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Thread: Cost for a primary line

  1. #21
    Join Date
    Apr 2008
    Location
    Ann Arbor, Michigan
    Posts
    6,779
    180116-1157 EST

    electrofelon:

    I would be inclined to start them separately. This lowers the starting current and reduces the needed breaker size as well.

    Is there any dynamic stability problem? Don't know. Once running one might mechanically lock them together. This might be important if a high inertia load was added.

    It has been found in large auto plants that using multiple air compressors can be an energy saver. Much of the time full air capacity is not needed. In our case we have 1 5HP reciprocating unit that is normally used. Also have a 10 HP scroll type that is only used when more air is required. Seldom do we run both simultaneously.

    .

  2. #22
    Join Date
    Jan 2018
    Location
    SE Michigan
    Posts
    81
    Gar, as new member here, and in the same DTE district as you, I'll offer up a few pointers and experience with their planners, and some about phase converters.

    First thing is zoning of the proposed new location.

    Residential only, is a complete non starter for a 3Φ service. Several planners have told me, 3Φ on residential is against the public service commission rules. I never looked up the rules myself, but this is what the planners go by. If your in an area that is zoned for residential and light commercial on the same lot, that makes the provider rules different.

    As an example at one site years ago, we had a commercial building with a new tenant, on frontage of 8 Mile Rd. The building was on a corner lot, of a residential side street. The customer had a fair amount of 3Φ equipment they needed to run, and the building had a 3Φ 4W Service installed. 400A with a CT cabinet. After the equipment was installed and connected to the service, it was found that the high leg was not connected at the service point. The building service hi leg wire was existing, at the service connection point, but was not terminated to the drop, curled up and isolated. A quick look across the residential side road, revealed that the 3Φ primary was existing, but the pot for the open delta configuration was missing.

    The first planner had a look, and claimed unequvically that service commission rules prohibit 3Φ lines from crossing residential streets. We pleaded the customers case, but he wouldn't hear of it, at any cost. A few weeks later we tried again. The 2nd attempt got us a 2nd planner, 1st one was on vacation. After pleading the case again, he agreed to connect us and set the pot for about $1600 if memory serves correctly. He told me that the hard liner was gone for a week, and if he got the order in, before he returned, it would not get canceled. I had the customer hi tail the check over to his office, and it was a done deal. So if you have any contacts with people in the district, talk it up privately to see if you can get a reasonable planner that serves the district your in.

    I have found on multiple occasions that if you gave a load schedule prepared on their forms, ahead of time, before you contact them, helps them a great deal on seeing the load you want to connect. It can help, if you pad the load schedule a small bit for future loads, don't go way overboard here. List the loads as current or future. One planner allowed me to install an 800A service on one of their 400A rated banks that was existing. Having the load schedule with descriptions of the load types and duty cycles can help greatly on getting what you need, but its on you to PROVE it, not just state that you need it. Their internal standard for transformer bank sizing is way different than the NEC values, so focus on the load and use types, not the transformer size you want.

    Next thing is to have a copy of a higher than average invoice, for the existing shop location. This gives them the account number, so that they can easily look up the existing demand, and compare to your load schedule. In your case, invoices for all 3 meters you have at the shop location. I would also include one for the house meter as well, since that will need to be added to the requested service.

    Proof of the existing monthly spend with them matters a great deal, in my experience. It's been all over the map in my experience. Customers with a large monthly spend, normally get what they want, with little hassle, and for very low to no cost. They see the payback period, and calculate accordingly.

    On the other hand is the customer, that is a new customer, that wants a big service for something he plans to do, but has zero history with the company. This is a sure fire way to get the most denials and the largest costs, meaning all costs upfront, and no amortization factoring, for no history. They don't want to be caught holding the bag, if and when your plan goes flat.

    On to phase converters. I would suggest that if you run decent size CNC's that you consider dedicated converters sized for each CNC machine.
    Some are more sensitive to disturbances and unequal voltages than others. Some RPC manufacturers will suggest this as well. Then a smaller converter to run the remainder of the shop equipment.

    An overly large converter will normally be factory balanced at its full load rating. When lightly loaded, the hi leg voltage will be excessive for smaller loads and lead to current imbalance and overheating. Most manufacturers have a minimum motor size listed for each converter model to help prevent this situation. Sharp voltage fluctuation from a hard starting compressor cycling on and off can play havoc with a sensitive CNC or other load. One RPC builder that I like his write-up on can be found HERE
    Be sure to check the links at the top of the page as well, he covers the material pretty well.

    Paralleling RPC units is no problem even of different sizes or makes, you can even have one self starting unit, and the other compensated idlers, start from the first one as needed. As you stated earlier, two of the lines are common to all idlers, the only thing that needs to be done is check the phase rotation of each additional unit that you bring online so that they match. Swap the supply lines as necessary and leave the wild leg common to all units.

  3. #23
    Join Date
    Apr 2008
    Location
    Ann Arbor, Michigan
    Posts
    6,779
    180119-1116 EST

    MTW:

    Thanks. Very useful information.

    I am very surprised that south of 8 mile, east of Telegraph to the Canadian border, and probably north of Goddard is not almost all wired as delta primary with only three wires.

    In Ann Arbor much of what I see is 3 phase delta primary, no apparent neutral. In my neighborhood definitely no neutral, subdivided late 1950s. Recently DTE replaced a failed 25 kVA with a 50 kVA for my home and one other, no big load.

    On South Industrial, 1960s development, primary is wye, and we have 2 phases from that providing 3 phase wild leg.

    Glad to learn that you have had no dynamic instability with direct paralleling of phase converters.

    The property my son is looking at is near Peach Mountain, and there are various problems, zoning, that are of concern besides electrical. From my rough estimate his average daytime load would be about 15 kW. So on an average basis the existing 25 kVA transformer could be adequate. Total nameplate load is probably pushing 200 HP or 200 kVA. But machines are not all running at once and fully loaded.

    Why are many people so up tight about CNC machines? They have some single phase load, some small 3 phase motors, a few HP, and then DC powered servos, and spindles. Many machines are not heavily loaded. Our spindle loads, per machine meter, are usually in the 15 to 20% load with much of that friction. Mills have very little inertia load. Lathes have larger inertia loads, and tend to be cycled up and down.

    From my son's perspective we would probably only use single phase air conditioning, change the 5 HP air compressor to a single phase motor, put the single phase portion of CNC machines directly on the single phase wires (only how you run wires to the machine), possibly change the manual mills to VFDs (advantage of electrical variable speed), even a possibility on the manual lathe, and that leaves only a couple large 3 phase motors, that are not run much of the time, as major loads that require good 3 phase power.

    Need to leave.

    .

  4. #24
    Join Date
    Apr 2008
    Location
    Ann Arbor, Michigan
    Posts
    6,779
    180217-2025 EST

    This comment is to just cleanly close the discussion.

    Thanks for all the comments.

    My son and his wife, on their last look at the property, have decided that there are too many unknowns. Electrical is really only a small part of the consideration. So we will never get a determination on what electrical would have cost.

    A factor that they never considered was medical. As one ages this needs consideration. In my case I am legally within about 5 minutes of a very major hospital, about 1 mile, breaking rules 2 to 3 minutes. My son's present location is 20 to 30 minutes to the same location.

    .

  5. #25
    Join Date
    Dec 2012
    Location
    Placerville, CA, USA
    Posts
    19,134
    My wife and I made the same decision, moving from a nice rural property which was 30 minutes from the hospital (20 minutes to nearest grocery) and had several days of road closure due to snow each year to one 8 minutes from the hospital on a well plowed road.

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