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Old 05-10-2011, 04:39 PM   #16
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Voltage sag or VD. Where do they draw the line in the sand?


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Regarding the 300A draw, that was just an example but yes, I do have machines that will easily pull that BUT they are fused and breakered down to a fraction of that and controlling how much work they do. I have a couple 20kva rated machines and a 40kva rated machine. They are ALL protected correctly and I want power use like a hawk. Nothing illegal of about the install.

The fact you are drawing 100 amps continuously would show your service is undersized. So, what size are your SE conductors? what size are the feeders to the subpanel? What size are the branch circuit conductors to the machines you crank to draw 100 amp continuously (or the machine that draws over 150 amps).

while I won't say there isn't a problem with the POCO service, I think whatever is happening inside your house is complicating things more than you realize.

fusing a machine does not alter it's draw. While not loading a machine will help limit current draw, if you have a machine that is rated for 150+ amps or the 300 amps you said you have multiple machines that draw that much, I don't see you being able to load it little enough to reduce consumption by over 1/3-2/3 other than by just not turning it on.

so, rather than getting upset by the POCO, I would hope they don't realize you are illegally overloading their transformer and causing damage. Ya see, their equipment is rated for the listed load and you are listed as having a 100 amp service but have obviously altered the gear so you could draw considerably more. That causes damage to their equipment.

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Old 05-10-2011, 05:18 PM   #17
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Voltage sag or VD. Where do they draw the line in the sand?


control draw by using VFDs, running only one machine at a time, and limiting the amount of work done.


Motor loads seem to be voodoo for PCs so for all intensive purposes, this is a big welder for working on my race car. People do this all the time and rarely an issue.

Just as a simple question, do YOU think a service should sag 9V with a 20A load?
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Old 05-10-2011, 11:08 PM   #18
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Voltage sag or VD. Where do they draw the line in the sand?


VFD's can create all sorts of issues on power lines. Without a meter that reads true RMS, your volt readings could be tricked by the way VFD's use power in a chopped fashion.

I have worked industrial controls for over 30 years. Often, issues blamed on voltage fluctuations have been traced to the use of VFDs. The older ones are more of an issue than many newer units. In industry, they sometimes install isolation transformers between the power feed and VFD drive. This helps filter the power and smooth, to some extent, the pulses and noise issues associated with some VFD drives.

If the power issues are in your home, then you should be able to crank up some power using non-VFD loads by turning on the stove and over, dryer, and other heating loads. If these do not create the same voltage drops you see when using your VFD drives, you might be using the wrong meter.

A power line monitor will tell the power company if thier equipment is faulty. It will measure true RMS voltage of each leg, along with virtually instantaneous current demand readings. Their equipment logs data for a period of time and will log events with the time they occur. Their equipment will be certified and you should be able to request a certification log for it from the power company, if you don't believe it works right. They keep these units in good working condition since they use them to identify potentially critical issue with their grid.

You could repeat your test while the power company equipment is hooked up. You can log your voltages and compare them with what the power company reads. This will show if your test equipment is working correctly.

Your main panel should be fused (or have a circuit breaker) rated at 100 Amps, if that is what your service is. If you pull more than that, you may very well pull the voltage down. Your power company may tell you to upgrade to a larger service or have you fuse things properly if you are drawing too much power.

You are correct in your understanding that long feed and undersized wires from the power company could result in lower voltages. If the power company determines that their power is flaky without you pulling more that 100 amps, then they will have to fix it for you. This might mean a larger transformer on the pole, splitting the power feed to fewer homes and adding a second transformer, or perhaps providing you with your own transformer.
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Old 05-11-2011, 09:31 AM   #19
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Voltage sag or VD. Where do they draw the line in the sand?


Thanks Perry. I did use resistive loads for testing to maintain a 1.0 PF. Not even going over my allocated amperage, I could sag the line past 10%. Not all the time but I am hoping the PC can see that there "might" be an issue and simply run me some bigger wire or up a transformer one size to offer a buffer.

The lineman that visited did say that the 2ga Al that he just pulled over is the exact same wire that would be supporting a 200A service so for all intensive purposes, this service should have no problem with 200A because of the main service wire going to the breaker panel and the panel itself. As you know, wire ratings are a function of heat. More amperage, more heat, more resistance, more heat, until melt down BUT, even this system "could" sustain 150-200A for short durations without any concern at all.

The service wire is 2/0 Al, panel is 150A rated. These are continuous ratings. Again, I am not looking to overload my system and actually monitor things closely to ensure I am not being a nuisance. That being said, I think we all know that a breaker ha a large operating window. A 100A breaker can do full power for about an hour or even up to 150-200A for several minutes. I just want to make sure my voltage is not sagging to the point that it knocks stuff offline.

I might have mentioned above but the lineman and a good friend and design engineer said these old 100A meters are built exactly the same as the 200A meter. The head and lugs are the same but the physical box is bigger. Not saying I should be pushing the limits with it but just saying there is another reason why I should not see such sag on the line.

Last edited by viper; 05-11-2011 at 09:34 AM.
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Old 05-11-2011, 10:35 AM   #20
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Voltage sag or VD. Where do they draw the line in the sand?


where did you get the 2/0 al was rated for 150 amp continuous? It is allowed for a 150 amp residential service as the service conductors but the problem you have with that is a residential service is not really rated for 150 amp continuous. It is specifically allowed to use undersized wire because it is not considered to be a continuous use. Figure a resi service is rated for no more than 80% duty rating. That would mean, strangely enough, a 150 amp resi service is capable of 120 amps continuous.



So, now we have part of your problem. From all info I can find, 2/0 al SE is rated for 115 amps under use other than the exception as a service feeder for a residence. Who knows what else is illegal?

so now, we have discovered you have a 150 amp panel with a 100 amp meter. That alone is illegal so whether you illegally installed the panel or installed an undersized meter, there is an illegal installation there.

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A 100A breaker can do full power for about an hour or even up to 150-200A for several minutes.
You have apparently never checked the trip curve for your breaker. Guessing just doesn't cut it.

Last edited by nap; 05-11-2011 at 10:37 AM.
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Old 05-11-2011, 10:58 AM   #21
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Voltage sag or VD. Where do they draw the line in the sand?


I don't want to get into legalities of the service. I know everything in the entire system is rated to 100A with no problem at all. lets just stick with that instead of chasing tale and finding some way that my service is illegal for some reason in which it is not. It is old but old is grandfathered here.

SO, at 100A draw, I am below my 10% tolerance window, is that normal? YES, this is tested right at the meter so no chance of blaming the wiring in the house at all. This was also confirmed by a lineman but we are right at tolerance. IE, 108 and down . Obviously transients or inrush currents are permitted and expected and those transients will pull me below 100V. I understand those are instantaneous but will certain trip out UPS supplies and other more sensitive equipment.

Just not sure if these voltages are common to see around the country or if I indeed am seeing an issue here?

Last edited by viper; 05-11-2011 at 11:18 AM.
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Old 05-11-2011, 11:00 AM   #22
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Voltage sag or VD. Where do they draw the line in the sand?


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You have apparently never checked the trip curve for your breaker. Guessing just doesn't cut it.

Yes, I have and I was simply stating generalizations. breakers will handle more than the rating obviously correlating to the time/current graph.
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Old 05-11-2011, 11:16 AM   #23
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Voltage sag or VD. Where do they draw the line in the sand?


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SO, at 100A draw, I am below my 10% tolerance window, is that normal? YES, this is tested right at the meter so no chance of blaming the wiring in the house at all. This was also confirmed by a lineman but we are right at tolerance. IE, 108-110V.
so, what was used to apply the load? what were the actual readings at what verified load?
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Old 05-11-2011, 11:21 AM   #24
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Voltage sag or VD. Where do they draw the line in the sand?


All loads are resistive.

30A load per leg = 111V
70A load per leg = 108-109V
100A load per leg = 108V
60A constant with 100A inrush surge = 99V

These are all tested at the meter can.
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Old 05-11-2011, 11:23 AM   #25
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Voltage sag or VD. Where do they draw the line in the sand?


will you answer the other question I asked?

and if your area allows a 10%+- tolerance, you are legally being provided all you are required to be provided.
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Old 05-11-2011, 11:26 AM   #26
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Voltage sag or VD. Where do they draw the line in the sand?


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will you answer the other question I asked?

If you were referring to "what" was used as load, it was the oven, range top, and dryer. Yes, they commonly run together so that would be a typical load around here. that however is NOT accounting for the extra 10HP compressor, 5HP table saw, etc that run here.

I simply wanted to apply a uniform load purely for testing purposes. The only motor load that was presented was an unloaded 10HP motor across the line start.
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Old 05-11-2011, 11:53 AM   #27
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Voltage sag or VD. Where do they draw the line in the sand?


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If you were referring to "what" was used as load, it was the oven, range top, and dryer. Yes, they commonly run together so that would be a typical load around here. that however is NOT accounting for the extra 10HP compressor, 5HP table saw, etc that run here.

I simply wanted to apply a uniform load purely for testing purposes. The only motor load that was presented was an unloaded 10HP motor across the line start.
Unless the lineman applied the load directly to the feed at the meter, it does include the circuitry within your house at least the portion involving those loads. so, since you had load applied that is not considered in the requirements of the POCO and you still met the required limits, you are getting what you are paying for.

time to either install a proper system so the POCO will install the equipment needed for that installation or live with what you have.
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Old 05-11-2011, 12:49 PM   #28
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Voltage sag or VD. Where do they draw the line in the sand?


Just got the data logger hooked to the service and chatted with the engineer a bit. Sounds like regardless, they will be setting me my own 25kva transformer. 400ft between me and the transformer now, feeding 7 other customers, and too small of wire for what I am running. He said rest assured, one way or another, I will be satisfied with my service.

I cannot be happier with our power company!!! Yippy!!!

Inductive loads will be high on the hog and reducing current all around...

Last edited by viper; 05-11-2011 at 01:01 PM.
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Old 05-11-2011, 02:16 PM   #29
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Voltage sag or VD. Where do they draw the line in the sand?


There are two issues with wires, (1) the heating up of the wire, and (2) the voltage drop. You can run more amperes through a given overhead wire (suspended in free air) compared with the same gauge wire in a conduit or cable. Voltage drop has to do with the length of the wire, the thickness, the material and the maximum current flow but not surroundings (free air, etc.). Heating of the wire has to do with thickness, material, surroundings, and maximum current but not length. You compute the size of the wire needed to satisfy issue #1 and issue #2 separately and choose the larger of the two sizes you come up with.
Quote:
Your power company may tell you to upgrade to a larger service
The power company still has to upgrade the pole wires and/or pole transformer.
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Last edited by AllanJ; 05-11-2011 at 02:20 PM.
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Old 05-11-2011, 02:42 PM   #30
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Voltage sag or VD. Where do they draw the line in the sand?


I do understand how to calculate wire requirements. Actual engineering data does not really compute with NEC code but I DO understand there has to be engineered margins in there for protection.

Ultimately the electrical resistance of a conductor is what dictates how much power can go through it.

But, if we apply Ohms law to some of these calcs, it is pretty obvious that there are some margins in there. Otherwise there is no way the PC could be pushing 500-600A on a single 4ga solid copper conductor. heat dissipation of open conductors is great but I also have tested wire at certain currents looking for anything close to rated temperature and it never happens. Build a system for rated current at 75C and it would take a severe environment to ever get to 75C, at least in my tests.


Anyway, I did want to ask you guys about transformer ratings. I understand KVA and KW, and the relation within but curious where the engineered margins are in transformers? can they actually be pushed much harder than most books spec out?

Example is the PC in this case will likely set a 25kva transformer. By my math, that is only 104A everyday/allday and 130A short duration current. The PC indicated this would run way more than 200A which has me puzzled. I know the PC pushes their stuff hard to get max eff from it but what can a 25kva transformer 'really" take?

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