My water heater was broken and I traced it back to a problem with the power. I was only getting 50 volts for a 240v unit. I found this box connected between the 240v line from the fusebox and the water heater and I'd like to know what it's for. The 240v line is coming in just fine but breaks down to 50v when it comes out of the box and into the water heater. I can bypass the box completely but I feel like it's there for a reason.

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I can't find anything written on the box or components that would help identify its purpose.

  • What does the white card on the lower junction box that's out of focus in the first picture say?
    – Ecnerwal
    Commented May 18, 2017 at 12:36
  • It says the installation was performed by <local/defunct company> and to call for questions or assistance.
    – Mike B
    Commented May 18, 2017 at 12:39
  • That junction box is crazy. That's an awful lot of wires, way too many to just be for a power company controlled water heater. Even possibly too many for the box fill, and I think that's a jumbo 120mm box! I also see a paint shadow of what woild have been a third cable/conduit going through that hole. Where did that go. Any other mystery electronics in the house? Commented May 18, 2017 at 12:47
  • @Harper There is indeed a third outlet going out the left side of the junction box. However it was clipped. I have no idea what it was for - I don't believe the power-saver box feed was used on that line. The AC is to the left of the picture but as you said it looks like it was routed back into the wall. It was like that when I bought the house and the fusebox labeling (also before my time) only says 'Water Heater'.
    – Mike B
    Commented May 18, 2017 at 13:31
  • This is what I could find. aepsurplus.com/upload/attachments/DCU%20Service%20Guide.pdf Commented Jun 29, 2021 at 15:04

3 Answers 3


Mike - that looks like a power saver box installed by your utility company.

The utility can regulate the HW Heater on and off. Thus saving you energy as the theory goes (that's the theory).

My theory is if I want it low , I will set it there and not raise it high - thus I save energy and have hot water when and how I like it, not luke warm water.

  • Interesting! Thanks for the info Ken. How does it work? Is there somewhere I can read more on the device?
    – Mike B
    Commented May 18, 2017 at 3:33
  • @MikeB kind of difficult - Scientific Atlanta makes a lot of specialty vendor equipment - your utility company I think is responsible for its function - they might repair free - if not I would pull it. Of course some utilities give you a $ break for having it. It helps them manage their electrical load. They claim it saves you energy too - sure if it is off you can't use it.
    – Ken
    Commented May 18, 2017 at 3:51
  • 2
    isn't 1991 awfully early for that sort of thing? Commented May 18, 2017 at 5:25
  • 5
    @Harper - no, utility-controlled hot water heating has been around quite a while. Rather than "saving you energy" it's normally saving you money, by giving you a more favorable rate for the water heater (or possibly your whole bill) because the utility can switch it on or off to increase load when they have excess capacity and shed load when they have peak demand that stresses the generating capacity. If the water is already hot the thermostat won't heat it - the box does not control water temperature, just power delivery to the water heater. A minimum on-time ensures that the water is hot
    – Ecnerwal
    Commented May 18, 2017 at 12:31
  • In NC it is against state law to, "Alter, bypass, interfere with, or cut off any load management device, equipment, or system which has been installed by the electricity supplier for the purpose of limiting the use of electricity at peak-load periods. However, if there has been a written request to remove the load management device, equipment, or system to the electric supplier and the electric supplier has not removed the device within two working days, there is no violation of this section"
    – Glen G
    Commented Feb 11, 2023 at 15:12

That is from the utility company. I have installed several hundred of them. We give a $7 per month credit so we can lower the peak demand should the need arise.


I had one on the out side of my house and it was also connected to the phone lines that book was used in the 70tes. Probably about the time your house was built. I took it out and every thing still works fine and that small box workers great for little junk you have on your bench.

  • 2
    This seems unlikely. There's nothing in the box to indicate it's related to the phone lines. Furthermore, there's two answers indicating what this device most likely is.
    – Machavity
    Commented Aug 28, 2018 at 12:58
  • This one is obviously RF-based. You can see the antenna on the left, the receiver crystal, all the inductors, etc.
    – nobody
    Commented May 26, 2022 at 1:51

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