3-wire meter help

[pentium]

I have this Sangamo type HC 3-wire meter that I an stumped over.
I was using it for monitoring a 110v circuit but now that I am installing a second 120v circuit I need to monitor both with just one meter.
Now I know alot of people will cringe on this one but I am trying to use the meter's ability to meter a 220v line to in reality tell me how much power TWO 120v lines are using (Isn't 220v just +110v, -110v and neutral?).
Anyways, the instructions to convert from 2-wire, 110v to 3-wire, 220v is torn off and I don't know what to do. From my current knowledge I can see one electro-magnetic coil (that needs 110v and a neutral I think) above the spinning disc and two more coils that wrap around a steel block (which I think generates a stronger magnetic field as more current passes through the coils) which is located under the spinning disc.
When it was set to operate on 110v, a small metal clip connected line terminal 1 (hot) to the electro-magnet and the neural line from the electro-magnet connected to line terminal 2 (neutral).
In a 220v configuration having that clip connected would bridge both 110v circuits but if it's not connected the electro-magnet will not operate and I assume the metal disc will not spin.
I don't see any other places the neutral would come from so what needs to be done?
Below I attached a diagram of what the meter is wired like and included a photo of the actual meter with it's terminal cover removed and disc/gear assembly removed.

[gonzo0815]

Re: 3-wire meter help

No expert on this, but i think you can not add two 110v sources, if they aren`t two separated phases i.e.
Art least here in Germany, most buildings are equipped with a 3 phase supply.
As every phase is somehow pahse shiftet, there is a voltage difference between any phase at at any time.

But IMHO you should avoid by any means to connect two phases unless a consumer is between them which is capable in using more than one phase.
As there is a voltage difference between each phase, it would act like a short.
But hey, i have no clue on 110v mains and not mutch from our 230v mains, so may be some other member can tell your more.

[starfury1]

Re: 3-wire meter help

humm no electrician here either But I agree with gonzo on phase thing.


Here in Oz most houses are single phase mostly unless they had a need for 3 phase (415V) for hot water (mostly), motors etc.

Take what I've written below as pure guess work and possibly not correct

"Why" cause I found this and its got me now wondering exactly how the USA/Canada houses are wired in relation to Active Neutral Earth and the electrical box.

In North America the utility companies are required
to supply a split-phase 240 volt (+-5%) feed to your house.
This works out as two 120V +- 5% legs.

http://www.faqs.org/faqs/electrical-...ection-14.html

I'll leave the rest below as I have spent an 1Hr plus doing it and some is useful, I am now just not very sure I got it right in regards to the meter


The meter you have I suspect is for single phase use only and can be used to kilowatt hours (power) (if I got that right) it probably means by 110V/220V that it can monitor a single phase in either voltage
(I've got some info somewhere on how they work but Id have to dig it up and refresh my memory)

did find this link

http://www.traknet.com/wei/whatsnew.html

Now I think what you have,
if I remember correctly is a separate 110V line you had metered
(since you pay for what you use electricity wise)

You have since then added another line.

What you want to do is monitor both of them with the one meter but independently so you know how much was taken off each line
don't think you can do that with that meter.

You could monitor the sum total by putting it in place before the split.
(I suspect the meter is capable of that since it looks like one that monitors the total use of house power)

Otherwise I think you are going to need 2 of them one for each branch circuit you set up.

I could be wrong but fairly sure I am not.

from wiki

http://en.wikipedia.org/wiki/Electricity_meter

Electromechanical meters

The most common type of electricity meter is the electromechanical induction meter.

[edit] Technology

The electromechanical induction meter operates by counting the revolutions of an aluminium disc which is made to rotate at a speed proportional to the power. The number of revolutions is thus proportional to the energy usage. It consumes a small amount of power, typically around 2 watts.

The metallic disc is acted upon by two coils. One coil is connected in such a way that it produces a magnetic flux in proportion to the voltage and the other produces a magnetic flux in proportion to the current. This produces eddy currents in the disc and the effect is such that a force is exerted on the disc in proportion to the product of the instantaneous current and voltage. A permanent magnet exerts an opposing force proportional to the speed of rotation of the disc - this acts as a brake which causes the disc to stop spinning when power stops being drawn rather than allowing it to spin faster and faster. This causes the disc to rotate at a speed proportional to the power being used.

The type of meter described above is used on a single-phase AC supply. Different phase configurations use additional voltage and current coils.

another link

http://www.magnet.fsu.edu/education/...ter/index.html

while I was looking found this, the pdf might be of interest but not overly so

http://www.testequipmentdepot.com/am.../kwhmeters.htm

At this point I'll have to leave it

Hopefully someone that knows what they are talking about will pipe up

like I said no spark here

HTH anyway

Cheers

[pentium]

Re: 3-wire meter help

Sorry gonzo, but here in north america our wiring standards differ from yours.
Going 220V does not mean you are going multi-phase, it's just how you wire a single phase up. Don't forget that over here we use a standard 110V compared to your 220v when it comes to regular outlets and lights.

[pentium]

Re: 3-wire meter help

The meter you have I suspect is for single phase use only and can be used to kilowatt hours (power) (if I got that right) it probably means by 110V/220V that it can monitor a single phase in either voltage

Correct.

What you want to do is monitor both of them with the one meter but independently so you know how much was taken off each line
don't think you can do that with that meter.

No. It just needs to tell me how much power both lines use. Individual readings are unnecessary.

You could monitor the sum total by putting it in place before the split.

Impossible. Both lines run to the main breaker panel in the basement. It would cost too much to get a second panel installed and inspected. (required here)

(I suspect the meter is capable of that since it looks like one that monitors the total use of house power)
Otherwise I think you are going to need 2 of them one for each branch circuit you set up.

This meter is rated for a max of 30 amps and I only have one (next to impossible to find spare meters floating around).

I'm going to look at those links now but I think I need assistance from someone here in north america.

EDIT:Here we go, http://en.wikipedia.org/wiki/Split_phase
We use a different scheme compared to you guys.

[starfury1]

Re: 3-wire meter help

ok pentium then maybe what your after is the second diagram on this link

240V, 1 phase, 3-wire Connection

http://www.traknet.com/wei/whatsnew.html

like I said I am not sure

[pentium]

Re: 3-wire meter help

This one?

That looks about right but that diagram is confusing as hell.
That's also a different make meter than mine.
Not much is on the net about my meter.

[starfury1]

Re: 3-wire meter help

When I seen this thats when I realized were you were probably heading

In North America the utility companies are required
to supply a split-phase 240 volt (+-5%) feed to your house.
This works out as two 120V +- 5% legs.


"This works out as two 120V +- 5% legs." is what you wanted to wire the meter for to monitor both of you own personal legs together...so yeah it makes sense and I guess that diagram is the one you need

And yep someone Nth A based would understand what you were talking about...

I am really curios now how the Nth A houses are wired... and powered from the mains...interesting

[starfury1]

Re: 3-wire meter help

yeah that diagram but you are right it is a bit confusing when you got to wire it to the meter you got
I can't relate it back to your meter either.....

I think the 2 separate windings are to be done antiphase on the core
one for each leg ...input/Load (120V) Load/input (120v)

but how the rest ties together I don't know.

Possibly since it mains best to wait for a local lad from your neck of the woods to come on.

I'd really rather not try and guess at it, since I am way not familiar with KWh meters or your mains system.

[pentium]

Re: 3-wire meter help

okay, time for another horrible paint moment. (see attachment)
If you can't read the legend:

-The red wire is the first 120V line.
-The green wire is the second 120v line.
-The blue wires run to and from the upper magnet and according to the clip of metal that is covering one of the terminal screws on the lower left, the magnet is not connected (ie. the circuit is not complete).

Okay, I have to link you to the photo because the site is acting up again (calling topcat with a bug report)

Cluck here to see the photo.

[starfury1]

Re: 3-wire meter help

Well I am really out of my depth on this one....here it would be the home ground of licensed Electricians anyway so as much as I like to help I think I'll leave it to those that really know the Nth American wiring system and that meter in particular.

Seems unlike here, you guys and girls get 2 Actives a Neutral and an Earth as standard.
From what I gather its 2 phase Actives, which gives you the ability to get 220 Volt between both hot Wires or 110 Volt between Neutral and "either" of the hot wires.
(this explains something in another thread I'll have to add comment on, when I find it)

Seems the meter is capable of doing this I just don't have a real clue on how you wire it for this purpose
(it would be guess work and I'am not going there with mains )

From all my searching I cant find anything useful

cheers, hope someone post on it soon for you.

[starfury1]

Re: 3-wire meter help

Correction to the above
Split phase or "3-wire, single-phase, mid-point neutral system." (not "2 phase" actives)

To avoid confusion with split-phase motor start applications, it is appropriate to call this power distribution system.. 3-wire, etc

See;

http://en.wikipedia.org/wiki/Split_phase

I used an incorrect term,
(the method was what I was thinking of but wrong term applied)

There is a phase angle, voltage difference and so this need to be corrected

Three-wire, 120/240 volt single phase power used in the USA and Canada is sometimes incorrectly called "two-phase". The proper term is split phase or 3-wire single-phase.

See;

http://en.wikipedia.org/wiki/Two_phase

[Per Hansson]

Re: 3-wire meter help

I'm taking it the US system is not the same as ours

The 230v system is derived by having 3 coils on the generator, each at a 90° offset in a circle around the motors axle

Connect any of the phases to neutral/ground and you have 230v, connect any phase to another phase and you have 460v (using the neutral is also needed for complex loads)

So how does the US system work? I find it helps greatly to imagine how things actually work in reality, i.e. a picture showing the generator, coils etc...

We have another thread here somewhere in the forums, it was in it I got my grasp about AC electricity

[starfury1]

Re: 3-wire meter help

exactly how its done does differ
yeah thats the post I am looking for cause KB cowboy I think hit on this with his first query from memory...this info needs to be amended to the post because some confusion will come from that fact ...and I probably added to the confusion from my way of putting it in reference to our system and not how it arrives at a Nth American house.


3-wire single-phase system,

it appears to be the normal setup now but I don't know when it become the standard there (maybe it always was but not used as much)
I was under the impression they use a single phase like us
(seems that system does exist there but not use often or being made redundant with new installs, I dont know)

[davmax]

Re: 3-wire meter help

Hi Guys lets look at the fundamentals. The requirement is for a power meter to have one coil for voltage and another for current to obtain the product = watts. The picture shows are large coil with many turns on top, this has to be the voltage coil. There are two coils with few turns that are used for the current component. Only the two current coils can have their relationship to the outside world changed. The first diagram shows both coils connected in series with the load, this means both coils have the same current (Ampere turns 1 + 1 = 2). Now for the same wattage 240V has half the current compared to 120V. How does this meter deal with that? I am not sure but I would think that half the ampere turns is required somewhere for 120V operation (twice the current) this suggests using one current coil for 120V and adding the second in series for 240V. What happens to the changed voltage across the upper coil I cannot fathom yet. If the two current coil theory is correct and a seperate load is taken through each one (both in phase) the result should monitor the total power of both loads (120V supply).

Does this help?

[davmax]

Re: 3-wire meter help

The voltage coil. Theory and math suggest that the voltage coil of this meter is always connected to 120V (constant). Only the current coils are configured to change ampere turns and correct for the change from 120V to 240V.

[pentium]

Re: 3-wire meter help

Well before I got my hands on the thing it was wired for 220 volts however I never noted the wiring before I disconnected and removed it and then shipped the meter home.
I had some time today so I tried:

-running two 120v lines through each of the two lower coils with the upper coil disconnected. Meter didn't spin when a load was put in both 120v lines.

-Doing the same as above but conecting a neutral lead (via test lead I made) to the opposite end of the upper coil (as to make it work). Nothing

-Reverting back to 120, 2-wire mode.
--One of the lower coils had the hot 120v lead go through it and the other lower coil had the neutral lead go through it and the little clip was in place as to power the upper coil. A load caused the meter to work properly.

I didn't test the meter with that little clip in place.

It would REALLY be NICE if SOMEBODY FROM NORTH AMERICA would HELP ME OUT about NOW.

[davmax]

Re: 3-wire meter help

It is important that you get the two current coild in phase or you will get no action. I will put some diagrams together. Electrical theory and practice is universal so we should be able to get it going for you.

[davmax]

Re: 3-wire meter help

Continuing on. The original wattmeter connections diagram cannot create an operating wattmeter. As has been correctly stated. Where is the neutral? It must be there to make a functioning 120/240V meter. The connection diagram shows no neutral return for the voltage coil therefore no voltage contribution and no action. I have put together diagrams for different connects that will make a meter work. They all depend on finding the neutral connection, this is KEY. As said before current coil phasing is important, once you have 120V across the voltage coil you will get action with one current coil passing load current, connecting another coil into the load circuit whether in series or parallel may cause the meter to stop, if so reverse one coil connection.

This all is based on the fact that it has been stated that the 240V is a single split phase ie each split is in phase.

[pentium]

Re: 3-wire meter help

I can't read the PDF. acrobat keeps crashing on my laptop and every other computer I own is stored away until I finish renovations. So are all my cd's.

Where is the neutral?

It's not going through the meter right now. Only the two hot wires are passing through the meter (one per coil). The neutral bypasses the meter and continues on.