# Transformer help!



## telsa (May 22, 2015)

10,000 Amps -- get an EE.

Period.


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## Kevin (Feb 14, 2017)

This is something an Electrical Engineer needs to be involved with. 

Sticking a 1000kva transformer in one room sounds like a good idea in terms of equipment, but it's not the best way to do this, especially for VD.

Also, this site is for electricians only... a moderator will probably lock this when the see It, but that's up to them.

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## varmit (Apr 19, 2009)

Few, if any, utilities will install a single service of that size. The fault current is way too high and is a huge cost/ logistical problem for them to have spares if there is a failure. A 3000 amp service, or multiples there of, is usually the limit of the utilities that I know of.

There is a need for some engineering work on this project.


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## Southeast Power (Jan 18, 2009)

Dakotahm88 said:


> I have a licensed electrician willing to do installation from me. And I’m somewhat familiar with electrical. Anyways,
> We’re putting in a 10,000 amp service. Will enter from utility company provided transformer into a 10,000 amp 277/480Y MDP.
> 
> From there the MDP is geared as follows:
> ...


You are looking at it from the service side out to the loads, thats not how it's done.
You start from the utilization, go to the distribution and then to the service, grouping loads in areas that make sense to minimize voltage drop. You are starting out with 480 volts. You should use that as far as possible before even thinking about a transformer. Any equipment you can get onto your 480 volts will be a gift for your wallet. 

Hire an engineer, and electrical PE, and be very upfront about what you need short and long term so the design can scale either way if needed.


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## splatz (May 23, 2015)

Something doesn't add up here, would anyone think that being "somewhat familiar with electrical" would be sufficient to design this distribution? An electrical engineer will need to be involved at some point but didn't someone more than "familiar with electrical" already do the layout you're working from? 



As @Kevin_Essiambre mentioned due to the way the wire sizing and voltage drop work out it usually makes sense to distribute at higher voltages then step down to lower voltages for utilization.


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## Dakotahm88 (Sep 21, 2019)

Where I live electrical inspectors for residential don’t exist, therefore i’ve wired my own new house once in 2010 once in 2017. I’m smarter than your average DIYer, smart enough not to try this by myself. 
I’ve hired an electrician that was highly recommended, the reason for this post is a lot of stuff he says makes no sense and makes me feel as if he doesn’t know what he is talking about.

I’m building a 25,000 sq ft Medical marijuana facility in Oklahoma.

The 16 x 277 panels are for lighting and dehumidification.

The 10 x 120/208 panels are for oscillating wall mount fans etc..., i’ve Researched for hours and wasn’t able to find any oscillating fans or air circulation fans made for humid climates that accept 277/480.

So, while I know it’s less economical to transform to 208, there’s not really any other options.

I’m trying to wrap my mind around how this project should work, so I can ask him when I see something that should be done another way.

My main concern was if I should be using a single transformer, or splitting it into 3, or 20 small ones for each panel.... etc. 

Our electrical room is only 20 x 20, doubtful 20 transformers will fit without stacking. 

Just looking for cost saving advice. I don’t know any EEs and a google search brings up jobs for them on indeed!


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## joe-nwt (Mar 28, 2019)

A 10,000A service/distribution in a 20x20 room? That, right there, is why you are over your head. Hire an engineer.


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## Dakotahm88 (Sep 21, 2019)

All the panels are going outside each room on the wall. ATS is outside, The only thing in the 20x20 is transformers and MDP.

Saves a lot of time pulling wires and saves hundreds of feet of MC


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## cdslotz (Jun 10, 2008)

Way over your head....lol


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## CoolWill (Jan 5, 2019)

We haven't heard what the electrician said that made no sense. We have only heard the customer's "better" plan.

What is the total connected load? Why do you need 200 amp panels in 20 places? This is why engineering is good here. Customers say "Well, I have ten 20 amp breakers, must need 200 amps!" But in reality, they can get away with a 40 amp subpanel.

At any rate, let's say you do have it all worked out by load, I'd try to lower that 120 load. Use as much 480 and 277 as you can. Then put your put your transformers as close to the load as practical. A 112.5 kVA could feed two 200 amp panels moderately loaded.


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## telsa (May 22, 2015)

At his power level everything has to be co-ordinated with the Poco.

He's making astounding presumptions about whether the utility can even bring that many Watts to his site. Out in the sticks, the utility may only be providing one-phase power.

The Poco will also demand lead time to get their network up to requirements.

The Poco may insist that the Service be at medium voltages, too.

When anyone says that they can't easily locate an EE -- you know they are really out of town.


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## Wardenclyffe (Jan 11, 2019)

Not smart enough to read and follow instructions, 

ElectricianTalk.com is designed to be a pros only community serving professional electricians, apprentices, and related professional electrical fields. Anyone who works as a professional electrician, apprentice or in a related professional electrical field is welcome to join the site and participate in our forums.


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## Dakotahm88 (Sep 21, 2019)

I already have a building sitting next door on a 3,000 amp service, I paid 36,000$ to have the lines brought to me, had them brought in large enough for this future project. The service is here. Thanks for not helping at all. 

My buildings rooms are modular, they can be rearranged. The first stupid thing my electrician said was to feed every panel from underground.

Sure that works great, except when I go to move one of the flex mod wall systems into a different setup, then I have an electrical conduit sticking up out of the ground in the middle of a room.

No, everything needs to be overhead. Poured cement last week.


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## paulengr (Oct 8, 2017)

No fuses go to 10,000 A. Not sure breakers come that big. Pressure bolted switches...maybe. The only switches used by utilities I know that big are very slow using pressurized SF6 to blow the arc out. You can use a triggered current limiter though which is a busbar rigged with C-4 explosive as a fuse. Costs about $6,000 per replacement. Very reasonable size for what you are doing. Arc flash will probably kill anyone if you ever get an arcing fault.

This sounds like a typical engineer design...way,way too big and very dangerous. It’s in the category of just because you can does not mean you should.

Realistically although you can certainly purchase equipment up in the 2,000-5,000 A range for a lot of reasons (safety, costs) it’s best to aim for around 1200 A or less at 480 V off of a given transformer. This makes arc flash equipment reasonable (40 ATPV or less) which is becoming a bigger deal going forward. At higher voltages costs are much more reasonable at around 800 A or less because that is the limit of a single section vacuum bottle interrupter.

I’ll give you an example of what happens at those currents, with real plants designed in the 1960s and 1970s when bigger was “better”. We worked on a distribution panel for a college last winter that was designed for only 3000 A at 480 V. They had 8 separate 4” conduits with 4 500 MCM cables (roughly 1” diameter each) for the feed to the panel. Instead of a panelboard (MDP) which is only a few inches deep just like the one in your house but limited to 1200 A max it required a switchboard which is physically much heavier and larger. Switchboard breakers are usually bolted in so you can’t swap them energized and it was about 4 feet deep. Next up would be draw out breakers that can be swapped out hot but far larger and more expensive yet. Breaker prices in drawout frames are typically $10,000 each and as an engineering estimate I usually use $25,000 per breaker. The panelboard with breakers will cost around that much total. Another example is a chemical plant near Wilmington, NC, across the street from a power plant. Their process generates heat so they have 3 large turbine generators that feed the plant and some excess power. The plant started with two subs at either end with two 8009 HP compressors. The substations were split in half with a backup tie breaker in the middle for maintenance and emergency backup purposes (main-tie-main). This worked until the third turbine generator was added. At that point the current exceeded the plants two main feeders in terms of capacity so they closed the ties, forming a loop with twice the capacity. Well that and now the short circuit current was doubled. It was so high that their breakers would no longer trip! The solution of course is to add triggered current limiters on both sides of the plant so that when a dead short happens the TCLs split the plant and everything can safely trip, sounds great except for spending $12,000 on replacement cartridges (that are about 3 feet long and weigh about 100 lbs) every time they get a trip such as a ground fault on a big motor. Ouch!

As a modern design take for instance the main Electrolux dishwasher plant. They come into the plant at 12,500 V, same as the utility’s substation voltage. At that voltage your 10,000 A feed would only be 384 A from the utility. That is doable with a single 350 MCM cable per phase in a cable in a duct. Then they have one large 12,500 V distribution panel with 10 fairly cheap fused disconnects going to each internal plant substation. At each sub they have another fused disconnect connected to a transformer. They step down to 480 but you can easily do 208 instead. If the majority of your loads are 208 this saves all those extra transformers and distribution. Then these each feed an MDP with roughly an 800-1200 A main breaker and distribution breakers off those.

As you can obviously tell the cost for this design will be a fraction of what someone is trying to sell you with a 10,000 A feed. Changes to your facility also won’t cost an arm and a leg and inevitable damage won’t turn into a huge explosion and a plant wide blackout.



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## Dennis Alwon (May 9, 2009)

Dakota, listen to what the others are saying. This is a huge service and the utility transformer would be so large that the aic rating would be expensive as can be. The utility can bring 480/277 to the building and they can also bring 208v to the building. 

Whatever is done and regardless of whether it is inspected or not an engineer needs to be involved. You cannot imagine what can happen if there is a fault and the aic rating is wrong. 

This is not something you should play electrician on, and ,in fact, I would bet nobody here would want to attempt this without an engineers stamp. 

Anyway, I am closing this thread as the rules require

Be safe -- save a buck but not with that wiring


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