# Transformer, connecting the feeders



## dowmace (Jan 16, 2008)

daveygroovy said:


> I am a licensed contractor from California. I am installing a 480Y/255V 3P 4W to 208Y/120V 3P 4W Transformer. This is the first time I've installed one and I need some confirmations. I am not sure about the actual connections. For istance I can easily see the H1,2,3 connections for the Load side. Where do I connect the Line side and what how do I approach the Nuetral connections in a wye to wye. Just for my own information, whats the difference in Nuetral connections between a delta-wye and a wye-wye transformer. Thank you for your time.


Not to be a jerk but your a licensed contractor and you've never installed a transformer? Do you have an ugly's manual? have you read the schematic that should have shipped with the transformer? :001_huh:


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## chenley (Feb 20, 2007)

dowmace said:


> Not to be a jerk but your a licensed contractor and you've never installed a transformer? Do you have an ugly's manual? have you read the schematic that should have shipped with the transformer? :001_huh:


I agree the info that comes with the transformer lays it out pretty cut and dry.


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## Rong (Feb 23, 2008)

daveygroovy said:


> I am a licensed contractor from California. I am installing a 480Y/255V 3P 4W to 208Y/120V 3P 4W Transformer. This is the first time I've installed one and I need some confirmations. I am not sure about the actual connections. For istance I can easily see the H1,2,3 connections for the Load side. Where do I connect the Line side and what how do I approach the Nuetral connections in a wye to wye. Just for my own information, whats the difference in Nuetral connections between a delta-wye and a wye-wye transformer. Thank you for your time.


 Maybe it is a 480/277 primary? And are you a licensed ELECTRICAL contractor? Makes a fella think with this kind of simple question.


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## nick (Feb 14, 2008)

*wye to wye*

with due respect to you as a electrical contractor and as a fellow electrician,i will give you my best not a expert , not to offend anyone but i agree with other post. primary and secondary are star star or wye wye taps ,it is most important to tie the pri neutral to the secondary neutral and earth together not clamping cad weld it ,heres why , if any phase is unbalanced part of load current flows in that primary neutral, also 3rd harmonics of exciting current flows in the pri neutral under no load .the neutrals must be connected together yes . if the load was high on one phase lets say[ a ]phase the voltage will be dropped on that [ a ]phase and the voltage on the c and b phases,s would rise up which is real bad on computers and your color tv ,also large harmonics are now on the lines between the neutrals and the phase,s not a good thing !meaning for a given voltage rms the peak voltage would be god knows what. its not good for your wire insulation or your terminations . just a hint this better be a crimp get the burndy out of the box now on that neutral .can i ask why you have to use this ? mostly you see this in a high voltage area like a plant or the like , not commercial 480 volts ? and now your x1 x2 x3 x0 is your load side h1 h2 h3 ho is the line side ,id call the factory as i do not connect any transformer up unless it has a name plate on the trans and marked on the taps . rotation is needed a b c it will work cba bca if you dont have motors on line or rotation is not a issue ? but these must be marked on the transformer and a diagram of connection must be on that transformer .i hope this helps you good luck best to ya .i just run pipe and pull feeders not a expert just have a little electrical back ground . i would needed another post for the delta to wye differance but just get the wye to wye done and post another question .are you sure about this transformer its not a zigzag it only has 3 legs ?


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## daveygroovy (Jan 23, 2007)

firstly it is a 480Y/277V, 255 was a typo. thank you for your help. i got my electrical license two years ago and have been an electrician for 5 before that. mostly residential and light commercial infills. this job i have is a retail infill and the switch gear is 480Y/277V 3P 4W. The small coffee shop needs of course lower voltage. I hadnt yet had the opportunity to choose and install a transformer until i started this job. I came to the conclusion I required a 75kva transformer. I chose the Square D model EE75T3H. It is a delta-wye with a 208Y/120 secondary. I read there was a way to wire a delta-wye, into a wye-wye by connecting the nuetral in a particular way. I have read a lot of materials but I just really wanted to discuss it with someone more familiar with the details and with more experience. Also can you explain discharging the static charges. Thanks alot for your time.


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## daveygroovy (Jan 23, 2007)

I meant to say thanks to you nick


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## nick (Feb 14, 2008)

*wye to wye issue*

no you cant change that transformer its factory made and the coil connections on the coils can not be changed from a delta -wye to a wye- wye it is not going to happen in this life time unless you un wind the coils which is not a good thing to try its one completed package from the factory , i see its not a wye to wye , i didnt think it was most contractors dont use them there only use in special areas for certain applications and the danger with these are not good if you dont do it correctly , and a engineer would be the one to pick that type if used. best thing i found is to get a good book on transformers or what ever your interested in learning read ,i was schooled in the military as a electrician .but i still learn everyday and have never stopped i come on site to see how other electricians work in different states,ya know problems or find out theres a better way or a new tool out .but you got to respect these old timers on this site they been doing work longer then me or you and they will let you know what is what in a heart beat . but if you got a electrical question ask .explain static ? whats that ?


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## ron_b (Jul 15, 2008)

*"your x1 x2 x3 x0 is your load side h1 h2 h3 ho is the line side"*

please, for your own good, heed the above quote from Nick!!


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## John (Jan 22, 2007)

Here is a drawing for connecting a 480 Delta/Wye primary to 208/120 Wye transformer. The primary can be connected using a 480/Wye system by just not using the neutral. 
And make sure you ground the X0 on the secondary.:bangin:

View attachment 586


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## nick (Feb 14, 2008)

*transformer issue*

yes i agree rob b thanks i should have change my last post , after we found out it was not a wye to wye transformer the tap for him now x1 x2 x3x x0 load side . but davegroovy now that you have a delta /wye you will not have ho on primary just h1 h2 h3 3 phase taps thanks rob no neutral on primary anymore only on wye to wye . and jhon he was asking about rewiring that transformer so i told him no way but yes now with the delta wye he can just wire it up to a wye or delta service 3 phase , thanks for the input hope he reads this , dont want to blow anything up out there in calif they already had one earth quake last week .


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## micromind (Aug 11, 2007)

This is a very common scenario around here as well. Most likely you're using brown-orange-yellow for 480 colors, and black-red-blue-white for 120/208. 

Bring 3-#2's (no neutral) from a 100 amp breaker in the 480 panel to the transformer. Brown goes on H1, orange on H2, and yellow on H3. The minimum ground would be #8. 

The 120/208 panel must have a main breaker in it, if its a 200, use 3/0; if its a 225, use 4/0. Phase A goes to X1, B goes to X2, C goes to X3, and the neutral goes to XO. Most of the time we use full size neutrals. The above assumes copper wire. The minimum ground size would be #6 for a 200, #4 for a 225. 

XO must be bonded to the ground somewhere, most transformers have a factory installed bonding jumper from XO to the case. If this is true, you can land your grounds on the XO bus, or anywhere on the case. If possible, I like to land them where the bonding jumper bolts to the case. If neutral to ground testing is ever needed it's much easier this way. 

Most of the time, I pipe transformers like this with EMT, or IMC. Flex or sealtite is OK too. In any case, make sure you enter the transformer below the bottom of the core and coils. This prevents heat from traveling up the conduit and heating up the panels. 

When a transformer like this is first energized, it'll likely make a sort of bang, then just hum quietly. The bang sounds sort of scary until you get used to it, but it's completely normal. Once you hook one of these up, you'll be amazed at how easy it really is. 

Rob


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## daveygroovy (Jan 23, 2007)

*thank you*

thanks again to everyone who left replies. Let me also ask (micro) what if my supply breaker is 200amps. I do think there is also a meter socket with a 100A breaker available, but we were designated a 200A meter socket. Yes I'm using a 225A 208Y/120v panel for the store. Thank you for all your time and advice. Believe me, I can understand the harsh criticisms but sometimes the best place to learn things is from experienced electricians themselves. I live in a small town with a lot of competitiveness as well as supplyhouse gossip, so it makes it awkward to ask my colleagues. I want to learn as much as I possibly can.


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## brian john (Mar 11, 2007)

Fellow forum members I am hired regularly by LICENSED CONTRACTORS to connect all types of transformers. Many light commercial and/or residential contractors have little or no expierence with transformers. Additionally other than a dry type standard off the shelf delt/wye many contractors freak. Lets not be so quick to condemn someone looking into some insight here.

Several issues here

1. The transformer has to be 480/277 or 440/255 additionally it is rare to have a 3 phase 4 wire wye primary, they exist but are rare. You did not mention an H0.
2. The LINE is commonly refered to as the Primary so your 480 delta A-B-C is Primary H1, H2 and H3. No Neutral/grounded conductor.
3. The load is the secondary and it is common for a 3 phase 4 wire wye secondary that is X1, X2,X3 (A-B-C phases) and X0 would be the neutral/GROUNDED CONDUCTOR.


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## micromind (Aug 11, 2007)

According to table 450.3(B) in the 2005 NEC, the primary overcurrent protection of a transformer with a current of more than 9 amps can be as high as 250% of the rated current. A 75KVA 3 phase transformer has a 480 volt primary current of 90 amps. 250% of 90=225. Thus a 200 would be OK. 

Wire size between the 200 amp breaker and the transformer gets a bit tricky. According to 240.21 (B) (3), if the length of the wire between the 200 amp 480 volt breaker and the transformer + the length of the wire between the transformer and the 225 amp 120/208 volt breaker doesn't exceed 25 feet, you can actually land a #2 under the 200 amp 480 volt breaker. If the total length is longer than 25 feet, you'll need to use 200 amp wire. 

This article in titled "Taps Supplying A Transformer". The word 'tap' is defined in 240.2. (The definition of 'service conductor' is found in article 100). If the inspector is not familiar with transformers, you might need to point out these provisions to him. 

Rob


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## Rong (Feb 23, 2008)

brian john said:


> Fellow forum members I am hired regularly by LICENSED CONTRACTORS to connect all types of transformers. Many light commercial and/or residential contractors have little or no expierence with transformers. Additionally other than a dry type standard off the shelf delt/wye many contractors freak. Lets not be so quick to condemn someone looking into some insight here.


 Brian you are so right. I had forgotten my "wire roping" days of yesteryear. I apologize for being unhelpful , sorry Daveygroovy.

In fact right now I could not wire a house today without ALOT of research on all the code changes since 1983!! From 1971 - 1983 to me a transformer was the thingy hanging on the pole with wires going to the house meter!!!


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## brian john (Mar 11, 2007)

A 75 kva transformer is rated 90 amps primary at 480 Delta that is 3 wires A-B-C phase no neutral/grounded conductor is required. The secondary is 3 phase 4 wire A-B-C-N, at 208 amps. In the secondary the neutral is grounded/bonded to the metallic frame the equipment grounding conductors and a grounding electrode conductor is routed to an approved grounding electrode. See article 250.

Transformer overcurrent protection is per article 450 and a NEC handbook can be very helpful. Also ask you AHJ for his thoughts.

Take a look at this.

http://www.electricalknowledge.com/forum/forum.asp?FORUM_ID=11

part 1 and part 2


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