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#129376 - 02/09/05 10:37 PM unbalanced load  
BigB  Offline
Member
Joined: Mar 2004
Posts: 719
Tucson, AZ USA
A POCO representative told a customer that had complained of excessive bills that her panels load was not balanced and could be part of the problem. I cannot see how a load imbalance would use more wattage??? Or make the meter turn faster??? Watts is watts, right?
I have to go there tomorrow to check it out.


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#129377 - 02/10/05 11:20 AM Re: unbalanced load  
sabrown  Offline
Member
Joined: Dec 2002
Posts: 302
Ogden, Utah, USA
Yes watts are watts, but, as is most likely the case in commercial services, there are often demand based charges.

I believe that with demand based charges they record the maximum demand on any of the three lines (assuming 3-phase) that last for more than about 15 seconds anytime during the month, and then the power company charges you a fee based on this demand along with your normal per KWhr fee. The demand portion of the meter is monthly reset.

The demand charges can easily make up the lion share of your bill, especially if you are a low KWhr user. Also if you are unbalanced, these demand charges are multiplied by the peak which is higher than it would be if the system were balanced.

Look at a rate structure for your area. The big users have a relatively low per KWhr charge which is often easily compensated for by the heavy maximum demand charges.


#129378 - 02/10/05 09:08 PM Re: unbalanced load  
BigB  Offline
Member
Joined: Mar 2004
Posts: 719
Tucson, AZ USA
Sorry I should have mentioned it is single phase residential. Went there today, the panel is full of two pole breakers, not one single pole. So there is no way the load could even be unbalanced! All the single pole breakers are inside at the sub panel.
The house is all electric and the residents have only been there a few months. I think they just don't realize how much their furnace is running.


#129379 - 02/11/05 06:55 AM Re: unbalanced load  
pdh  Offline
Member
Joined: Jan 2005
Posts: 354
Just because there are all 2-pole breakers does not mean that the circuits they feed are themselves in balance. For example, perhaps all the receptacles are on shared-neutral or neutral-per-leg multi-wire circuits, and were wired up split. If they were consistently phased, you might end up with everything on the lower half always on one phase side. And then out of habit, people would consistently use maybe the upper outlet first. Then the load can get way out of whack fast.

I've heard of this in kitchens where multi-wire is common. Someone wires up all the lowers on one phase and the uppers on the other. To an electrician it would even make sense as it gives them control over how they use the phases. But the average HO has no idea and probably consistently uses lowers (except where a 2nd is needed). And even GFCI doesn't stop that practice since you can still do neutral-per-leg on the GFCI load side and split ordinary receptacles after that.

FYI, my house plans call for a double duplex at each receptacle location in the kitchen with one duplex on one phase and the other duplex on the other phase upside down, with 2 sets for a total of 4 20-amp circuits. The idea is I have 2 lowers I can use at each location and still balance the load and have the uppers as extras just in case (basically twice what the code requires).

Did you check the current on each phase?

Electric heating certainly can drive up the bill (but hey, no NG or LP bill). I hope the house was built to proper energy conservation codes or better.

And a really crazy thought hit my head first regarding this. What if this was a DIY special and someone wired up one bus to one phase, and the other bus to the neutral, leaving the other phase unconnected? I've heard stories of worse.

Still, all 2-pole breakers has me wondering. Even I'm not that crazy. Do they have AFCI in there (only 2-pole AFCI I've seen are from Cutler-Hammer).


#129380 - 02/11/05 10:29 AM Re: unbalanced load  
BigB  Offline
Member
Joined: Mar 2004
Posts: 719
Tucson, AZ USA
The main panel contains: one 50A 2 pole for the range, one 60A 2 pole for the electric furnace, one 30A 2 pole for the electric water heater and one 2 pole 40A for the interior subpanel. It is an older, small rental house, all electric. The landlord had called me to check it out. Before I report back to him I will call the utillity for a usage history. I think they are just using the furnace plus the WH is outside plus they are probably taking longer hot showers in the winter. By the way the water heater is new.


#129381 - 02/11/05 01:05 PM Re: unbalanced load  
BPiersel  Offline
Member
Joined: Jan 2005
Posts: 18
Minnesota
If there is no demand based charges (since this is residential), why would a load imbalance make the meter read incorrectly?


#129382 - 02/12/05 02:36 PM Re: unbalanced load  
BigB  Offline
Member
Joined: Mar 2004
Posts: 719
Tucson, AZ USA
Thats just it JP I don't see how it can, I just wanted to double check myself, sometimes when you hear statements by others in the trade you tend to second guess your own knowledge.


#129383 - 02/16/05 09:40 AM Re: unbalanced load  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,211
SI,New Zealand
Listen,
I think that there has been a mis-understanding in terms here.
A Demand (As in Maximum Demand) meter is supplied via CT's, it takes two readings of the Demand of 15 minutes over a 24 Hour period.
Anything else is a kWh meter, especially in a Single Phase installation.
A kWh meter only measures True Power (V x I).
Did anyone think to check the meter for a shorted turn or two on the Potential coil?. [Linked Image]


Let's face it, these days if you're not young, you're old - Red Green grin


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