Amp draw measurment on main power feed residential

Ashton Crusher · 2020-07-03T09:40:11+00:00

I'm looking at a device to monitor my power. It hooks around the mainpower feed wires that feed the breaker panel. It has a sensor foreach of the two main wires (240 volt standard setup). I measured theamps separately for each feed wire with a clamp around meter and getwhat seems like the total draw on each wire. So for the "left" wire Iget around 80 amps. For the "right wire" I get around 80 amps. 80Amps is just about what I would expect to be getting based on what'srunning. If there is really 80 amps on each wire that would be atotal of 160 amps which I cannot imagine I could possibly be using.It's a 200 amp service.. I'd have to have literally everything in thehouse on, stove, oven, water heater, both AC's, toasters, coffeemaker, etc and I don't have all that stuff on. So why does themonitor need to measure on both of the wires? It looks like eitherone alone gives the amp amount. The only thing I can think of thatmight explain it is all teh big stuff taht was running was 240 voltstuff, the only 120 stuff was lights. Is it possible there was 82amps on one side and 77 on the other and the large 240 draw masks thesingle side draw?

G

gfretwell 6 years ago

He is right about Germany as far as the 3 phase is concerned. 3p wye

400/230 at 62 amps is pretty common for a dwelling. Also throughout a lot of Europe and UK you might be seeing 230 single phase (derived from that 400/230 wye) as low as 25a serving a dwelling. My Austrian friend wonders what the hell the average American needs 48KVA for. This was in a condo sort of place we rented in New Zealand. You can see there is a hot and a neutral (red&black) feeding the RCD and a green wire ground that is not shared with the neutral but this is a sub panel so I assume the service could just be 2 wires. Maybe Bod can weigh in here since he lives on that side of the ditch. My knowledge of that is fairly limited. I do know plenty of guys on my EC group who can fill in the blanks tho.

formatting link

am not sure where he is going with the "500 wire cable". That is not metric because a 500 mm2 conductor would be around 1000 Kcmil and nothing you would see in a dwelling. They are even rare in big industrial. You would see parallel conductors when the circuit gets that big. You can see 500 Kcmil on a 230a service tho.

Vote

I

invalid unparseable 6 years ago

On Mon, 06 Jul 2020 12:42:57 -0400, snipped-for-privacy@aol.com posted for all of us to digest...

I can see a white & red connected together with their version of a wire nut (name?). Interesting...

Vote

I

invalid unparseable 6 years ago

On Fri, 03 Jul 2020 21:24:34 -0400, Clare Snyder posted for all of us to digest...

Aw, come on, check your shorts...

Vote

G

gfretwell 6 years ago

I am not sure what a white wire is in NZ. Neutral is black. It might have something to do with the RCD

Vote

A

Ashton Crusher 6 years ago

To all the replies, thanks, it makes sense.

I'm pretty confident it's just single phase 240/120 based on what I've checked as tell tales for multiphase, such as the type of main breaker.. it doesn't have the kind of breaker google suggests I should have for any sort of 'phase' service.

Vote

A

Ashton Crusher 6 years ago

Trader4 said...

It's 80A at 240V or 160A at 120V, depending on what the loads are. They would only need to monitor one hot if all the loads were 240V or if there were also 120V loads and they were perfectly balanced, eg 30A on one leg, 30A on the other. If not, then the power is

240V * (min of the amps in the two hots) + 120V * (the difference between the two). That's without the complication of power factor.

.... which makes total sense to me and would explain the nearly balanced load of my two AC units plus the 120 loads which are probably not perfectly balanced.

Vote

A

Ashton Crusher 6 years ago

That's a bit surprising... you mean my 200 amp panel can theoretically deliver 400 amps if I only run 120 loads??? I would have thought the amp rating was just that, amps total.

Vote

G

gfretwell 6 years ago

That is why I suggested that it is easier to just look at the total KVA (48KVA). Assuming you are really using the total load at 120v, it is still only 200a because there are only the two ungrounded conductors involved. Those 120v loads are simply in series. If the loads are balanced, the neutral is not involved at all.

Vote

T

trader_4 6 years ago

It is just 200A. And you can only power 400 amps worth of 120V loads if the loads are equally balanced, half between one leg and neutral, the other half between the other hot and neutral. In the case of

240v loads you can have 200A coming in one hot, through 200A of 240V loads and out the other. With 120V loads, you can have two groups of 200A worth of 120V loads that are placed in series. Now you have 200A flowing through group A and the same 200A flowing through group B. It's supporting a total of 400A of 120V loads. If it's totally unbalanced, all the loads on one side, then you can only support 200A of 120v loads. Typical case is somewhere in between, more toward balanced though.

Take three 3 ohm resistors, put them in parallel. Make another group like that. Put the two groups in series and connect them across 240V. The resistance of each group is 1 ohm. The two connected in series is

2 ohms. So you have 240/2 = 120A flowing. The voltage across each group will be 120V. You're running 120A through two groups of 120V loads, 120 watts each group, 240 total. You're powering 240A worth of 120V loads.

Vote

S

Sam E 6 years ago

[snip]

Of course you don't get 400A from a 200A panel. That's 200A/240V. You've got 2 120V loads in series (balanced loads) so there's no neutral current. Both groups of loads are using the SAME 200A.

Adding the current on both sides doesn't make sense.

Vote

S

Scott Lurndal 6 years ago

Converting to a more useful measure (power) makes it easier to compare.

A 240 volt, 200 ampere service provides (P=VI) 48,000 watts of power.

Two 120 volt, 200 ampere services provide (P=2VI) 48,000 watts of power.

Vote

T

trader_4 6 years ago

The remaining difference is that with 120V loads, you could use the full

48KW of the second case, but you can only get 48KW out of the 240V service if the loads are perfectly balanced. Worst case, if they are all on one leg, you only get half that.

Vote