Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

Boiler electric feed on a male 3-prong S/O cord plug?

I want to change my boiler line voltage wiring so that the boiler and circulator power is on a 3-prong male electrical (extension) cord.   It will then plug into an electrical outlet right at the boiler. During a prolonged power failure I can unplug from the house wiring and then plug into a generator.

The generator will not be able to back-feed into the house wiring.  But is this code legal?

As an alternative I can get an individual transfer switch for the boiler power like the attached pic.  A regular 3-prong extension cord goes from generator to the transfer switch's recessed male plug.  The transfer switch is double-pole,  switching both neutral and hot.

Is this transfer switch code approved?


  • nicholas bonham-carternicholas bonham-carter Posts: 7,519Member
    edited March 13
    Try before you buy.

    Be sure it provides the clean power needed--NBC
  • Patchogue Phil_2Patchogue Phil_2 Posts: 285Member
    Clean enough power.

    I do not have fancy electronic controls on my oil burner.

    Is either option code legal?
  • SWEISWEI Posts: 7,356Member
    EZ Generator Switch

    I've built similar stuff on site for years, but I like the packaging job they did.

    I see a UL stamp on the plate, but I'm not sure if that applies to the assembly or just the component.  Might be worth calling them to ask about the listing.
  • Patchogue Phil_2Patchogue Phil_2 Posts: 285Member
    EZ Generator Switch

    I originally found the item on eBay.  They also have their own web site and are on Facebook.

    The company states that every jurisdiction is different so one should contact their own code officials to see if a manual transfer switch is code compliant. 

    I was hoping someone could answer my original question,  if using an extension cord male plug on the 120v load wires feeding  a boiler and/or furnace is allowed by NEC?

    Then you either plug into the utility line voltage outlet or into a generator.

    Any one know?

  • SWEISWEI Posts: 7,356Member
    what you have there

    Is properly referred to as a flanged inlet.  The NEC permits them when used appropriately.
  • Patchogue Phil_2Patchogue Phil_2 Posts: 285Member
    other option

    I was just asking about the other option,  just hard-wiring an extension cord to the boiler power feeds L1 L2.  Not the green cover plate with flanged inlet.
  • JaredMJaredM Posts: 57Member
    Cord Connected Boiler

    I have seen it done many times and it's a practical solution.

    -But- It's a violation of the NEC electrical code.  The NEC allows for cord connected appliances when they will be disconnected frequently and a boiler or furnace would not be disconnected frequently.  It also has specific exceptions for things like dishwashers and garbage disposals.  If memory serves the NEC section to check out is 422.16 .

    Good luck.
  • TRobTRob Posts: 20Member
    what worked for me

    We are in coastal NYC and lost power for over a week. Hence, no heat at first.

    For our atmospheric steam boiler I was relieved to have success in wiring in a cordset for an emergency power source.    The 120 volt load was all of .25 amps.  At first I used a 12 volt inverter off the car battery, and later on powered from a small generator set. Not trusting how the flue damper would work on 'square wave' AC, I bypassed the motor and clamped the damper shaft in the open position. The 25 v control transformer probably was 'unhappy' with the voltage waveform, but there was no indication of damage.
  • SWEISWEI Posts: 7,356Member
    edited November 2012
    square wave AC

    It's not quite as bad as that -- there are sharp edges to the stairsteps on any inverter output.  Sharp edges = harmonics, and the steeper those stairs, the more HF trash ends up on the line.  I've written before here that filtering a low frequency AC line requires "big hunks of iron and copper."  Within the power budget of a control circuit, that little 40VA transformer constitutes a big hunk of iron and copper -- an effective low-pass filter.  The HF noise becomes 'stuck' in the magnetic circuit, eventually being converted to heat.  Better transformers pass less of this noise on to their secondaries that feed the low voltage part of the power supply, which then has to filter out less of it.  If either or both falls down on the job, that noise ends up on the supply and reference lines of sensitive control circuitry.  Bad things ensue.
  • GordanGordan Posts: 891Member
    Is the Grundfos Alpha 15-55F/LC...

    ...a violation of that section?

    Can't imagine a circulator being connected and disconnected frequently.
  • SWEISWEI Posts: 7,356Member
    cord-connected pump

    If it came from the factory with a cordset, plug, and listing, it's considered a cord-connected appliance.  The plug then qualifies as a disconnect.
  • The Switch is Now UL Approved

    I know this posted is dated a bit, but there was a question I have been longing to answer. Is the switch UL approved? As of this week, the certification is complete, the entire unit is now UL certified.

    The folks at Underwrite Laboratory(UL) are very thorough, they do not mess around and it's quite the accomplishment to be able to say everything was approved.

    If you have any questions, feel free to ask.
  • jumperjumper Posts: 1,221Member
    codes are funny

    For emergency cut off plugs are often verboten but wall switches are demanded? Can't the latter fuse closed?
  • Patchogue Phil_2Patchogue Phil_2 Posts: 285Member
    Not understanding you

    "For emergency cut off plugs are often verboten but wall switches are demanded? Can't the latter fuse closed?"

    Please explain further.  Thanks.
  • Patchogue Phil_2Patchogue Phil_2 Posts: 285Member
    Happen to find this thread again....... The price has gone up a bunch for the EZ Switch.
  • LeonardLeonard Posts: 483Member
    edited March 13
    I remember reading in an electricians magazine EC&M that code doesn't want plugs on "permanent appliances" like furnace.

    Think home depot has a furnace "transfer switch and male plug kit" for ~ $85.

    Makes me wonder if couldn't just use a SPDT switch as a transfer switch.

    OR a DPDT switch if you have neutral/ground double bond issues.
  • Jamie HallJamie Hall Posts: 8,958Member
    An appliance such as a boiler -- which is rarely moved -- must be hard wired and protected appropriately. Sorry...

    As to the generator, to meet code for such an appliance the generator must connect to a break before make, approved, transfer switch, which breaks both hots (if 240) volts. Further, the cord set from the generator must end in a female socket, not a male plug, with protected contacts. This is for your safety.

    For better or worse, if it's your own house in most jurisdictions you can do it yourself, pretty much as you please. Just keep in mind that if you do, and something goes wrong, you insurance company may prove to be a wee bit difficult about settling your claim. The exception to that is the transfer switch; if your grid power supplier finds that you have an arrangement which -- however inadvertently -- might allow you to back feed the grid -- the lines in the street -- they can and will disconnect you permanently from the grid at their disconnects. This is for the safety of their linemen.

    Do it right. In many cases its only slight more expensive than some Heath Robinson arrangement, and much safer.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • AnthraciteEnergeticsAnthraciteEnergetics Posts: 77Member
    Put a cord on it. 12-18 inches of cord from the switch box to an adjacent single outlet. The only "safety" hazard is you kid or other household member unplugging it and forgetting to plug it in, leaving a no-heat condition. No added risk of fire, shock, etc. No different than any other appliance in the house.
Sign In or Register to comment.


It looks like you're new here. If you want to get involved, click one of these buttons!