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Thread: Just how lazy can an electical engineer/draftsman be?

  1. #1
    DIY Senior Member Homeownerinburb's Avatar
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    Default Just how lazy can an electical engineer/draftsman be?

    I was just offered an electrical plan to bid, will go look at the job after the 4th.

    It looks to be a coffee shop, the service items needed to make it work, must already have lights and signs and emergency lighting, as none of that is indicated in the plan.

    Am to add a 3ph 200a 42 space panel protected by a 100a breaker on a main panel.

    What is a nuisance is that I cannot make out from the drawing if this is a delta arrangement with a wild leg or a balanced Y.

    And it looks to be all about the draftsman just doing a cut and paste. The panel is called out as 120/240v, and there are several references to "high phase do not use" on the B phase, yet elsewhere on the schedule of circuits that phase is clearly being used to create 208. with either A or C phase.

    And there is a three phase 208v water heater specified.

    I'd ask the General what the deal is, but then I'd need to explain delta and Y to him, and he gets testy when I do that.

    I'll be making a point of taking a meter with me to the walk thru! Could easily be that they have one and think they have the other. Scary, actually.

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    Electrical Contractor/Instructor jwelectric's Avatar
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    Could be that they have one service and the other voltage is obtained from a transformer.

    If the service is labeled 120/240 volts it might be a single phase service. If it is labeled as a 240/120 it might be a 3 phase and if it is it has a high leg delta.

    If the voltage is labeled 120/208 it might be a single phase but if labeled 208/120 then it might be a three phase wye.

    If I were you I would establish my service voltage before doing any estimates as the price for material of one voltage is different than for the other.

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    DIY Senior Member Homeownerinburb's Avatar
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    Quote Originally Posted by jwelectric View Post
    If I were you I would establish my service voltage before doing any estimates as the price for material of one voltage is different than for the other.
    Oh, that will certainly be the first thing I establish.

    It is a commercial space in a fully developed area, I doubt very much that it is single phase. There are clearly several other businesses and an elevator in the building.

    And the engineer's drawing is emphatic about this being a three phase arrangement. My point is that the drawing I was given references both elements of 240/120 delta and 208/120 wye.

    I think it is the second but the draftsperson was lazy and did not delete all the indications of 240/120 and a wild leg.

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    DIY Senior Member Homeownerinburb's Avatar
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    Quote Originally Posted by jwelectric View Post
    If I were you I would establish my service voltage before doing any estimates as the price for material of one voltage is different than for the other.
    Oh, and just to continue the confusion:

    I am to instal a 3pole 100a QD (SquareD) breaker in the main panel to take off to the new sub panel.

    Three poles. And I am to run ~50' of 1 1/4 conduit with 3x #1 thwn.

    No neutral? Or if the engineer was going to let me down size the neutral, you would think he would calculate that and specify it, yes? I don't like the balance he worked out in the panel anyway, I'd as soon not downsize considering it is just 50'. And that is max fill, I will budget to do it in 1 1/2, no reason to be miserable pulling the cable.

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    Electrical Contractor/Instructor jwelectric's Avatar
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    Okay I understand now, they gave you a set of boilerplate prints that covers everything. They leave it up to each job site to determine the voltage and type system they intend to use.

    You see this type of print going out to places in strip malls as this mall might be a wye while a mile down the road the mall might be a delta and another half mile down the road that mall is supplied by an open delta.

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    DIY Senior Member Homeownerinburb's Avatar
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    Quote Originally Posted by jwelectric View Post
    Okay I understand now, they gave you a set of boilerplate prints that covers everything. They leave it up to each job site to determine the voltage and type system they intend to use.
    Yeah. I'd be more comfortable with the engineer actually being specific, but this is probably a small job in his life.

    I mostly do home remodels and upgrades, so when I run into three phase, I takes my time! But this one is pretty trivial. Not like I am setting a transformer up or anything.

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    DIY Senior Member Rich B's Avatar
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    In my world.....backup generators.......120/240 3 phase is always a Delta configuration with a high leg...

    120/208 is a low wye and 277/480 is a high wye......Leg to leg is all the same....

    We have some trailer mounted units that are switchable and 120/240 3 phase is not always one of the outputs available on smaller units. It is usually a single phase configuration.....


    I just wired up an old 400 KW unit that we are using as a backup for our own building.....120/240 Delta.....Did a lot of checking to make sure it was right along with the generators internal 12 lead connections and VR connections.....

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