Electric - Demand Meters

Can someone provide me a "Demand Meters 101" class? Never had one before.

The only thing I know about it is if you increase your demand, the price seems to go through the roof. (We've been "tinkering" in the bunker and just quadrupled their electric bill Oops...). Someone looked at the demand meter and saw it at 9 (whatever that means but also mentioned something about it being 3).

Demand meters record whenever there is a large demand on electric supply. An example of this would be the start up of a large motor. It is a way for the power company to put the screws to you for having a appliance that requires more power to start than it does to run. They are only used on commercial properties. If you had one on your home, every time that your AC came on, the demand meter would take a jump. I believe that it counts the times and after a certain (unknown) amount of start ups, it will record 1 tick. We had one at one location, and someone unknown broke the seal and would reset the meter. Then the meter reader would come and take the reading and put a new seal on. I am not advocating this, but you have no control over the meter if it is on the outside of the building where anyone can tamper with it.

Thanks Junk.

Do commercial properties have to have them? Why not a regular meter like a house?

bczoom said:

Thanks Junk.

Do commercial properties have to have them? Why not a regular meter like a house?

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Usually they install there anywhere there is a higher amount of wattage entering the building. Not all commercial buildings have them, but most of the time they do install them hoping to get the extra amount of money out of you. If you had a single phase 200 amp service, they might not use the demand meter. I know of a campground that has them on every building even if the building is only a 12 x 20 one room rental sleeping unit. A demand meter can pay for itself in very little time, so it is worth it for the electric company to put them anywhere they are legally allowed, and that means any commercial account.

Well I think I'm going to try and get that changed.

We have a huge transformer next to the building and probably 5 more to step it down even more inside.

The utility is required, usually by law or ordinance, to ensure enough electricity for all customers, all the time.

Motors draw more current at start up. Imagine if there were 1000 100 hp motors all hooked up to a generator, and you started all simultaneously. You'd need a MUCH bigger generator to provide that little instance of starting power than if they were simply just running. Like maybe 2 or three times the size needed for steady state running.

Having said that, a demand meter reads the highest use and records the time of day it occurs. So you have to pay for that connected load capacity that you hardly ever use, but when you do, the utility must have enough assets on line ready for you. What large users do to reduce demand charges is to start their motors before peak time. The utility will gladly work with you to find an equitable solution to peak demand; they really do not like going to the commission to ask for more money for extra assets.