RESIDENCIAL POWER LIMITER 2

[JAMartinezB]

Hi, I would like to know if there is a device like a circuit breaker that could be used to limite the power of a household to a selectable value like 10 kW or below and with automatic reset.

I have heard about something call MCB (Mini Circuit Breaker), but I'm not sure if these devices have these capabilities.

Regards.

 

[EEJaime]

It is called an MCB, but it's the service's MAIN CIRCUIT BREAKER.

You want to trip a breaker on peak demand? What for? The service drop and Service disconnect/OCP already limit the amount of load a service will carry.

If it's the ability to vary the trip value you are after, then I guess you can buy an electronic or analog breaker with resetable trip values, but that's expensive and only allows you to LOWER the trip setting, but I am not sure what that buys you.

Regards,
EEJaime

 

[davidbeach]

So, at 10kW you would turn everything off? So then it resets and everything comes back on? So then it all trips off again? Either you haven't really thought it through or you haven't presented the question in a readily understandable form.

 

[jghrist]

I think what the OP wants is a device to limit the power to 10 kW but not shut it off. A circuit breaker won't do this. An sophisticated building energy management system will by controlling controllable loads like A/C, but not with a single inexpensive device. See

http://en.wikipedia.org/wiki/Building_Management_System

 

[waross]

In some jurisdictions, the utility installs a breaker to limit maximum demand. If you exceed the breaker setting and the breaker trips, you reduce your connected load and reset the breaker manually. If resets are frequent then you pay more for a higher rated breaker and a higher allowable maximum demand.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dpc]

http://www.woodtv.com/dpp/news/wood_mpsc_discouraged_use_of_power_limiter

Yep, some utilities use them in lieu of a service disconnection for unpaid bills. A 93-year man in Michigan froze to death a few days ago because his power was tripped off, apparently.

 

[stevenal]

Sometimes part of an AMI system. Some utilities or commissions may prohibit a total disconnect for some situations. Perhaps refrigeration is required for insulin, for example. Reset can be manual after a demand is exceeded, or automatic to limit energy use (time), or a combination. 15 minutes on, 45 minutes off will keep the fridge cold while keeping someone from watching an entire TV show.

 

[JAMartinezB]

Hi, thank you for your answers. Let me explain myself better, where I live the law allows the utilities to charge the demand to the customers if they pass the 10 kW limit. Other away, the customer just pay energy.

So, once you sign a contract with the utility and they determine that your demand will be above the 10 kW, then they assign you a rate with demand charge and to ask for a rate change you need to install a power limiter. But the utility doesn't supply this power limiter. Like Jghrist says there are some sophisticated management systems that cost a lot and let you control each independent circuit within a panel board.

Then, I was wondering if I could find a simple device, like a breaker, that allows me to control the maximum demand and let me set the demand value, that would turn everything off at the set point, but with a adjustable time delay to reset. I have to say that I have a backup power source (an inverter), that would supply only part of the load (lights mainly) while I shed some loads to avoid the power limiter to trip again.

Regards.

 

[waross]

Demand Miser;

http://www.egenergy.com/pdf/demandmiser/large/DM_eng.pdf

http://www.egenergy.com/pdf/demandmiser/small/dmz_eng.pdf

Load miser;
The load miser is a switching devise that supplies current to one of these two appliances at a time since there isn’t enough current carrying capacity in the 10 gauge wire to operate both appliances simultaneously. Therefore, the load miser gives one of the appliances priority. The load miser cuts off power to the non-preferred appliance when the current flowing through the miser reaches 80% of the upstream fuse or breaker rating.
From>

http://www.lynchinspection.com/article-electrical-10.html

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[bacon4life]

http://powerguard.co.za/

looks like exactly what you are looking for, unfortunately looks like it is only available in Africa.

The Guardian Power Master Load Shedding Device Part# 5239 could be used if there are some loads you know will push demand over 10 kW.

http://www.norwall.com/newimages/PowerMaster 5239.pdf

http://www.norwall.com/product_info.php?cPath=17_21&products_id=728

There are quite a few products on the market that are designed to shed load while running on emergency generators.

 

[itsmoked]

Sounds draconian..

Where are you located JAMartinezB?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

Hmmm... Why couldn't one set up a variation of a saturable core reactor with a kW demand feedback loop so that if you exceeded it's design demand, your voltage would start to decay, letting you know you have a problem. Then put your critical and sensitive loads on UPS systems so you have time to decide what other superfluous loads to shed and reduce your demand. That way, you don't have to shut everything down first by tripping something.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[waross]

I had a similar challenge once. Here it was a small generator and a big generator. When only the caretaker was in residence the small generator was adequate. If a few meeting rooms were in use the small generator would usually handle the load. But invariably the load would be increased to the point that the generator would blow smoke and slow down. The caretaker could usually be seen on the run to the generator house to start the big set.
I used a couple of old Square D overload relays with bi-metal mechanisms and automatic reset. I wired the output of the small generator through the overloads. At about 80% load they would trip and sound an alarm to give the caretaker time to get the big set started.
Comparing Cadillac solutions with Volkswagon solutions, this would probably come in at about Mountain Bike.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

I don't know of any circuit breakers or simple overload relays that measure the kW. Seems to me they all trip on current.

I'd think you could install an energy transducer and feed the output to a small PLC. Then, you can program the PLC to activate shunt trips in different circuit breakers to shed load. Shouldn't be too expensive if you are capable of doing some integration and PLC programming.

You could use a Tyco Quadratic Integra 1530 meter cost ~$600 connected via modbus or pulse or analog to a small PLC of some sort.

 

[stevenal]

http://www.brookseals.com/images/product/pdfs/service limiter.pdf

Use the single pole device to interrupt half (roughly) the 120 V and all 240. The double pole device at 30A will get you closest at 7.2kW.

No reason a current limiting device won't work, since voltage should be reasonably constant (within ANSI).

This is a high price to pay to stay within your rate case. Think of all the clocks to reset, computers, etc.

 

[waross]

You should do a load analysis to determine if you can service your load without exceeding the 10 kW limit. If it is feasible to stay within the 10 kW limit,then look for large loads that may be shed or disconnected in times of high usage. Hot water tanks are a prime choice. Electric heat may be cycled on a rolling blackout. There are a lot of things that can be done, but first you need an understanding of the major loads. You can't just buy a device that will magically limit your consumption. You need to intelligently reduce the connected load by cycling off non critical loads.
There are some horror stories about load limiting schemes where a load analysis was not done properly and an attempt was made to limit the load to less than the safe minimum.


Bill
--------------------
"Why not the best?"
Jimmy Carter