[ETD66SS]

In reference to this thread: http://www.diychatroom.com/f18/max-cable-length-between-padmounted-transformer-structures-398362/

I have reconfigured my site layout so that the max cable run to any planned structure is about 120 ft. The site layout can be seen here: http://i.imgur.com/FLW8BjW.jpg

I would like to have a shop someday and be able to fill it up with equipment I get at auction, which means it will likely be 3 phase. I also want to have an overhead 5-7.5 ton crane, which will be 3 phase.

There is 3 phase available at the road, and I'd need to have a transformer installed with ~525 ft of HV cable.

The 3 ph options are:

1) 4-wire 208 wye/120 300 kVA max load
2) 4-wire 208 wye/120 1000 kVA max load
3) 4-wire 480 wye/277 500 kVA max load
4) 4-wire 480 wye/277 2500 kVA max load

I have a few questions:

1) The HV cable from the road to the transformer, from single ph to 3 ph, that becomes 3 cables? So likely 3X the cost of installation? I was quoted $17 ft for the power company to install the transformer and lay the cable in a trench I dig and backfill myself. That's 525 X $17 = $8,925. I have asked the power company about 3 ph costing, but they have not answered me yet. Would it really be ~$27k? Would I also pay a higher commercial rate for the power?

2) Once I have a 3 ph transformer installed, how do I get single phase out of it for my house etc? Would each structure need a separate transformer to get single phase? Or would I have an out building with a transformer in it to supply all the structures with single phase? Or do they make 3ph transformers that have a single ph tap? Delta-WYE transformer would give me all options?

3) Is it wiser to just have single ph installed and then if I get 3 ph equipment someday buy a converter?

 

[rjniles]

They will use a different cable. Single phase will use a 2 wire primary cable, 3 phase will use a 4 wire cable. I would not expect the price to double.
You will want the 208/120 transformer. Amperage depends on you planned load.

 

[ETD66SS]

They will use a different cable. Single phase will use a 2 wire primary cable, 3 phase will use a 4 wire cable. I would not expect the price to double.
You will want the 208/120 transformer. Amperage depends on you planned load.

So, if I get the 208/120 transformer, is there any equipment I'd run across out there that requires 480 volt? Or is pretty much all 3 phase equipment able to run 208v?

Also, as far as load, I will not be creating a shop full of employees, this shop will pretty much for myself, so these 300 & 500 kVA max loadings seem way overkill.

If I were to turn on everything in my house, shop and barn all at once, I don't think I'd be near 300 kVA max load.

I did a max loading calculation for my house and it came in around 13 kVA. I don't really know yet what equipment I will end up with in my shop...

 

[Daniel Holzman]

I find your post confusing. You say there is three phase available at the road. Then you say "The HV cable from the road to the transformer, from single ph to 3 ph, that becomes 3 cables?". The high voltage from the road will be three phase, and will go to a three phase transformer. If you select a delta transformer, there will be three hot wires from the road, and possibly a ground wire. If you select a wye transformer, there will be four wires, three hots and a neutral, and possibly a ground.

Most common I think is a delta primary transformer, with three hots. If you select a delta primary wye secondary, then you could produce 208/120 on the secondary, or 480/277 on the secondary. Since appliances in your house need 120 volts, the 208/120 would seem like the obvious choice, but then you would need to purchase 208V three phase equipment rather than 480V three phase equipment.

In any case, there are options, and you need to discuss this with the power company, who ultimately has to agree to supply you with three phase power, which is unusual for residential use. You probably also want to bring in a local electrician when you get serious, who can discuss the options, and may have some pull with the electric company to get what you want at a realistic cost.

 

[rjniles]

13KVA is only about 60 amps at 208 volts. Pretty small for a house if it is all electric.

 

[ETD66SS]

13KVA is only about 60 amps at 208 volts. Pretty small for a house if it is all electric.

Oops, I gave the wrong number, 13 kVA was the appliance demand load, service demand load for the house was 43 kVA.

However, I had an electric water heater in there, I will likely go with natural gas.

I also plan to use geothermal heat system and in-floor tubing style heat with heat pump.

AC will probably be a 3-4 ton unit in attic.

 

[mpoulton]

The 3 ph options are:

1) 4-wire 208 wye/120 300 kVA max load
2) 4-wire 208 wye/120 1000 kVA max load
3) 4-wire 480 wye/277 500 kVA max load
4) 4-wire 480 wye/277 2500 kVA max load

There's no option for 120/240V 3ph 4-wire delta ("high leg delta")? That would be the best suited option for a house with minor 3-phase loads. It's an old-school service and some power companies are trying to phase it out, but it's really useful for these kinds of installations. If they can do a high leg delta service for you, that would probably be the best choice. It gets you normal 120/240V single phase power for all your single phase loads, plus 240V delta 3-phase for the shop equipment. If that's simply not available, then 120/208 is the only other option for you. 480V is not appropriate for a residence or small shop. 300KVA is overkill for a house or small shop.

I have a few questions:

1) The HV cable from the road to the transformer, from single ph to 3 ph, that becomes 3 cables? So likely 3X the cost of installation? I was quoted $17 ft for the power company to install the transformer and lay the cable in a trench I dig and backfill myself. That's 525 X $17 = $8,925. I have asked the power company about 3 ph costing, but they have not answered me yet. Would it really be ~$27k? Would I also pay a higher commercial rate for the power?

The cost will be higher than for single phase, but not triple (unless they're ripping you off, which they might since you can't do anything about it). They will run a 3-phase primary cable instead of single phase. The cable costs more, but not three times more, and the trench is the same. Whether you would be on commercial rates or not (and what those rates would be) depends on the power company's policies. You'd have to ask them.

2) Once I have a 3 ph transformer installed, how do I get single phase out of it for my house etc? Would each structure need a separate transformer to get single phase? Or would I have an out building with a transformer in it to supply all the structures with single phase? Or do they make 3ph transformers that have a single ph tap? Delta-WYE transformer would give me all options?

If you had a high leg delta service, your house would not necessarily even have the third phase present. You'd just have a regular 120/240V 1ph service. Only the shop would use the third phase. Three phase wye power is three single phases that can be used independently or together. With a 280/120V wye service, you'd use all three phases at the house. Your 120V stuff would go on any of the three phases the same way it goes on either of the two hot legs in a regular single phase panel. Your 240V stuff would have to be 208V stuff instead, and would use two phases (a double pole breaker just like in a single phase panel).

3) Is it wiser to just have single ph installed and then if I get 3 ph equipment someday buy a converter?

Depends. For motors under 5HP, you can use a VFD with single phase input to run the motor from 240V 1ph just fine. Those VFDs cost about $300-400, and provide many advantages beyond just phase conversion - variable speed (including above normal speed!), soft start, and all kinds of programmable stuff like torque limiting, speed ramping profiles, and automatic control by other equipment. If you only have a few motors and they are no larger than 5HP each, then VFDs would likely be the best bet. Much cheaper than installing 3ph to the shop! You can find single-phase input VFDs up to maybe 10HP max, but they get expensive. If you will have a large number of motors, or if you have any big ones, then 3ph service may be the only good choice.

 

[micromind]

I'd go with the 120/208 300KVA system. The vast majority of 3Ø equipment will run just fine on 208. Some of it, you'll need to change taps because it'll come connected for 480, but it's pretty easy. If it has a 480 volt VFD, it cannot be changed to 208, you'll need a transformer. And not a basic standard one, it needs to have 277/480, not just 480.

Why have a single phase panel in the house. My house has a 120/208 3Ø panel and it's just fine. Everything wires the same as a single phase panel.

Actually, there's no way I'd ever install a single phase panel on a 120/208 3Ø service. Total hack.

BTW, 300 KVA at 120/208 = 833 amps.

Also, around here, a single phase transformer needs one primary cable from the POCO. A 3Ø one needs 3 cables.

 

[ETD66SS]

I think I am going to look at some of the old equipment we have at work, lathes, mills, shear presses etc. I'm pretty sure those machine tools need 480 3ph (as well as overhead cranes). I have not heard back from the power co. on what kind of 3ph they'd be willing to set a padmounted transformer. They might tell me I would not use enough power to deliver 480/277 to a residence. It's possible I could start an LLC and claim to be some type of farm. Farms can get certain things normal residences cannot.

 

[rjniles]

If you opt for and the POCO will install 480/277, either you or the POCO will have to install a 120\240 transformer.

 

[47_47]

I'll let the more experienced advise on size, but your biggest cost may be your ongoing monthly supply service charge.

My 24000 ft² warehouse used to be a CNC machine shop. Last month we paid 300.00 in energy usage and an additional 1250.00 in supply service charges and I own all of the transformers. This is through NYSEG in New York. I have seriously considered down-grading the service, but plan to retire in 5-7 years and elected to keep it as is, for resale. Just some food for thought.

 

[ETD66SS]

I'll let the more experienced advise on size, but your biggest cost may be your ongoing monthly supply service charge.

My 24000 ft² warehouse used to be a CNC machine shop. Last month we paid 300.00 in energy usage and an additional 1250.00 in supply service charges and I own all of the transformers. This is through NYSEG in New York. I have seriously considered down-grading the service, but plan to retire in 5-7 years and elected to keep it as is, for resale. Just some food for thought.

Yeah, one thing I don't understand yet is what the delivery and service charges will be.

Your cost sounds extreme.... But my shop will only be ~3800 sq-ft, and I am only one person. But if the delivery charge is outrageous, then it won't make any sense at all.

I'm used to an $85/month electric bill at my current home.

 

[ETD66SS]

Here is an example of a piece of equipment I'd want in my shop:

It's a Cincinnati 1/4" x 10' shear press. It has a 7.5 HP motor and it says 240/440 3 phase on the label. We have one here at work.

I would need 277/480 3 phase in my shop to run this thing? I'm a bit confused on the 240/440...

 

[mpoulton]

Here is an example of a piece of equipment I'd want in my shop:

It's a Cincinnati 1/4" x 10' shear press. It has a 7.5 HP motor and it says 240/440 3 phase on the label. We have one here at work.

I would need 277/480 3 phase in my shop to run this thing? I'm a bit confused on the 240/440...

It's a dual-voltage motor, like most 3ph motors. It runs on 208-240V if you connect it one way, or 440-480V if you connect it the other way. You could run that from a VFD on a single phase supply, but it's on the big end for that kind of setup and would require an expensive VFD. Still probably cheaper than installing 3ph service and paying for it every month.

 

[gregzoll]

If this is out in rural area. Do they even have 3 Phase out there? Most times it is just Single.

 

[ETD66SS]

If this is out in rural area. Do they even have 3 Phase out there? Most times it is just Single.

It's rural, but I am flanked by a couple farms, so they poco has already confirmed to me 3 ph is available. But I'm finding it difficult to figure out exactly what installation will be, as well as service and delivery charges.

It is true that the 3 ph equipment will get sparingly used, weekend type stuff etc...

I have enough land that I could actually incorporate as a farm, and get the farmers rate, which is lower than commercial rate. But getting the info out of the poco is like pulling teeth. The guy they assigned to me never answers my questions with concise answers.

And I guess I still don't get it, how to you get 220V from 208V lol. Sorry, I'm a mechanical engineer, and don't understand electricity all that well.

 

[micromind]

I guess I still don't get it, how to you get 220V from 208V lol. Sorry, I'm a mechanical engineer, and don't understand electricity all that well.

Over the last 26 years, I'v connected a LOT of industrial equipment. Most of it was 480 but some was 208 and a few were 240.

I've never had any sort of problem connecting something rated 220 or 230 to a 208 system.

If absolutely necessary, 208 can be raised to 220 or 230 or 240 fairly easily using buck-boost transformers. These are MUCH smaller than regular transformers and two of them will raise the voltage in 12, 16, 24, 32 or 48 volt increments.

Changing the voltage on 220/440, 230/460 or 240/480 volt equipment is easy. Simply re-connect the motors as well as the control power transformer.

The exception here is if the equipment uses VFDs. I've never seen a VFD that is 240/480. Further, using a transformer to go from 208 or 240 up to 480 is not as easy as it seems. A basic standard transformer can be used but it requires modification to the VFD and I do not recommend it. A transformer with a 277/480Y winding is needed, not a 480∆.

That shear shown in the pic a few posts back will almost certainly work on 208, as will the vast majority of other shop equipment. Generally speaking, the cheaper and chintzier it is, the lower the possibility that it'll run on 208.

Rob

 

[gregzoll]

You will not know until you get the bills. Just because there are farms in that rural area, does not mean that they have 3 phase service. It just means that out of thr 3 phases, they can better balance the loads that could possibly occur if one customer ends up introducing more load on the service then another.

Also it helps with keeping the power more stable on the grid.

You could end up with two sets of wires to feed the 3 phase service. As for that equipment you posted a picture of. You normally do not see that in someone's shop. It is normal to see it in a manufacturing environment.

 

[ETD66SS]

Just because there are farms in that rural area, does not mean that they have 3 phase service.

I've already been told by the power company 3 ph is available at my lot. What I have not been able to get out of them yet is if they would provide a 3 ph padmounted transformer, and how much the delivery & service charges will be.

As for that equipment you posted a picture of. You normally do not see that in someone's shop. It is normal to see it in a manufacturing environment.

All I can say to that is I'm not "normal"...

 

[gregzoll]

The person on the phone is only going by what the computer shows. You need to actually get in touch with the engineers and thry can sit down with you to go over what your plans are.

Depending on future demands. Their infrastructure may not be able to carry that load on that section of lines that you are on, unless they have all of the information about it.

The biggest factor that you are going to run into in a rural area is Lightning strikes. If the system on your side is not well protected with a well designed Ufer system in the building that you are going to use as the shop. You could end up losing thousands of dollars of equipment.

Get ahold of the IEEE books on this subject area. They explain things a lot better than the NEC and local.

I can post which ones, once I get back to pull thr DVD that I have them on.