Ran into a unique situation at a project. Customer sent in a load data sheet to the local utility before I got involved with the project. They had asked for at least 250 kVA for a new building, with room for expansion. The utility is installing another new service on site with a 500 kVA 12470V Delta Primary - 480Y/277 Wye-N Secondary pad mounted transformer ahead of the project. This is a large industrial park add-on. Customer now wants to have at least a 1200 amp 480v main panel with an 800 amp main for future expansion. I have never sized service equipment after the POCO has been involved and already sized the transformer. The utility transformer is good for 601 amps at 480v 3-phase, and I know they size differently than we do...and drive them over their ratings, buts that's always their call and risk. I am inclined to tell them to stick to 600 amps, which is still double their request and allows expansion. Has anyone dealt with this situation or have an opinion on what is the best option? Not sure about 800 amp main on 500 kVA utility from a liability standpoint, even if calculated load is well under that.
Sizing service to 500 kVA utility transformer
- Thread starter Russell39
- Start date
Elect117
Senior Member
- Location
- California
- Occupation
- Engineer E.E. P.E.
Put in what they want. It is on the utility to size their equipment and it is on you / the engineer to size the customer's.
The only thing I would advise is looking at the utility's service guidelines and see if they are putting in the number of secondary conduit needed for a 800A service or a 1200A service. They are typically two different duct bank configurations.
You can always oversize the service to the customer's request. I have seen a bunch of 4000A switchgear with only a couple hundred amps on it because some new build tilt up wanted to be able to use it as a selling point. "4000A / 3MW ready". Even though the utility put in a 300kVA transformer lol.
The only thing I would advise is looking at the utility's service guidelines and see if they are putting in the number of secondary conduit needed for a 800A service or a 1200A service. They are typically two different duct bank configurations.
You can always oversize the service to the customer's request. I have seen a bunch of 4000A switchgear with only a couple hundred amps on it because some new build tilt up wanted to be able to use it as a selling point. "4000A / 3MW ready". Even though the utility put in a 300kVA transformer lol.
Thanks. Yeah, I have oversized services to give the customer what they wanted, but that is usually ahead of the utility having set their transformers, so there is always that “that’s on them” attitude as to what size they supply. We are covered on the conduit, so 1,200 amps isn’t an issue from that standpoint. I just have never gotten involved after the utilities transformer has been set for a customers supplied load calculation. Appreciate the input.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
What I would generally end up seeing in similar situation here is the POCO will size their transformer to the expected demand.
If customer wants bigger transformer, they likely are going to pay a higher demand fee every month for such commercial/industrial applications like OP has even though they don't use that capacity.
Nothing wrong with putting in the larger service equipment for future use and having POCO upgrade the transformer when you do add the load. They will penalize you when that time comes if you don't upgrade with demand penalties - if you exceed their demand arrangements. You need to get new demand arrangements when that additional load is added to get the best rates for your application. Sometimes just making attempts to schedule loading so you do certain activity during off peak periods if your operation can handle that might be all that needs to happen .
Some this can vary from one POCO to another but concepts are common to some extent with most. If you only have 250 kVA of demand but want a 500 kVA transformer, it usually will be costing you more on a monthly basis to have that capacity than to have whatever they want to use for a transformer. If the peak is short enough in duration they may only want a 225 kVA transformer.
If customer wants bigger transformer, they likely are going to pay a higher demand fee every month for such commercial/industrial applications like OP has even though they don't use that capacity.
Nothing wrong with putting in the larger service equipment for future use and having POCO upgrade the transformer when you do add the load. They will penalize you when that time comes if you don't upgrade with demand penalties - if you exceed their demand arrangements. You need to get new demand arrangements when that additional load is added to get the best rates for your application. Sometimes just making attempts to schedule loading so you do certain activity during off peak periods if your operation can handle that might be all that needs to happen .
Some this can vary from one POCO to another but concepts are common to some extent with most. If you only have 250 kVA of demand but want a 500 kVA transformer, it usually will be costing you more on a monthly basis to have that capacity than to have whatever they want to use for a transformer. If the peak is short enough in duration they may only want a 225 kVA transformer.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
In theory it is very simple: the customer provides the utility their loads and utility installs their equipment. If equipment is already set and you have a change or addition, you let them know and they will either upgrade their equipment or deem it not necessary. There would probably be construction charges for the former so some would find it tempting to not involve the power company and just run with it and see what happens.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
If their demand goes up enough they may pay (possibly pretty hefty) demand penalties is one potential risk of not informing POCO of added loads.
Is going to cost more regardless but can be more reasonable cost to get new service contract then to pay demand penalties against your old contract terms.
Elect117
Senior Member
- Location
- California
- Occupation
- Engineer E.E. P.E.
As an FYI going to 1200A adds
110.16(B) - Arc Flash Study / Labeling
240.87 - Arc Energy Reduction (sometimes referred to as energy reduction maintenance switch).
230.95 - Ground Fault Protection of Equipment
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
I wonder if going with 2 600s would be better?
Elect117
Senior Member
- Location
- California
- Occupation
- Engineer E.E. P.E.
That is probably dealers choice. 1200A 277/480V, I would guess that they might have some light manufacturing in a larger building. I am also going to guess at this being an electrical room and the possibility of limited space. Two 600A might have a larger foot print with each having their own distribution. But it is all guessing lol.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- Semi-retired engineer
I wonder how much extra cost you have added by choosing this option. I guess as long as the guy footing the bills is onboard it does not matter much but it seems to me that the low cost option is to install a 600 A panel with provision to add a second one if it becomes necessary down the road. Most times unless someone has some pretty good Intel about future plans guessing what makes sense does not get you much other than spending a lot of someone else's money.
Strathead
Senior Member
- Location
- Ocala, Florida, USA
- Occupation
- Electrician/Estimator/Project Manager/Superintendent
The thing is, the calculation is the calculation, it doesn't depend on the size of the breaker on the premises. It wouldn't change just because they are putting in a bigger service, it would only change if they increased their load. Curious about Illinois. I have worked in California and in Florida. In Ca we used to install 5-5" conduits for wire by the utility for any building in the 600A plus range. In Florida, the Electrical Engineers always size the secondaries to the service breaker and they are provided and installed by the electrical contractor. How do they do it in Illinois?
Elect117
Senior Member
- Location
- California
- Occupation
- Engineer E.E. P.E.
On new builds, the cost of labor + material to put in the 1200A vs value to the building on being able to rent it, sell it, or increase production.
Labor + material doesn't get cheaper over time. So when the price tag on the new building is $1 mil and the added cost of putting in the 1200A is adding maybe 50k then does it really change much? Especially when expedite fees are about that much anyway. I think they just add the extra cost as value to the building.
Labor + material doesn't get cheaper over time. So when the price tag on the new building is $1 mil and the added cost of putting in the 1200A is adding maybe 50k then does it really change much? Especially when expedite fees are about that much anyway. I think they just add the extra cost as value to the building.
They chose this option. I have explained the extra cost and all the options to the customer and they want the 1200 amps. I have even offered to set it up with 600 amps but in a way that is easily expandable IF they need it and given them a quote for each. This is definitely more expensive, but they seem to not see the extra cost as a problem...so they will get what they want. I have contracted with them for years with both maintenance and new installs.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
One strategy, which I usually prefer, is to use 220.87 for future additions. Get away from those bloated unrealistic NEC calcs
When you consider that the actual demand will typically be half or less than an NEC load calc, it likely makes a lot more financial sense to install something like an 800A service, and throw a logger on it. Likely if you have that data for your own knowledge and for any permit or plan reviewer, you probably won't need to upgrade any equipment when stuff is added. For example, for well under a grand......compare that to nearly doubling the service size.
3-Phase 4-Wire Metering Package
This metering package includes everything you need to meter 3-Phase 4-Wire electrical systems and to send your meter data to the cloud. Please customize your metering package by choosing the products you wish to order from the drop-down lists and check boxes above. ~section 2~ To simplify the...
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kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Some of the details still matter though.
A school I used to do most their electrical had 2000 amp switchboard as the main service equipment and distribution center in the newest major addition to the facility. Breakers in that switchboard fed the original service equipment (or what might have replaced original) in each of the older portions of the facility plus whatever new branches/feeders were deemed necessary at that time. This switchboard however was only supplied with single phase power, the breakers that were over 200 amp were all three pole frame breakers but with no guts in center pole so effectively were two pole breakers.
When the time came and the board wanted to install a heating/ cooling system that would cover all the facility (particularly with A/C that was previously only smaller units in select areas) We really needed three phase in a serious way. 2000 amp switchboard was plenty of switchboard but reconfiguring it for three phase was not all that much of a reality. Faster and likely less cost - we ended up going with 1200 amp Fused switch for service disconnect and I-Line for a distribution panel. 800 amp possibly would been enough we went with 1200 for possible future loads. But I guess maybe future loads was what they were thinking with that 2000 amp switchboard? Might been fine if they had it built so it could be converted to three phase easier. Also upgraded some the existing subpanels to three phase for load balancing reasons and at least two of them from recollection did have some three phase load added to them in this whole project.
I like that idea for this install and future installs. Makes the whole 30-day data logging or 1 year worth of maximum demand fast and easier to acquire. I do a lot of industrial work and have had to use 220.87 more than a few times. Thanks.One strategy, which I usually prefer, is to use 220.87 for future additions. Get away from those bloated unrealistic NEC calcs
When you consider that the actual demand will typically be half or less than an NEC load calc, it likely makes a lot more financial sense to install something like an 800A service, and throw a logger on it. Likely if you have that data for your own knowledge and for any permit or plan reviewer, you probably won't need to upgrade any equipment when stuff is added. For example, for well under a grand......compare that to nearly doubling the service size.
3-Phase 4-Wire Metering Package
This metering package includes everything you need to meter 3-Phase 4-Wire electrical systems and to send your meter data to the cloud. Please customize your metering package by choosing the products you wish to order from the drop-down lists and check boxes above. ~section 2~ To simplify the...
From a utility guy perspective.
Put in what the customer wants..
we will get a bigger transformer.
More kWh = more revenue..
We have a mill that shut down. They have a couple of 2000 amp panels. The usage is so low there we put in a 150kVA.
If they get cranked up again we will make it bigger.
No load losses add up pretty quick
Put in what the customer wants..
we will get a bigger transformer.
More kWh = more revenue..
We have a mill that shut down. They have a couple of 2000 amp panels. The usage is so low there we put in a 150kVA.
If they get cranked up again we will make it bigger.
No load losses add up pretty quick
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Was there enough room in the terminal cabinet of the 150kVA transformer for all the conductors (presuming you have at least 4000 amps of conductors to terminate there)? Or was this more of an open transformer inside some kind of enclosure/barrier or even up on pole/pole supported platform?