Installing my first transformer part 2

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mark32

mark32

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Currently in NJ
Hello again!

So I snapped a couple of pics from the install yesterday. You may notice I tapped and threaded my own lay in lug in order to land the system bonding jumper, which in turn is bonded to nearby building steel. I do have a question though, according to the tap info on the transformer cover (As shown) I chose to use tap #4 because the equipment is rated for 460v. My math (480 × .975) = 468v sounded pretty good to me. However, once energized, I was getting 485v - 489v across the h1, h2, and h3 terminals. Am I looking at the tap info wrong, should I have gone up to tap #2 instead?? The equipment is not on-site yet, so, there was no load on the transformer.
 

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What exactly are the primary x's voltage? Invest in some grade 8 hardware and dble barrel lugs.
Good job cleaning the busses but scraping the paint at the lay in is needed- and you should use a 1/4-20 hex with a nut on the back/bottom...
 
Mark - you went the wrong way ;)

The tap table you looked at is always trying to get 480VAC on the Secondary if you have a little under or over voltage on your 208VAC Primary.

You went to tap#5, which is for 2.5% undervoltage on the Mains Primary.

But assuming you have something close to 208 coming in, then "tricking" the transformer (with the tap change for slightly low Primary voltage) it will adjust the turns ratio to get ~2.5% more than 480 (~492 VAC). Which is close to what you measured.

Try moving them down to tap#2. Then your math should get you the 468ish.

This will trick the transformer into thinking your Primary is a little hotter than 208, so it will adjust the turns ratio to keep the output at 480. But you really aren't hotter, so the output will be lower than 480.

Clear as mud, right?

Good luck.
 
I agree that unless the lay-in lug is factory installed the paint needs to be removed. The #6 GEC is oversized but that allows it to be run exposed. I probably wouldn't bother changing the taps if the output was 480 volts.
 
Thank you fellows for all the replies!

Rambojoe, the primary voltage is 208v. The mounting hole for the lay in lug is too small for a 1/4 -20, I suppose I could've drilled it out some, but unless I am mistaken, a 10/32 is sufficient. It's funny you and Infinity mentioned removing the paint for the lug, but I almost never bother scraping off the paint when I tap a lug/ground bar to an enclosure. I'm not saying I'm against it, but if removing the paint was an issue, then the factory would/should do the same. How about when one bonds a floating neutral bar to it's enclosure in a main panel using the supplied screw, the bar is not touching the enclosure at all, it's relying on the head of the screw for this connection, so what difference does it make if the paint is scraped off or not?

Hillbilly1, when we placed the order, I told them the primary was 208v and the secondary is to be 480v, delta to wye. How could you tell if it were being backfed?

MD Automation, yes, yes! I understand now, that thought crossed my mind as soon as I saw what my meter was reading. But, the shop was closing for the day, so I didn't have time to change the taps.

Infinity, you have good eyes my friend! You are correct, that is #6.
 
mark32 said:
Hello again!

So I snapped a couple of pics from the install yesterday. You may notice I tapped and threaded my own lay in lug in order to land the system bonding jumper, which in turn is bonded to nearby building steel. I do have a question though, according to the tap info on the transformer cover (As shown) I chose to use tap #4 because the equipment is rated for 460v. My math (480 × .975) = 468v sounded pretty good to me. However, once energized, I was getting 485v - 489v across the h1, h2, and h3 terminals. Am I looking at the tap info wrong, should I have gone up to tap #2 instead?? The equipment is not on-site yet, so, there was no load on the transformer.
Click to expand...
Interesting that your first xformer is a step up application. Good to see that the correct 208 delta 208 primary and 480Y secondary was correctly chosen. I think you did well and demonstrated that you understand the NEC concepts for a compliant installation.
 
For a installation like that you shouldnt rely on threadeds for bonding- especially with pricey equipment. And like tulsa shared- it should hit all the grounds, but im not a stickler for that...
Removing paint is good practice, removing plating on oe busses is not. Not the end of the world.
Putting a 10-32 star washer and nut on the back of that p2 will make it sorta compliant.
Most guys here have wired up a few xfrmers, take it for what its worth.
 
mark32 said:
Hillbilly1, when we placed the order, I told them the primary was 208v and the secondary is to be 480v, delta to wye. How could you tell if it were being backfed?
Click to expand...
Mark, no worries. It's not being backfed. Like Texie pointed out, you got the correct transformer for the job.

Based on your original post, I assume you got the Maddox 30 kVA.

What Hillbilly1 maybe was guessing at, the most common transformer is a step down, like a 480D to 208Y. So, that transformer is the easiest to get. Your application is less common (step-up) and sometimes the right step-up transformer can be a long lead time part. So people tend to backfeed a more common step-down, because they are easier to get or they have one lying around.

Typically you can tell the side meant to be the Primary by looking for the windings with the taps. They will almost always be on the Primary, in your case the X1,X2,X3 coils. So you know your Low Voltage windings (X) are the Primary, and the High Voltage windings (H) are the Secondary. So your transformer is designed as a step-up (low primary to high secondary) unit.

For the grounding lug issues, is one option to replace that stupid small grounding bar with something like this???

1680742484106.png
Have to drill a thru hole to bolt it in, but they are super easy to get and cheap too. It's silly for them to install such a tiny grounding bar with 2 holes to save a few dollars.

On a related note - I purchased a Square D transformer a few years back that had an oddly reverse problem, it's grounding bar was hilariously oversized. It's nice it had 4 holes, but they were stupid huge for the size of the transformer.

1680742785527.png
 
Thank you Texie 👍👍

And thank you again rambojoe. I agree that, according to 250.12, (As Tulsa also pointed out and provided the article section :) that removal of the paint is required to be compliant, and is good practice as you stated, it just rubs me the wrong way that we have to do it, but factories/manufacturers do not, plus, clearly, these factory made connections (Ground bars bolted/threaded to the enclosure without removing the paint) far outweigh the number of field made connections, with no adverse results that I am aware of. (That's a long sentence:) To continue, I am curious though, at what point does one choose a nut and bolt over a threaded screw/bolt connection? As for 450.10, if I'm reading it correctly, there should be a single ground bar for all such terminations. I'm not sure if you saw my first thread with the same title, but I questioned why the manufacturer only put a two hole ground bar when I need to land the SBJ somewhere.
 
MD Automation, thank you kind sir for your time :) I didn't realize this at first, but it now seems step down installations are more common as you had mentioned. Reason being, in all of the transformer posts I read leading up to this install, they mentioned terminating the SBJ to the XO terminal. Yet, when I took the cover off, there is no XO terminal, where the hell is XO?? Haha! But then it dawned on me that, because the neutral is being generated on the secondary side, plus the secondary is the higher voltage, it made sense that the terminal would be HO. You didn't happen to go by a different user name in the past have you?
 
mark32 said:
Thank you Texie 👍👍

And thank you again rambojoe. I agree that, according to 250.12, (As Tulsa also pointed out and provided the article section :) that removal of the paint is required to be compliant, and is good practice as you stated, it just rubs me the wrong way that we have to do it, but factories/manufacturers do not, plus, clearly, these factory made connections (Ground bars bolted/threaded to the enclosure without removing the paint) far outweigh the number of field made connections, with no adverse results that I am aware of. (That's a long sentence:) To continue, I am curious though, at what point does one choose a nut and bolt over a threaded screw/bolt connection? As for 450.10, if I'm reading it correctly, there should be a single ground bar for all such terminations. I'm not sure if you saw my first thread with the same title, but I questioned why the manufacturer only put a two hole ground bar when I need to land the SBJ somewhere.
Click to expand...
Let's say you use the single lug as you did. You taped the the screw into the metal and it has two threads of contact. No nut required.

I and most add nut to secure to make sure it does not loosen during wire installation. Tightening the screw on conductor some times will loosen the screw on a single lug install.

Since this wire is the GEC and being used as a bonding jumper a loose connection to enclosure is not a good connection between the lug and bar where other wires are attached. The important one being the supply side bonding jumper (SSBJ)

Your supply side bonding jumper conductor is under a different lug attached to the enclosure. Your relying one the case to establish this connection. This is why they all should be under a single bar. A single bar uses two screws or bolts. Now as you tighten the conductor it should not loosen the screws due to twisting. If the bar was bolted then clean paint and bolt down tight as there is not two threads in contact as per code. The bar also establishes good connection between all grounding and bonding conductors. The enclosure is simply bonded by the attachment of the bar. Two machine screws with two threads of contact or clean surface and bolted.
Since your system bonding conductor attaches to this bar your GEC can pass Thu to the HO like you have and can serve as a Bonding jumper. Other wise your supply side bonding jumper needs to go to HO.

Since you install has a spare hole on the bar you can add a jumper from the lay in lug to the bar. Still a violation however now the enclosure is not the sole connection. A lay in lug usually is listed for two conductors. Just like in a disconnect.
If the single screw/ bolt and nut for any reason becomes a poor connection the enclosure is bonded via the bar and it's factory
connection. Better yet run from third hole in ground bar to HO.
The SSBJ now would have a low impedance path to HO for clearing ground faults.
Remember there is no netural connection to EGC on after the SDS in this case. Your SSBJ to HO is very important. Right now it goes to a bar then to the enclosure over to the lay in lug and up to HO. Any loose bad connection there is not good. It could have an impact on clearing a ground fault or at the least a delay. I feel this is the main reason for the change to a single bar connection then bond enclosure. It's the little things that make a huge difference in safety. Scrap a little paint put in a nut. You get the picture. Single bar not as big of deal. The fault will come back on the EGC to the SSBJ to HO. Breaker trips. So take the paint and nuts out of the equation for fault clearing by way of single bar attachment. Now all your considered with is bonding the enclosure. Two machine screws with two threads or clean and bolt. If there a core fault the good workmanship will clear fault on the primary side due to good bonding. The EGC on the primary side attached to that bar will or should open the OCPD on the primary very quickly. Now fault clearing on both primary and secondary side is in check as per code.


Again, first one very nice job.
I like the way your GEC is continues to HO thru the lug.
I also like the use of bonding bushing.
The #6 GEC good choice.
 
Thank you Tulsa for taking the time to write! I'm not 100% certain I am going back to this job, as I'm basically done there. But, I'm sure I could make an appearance to take care of a couple of things. And that being, I would like to change out the existing two port ground bar with a larger one, like the one MD had included in his post. I was unaware a lay-in lug is rated for two conductors, so, I would keep the lay-in in place, and just jump from that to the new ground bar. Or, I could take the #6 off of HO and terminate it to the new ground bar, and run a new #6 from HO to the ground bar, nothing would be attached to the lay-in lug in this scenario.
 
I would say you have few options if you choose to.
The factory would be fine if hole is large enough for a system bonding jumper to HO. Then your compliant.
It appears large enough.
Then your EGC attaches to HO and your system bonding jumper attaches to HO. Your good.
Then you can do different on next one.

You can look at this way. If was a service your MBJ attaches to enclosure and netural bar. Your GEC also attaches to the netural bar. Your SDS now has a system bonding jumper to HO and a GEC to HO.

Same set up with different names.
We use Main Bonding Jumper on the service.
We use a system bonding jumper on a separately derived system (SDS).
This takes some of the confusion out of what your doing. The use of a system bonding jumper from HO to single bar allows for your SSBJ,EGC, bonding jumpers and GEC to attach to this bar. You could also run the GEC to HO if you want.
I loop the GEC thru the bar unbroken and go to HO. Then it serves as the system bonding jumper as well.



The lay in lug can stay if you like as it is just there.

Little more clarification on the lay in lug. I may have mis spoke. I know in a switch you can put two under the lay in lug as long as it's the same wire Guage. I would need to find supporting reference for use other than switch ( disconnects ).

Still fun doing SDS work. It will work just fine the way you have it so don't rush to fix.

Few pics to share.
Mike Holt and ECM
 

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Thanks again Tulsa for your continued efforts! I will go back to the job within a couple of weeks and change out the factory two hole ground bar for a larger one, I'll report back with a photo when it's completed, you're going to like it :)
 
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