What's this?

Hi guys,

Found this black box (okay, gray) in circuit with the W.H.
I’m no EE, but from the schematic is this a surge protector?
(yes, I saw the tpr)




Looks like a transformer.

I take it this was a electric HWH.

It’s a relay used to control the water heater,

Any idea what DCU stands for?

What I believe that is, is a timer to turn on the water heater at non peak hours to save on energy costs. Sometimes there would be a second meter on the outside just for the hot water tank. That red tag looks like a utility’s seal. Rick

(Deleted prior post… wrong link… can’t locate correct one)

Mike is correct. Allows the POCO to control the energy during peak usage times. Usually get a lower electric rate for being on the program. (note the FCC approval).

Bob… Linas must have really got to you… look at the photo again.

Possibly Demand Control Unit

Something to that effect, being FCC approved, it probably incorporates wireless technology.

I have never seen that kind of unit.

My first thought was Direct Current.

Started trying to remember my HS electronics class studies.
Past E over IxR it is a wash.

Hey Linus is Linus :slight_smile:
But jumping in to defend a well known NACHI basher ? I do not get it.

Wow, learn something new every day. I didn’t know big brother was controlling our houses…


Good call Jeff.


Load Controller, i always note it and disclaim them… Here they were installed in the 70’s and who knows if they are working or not???

Careful Jeff, stop stalking Bob. Bob is flustered, he got tossed off a 3 member message board. Now I’m the evil one:twisted:

We call them On-call boxes, if it is the same. This is what I put.

Not inspected:

There are Big Power on-call boxes on the premises. These units allow Big Power to turn off the power to appliances such as Hot water heater, A/c, Heat and pool equipment at their discretion. I recommend contacting Big Power for operation and discounts available on the electric bill, or removal.

Thx, John.


I think the evil one is a government that wants to control your energy usage.

Maybe it is a good thing we are getting handguns back .:):twisted:

Home Inspections RI Rhode Island 401-782-5589
It is an old demand control, the utility company used to give electric bill discounts for having it installed, I have a pile of these boxes from remodeling jobs. I reuse the boxes when I custom wire boats.