles that! Boy what a mess! Its premise wiring in my case. Now the engineer has to provide everything transformer grounding bonding, tap rules discos, primary secondary overcurrent protection and cables per NEC 2014

 

[MTW]

Glad to hear that you got the answers that you needed, and that you returned to share with us what you learned.