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Power Limiter or Current Limiter

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bbgg

Electrical
Sep 15, 2003
16
I need technical information about power limiter for dwelling. Is there any standard or rule about what is consider a limiter and what not, and what are its specifications for dwelling. Thank you in advances.

 
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What do you mean by "limiter"? Are you talking about fuses & circuit breakers, or something else? Maybe, "load shedding"?
 
I am talking about load shedding. The unit doesn´t allow that the consumer exceed a setting of power (like 10 kW).
 
Does the NEC or NESC has some rule or standard about this service limiter?
 
Both codes require breaker interrupting ratings to exceed the available fault current.
 

More likely state PSCs/PUCs would have interest in their use and capabilities.
 
I can't think of anything in the NEC that would forbid this. And if this is going into a utility socket, I wouldn't think NEC would even be applicable.

I would check that meter socket daily, otherwise I think you'd soon find a clipped utility seal and a couple jumpers stuck in the socket.

That limiter is pretty funny -- especially the discontinued 5-amp model -- I'd never heard of them before.

When you first said you were interested in "load shedding", I had something much different in mind. Something more like a computer that would automatically shut down loads in a graceful way based on total demand load.

 
Let me explain the problem. I work for a utility and we have two diffents fees for low voltage conection, depending on the power the consumer demand. If the costumer consumes more than 10 kW it receive the BTD fee, this means the consumer will reiceve a bill with charge for energy and power. If the power is under 10 kW the fee is BTS and the consumer recieve a bill only with energy charge. But the regulation permits the consumer to install a service limiter (running by his cost) that avoid that he consumes more than 10 kW. If he install this device he can obtain the BTS and pay less.

Our problem know is to establish technical specification for this device, since the regulation doesn't establish then. But does establish that it has to be install as close as posible to the meter but not inside it. I want to know is any have had this problem or your local utility has use this device and what should be the feature to accept a device like a service limiter.

Thanks your answers.
 
I have worked for three utilities, and two of them have used service limiters. AFAIK, these devices are intended to severely limit the consumption to a service to a tiny value (we use the 10A ones where I am now). 10A =~2400W if used perfectly balanced.

This is just enough for a few light bulbs or for the igniter/control on a gas or oil heating system.

The intended use is to assist in credit/collections for nonpayment. If a customer is about to be cutoff, this is sometimes used in 'hardship cases' so that they have a little available.

bbgg, I have not heard of any used in your type of application. 10kW on a 120/240 system is more like 40A, which is larger than the largest rating in the above references.

Could you not install an interval revenue meter to record the demands, and only collect the demand fee if the demand exceeds 10kW? Most of these meters have displays that can show the consumer their instantaneous demand.
 
This would seem to be the customer's problem, rather than yours, no?

I'm looking at this the same way as tinfoil -- bill them at BTS (kWh only) when the demand (kW) is less than 10kW. Bill them at BTD (kWh & kW demand) when demand exceeds 10kW. (Please define BTS & BTD?).

The "limiters" we've been talking about here are nothing more than circuit breakers -- you (or your customers) could certainly put in a 40A circuit breaker as the service disconnect. That would definitely limit power. But this is a rather crude way to do so -- go over your 10kW threshold and everything shuts off.

You could do something a bit more elegant with a fancier control system -- like a PLC or even a current relay or something -- that would perhaps shut off air conditioning (hmm, not much AC at 40 amps!) or other loads when demand exceeded perhaps 35 amps, and then permitted the AC to start again when demand fell to 30 amps or so. Similarly, you could segregate your loads onto "more critical" and "less important" panelboards, and shut down the "less important" board during periods of high demand. I've never seen such devices used in residential applications, only commercial & industrial systems, but there's no reason you couldn't do this at a reasonable cost.

But still, this would seem to be the customer's problem. Every commercial & industrial location I've ever seen such load shedding installed at, it's always been done at the customer's initiative.

By the way, "peak shaving" is a very similar concept -- if you're doing Google searches on this stuff, you might want to look at that as well.

One more thought, that is probably not economically justified in residential applications, but I'll throw it out there anyway: Energy storage. Use some kind of battery system, or thermal storage, or flywheel, or any sort of energy storage system. Charge the storage system during low-demand periods, and then release/use that energy during periods of high demand to avoid drawing energy from the utility source. This also falls into the "peak shaving" category. The one place where this seems to be *relatively* common in residential applications is the concept of passive solar heating/cooling, putting in a big stone wall or something that stores the "coolness" at night and then "releases that coolness" during the daytime to shave AC costs. Similar ideas might help you achieve your goal as well -- if you could keep your customers drawing at exactly 10kW, 24 hours a day, that's better than if they draw 0kW at night and 20kW during the daytime.

Hope this helps. Very interesting thread.
 

Demand charge in a residential rate schedule? If on the North American continent, would you please tell us where it is implemented?
 
I'm curious to know where this is going on even if not in North America. . . .
 
Thank you for your answer. This is going on in Dominican Republic. Our system and regulation is not as develop as yours and we have a lot of problem collecting the energy we send in our lines.

About your suggestion Peebbe, I know that this problem is the client´s problem, but if we accept a single breaker as limiter whenever the breaker tripped we would have a call from the client saying that he has a problem and our technician would have to move, increasing our costs. Here most of the consumer don´t know anythig about electricity or electrical device, they just know the phone number of the utility. That's why we prefer to establish features of what should be consider a service limiter in order to avoid the increase in the consumer's call. A device with self set up after a trip is preferable.
 

bbgg, thank you for the followup response.

It looks like the Marwell device definitely contains a manual-reset circuit breaker. It is not clear from online information if the Ekstrom product is similar.

One thing to consider with a manual circuit breaker is that repeated reset/overcurrent will require longer ‘cooldown’ intervals between resets. For an auto-reset device, the amount of time needed for reset will present a different {possibly less convenient] level of attention from the customer—whether that is desirable from your and your employer’s view has to be weighed.

Good luck in your efforts to resolve the problem.
 
Thank you again for all your answers.
 
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