867-5309 . . . Talking about (G)Jenny

firefighterjake Posted By firefighterjake, Nov 2, 2017 at 2:33 PM

  1. Ashful

    Ashful
    Minister of Fire 2.
    NULL
    

    Mar 7, 2012
    10,829
    4,652
    Loc:
    Philadelphia
    @fbelec, you’ve got the idea. To be honest, I had trouble following the original post, so it’s possible I was answering a scenario other than that which you were describing. The typical situation in which circuits may share a neutral is not two circuits on the same leg, which would be an illegal setup, but situations where two circuits are on opposing legs, with a shared neutral. This is legal and common, eg. 4-wire electric range hook-ups. In that case, which I was describing, the current on the neutral is simply the difference (“imbalance”) in the associated legs.

    The very reason it’s not legal to share a neutral between two circuits on the same leg is what you may have been describing, the currents would be summed, and the neutral would not be properly protected by the breakers.

    In my shop, I ran 12AWG 3C+GND to quad receptacle boxes, so that I could populate those boxes with both NEMA 5-20 (115V) and NEMA 6-20 (230V) receptacles, using one “hot” and the neutral for the NEMA 5-20’s and both hots (no neutral) on the NEMA 6-20’s. Which hot leg is used alternates in each box down the length of the circuit, and the current on the neutral ends up being just the imbalance on this circuit. I verified this with two commercial electrical contractors before doing it, and after some debate in their own offices, both agreed it was safe and legal. A residential electrician ended up doing the work for me, and he reported having done the same setup before.
     
  2. fbelec

    fbelec
    Minister of Fire 2.
    NULL
    

    Nov 23, 2005
    2,146
    101
    Loc:
    northern massachusetts
    jatoxico in your case no harm as long as it's not that way in the main box.

    ashful i have had other electricians tell me that what you have is wrong but they don't comment when i say to them other than amperage show me how it's different from that circuit to a main panel. it's wired the same way but with breakers in line.
     
  3. jatoxico

    jatoxico
    Minister of Fire 2.
    NULL
    

    Aug 8, 2011
    3,577
    1,093
    Loc:
    Long Island NY
    How many breakers in the main panel for this, separate one for each or a double pole (if that's the right term)? As I understand it current code requires the breakers to be tied together for standard 115V MWBC's so no one turns off one thinking the circuit is dead and then gets zapped because the other hot is still closed. Curious how you did it.
     
  4. Ashful

    Ashful
    Minister of Fire 2.
    NULL
    

    Mar 7, 2012
    10,829
    4,652
    Loc:
    Philadelphia
    In my case, each of those circuits was fed with a dual-pole GFCI breaker, which are single-levered (internally-linked) on my panel type. It's a "garage", in terms of code definition, which requires GFCI on 115V circuits. However, due to the odd wiring configuration, it was not possible to use GFCI outlets, so 230V GFCI breakers was the way to go.

    It's a wonderfully convenient setup, if you have a mix of low-current (eg. up to 2 hp) 230V portable machinery, and the usual need for plenty of 115V receptacles. I have dedicated circuits for the machines that are above 3 hp.
     
  5. jatoxico

    jatoxico
    Minister of Fire 2.
    NULL
    

    Aug 8, 2011
    3,577
    1,093
    Loc:
    Long Island NY
    Sounds like it's working good for you. My shared neutrals are wired correctly (hots on different legs) excepting that the breakers are not connected as now required. Actually using this to my advantage when running the generator because it allows me to shut down the hot not in use so no possibility of overloading the neutral.

    The one MWBC circuit I'm using with the generator has GF receptacles (kitchen) that I was worried would fault but I tested with combination of a good load, a kilo-watt and multi-meter at both the panel and the receptacles and everything checks out. With the other hot breaker open there's no unexpected power making its way to the receptacles fed by the other hot. As maybe you can tell I'm still looking for the gotcha since this is not a standard setup but I think I have it surrounded.
     
    Ashful likes this.
  6. metalsped

    metalsped
    Feeling the Heat 2.
    NULL
    

    Jul 24, 2011
    306
    73
    Loc:
    In the slight space between dark and light
    Have you (or anyone else here) ever thought about diesel? Specifically, military MEP machines? These beasts are available either as a genset only, or on a military trailer. They features choice of 120V single phase, 120/240 single, or 120/208 three phase (user selectable).

    These machines are built as 'prime power' generators, which means they are DESIGNED to run 24x7. Not so for any of these suitcase generators I have heard mentioned thus far (not a knock against them... different tools for different needs). Especially for places like rural Maine, who frequently see long power outages (I am still getting customers coming to me looking for sets after last months storm... have one going to Bangor in about two weeks time!)... these represent a way to ensure that you will always have power.

    They run at 1800rpm, and are quite fuel efficient. You can fine tune hertz and voltage down in .1 increments! They also feature fuel provisions which allow for the sets to refill themselves from 55g drums, 275g oil tanks, etc. They aren't thief bait either (800-1200+lbs).

    I do not want any of this to come off as a sales pitch. It is not. I do sell these on the side, but I feel they are a method of power generation that more folks should look into! Especially those in the rural parts of the world!

    I could talk all day about these, from a sheer enjoyment standpoint. We lost power in 2013 for 9 days. In that same timeframe, we lost our oil furnace, and all the baseboard in the house. Almost $20k later.. I told myself I would never go through that again. Thats why I started doing this.

    I'd love to talk diesel gensets with anyone that would listen! They can be had somewhat more affordably than most folks think too (especially when comparing to the lawnmower engine Generacs that are all the rage today).
     
    Highbeam and Ashful like this.
  7. metalsped

    metalsped
    Feeling the Heat 2.
    NULL
    

    Jul 24, 2011
    306
    73
    Loc:
    In the slight space between dark and light
    There is no way to share my enthusiasm about these machines, without it sounding like I am trying to sell them. Please understand I only bring it up because I am pretty knowledgeable about these sets (I have had about 20 go through my hands in the last year), and information is power!
     

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