Controlling a panel with a relay

Merry Christmas
Status
Not open for further replies.
F

flashlight

Senior Member
Location
NY, NY
Occupation
Electrician, semi-retired
In the interest of saving energy, the customers at a job I am managing wish to be able to turn off their electrical panel almost completely when they leave their apartment. Obviously a few items, such as the refrigerator, must remain powered.

I figure (apart from something clumsy like a disconnect at the door or installing a subpanel with a main breaker and switching that on and off) that they have 2 choices: 1) install a contactor controlled by a switch at the front door which gives them a max of 12 circuits that can be switched off, at least with those models carried by local suppliers, or 2) add a subpanel which carries all the circuits meant to be turned off, and control that via a relay which can have the control switch next to the front door.

I am leaning towards option 2. The existing panel is 60A, which is not uncommon in apartments here (NYC). An electro-mechanical relay with the proper rating is considerably less expensive than a similarly rated solid state one. Does anyone know any reason I should use one rather than the other?

Thanks for your thoughts on this.
 
Last edited:
First of all, I think it's a terrible idea, although nobody asked my opinion on that. They do understand they'll have to reset clocks, VCR's, etc., daily, right?

Second, I agree with #2 also, but with some random thoughts:

A. A 12-pole contactor costs hundreds, while six 2-pole, four 3-pole, or three 4-pole relays would cost a lot less.

2. It might be cheaper/easier to add a 2-circuit panel for what should be left on, and switch the main panel.

D. A simple wireless setup, such as X-10, would cost less than the materials and labor to hard-wire it.
 
I couldn't possibly see where the savings would come from on doing such. What load could they possibly shut off that would create such a savings? If heat for instance was a concern, a programmable thermostat wouild be the answer to that. I think I would ask a few questions before delving into this.
 
i found that its easier to get in the habit of turning everything off when I get through using it. For about 6 mo. now I have been turning off every light, TV, a/c, and computer when I leave in the morning. My power bill went down maybe $10/mo. and that's most likely from just leaving the a/c off all day. Anyhow, I'd go with larry's recomendation for several smaller contactors. I think the last 3-pole 30A I bought was around $30. Not sure I'd recommend the X-10 setup. You might sell them some occupancy sensors and timer switches, and some CFL lighting.
 
080429-2116 EST

flashlight:

I vote against solid state. The voltage drop is substantial compared to mechanical contacts. That means power dissipation concentrated at that switch point.

Apartment means temporary I would guess. The X10 idea for that kind of application seems appropriate. Many of the X10s are solid state but they would be distributed at the end use point so power dissipation is not as much of a problem. However, I have experienced very low quality, meaning reliabilty problems, with X10 components. If it were a permanent location I would use GE RR relays.

nizak's point is good. But these people probably have no comprehension of relative costs of various loads. A number of years ago our state made residential electric rates increase above a certain consumption level. The idea to reduce energy consumption. So in the winter if I use less electricity I will use more gas. Much of our electric supply is coal. True in the summer it would be better to reduce un-necessary electrical dissipation.

.

.
.
 
I dont recommend powerline controls in a residence. I used one in my house and my wife said some terse remark towards me every time she turned the light on. "I live with a dad gum Electrician and I can't even turn on the cotton pickin' lights right"

I use the RA lutron stuff and she loves it and all my customers. Lutron is good stuff, been around for a long time.

Not to mention you need neutral at all the switch locations to make a power line control work. Doubt you have that in an appartment/condo situation.
 
Last edited by a moderator:
My bad. When I mentioed X-10, I meant as a way to control the panel relay(s), not the loads directly.

What specifically do they want deenergized?
 
Palmbay said:
"I live with dad gum Electrician and I can't even turn on the cotton pickin' lights right"
Click to expand...
I think I married her long lost twin.
 
Last edited by a moderator:
I have done this on several commercial properties, mainly for safety and security, but also for energy savings (more on that at the bottom). Here are the pitfalls I am aware of:

  1. Contactors should be mechanically latched type. Electrically held contactors mean the coil is energized the entire time they are on, so if that is hours per day, you eventually degrade the coil winding insulation and they fail. In the old days, that may have taken 25 years to happen. Not so much any more.
  2. AC coils also hum at the very least, some outright buzz. In a residential setting, that is noticeable because the wall structures will act as a sounding board to amplify it. It will drive you crazy in short order. I have a friend who recently retrofitted 3000 electrically held lighting contactors in rooms at a Vegas hotel because the guests complained about the hum in the walls from the relays.
  3. Latched coils then make the control circuit different, i.e. a "Latch" pulse and an "Unlatch" pulse. That's why you see the 3 position center return toggle switches. Up is On, springs back to center, Down is Off, springs back to center. Because of that, most people don't like the "non-standard" switch operation (see wife story above). So for that reason, I would opt for the single larger contactor feeding a sub panel. One "Power Off" switch controlling the contactor feding your sub-panel.
  4. Make sure you leave extra spaces in both panels so that in the future, you still have a choice as to which one you want your new circuit in.
  5. Do not use solid state relays, they reject 1.5W of heat per load amp. So in some cases, say a kitchen circuit with a good sized appliance running at 15A, you can easily get 25W of heat dissipated into the box you put the relay into. If it s not vented, it will cook itself. If it is vented, the heat goes into your living space and increases your AC load. Not much on each circuit but it adds up. So the energy you think you are saving is immediately re-consumed elsewhere.

The energy savings actually can be noticeable. TVs in particular use a surprising amount of power even when you think they are "off" because they are all now "instant-on" which means the power supply is never truly powered off. Otherwise, you would have to wait a few seconds every time you turned it on and we are an impatient society now. Most things with power supplies are like this now. It is called "parasitic load" and can add up to a lot of energy at the end of the year, not to mention the fire hazard.

But you have to learn to live with the "12:00" flashing at you all the time on the clocks in your appliances...
 
Thanks, everyone, for weighing in on this.

I, too, was skeptical when this was brought up, but
customers are insistent.

Jraef, your point about parasitic load is I think the crux of the issue for them.

I believe we will be seeing a lot more of this sort of thing in the future
as a result of the "green" building movement.
 
080430-0627 EST

On average my electric bill is 160 per month. Total useage for last year 16393 KWH, 44.91 KWH/day, 1.87 KWH/hour for 24 hrs, likely average useage while awake is 2.81 KW. As an aside if I assumed 6 hrs per day of useful sun light or wind power I would need about 7.49 KW capability. More realisticlly it would be 10 KW. Probably more than 100 sq-meters (1075 sq-ft) of solar collection, assuming 10% efficiency.

My residual load with refrigerators off is about 100 W. At 8760 hours/year that is 876 KWH, and at .1178/KWH my cost is $103. What inconvenience and/or cost should I accept to save some of that base cost? Basically none.

These above comments were just for background.

An apartment dweller would probably be 1/4 my useage. Generally I have at least two computers on with 20" CRTs for a good part of 16 hours per day and a number of 8' Slimlines.

I am a great fan of the GE RR relays. I have had failures as I discussed elsewhere. But the logical functional capability makes them a great asset. Mine have now been in use for over 40 years.

If you wanted to you can use one switch that will turn on or off all relays or any desired group. The RR is a bistable (latching) mechanical relay. But as I mentioned in my previous post not applicable to this particular apartment application.

Jraef:

It is interesting that there is objection to the 3 position switch. But I guess there are a lot of people that can not think logically and/or learn new ways when there is a distinct advantage to the new way.

.
 
gar said:
080430-0627 EST

...

Jraef:

It is interesting that there is objection to the 3 position switch. But I guess there are a lot of people that can not think logically and/or learn new ways when there is a distinct advantage to the new way.
Click to expand...
I think that those of us in "the industry" have a general bias that all things that work well and make sense are inherently better than those that do not. While that seems simple on the surface, one can't deny there is a widespread attitude out there which says "We dislike learning new tasks, however simple they may seem to you." It never ceases to amaze me.
 
gar said:
080430-0627 EST

As an aside if I assumed 6 hrs per day of useful sun light or wind power I would need about 7.49 KW capability.

.
Click to expand...

Hi Gar,

I don't have the #'s for Ann Arbor, but Detroit averages
4.3 KWh/m2/day, 6.1 in June/July, and 1.9 in December.
Even if you went latitude-15, it would still only be 2.1 in Dec.,
and a dual axis tracker would only help max 20%, so
your statement that 10 is probably closer to the mark
sounds right.

rexowner
 
Last edited:
One last query...

One last query...

Just checked my standing load, w/o refrigerator, about 100W ! So every 10 hours is like running a space heater for 1 hour, not chickenfeed over time. This is a 600 sf coop apartment in NYC. There's a home office, and kids have usual gadgets.

One last query: does anyone have a recommendation for a brand of 2P 60A latching type relay? I'm finding lots of EMRs of the constantly energized sort but a lot fewer of the latching type. Of course, prefer to get something proven.
 
080501-0918 EST

flashlight:

From a foggy memory I believe AB or Sq-D made a mechanically latching contactor. It was sort of a monster.

.
 
080501-1016 EST

This 10 minute edit is a problem.

You could maybe use 4 to 5 GE RR-7 relays. These are compact and rated 20 A resistive, 1/2 HP at 120 V. All could be simultaneously operated from a single SPDT spring return to center switch.

I would not use the normal GE SPDT switch to operate them in parallel. Paralleling requires some thought on the control means and power supply.

Also there are sequencers made or were made in the past that from one control switch would turn on or off many relays.

.
 
Awhile back, I installed a simple ice cube relay in the loadcenter in my house, to toggle the occupancy-sensor having master control of my lighting (reference this thread for more details).

Essentially, I have it set up so when I turn a breaker on in the panel, it energizes the coil of the relay and isolates the occupancy sensor, and renders the effected circuits always on while the breaker is energized.

I do not notice a hum from the ice cube when it is energized.

I would lean towards running a 14-2 home run from the panel for use as a switchleg.

View attachment 1616

I would use a threeway switch at the new (front door) switch location, so that I could configure the relay to be deenergized while people are at home and not have a switch that would seem to the customer that it should be "on" when it should actually be "off".
 
Status
Not open for further replies.
Top