unbalanced light poles

[chrsb]

I went to a service call today to reduce the number of light poles that run at night to reduce the electric bill of $4000 and month. What I found was astonishing-

1. 3 phase breakers feeding single phase light poles.

2. the "B" phase was rotated among poles, so one pole was A,B, another B,C, etc...

3. Some poles were two diffrent phases and diffrent breakers.

Now my question is could this be part of the high electric bills? I was wondering if the unbalanced load of the light poles would cause the high bills? Each pole has 4 400W MH lamps. I am going back tommorow to put things right and am wondering if just doing that would reduce the bills.

 

[Nick]

Re: unbalanced light poles

Watts are watts so no you won't reduce the bill. This is a common way to feed parking lot lighting but the poles should be balanced between all three phases. Poles should not be fed from different breakers. Usually each pole will be individually fused so a fault doesn't take out the whole lot.

 

[charlie b]

Re: unbalanced light poles

Not so fast. It is true that watts are watts. But the watts you measure might not be the watts you are using. I would need a person more knowledgeable in the functions of meters to confirm or refute my point here. But it seems to me that if you have all the lights on B-A or B-C, then phase B will be far more heavily loaded than the other two. If the utility's meter takes its input current from phase B, and if it thinks that that reading is representative of all three phases, then it might be seeing a higher load that the customer is actually using.

In any event, two things that I think might be worth "fixing" are (1) To balance the loads, by serving loads evenly from A-B, B-C, and C-A, and (2) To replace the three-phase breakers (with two wires attached to each) with single phase breakers. As I read your description, the three-phase breakers are not being used to serve multi-wire circuits.

 

[Flyersfan]

Re: unbalanced light poles

I think it is a multiwire circuit and using a three pole breaker is the way to go. You want to open all conductors simultaneously in the event of a fault or overload.

 

[peter d]

Re: unbalanced light poles

Originally posted by charlie b:
If the utility's meter takes its input current from phase B, and if it thinks that that reading is representative of all three phases, then it might be seeing a higher load that the customer is actually using.

Wouldn't that be penalizing the customer for having unbalanced phases? If so, I can't imagine that is even remotely possible.

 

[steve66]

Re: unbalanced light poles

Wouldn't that be penalizing the customer for having unbalanced phases? If so, I can't imagine that is even remotely possible

I think it's more likely the utility wouldn't risk not getting paid all they are due (if the meter was on a less used phase).

But for a three phase service, I think we can safely assume the POCO uses a 3 phase meter.

But that's $16 an hour (8 hrs a day and 31 days a month), at .05 per KWH, that would be 320KW of light.

I could believe 4000 a month if your client has 400 or more 400w fixtures.

Steve

 

[charlie b]

Re: unbalanced light poles

Originally posted by Flyersfan: I think it is a multiwire circuit and using a three pole breaker is the way to go. You want to open all conductors simultaneously in the event of a fault or overload.

I was referring to this statement in the original post:

Originally posted by chrsb: 3 phase breakers feeding single phase light poles.

That sounds to me like you have a three phase breaker with only two wires connected.

chrsb: Can you clarify?

 

[charlie b]

Re: unbalanced light poles

Originally posted by steve66: But for a three phase service, I think we can safely assume the POCO uses a 3 phase meter.

I was fishing for an explanation of the internal workings of the meter, from someone who knows that subject.

Even if the meter senses all three phases, how does it do its math? If it takes the highest line current times the highest phase voltage, then phase balance would have an impact on the meter reading.

Any meter experts out there?

 

[peter d]

Re: unbalanced light poles

Originally posted by steve66:
But that's $16 an hour (8 hrs a day and 31 days a month), at .05 per KWH, that would be 320KW of light.

I could believe 4000 a month if your client has 400 or more 400w fixtures.

Steve

It sounds like the $4000 is the total bill. chrsb, what kind of business is this? What is the climate? I can understand $4000 for some kind of retail store with a heavy AC load, say Florida or Arizona.

Turning off a few parking lot lights is not going to put any significant dent in the electic bill.

Steve, where can you still get electricity for .05 a KwH?? We are looking at rate increases to .16 in my area!!!

 

[peter d]

Re: unbalanced light poles

Nevermind, I see you're in Michigan. So much for the AC load.

 

[chrsb]

Re: unbalanced light poles

Sorry for the late response. I went there today to try and get a better ideal what is going on. First it is a Church with nine 4 head poles. They all do have inline fuses, but this is where it gets interesting. One pole is taged 7 and 9, I turn on 7 and nine and get 30 volts(which was probally back feed from only having a single leg hot) on one leg and 120 on the other and between both phases. I now know that the wires are not marked correctly.

I have never seen 3 phase breakers feeding single phase poles before so what we proposed to the client today is we will come in and open up each pole, trace the wires out and label them correctly. We tried continunity but were reading through the ballast. We will then put in 2 pole breakers and be done with it.

If the unbalanced load will have no effect on the electric bill (even at .16 an KW it is only 2.30 an hour or 570 a month) I am wondering if it will be cost efficient) It would take 4 months to pay back what we are charging to fix it.

I tried explaining that those 9 poles probally were not the reason for the high bills. the Church is not that big, probally 30k sq'.

My only thought was that with the unbalanced load it could be causing the meter to read wrong. The legs are messed up and you do need to turn on 2 breakers to get one pole to work.

[ October 12, 2005, 05:31 PM: Message edited by: chrsb ]

 

[steve66]

Re: unbalanced light poles

Charlie B:

I'm not a meter expert, and our other Charlie must still be too busy to post. But I'm sure the standard power meters are very accurate. I believe they integrate the area under the V*I curve and account for all three phases and power factor as well. If they didn't, some people would figure out how to get more power than they are paying for

I seem to remember something from school about the "two wattmeter" method where only two voltage and two current meters are necessary to determine the exact 3 phase power.

STeve

 

[steve66]

Re: unbalanced light poles

Steve, where can you still get electricity for .05 a KwH?? We are looking at rate increases to .16 in my area!!!

I think I pay .10 or .11 at my house, and I assumed commercial or industrial would get a cheaper rate.

But I actually used .10 to come up with the 400 fixtures. Anyway, looks like the $4000 is a total bill.

Steve