Getting a 480v service installed, step down to 208 or 240?
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  1. #1
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    Default Getting a 480v service installed, step down to 208 or 240?

    I am in the process of getting a 480v 3ph service installed on a shop property. I told the electrician doing the work that I wanted to step back down to 240/120, and re-feed the existing 240/120 1ph panels from that.

    They dropped off the transformer two days ago and it is 480v to 208y/120. He basically brushed it off as not a big deal, and said he wasn't sure he could get one in 240v with a neutral tap. I don't seem to have much trouble finding a 75kva 480 to 240/120 transformer.

    Should I be okay living with having 208 in this building now, or make them get me the 240v transformer that I originally requested. (And that they referenced on the quote)

    I have a suspicion that the 208 transformer was cheaper...but maybe that is just the skeptic in me.

    Any input is appreciated, thanks.

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    If you use 480 to 120/240, those panels will be fed off single phase. That means that your incoming 480V will be less evenly loaded.

    Whether that's an issue will vary.

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    Quote Originally Posted by SomeoneSomewhere View Post
    If you use 480 to 120/240, those panels will be fed off single phase. That means that your incoming 480V will be less evenly loaded.

    Whether that's an issue will vary.

    Does going to 208/120 make any difference in the balance of the incoming 3ph?

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    Three Phase Four Wire Wye Electrical Service
    The most common commercial building electric service in North America is 120/208 volt wye, which is used to power 120 volt plug loads, lighting, and smaller HVAC systems. In larger facilities the voltage is 277/480 volt and used to power single phase 277 volt lighting and larger HVAC loads. Talk to your power company!!

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    Unless you install two services to the building you still need to step-down somewhere to run 120v and 208-240v power. The balancing of the phases does not seem to be an issue to anyone at the PC, and I know of other buildings who have similar step down configuratuons.

    Given that I am setting this up from scratch, and I think have the option now. Would I be better suited to have 240v in the building, or will I not see any difference in running 208v? I have never been on a 208v service, and as best I can tell most things I have now should work on 208v though less efficient.

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    [QUOTE=johfoster;3487351]Unless you install two services to the building you still need to step-down somewhere to run 120v and 208-240v power.

    This is not true. Talk to your power company.

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    Quote Originally Posted by tommy1010 View Post
    This is not true. Talk to your power company.

    Can you elaborate on how this is possible please?

    Does anybody have any input on the 208v vs 240v situation? Thanks

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    I have been running on 120/208 for over 15 years and have seen zero problems

    Don't run much single phase equipment, couple ACs, drill press, lift, welders....everything else is 120 or 3 phase..... no failures or misbehavior

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    To the OP. Since i reread your original post I am inclined to believe you are getting a service in an existing building with a 480 volt distribution panel? If this is correct the electrician is correct on his choice of transformer. Older industrial buildings were wired delta-delta but the common voltage was 440 volts. 440 volts between phases and 440 volts to ground! You need a way to trip on an electrical fault to ground. You can take a phase on a delta-delta system right to ground and not trip a breaker or blow a fuse. This is highly undesirable in modern wiring systems and not allowed. 480 volt wye supplied power is 480 volts between phases and 277 between phase and ground. It will trip a breaker if there is a phase to ground fault. If you are getting a new service from the power company 208 3 phase with 120 single phase will come right into you panel and no transformer paid by you is needed. If I remember a 240 volt motor can run easily on voltage as low as 207. In industrial settings it very common to have voltages vary. Most will be higher. 115-120-126 230-240-248 etc. I am sure there are many people that can chime in here with their knowledge if we know all the facts of you situation.

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    Default 208 volt

    Here is a 208/120 volt setup3-phase-distribution-panel.jpg

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    How many 120 or "220" circuits do you anticipate needing?

    Do you have any 240V 3 phase needs?

    The 208/120 will serve all of the 240 3 phase, and as many 120V as you need, up to the transformer capacity. The 120V will be circuits distributed between the three phases of 208, each wired from a 208 line to neutral.

    But if you need only a couple 120V circuits anywhere in the building, then just having a 120/240 single phase would be fine, and likely cheaper. Since you were looking at a 75 kVA unit, maybe you have considerable 120/240 needs.

    The electrician may have referred to a 240 3 phase transformer, and he is correct that you do not often find them with a 3 phase neutral, since neutral to a phase is about 139V, not useful for much. There is a solution to that, though.

    The most common 240V 3 phase one finds is a "lighting tap" transformer, which is 3 phase 240V, with the neutral tapped on ONE winding, giving 120/0/120V on that winding, That provides "stinger" 3 phase, where the 3rd wire is about 210V from the 120V neutral. So there is only a neutral for the 120/240V output.

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    Thanks for all the replies. Let me try to clarify what I am doing.

    I currently have a 200amp 1ph service and nothing else on this property where we are doing the improvements. I now have a need for around 225 amps at 480v, so therefore we are installing a 400amp 480v service that replaces the existing 200amp 1ph completely. Current 1ph service will be totally removed from the property as it is now, and the only incoming from the Power Company is the new 400amp 480v service.

    In order to re-feed the existing panels in the building we have installed the 75kva step down transformer (75kva just to keep the secondary the size of the old service), and while this will create an unbalance across the phases both the Electrician and the Power Company seem to think it will be within a reasonable amount and not create issues on the 480v lines. (existing 1ph usage is low enough, and as time goes on things will surely get wired/re-wired to balance things back out closer)

    I guess that I do not see much use for 240 3ph with much of my equipment since most of those loads are easily wired for 480v instead, which is more practical anyhow. The 240v 1ph loads are welders, two smaller AC's, two water heaters, and an electric clothes dryer. Having never had a building with 208v I am just unsure of how things will run, and if since it is all being installed from new right now should I install it to be 240/120 instead.

    Sounds like I shouldn't worry about it being 208v, and to just carry on with things. Thanks.

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    I have had to deal with two plants with 120/208 services and hated both. Their only value is to save the contractor money. 240 volt motors will run on 208, but don't develop rated horsepower and run hot. If you have single phase appliances that use 240 with a center ground, you have to have another transformer. The transformer Jerry describes in his last paragraph would be far superior. Don't let the contractor slip a loser past you that you will always regret.

    Bill

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    Bill, as mentioned, I have never really seen any issues in many years with this service.

    If phase imbalance was an issue, changing the existing single phase panel to a 3 phase would solve it, as you would have feeds from all 3 phases. Would also simplify wiring as you would not need a different panel for 3 phase 208 feeds

    This is assuming the transformer is a 4 wire out, 3 phases of 208 and a center tap neutral. If it was some other weird thing with a separate 120 volt out then I don't know.

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    Quote Originally Posted by JST View Post
    The electrician may have referred to a 240 3 phase transformer, and he is correct that you do not often find them with a 3 phase neutral, since neutral to a phase is about 139V, not useful for much. There is a solution to that, though.

    The most common 240V 3 phase one finds is a "lighting tap" transformer, which is 3 phase 240V, with the neutral tapped on ONE winding, giving 120/0/120V on that winding, That provides "stinger" 3 phase, where the 3rd wire is about 210V from the 120V neutral. So there is only a neutral for the 120/240V output.
    So does the lightning tap setup then only provide 1/3 the rated KVA output worth of 120/240 1ph?


    Quote Originally Posted by 9100 View Post
    I have had to deal with two plants with 120/208 services and hated both. Their only value is to save the contractor money. 240 volt motors will run on 208, but don't develop rated horsepower and run hot. If you have single phase appliances that use 240 with a center ground, you have to have another transformer. The transformer Jerry describes in his last paragraph would be far superior. Don't let the contractor slip a loser past you that you will always regret.

    Bill
    The only concerning appliances to me are the 230v mini-split AC's and the Inverter welders. I feel like the heating element appliances will work okay, and just not as hot. I could be wrong.

    That is essentially what my thought was when I saw the 208 transformer is that he just went with whatever was cheap...At this point I have a large sum of money tied up in Waterjets that are sitting Idle, and am probably happy to just live with it for now and can swap it out myself later for a 240v unit. If it was a guaranteed problem I would deal with it now, but it sounds like it will at worst be more of a nuisance possibly.



    Quote Originally Posted by gustafson View Post
    Bill, as mentioned, I have never really seen any issues in many years with this service.

    If phase imbalance was an issue, changing the existing single phase panel to a 3 phase would solve it, as you would have feeds from all 3 phases. Would also simplify wiring as you would not need a different panel for 3 phase 208 feeds

    This is assuming the transformer is a 4 wire out, 3 phases of 208 and a center tap neutral. If it was some other weird thing with a separate 120 volt out then I don't know.
    The current layout has two 100amp panels serving the building, so I can at least spread those out by installing a new 3 phase panel in place of the current service entrance. This the electrician was not planning to do which I didn't like. He planned to just wire the transformer straight into the existing disconnect with no panel.

    I am certainly not impressed with the electrician, but I am stuck having someone with a commercial license do the work as the city won't let me touch my own stuff on a commercial property. The PC is not charging me anything for the work on their end, which includes two new poles, a 150kva bank for me, a new setup to power a neighbor, and removal of an existing pole. Based off of prices I have heard from other guys over the years I am feeling like the $23k I am paying total could have been worse, and I just want to get up and running as that downtime costs me a lot more than anything else in the long run. Once I have the service in I can always change things up as I see fit without too many eyes on it.

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    One plant had several injection molding machines that had been in another location, presumably on 240V. I was hired as part of the expansion into the new building, so the machines were already there when I arrived. They had to put boost transformers on the heaters and the motors driving the hydraulic pumps ran blistering hot. The machines ran, but not really right.

    The other plant made a lot of 400 cycle equipment and had a 75 KVA 60 to 400 cycle motor generator. It also had been in another building and moved to a new one with only the 120/208 service. I wasn't personally involved with it, but they couldn't get it to run properly on 208V. Fortunately, they had three 25 KVA single phase transformers and arranged them to get full voltage to the MG. While I didn't work on the MG, I did participate in tests on 60KW load banks, so they were working it to near capacity.

    The only justification for the 208V service is to save a separate single phase one. Otherwise, it sucks.

    Bill

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    Since you asked for and they quoted a 240v xmfr, isn't it better to just have him put in what he said he would? Better for you in the long run. If he dosn't want to, ask him what the credit for the 208v downgrade is.

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    Quote Originally Posted by johfoster View Post
    So does the lightning tap setup then only provide 1/3 the rated KVA output worth of 120/240 1ph?

    .....
    Yes. It's a current limit, actually, and just one winding supplies that, so you get 1/3 rating.

    If you only have 120/240 for single phase, then just get a single phase transformer.

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    Thanks for all the replies. I have done more reading elsewhere too, and will stop worrying about it for now. The welders should all adjust for the 208v as far as I can tell, and the new mini-splits I was worried about are rated 208-230v after looking up the specs. The water heaters I think I can just swap out the element for a 208v if needed for cheap, and the clothes dryer is fine if slower anyway. Since I am creating the 208v in the building from a 480v I can adjust at the transformer to have a better chance of not being any much below 208v. (I think so at least)

    It may be the case that most of the 230v 1ph loads get switched out to 3ph over time anyway now that I will have 3ph at this building. If the vast majority of 1ph loads will all be 120v then I suppose that is where it might make more sense to keep it 208/120 so that all three phases can carry 120v circuits. Seems I will do okay if I just go forward with it like this. Thanks for all the help.

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    I do a lot of welding in industrial buildings. Some have 240v D some have 208 Y. I have all newer miller welders, dynasty 350p Invision maxstar... they all run in 208 vs 240 but your weld settings will not be the same. Like on my passports, it says to run at 7.1 v (on dial) and 80 on wire speed. Well you will need to click it up 1 to 7.2 (only 3 clicks between numbers) to achieve normal 240v weld paramaters.

    You also have to remember that 240v is +/- 3%. So 208 is also +/- 3% so dont think a 208 is 208, it could be 201.

    Sent from my SM-G960U using Tapatalk

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