what if single phase is fed through 3 phase meter
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I imagine the same as a high-leg Delta with no load on the high leg: it'll read normally.
- Location
- Massachusetts
This happens all the time if you think about it.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
It accumulates wattage?:grin:
since I assume three phase meters are something like 3 phase motors I guess the meter wont register single phase perhaps, but speaking for digitals might be that they register the wattages separately and digitally it might not be effected by the lack of others phases..what would you say?
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
This is a wrong assumption, meters will register the correct wattage no mater what, as long as they are correctly wired, if what you say was true, then anyone could turn off breakers of one phase and cause the meter to not read, It is not uncommon for a three phase service to be used for a large apartment complex, and have all the loads single phase, so there is no controlling how the meter is loaded and balanced.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
There is a web site that has all about meters on it, maybe someone will chime in and post the link or I will when I get back home later.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Because it doesn't work like a motor, it's nothing like a motor other wise it would only turn at one speed, it uses a whole different principle.
I'll try to find that site.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Not exactly, it more of how many phases are used, all phases have to land at the meter for the correct measuring of voltage and current, but after the meter applying a load between any two phases or a phase and neutral will not have an effect, this is the same in a single phase service where you only might have one phase to neutral load, as long as both legs of the meter see a hot it will still register the correct amount, in some cases where we install a temporary service for a job site and only 120 volt loads will be used, we will place a jumper from one leg to the other to achieve this.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
There was a test I once used to test a customers meter, it was a 1kw load (heater) wired to a one hour timer, I would turn off all the circuits of the building and place this timer fed load on one of the breakers, read the meter then set the timer for 30 minutes, after this time I would check the meter again and make sure .5kw would have been registered on the meter, I would do this for all 3 phases, one at a time, and I have never found a meter that over read, just under reading ones.
After learning that a mechanical meter can't over read, I stopped doing this test, it made no sense. and would explain this to a customer.
After learning that a mechanical meter can't over read, I stopped doing this test, it made no sense. and would explain this to a customer.
Sorry but I couldnt get what u mean with "I learned that a mechanical meter can not over read". You found that every measurement was right or not? From what you explained in the former post what you did to test the meter was right since it would register ,5 kw for 30 minutes on every try true?
So what was the thing which made you quit testing again such a thing? Excuse me but I couldnt get what u tried to explain with this example .Pls make it more clear to me
So what was the thing which made you quit testing again such a thing? Excuse me but I couldnt get what u tried to explain with this example .Pls make it more clear to me
lakee911
Senior Member
- Location
- Columbus, OH
1KW for 30min leaves a lot of room for error. Better off doing something like many KW for a long period of time.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Actually 3-phase mechanical meter is more like (3) 1-phase motors with a common shaft. So, feeding it properly wired single phase makes no difference in its performance.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Mechanical meters will slow down, they never speed up, and the design of how they operate will not allow them to read more then what was actually used (over read) so if something goes wrong with them they will read less usage then that was used (under read)
Hope this helps.
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mivey
Senior Member
Jim is correct and the analogy is spot-on for wye banks.
For accuracy, the meter is supposed to have the same number of elements as there are current-carrying conductors (the neutral is included, of course). You can leave out one element if all of the voltage coils have a common tie to the conductor which is missing a current coil (Blondel's Theorem).
But, there is some "cheating" going on with some 4-wire delta meters. The grounded conductor and the two adjacent ungrounded conductors are read just like with a single-phase 3-wire service. The high-leg is metered with a separate single-phase element.
The meter is totaling single-phase readings like Jim said. The high-leg acts like its own single-phase meter. The "cheat" is that for the other conductors, one line-line voltage is used instead of using two voltages tied to the common. This cheat is done with a residential single-phase meter. By using this cheat, the assumption is that the voltages are essentially balanced (usually a fair assumption) but you do sacrifice accuracy if the voltages are unbalanced.
In that respect, you do take a performance hit when this configuration is used and unbalanced single-phase loads are usually the main contributer to unbalanced voltages.
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