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Measuring the home current consumption

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alphacat

New Member
Hello.

I'd like to connect a current transformer in series with the Live wire which is in the panel box in an house, in order to measure how much current that house is drawing in every moment.

How can I know what should be the current rating of the transformer's primary coil?
Meaning, what is the maximum current that can be drawn by an house?

Thank you.
 

Chippie

Member
Hello.

what is the maximum current that can be drawn by an house?

Thank you.

Your current is limited by the fuse provided by your electricity service provider(Least that's how it works here in the UK)....Exceed the fuse rating and it will blow...

The maximum current drawn by your house is dependant on how many lights you have switched on simultaneously, how many appliances plugged into sockets being used simultaneously...although in the UK, a socketed ring main is backed by a 30 amp fuse ( or an equivalent mcb ) so the max loading on the ring circuit is limited by the fuse (or mcb)...
Lighting circuits here in the UK are radial with a 5 amp fuse protecting the circuit (again could be an mcb)...House wiring can vary, my for instance has 2 ring mains backed by 30 amp fuses ( one upstairs ring one down) but my lights are on one cct....backed by a 5 amp fuse....So I'm limited to around 1000watts for lighting, if you take into account diversity factor you wouldnt actually reach that value unless you like wasting money?
 
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jimlovell777

New Member
I'd like to connect a current transformer in series with the Live wire which is in the panel box in an house, in order to measure how much current that house is drawing in every moment.

If I read and understood that right it sounds like a bad idea and dangerous. I think what you want is a Clamp Meter. There is also a device called the Kill-o-watt you may be interested in. It only works one outlet at a time though.
 

Chippie

Member
I'd second the clamp meter...far safer than messing with 230v....
 

tcmtech

Banned
Most Helpful Member
Just buy a stock current transformer and meter and install that over your main line/s comming in. If you set it up right you will need a current transformer rated for what your main fuse or breaker capacity is and a meter that is scaled to that value to get an acurrate current reading.
 

Mike_2545

Super Moderator
Go outside to the meter, write down the number and then compare that with a reading in a day or two...you will see how much electricity you are using...
 

Chippie

Member
Go outside to the meter, write down the number and then compare that with a reading in a day or two...you will see how much electricity you are using...

He should know how much he is using when paying the bill......
 

tcmtech

Banned
Most Helpful Member
Knowing total usage is not the same as knowing peak usage. Saying your electrical bill works out to an average power consumption of around 1.5 KWH per hour is not an accurate way of finding your actual peak demand and loads being placed on your supply source.
My place averages about 2.5 KWH per hour typically per month but my peak loads may reach near 70KW for several minutes while all of my high powered shop equipment and home systems are on at once. A 20:1 ratio of peak VS average wont be shown by a KWH per month reading.


When I rework the electrical panel in my shop (closing in the walls) I plan to put a set of current and voltage meters on the two lines coming into it just for a personal reference to how much amps draw I take during peak loads and how much voltage drop I get as a result as well.
Its not necessary of course but them neither is my own personal KWH meter I installed for the shop as well. Its just a good reference device for my interests. Knowing what my total billed KWH's are for a month and then being able to see what uses more power is very useful for determining if the house or the shop is the bigger power user at any one point in time.

The shop uses about 2/3 of my average yearly power by the way. ;)
 

Chippie

Member
It shouldnt be too difficult to work out what your power consumption is based on the loads placed on the supply.........How much does the electric kettle load up? How much does a 60w light bulb consume....count how many light bulbs are lit at anyone time......

At the end of the day what does it matter the bill has to be paid......?
 

smanches

New Member
It matters because of all the things that are automatic.

How often does your hot water heater turn on and for how long? How would that change by lowering your water temp 5F?

How often does your refrigerator turn on? How is that affected by turning it down a bit?

How often does your furnace turn on...

etc. etc.
 

Chippie

Member
It matters because of all the things that are automatic.

How often does your hot water heater turn on and for how long? How would that change by lowering your water temp 5F?

How often does your refrigerator turn on? How is that affected by turning it down a bit?

How often does your furnace turn on...

etc. etc.


Well,....My hot water is heated by gas boiler that also supplies heat for the house during the winter...

During Summer, the heating isnt on, and the timed duration the boiler is on for hot water is reduced to 2 hours per day...1hr for the morning and 1 for the evening...
Water temperature is governed by the boiler stat, again that is adjusted so that the hot water isn't being overheated...what's the point in having it too hot?

As for the refrigerator, its essential from a food hygene perspective that it mains temperature to prevent food poisoning....its set to an appropriate level

Furnace? whats that?

I re-iterate what I said earlier....the bills need paying irrespective of how much gas or electric has been used....What's the point in being paranoid about it?...

Mebbe instead of posting here I ought to turn off my pc and never come back again!

There's a difference in being green and being mean.....
 

tcmtech

Banned
Most Helpful Member
So why cant alphacat have an amp meter on his service line to see what his moment to moment amps draw is?
And am I not allowed to put one on my place as well now? :confused:

If you think we shouldn't have them just try and stop us!:D
 

Mr RB

Well-Known Member
There are tons of cheap products on the market now that will display how much power a device is using, or slightly more expensive ones you put in your switchboard to show total household use. Many of the junkmails i get have these things for sale.
 

Chippie

Member
So why cant alphacat have an amp meter on his service line to see what his moment to moment amps draw is?
And am I not allowed to put one on my place as well now? :confused:

If you think we shouldn't have them just try and stop us!:D

I'm not saying he can not or should not have a device to measure.....At the end of the day he still needs to pay the utility bill....

Like I said...there's being green and being mean...
 

alphacat

New Member
Thanks a lot guys for your kind help.

I'll listen to your advices and look at the fuses' rating inside the panel boxes and see what it says.
 
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MikeMl

Well-Known Member
Most Helpful Member
In the US, typical residential service is 100A, 200A or 300A, three wire. It is 240V single phase split into two 120V circuits by a Neutral wire, which means if you want to meter your own usage it would take two current transformers, one on L1 and the other on L2 because the currents are not balanced all the time. A high-current load like an air-conditioner runs on 240V(L1 to L2), while most small appliances and lighting runs on 120V (L1 or L2 to N).

Installation of the CTs would have to be done downstream of the main disconnect switch and upstream of the main circuit breaker panel.

Here is a good introduction to CTs
 
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Sceadwian

Banned
Thanks for the tidbit there Mike, I wasn't aware of typical house installations being two phase like that, then again I don't typically go around comparing the phases of the live on different branch circuits (meter leads aren't that long anyways =)) Though in hindsight it does make sense. I'm in an apartment now and the AC and electric stove are both 240V
I guess I don't give much thought to what's further back along the circuit from the breaker box. I still look at pole pigs and power company transformers and distribution sites with a certain amount of awe.
 
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tcmtech

Banned
Most Helpful Member
Not two phase! Its still single phase actually, its just center tapped. Two phase would require a 90 degree separation of the two line currents. ;)

The two lines used in a single phase circuit can be easily sensed with just one current transformer.
They just get a single criss cross at the point that they go through the center of the current transformer.
The current transformers ratio however needs to be 2x the actual circuits rated amps though to get an accurate reading of both lines combined total amps draw if it is to be referenced to an equivalent 120 volt source.;)

Think about the 180 degree phasing relationship and current flows and you will see why it works!:)
 

Sceadwian

Banned
tcmtech, just because it's single phase 220v in doesn't mean it's not 2 phase out. Doesn't matter what it is on the other side of the transformer, if the center tap is grounded for the neutral on the house side it's two separate 120 volt circuits 180 degrees out of phase then you clearly have to call it a two phase system at that point. You might not call it two phase, but it is.
 
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tcmtech

Banned
Most Helpful Member
Nope. Still single phase. ;)

A true three wire two phase can have both lines at 120 volts in reference to the common point but the line to line will be √((120) + (120)) = 169.7 volts.
True two phase has an 'L' shaped line connection configuration. The two ends of the 'L' are the lines and the corner is the common. The 169.7 volts come from the phase angle difference between the two ends.

There are also four, five, and six wire two phase systems as well. Think of the many stepper motor winding configurations. :)

It can hurt your head if you really get into the countless phase system configurations and their related applications deep enough. :D
 
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