Transformer and panel install questions

[florida-sparkey]

Hello, I would very much appreciate some help in looking over my design.
I wish to install a 200 amp 3 phase, 4 wire 240/120 volt panel for small machine shop loads.
This panel will be fed through a transformer powered from an existing 3 phase 480V service.

Three phase 230 Volt 30 amp MOCP is largest motorized device (saw) that will be connected to new panel, remainder of panel capacity is for future use at this time.

Here is my plan:
Set new fused disco rated 600V with RK1 150A fuses and connect to 480V service conductors in trough per below (connection is on load side of a 400A fused service disconnect)

Feed xformer primary with 4/0 XHHW less than 25 feet, in conduit.
240.21(2) Math: 400A/0.33 = 132A minimum conductor size
Xformer primary math: FLA= 270A, PV480, SV240, so 270/(480/240) = 135A primary full load Amps
Both above good with 4/0 XHHW feeders

Install dry type 112.5KVA 480-240/120 Volt Delta standard duty transformer on floor (Transformer is oversized for safety, motor starting and minor nonlinear loads. Secondary FLA = 270 Amps)
Secondary taps will be less then 25 feet, terminate in a 200A main breaker and be 250KCM XHHW in conduit.
240.21(6) Math: Prime to secondary voltage ratio = 480/240 = 2 so 2*(0.33*150) = 99A minimum conductor size. 250KCM XHHW is good

Bonding for over 250 Volts as needed per 250.97
Bond grounded conductor in xformer and no bond connection in panel 250.30(1)
#4 CU Electrode conductor to building steel
#2 XHHW grounding conductor to disco and panel

I figure AIC at the new transformer fed panel main breaker -
Math: Transformer Z=4% and secondary FLA=270 (100/Z*I) so 100/4*270 = 6,750A minimum AIC rating required for the main Is this correct?
For above AIC, I assume infinite capacity on the primary and no impedance for the secondary conductors. Lastly on this question, I have assumed the Z at 4% because in all my looking I cannot find the exact part number my supplier has quoted me so I have gone below the lowest I could find for a 1K-factor unit rated at 112.5KVA per the supplier PDF spec sheet.

My first question is did I miss anything?
My second question is did I get the primary and secondary feeder tap requirements correct?
My third question is: Is a 10K AIC rated panel sufficient?

Thank you!

 

[Fnewman]

Without checking any of the calculations, I can tell you that you will most likely not have a 3 phase 120/240 available because normal 3 phase voltage derived from a 480 volt system is 120/208. In practice, however, your load can likely operate at either voltage.

 

[electrofelon]

Hello, I would very much appreciate some help in looking over my design.
I wish to install a 200 amp 3 phase, 4 wire 240/120 volt panel for small machine shop loads.
This panel will be fed through a transformer powered from an existing 3 phase 480V service.

Three phase 230 Volt 30 amp MOCP is largest motorized device (saw) that will be connected to new panel, remainder of panel capacity is for future use at this time.

Here is my plan:
Set new fused disco rated 600V with RK1 150A fuses and connect to 480V service conductors in trough per below (connection is on load side of a 400A fused service disconnect)

Feed xformer primary with 4/0 XHHW less than 25 feet, in conduit.
240.21(2) Math: 400A/0.33 = 132A minimum conductor size
Xformer primary math: FLA= 270A, PV480, SV240, so 270/(480/240) = 135A primary full load Amps
Both above good with 4/0 XHHW feeders

Install dry type 112.5KVA 480-240/120 Volt Delta standard duty transformer on floor (Transformer is oversized for safety, motor starting and minor nonlinear loads. Secondary FLA = 270 Amps)
Secondary taps will be less then 25 feet, terminate in a 200A main breaker and be 250KCM XHHW in conduit.
240.21(6) Math: Prime to secondary voltage ratio = 480/240 = 2 so 2*(0.33*150) = 99A minimum conductor size. 250KCM XHHW is good

Bonding for over 250 Volts as needed per 250.97
Bond grounded conductor in xformer and no bond connection in panel 250.30(1)
#4 CU Electrode conductor to building steel
#2 XHHW grounding conductor to disco and panel

I figure AIC at the new transformer fed panel main breaker -
Math: Transformer Z=4% and secondary FLA=270 (100/Z*I) so 100/4*270 = 6,750A minimum AIC rating required for the main Is this correct?
For above AIC, I assume infinite capacity on the primary and no impedance for the secondary conductors. Lastly on this question, I have assumed the Z at 4% because in all my looking I cannot find the exact part number my supplier has quoted me so I have gone below the lowest I could find for a 1K-factor unit rated at 112.5KVA per the supplier PDF spec sheet.

My first question is did I miss anything?
My second question is did I get the primary and secondary feeder tap requirements correct?
My third question is: Is a 10K AIC rated panel sufficient?

Thank you!

Looks good to me, without an exhaustive analysis. Just a few minor terminology corrections:
1. You are not connecting to service conductors, those are feeders. you have a feeder tap from the tap point to the fused disco
2. The #2 XHHW is a SSBJ

Also dont forget about 408.36 (usually "automatically" met with typical install of MB panel)

Is the XHHW aluminum? (would be fine either way)

 

[GoldDigger]

Without checking any of the calculations, I can tell you that you will most likely not have a 3 phase 120/240 available because normal 3 phase voltage derived from a 480 volt system is 120/208. In practice, however, your load can likely operate at either voltage.

You appear to be new enough to the forum that you are not familiar with the three phase four wire high leg delta, with the center point of one delta winding connected to ground and used as the neutral for 120/240 circuits.
It is not uncommon, although not all POCOs will allow it for a new service.

It is very useful when you need a lot of 120 or 240 for lighting and general use but have one or more three phase motors, etc.
It is often implemented by POCO as an open delta with a large 120/240 single phase three wire pot and a smaller "stinger" pot sized just for the motor load(s).

One reason POCO may not like it is that it is not as inherently balanced across all three distribution phases as 208Y/120 three phase four wire.

 

[dionysius]

Hello, I would very much appreciate some help in looking over my design.
I wish to install a 200 amp 3 phase, 4 wire 240/120 volt panel for small machine shop loads.
This panel will be fed through a transformer powered from an existing 3 phase 480V service.

Three phase 230 Volt 30 amp MOCP is largest motorized device (saw) that will be connected to new panel, remainder of panel capacity is for future use at this time.

Here is my plan:
Set new fused disco rated 600V with RK1 150A fuses and connect to 480V service conductors in trough per below (connection is on load side of a 400A fused service disconnect)

Feed xformer primary with 4/0 XHHW less than 25 feet, in conduit.
240.21(2) Math: 400A/0.33 = 132A minimum conductor size
Xformer primary math: FLA= 270A, PV480, SV240, so 270/(480/240) = 135A primary full load Amps
Both above good with 4/0 XHHW feeders

Install dry type 112.5KVA 480-240/120 Volt Delta standard duty transformer on floor (Transformer is oversized for safety, motor starting and minor nonlinear loads. Secondary FLA = 270 Amps)
Secondary taps will be less then 25 feet, terminate in a 200A main breaker and be 250KCM XHHW in conduit.
240.21(6) Math: Prime to secondary voltage ratio = 480/240 = 2 so 2*(0.33*150) = 99A minimum conductor size. 250KCM XHHW is good

Bonding for over 250 Volts as needed per 250.97
Bond grounded conductor in xformer and no bond connection in panel 250.30(1)
#4 CU Electrode conductor to building steel
#2 XHHW grounding conductor to disco and panel

I figure AIC at the new transformer fed panel main breaker -
Math: Transformer Z=4% and secondary FLA=270 (100/Z*I) so 100/4*270 = 6,750A minimum AIC rating required for the main Is this correct?
For above AIC, I assume infinite capacity on the primary and no impedance for the secondary conductors. Lastly on this question, I have assumed the Z at 4% because in all my looking I cannot find the exact part number my supplier has quoted me so I have gone below the lowest I could find for a 1K-factor unit rated at 112.5KVA per the supplier PDF spec sheet.

My first question is did I miss anything?
My second question is did I get the primary and secondary feeder tap requirements correct?
My third question is: Is a 10K AIC rated panel sufficient?

Thank you!

First let me check this before I continue???

Primary V*I = 480*135 = 64,800
Sec V*I = 240*270 = 64,800

Why such a big trafo 112,500 VA or is it you want to double it approx for expansion in future???
Is this a 3 phase delta to delta trafo??

Also could I request that you sketch a drawing with the details on it to keep it easier to follow......

 

[roger]

Three phase 230 Volt 30 amp MOCP is largest motorized device (saw) that will be connected to new panel, remainder of panel capacity is for future use at this time.

So this one piece of equipment is the reason you want to install a Delta? It might be better to use a Buck Boost transformer for one piece of equipment and install a more usable Wye system for future.

Roger

 

[augie47]

So this one piece of equipment is the reason you want to install a Delta? It might be better to use a Buck Boost transformer for one piece of equipment and install a more usable Wye system for future.

Roger

That would be my first thought. I believe you will find that your 240/120 transformer has a very limited neutral capacity which could pose a problem if you end up with much of a 120v load,.

On a second point, your grounding electrode conductor appears to be undersized. The size would be based on your secondary transformer conductors and based on 250.66.

 

[florida-sparkey]

Without checking any of the calculations, I can tell you that you will most likely not have a 3 phase 120/240 available because normal 3 phase voltage derived from a 480 volt system is 120/208. In practice, however, your load can likely operate at either voltage.

I specked the transformer with supplier and see others like in there listing so I do not understand why you would expect 120/208. This would be a huge concern so please elaborate if I'm missing something.

Yes my load may work but it may also get damaged due to heating no? Other loads on site have electronics so the voltage is more critical I think? These loads will be connected to the new panel over time.

 

[florida-sparkey]

Looks good to me, without an exhaustive analysis. Just a few minor terminology corrections:
1. You are not connecting to service conductors, those are feeders. you have a feeder tap from the tap point to the fused disco
2. The #2 XHHW is a SSBJ

Also dont forget about 408.36 (usually "automatically" met with typical install of MB panel)

Is the XHHW aluminum? (would be fine either way)

Ha, you got me. I forgot about the main disco as I wrote and then remembered. I went back and thought I corrected the terminology. Also I had open my 2008 so I think that SSBJ is not in that one? 2014 in truck.
Yes XHHW is AL
Thanks so much for your time!!

 

[iwire]

I do not understand why you would expect 120/208. This would be a huge concern so please elaborate if I'm missing something.

In my area 208Y/120 would be what I would expect in a building with a 480 volt service.

 

[florida-sparkey]

So this one piece of equipment is the reason you want to install a Delta? It might be better to use a Buck Boost transformer for one piece of equipment and install a more usable Wye system for future.

Roger

No sir. There are 3 or 4 machines. I was trying to keep it simple and list only one.

The backstory is that the customer is moving over a space into this unoccupied and larger unit. Old customer had overhead cranes. I suspect that's the reason for the 480V.
All of the the customers was purchased for and run on a 240V delta system.

A small 208/120 Wye transformer and panel exist on site. They power the 120V loads at this time.

I have considered the buck boost but the customer was not crazy about it. I may look at this again for costs. Not sure if that best serves the customer long term though. I felt a panel was better option long term.

Thanks for your time!!

 

[augie47]

My concern with a 3 phase 480 to 240/120 comes from the neutral loading as expressed in this post from an earlier thread from Jim Dungar and from manufacturing data sheets I have reviewed:

• It really has to do with the laws of physics and things like magnetic fields and circulating currents. But, the fact of life is: a single core transformer connect in a 4 wire delta is limited to 5% neutral loading. Multi-core transformer banks (i.e. using single phase transformers) do not have this problem.​
  
  
  

 

[florida-sparkey]

First let me check this before I continue???

Primary V*I = 480*135 = 64,800
Sec V*I = 240*270 = 64,800

Why such a big trafo 112,500 VA or is it you want to double it approx for expansion in future???
Is this a 3 phase delta to delta trafo??

Also could I request that you sketch a drawing with the details on it to keep it easier to follow......

I am so sorry but I am afraid I do not understand your answer or your math. 270 Amps is the maximum secondary current with a 112.5KVA is it not?? That is per the manufacturer and I have checked it mathematically or so I thought.

Next smaller xformer secondary is 180A unless I and the manufacturer rep have missed something? 180A will not support a 200A panel.... Well ok, it will at 80% of 200Amps but that is maxed out.

With starting motors you should add 20% per manufacturer so I cannot see how a smaller xformer could be used.

Thank you for your time!

 

[GoldDigger]

N.B. : 80% of 200 is 160, not 180.

 

[florida-sparkey]

That would be my first thought. I believe you will find that your 240/120 transformer has a very limited neutral capacity which could pose a problem if you end up with much of a 120v load,.

On a second point, your grounding electrode conductor appears to be undersized. The size would be based on your secondary transformer conductors and based on 250.66.

Thank you for catching the ground size screw up!!! I did not know it was based on the secondary. Size per 250.66 is #2 CU.

I am using a 240 panel with 120 for two reasons. (was thinking of using just a straight 240 panel but see reason 2 below)

1 I was basically told that was my transformer option.

2 Just in case a machine later needs a neutral for the brain or computer.

120 volt loads will (do) come from the existing 120/208 panel that is on site

Thank you sir!

 

[florida-sparkey]

N.B. : 80% of 200 is 160, not 180.

Your killin me. LOL.. Wife is fuzzy eyeballin me to eat breakfast she made so I was in rush.

 

[florida-sparkey]

In my area 208Y/120 would be what I would expect in a building with a 480 volt service.

I am not sure about what is standard but the 480V services I have seen in my area are 480/277

 

[iwire]

I am not sure about what is standard but the 480V services I have seen in my area are 480/277

Yes, a building with a 480Y/277 service would have 208Y/120 transformers supplied from the 480 to supply 120 through 230 volt loads.

If I had only one piece of equipment that requires 230 volt I would use a 208Y/120 volt transformer that can supply many things and just boost the voltage for the one load.

 

[florida-sparkey]

Looks good to me, without an exhaustive analysis. Just a few minor terminology corrections:
1. You are not connecting to service conductors, those are feeders. you have a feeder tap from the tap point to the fused disco
2. The #2 XHHW is a SSBJ

Also dont forget about 408.36 (usually "automatically" met with typical install of MB panel)

Is the XHHW aluminum? (would be fine either way)

The #2 XHHW AL you are referring to is an ECG, ground wire from xformer through disco to panel that has no MBJ. (here, we are required to pull a ground wire in all conduits) While in this case, I am not sure it is required on the service side or from trough to the disco, I see no harm in installing it? (if we use non metlic conduit then it would need to be sized per SSBJ below but as of now, EMT is my choice)

I think SSBJ is service side bonding jumper and that is not that wires function. Others have pointed out that my GEC was to small and so any SSBJ's have to be increased in size to match the new GEC size of #2 CU

Thanks again for the help

 

[florida-sparkey]

Yes, a building with a 480Y/277 service would have 208Y/120 transformers supplied from the 480 to supply 120 through 230 volt loads.

If I had only one piece of equipment that requires 230 volt I would use a 208Y/120 volt transformer that can supply many things and just boost the voltage for the one load.

I get a little lost in replying so forgive me. The flow can be hard to follow.

I have stated that yes, there are at least 3 or 4 machines that are rated 230V and that some have electronics. (I thought I was keeping the OP simple where I could)

Do you think buck boost is the way to go long term?

Also I have stated that there is an existing 120/208 xfrormer and panel but I do not think I could carry the machine loads from them. It is for some lights and receptacles but I honestly have not looked to hard at it because the panel is old FEC and is in bad shape.

I felt that giving them a 240 source in conjunction with the existing 120/208 would cover most all bases. One for machines and the other for lights receptacles or even a 208V machine if they later purchased one.
Is this bad thinking?