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jamiedolan 09-06-2008 12:44 PM

Clamp Meter Findings
 
Hello;

Thanks you again to those here that suggested the clamp meter to measure current amps on a wire.

I was able to get a meter yesterday, and it works wonderfully. Not sure if anyone has been following my situation or not, but I need to add in more circuits because my old pushmatic is full. I was debating if a service upgrade was necessary (currently at 100A service). The clamp meter has given me some very solid answers to my questions, and has helped me realize that I do not need to spend the money on a service upgrade.

I clamped onto some branch circuits and watched the amps. Then I clipped onto the main, (one side at a time) and watched the amps. I turned on all our lights, washer, dryer (it's gas so it only draws less than a amp) dishwasher, dehumidified, central air, outside floor lights, coffee machines, tv's computer, etc. I watched each leg for a several minutes at a time with everything on, so hopefully my fridges and freezers would cycle on, ( but even if they didn't I know all of them use very little - less than a amp each thanks to my kill-a-watt).

So running everything we have, minus say a vacuum or a power tool, the maximum draw I saw was 22 amps.

So I strongly suspect that we will be able to add in a hot tub with no problem. We are going to a gas stove, have a gas water heater, gas furnace.

Thanks so much for the info on the clamp meter. I am shocked that our big 3 ton AC only draws 3.5 amps, it requires a 30A cir.

Any ideas what a hot tub would draw in the real world, not just what it is labeled for?

Jamie

J. V. 09-06-2008 12:52 PM

What brand and type did you buy? 22 amps total load is very low. Are you sure you have the meter set correctly? Central air alone should be close to your total reading.

jamiedolan 09-06-2008 01:00 PM

Quote:

Originally Posted by J. V. (Post 155614)
What brand and type did you buy? 22 amps total load is very low. Are you sure you have the meter set correctly? Central air alone should be close to your total reading.

Before you yell at me. I normally buy quality tools, however, I only needed to use this one time, and wanted to buy one right away. So I got the harbor freight meter.

I can easily do a test to verify what I am seeing is accurate. How about a 100 watt incandescent light bulb? What would I see as amp if the meter is working correctly?

Thanks
Jamie

BigJimmy 09-06-2008 01:05 PM

Quote:

Originally Posted by jamiedolan (Post 155616)
Before you yell at me. I normally buy quality tools, however, I only needed to use this one time, and wanted to buy one right away. So I got the harbor freight meter.

I can easily do a test to verify what I am seeing is accurate. How about a 100 watt incandescent light bulb? What would I see as amp if the meter is working correctly?

Thanks
Jamie

Eeesh-Harbor Freight!

Anyway, P(watts)=I(amps) @ V(volts) and rearranging, I=P/V. So 100W/120V (nominal) = .8A. If you measure the actual voltage, you can get closer to reality.

BigJimmy 09-06-2008 01:07 PM

Quote:

Originally Posted by jamiedolan (Post 155612)
So running everything we have, minus say a vacuum or a power tool, the maximum draw I saw was 22 amps.

Jaime-

Is this the additive result of both incoming legs?

jamiedolan 09-06-2008 01:27 PM

Can I have an Idiot Award?
 
Quote:

Originally Posted by BigJimmy (Post 155619)
Jaime-

Is this the additive result of both incoming legs?

Yes, it was. I have to redo it.

The directions that came with this clamp meter were very poor. I had never even touched a clamp meter prior to this.

I was holding the wire right near the tip of the clamp and was not allowing the clamp to fully close, so it was not making contact with it's little metal contacts and it was giving false readings. Now that I put it on further and the clamp is closed and the wire is inside the clamp, I am getting accurate readings. I put my Kill-A-Watt on a shop vac, turned it on, and plug it into a circuit where it is the only thing on there. Then I went and measured that circuit, properly this time, and I got the same 11 A reading that the Kill-A watt was showing.

I feel pretty dumb. I was wondering all night how my 1000wats worth of spot lights outside where only taking up about 4 amps, when I calculated that they should pull 8.some amps. I was kind of puzzled on that one... I should have known better and known that my calculations were correct and that the laws of physical are still immutable.

I got the AC back on and am going to go take some new accurate measurements.
jamie

jamiedolan 09-06-2008 01:53 PM

New (Correct) readings
 
ok, I did the readings again, had just about the same things on, forgot to turn on a handful of lights that was on last time, so my numbers are likely a few amps low. Plus the dehumidifier was off, and it adds like 8 amps or so.

The AC is using 8 amps on the left side and closer to 7 on the right side, putting it around 15 amps for the central air unit. Sounds more logical.

The whole house measured 25 on the left and 23 on the right. So that puts my pull at nearly 50A.

I bet that I have had my panel very very close to being maxed out. I had the same type of load running, plus 1500W (12.5A) of indoor lighting during remodeling, a 15A belt sander, and 2 Vacuums (20A). So I may have been within a couple amps of blowing the main.- but thats not something I do everyday.

In the next year, I plan to install a new espresso machine that will have a slightly higher pull, maybe 5-10 more amps. Also the Hot Tub.

So do I add my sub panel and try watch my load levels and see where I stand once the tub is added or do I just need to bite the bullet and get 200 A service installed before the tub is installed.

Jamie

EBFD6 09-06-2008 08:21 PM

Quote:

Originally Posted by jamiedolan (Post 155629)
The whole house measured 25 on the left and 23 on the right. So that puts my pull at nearly 50A.

This is not entirely correct. You do not add the values of the phase conductors together. A 100 amp breaker can carry 100 amps on each phase, not 100 amps total.

Secondly, using an amprobe to measure loads in your house is not a truly accurate way to determine the capacity of your existing service, or determine the need to upgrade depending on the loads you plan to add.

The only way to determine if your service size is sufficient (per code) is to do a service calculation. Unfortunately this is a bit complicated to get into on a DIY website. You may be able to get assistance from the electrical inspector when you pull the permit for the work you intend to do.

jamiedolan 09-06-2008 08:44 PM

Quote:

Originally Posted by EBFD6 (Post 155731)
This is not entirely correct. You do not add the values of the phase conductors together. A 100 amp breaker can carry 100 amps on each phase, not 100 amps total.

Secondly, using an amprobe to measure loads in your house is not a truly accurate way to determine the capacity of your existing service, or determine the need to upgrade depending on the loads you plan to add.

The only way to determine if your service size is sufficient (per code) is to do a service calculation. Unfortunately this is a bit complicated to get into on a DIY website. You may be able to get assistance from the electrical inspector when you pull the permit for the work you intend to do.

So each phase could read 100 amps, so for what would appear to me to be 200 amps of service based upon the readings I am getting on my meter (when I add up both phases).

I am still a little confused as to if I even really need to do a service upgrade or not. If I really can run each phase up to 100A then I have lots of room to expand and am only using about 25% of my capacity. Am I understanding this correctly?

I was told today that if your phases are out of balance that you end up paying for the higher drawing phase. i.e. phase 1 25A, Phase 2 50A. I was told that you get charged for the 50A and the "extra power" on phase 1 (the diff between phase 1 and phase 1 - 25A) gets fed back into the grid. I was told that you could use that extra power at no cost.

i.e. if I am using 1 120 air conditioner on one phase I can out one on the other phase and run it for virtually no additional cost. Does this make track at all?

I am trying to get a better understanding of how this all works.

Thanks
Jamie

Silk 09-06-2008 09:52 PM

Quote:

Originally Posted by jamiedolan (Post 155742)
So each phase could read 100 amps, so for what would appear to me to be 200 amps of service based upon the readings I am getting on my meter (when I add up both phases).

You have 100 amps available at 240 volts
You have 200 amps available at 120 volts
The watts you have available works out to be the same
W=E*I

Quote:

Originally Posted by jamiedolan (Post 155742)
I am still a little confused as to if I even really need to do a service upgrade or not. If I really can run each phase up to 100A then I have lots of room to expand and am only using about 25% of my capacity. Am I understanding this correctly?

Yes, you are.

Quote:

Originally Posted by jamiedolan (Post 155742)
I was told today that if your phases are out of balance that you end up paying for the higher drawing phase. i.e. phase 1 25A, Phase 2 50A. I was told that you get charged for the 50A and the "extra power" on phase 1 (the diff between phase 1 and phase 1 - 25A) gets fed back into the grid. I was told that you could use that extra power at no cost.

Thanks
Jamie

Whoever told you that is clueless. First off, you only have 1 phase entering your house. You have 240 volts, single phase with a center tap which is the neutral. what you are calling "phases" are only two ends or "legs" of a big coil of wire which is what we call the "transformer secondary", with one more wire connected right to the middle of that coil of wire which we call a "neutral".
You don't pay for amps, you pay for watts. This stuff about "free electricity" on the other phase is complete bull. Tell that guy that he is a fool next time you see him.

jamiedolan 09-06-2008 10:07 PM

Quote:

Originally Posted by Silk (Post 155760)
You have 100 amps available at 240 volts
Whoever told you that is clueless. First off, you only have 1 phase entering
you see him.


I wonder if I somehow grossly misunderstood what he was saying. He said he was licensed as a electrician in 7 states.

So if I understand correctly now, you get charged for all watts used, regardless of what leg they are used on or how the loads are balanced in the box.

He also mentioned that 240 is more efficient because it uses more voltage and less amperage, so it ends up costing less since your taking advantage of the higher voltage. Did he get this part right?

So what would be the consequences of having your box unbalanced? Damage to the buss if the draw was too high on one side of the panel?

Thanks so much for helping me understand this. I did do a lot of searching and it was very hard to find clear answers about this topic in general.

Jamie

Silk 09-06-2008 10:28 PM

Quote:

Originally Posted by jamiedolan (Post 155767)
He also mentioned that 240 is more efficient because it uses more voltage and less amperage, so it ends up costing less since your taking advantage of the higher voltage. Did he get this part right?

So what would be the consequences of having your box unbalanced? Damage to the buss if the draw was too high on one side of the panel?

Jamie

A watt is a watt, no matter what the voltage is. The only thing thing that could be considered more efficient about the 240 volt system is that the reduced current would also reduce any I squared R losses due to the resistance in your wire, but those losses should be negligible if your conductors are sized right.

On the second part, I really can't think of any consequences to having one leg drawing significantly more than the other. I do know that if you are drawing power off of a 3 phase generator that you should try to balance the phases. I believe that is because of the differences in magnetic fields would cause stresses on the generator.

J. V. 09-07-2008 10:16 AM

Why don't you just make this easier on your part. How many spare breakers slots do you have. You can put as many breakers in your panel that it will allow. When you run out of breaker slots you can check your panel and see if slimlines or double throw single pole breakers can be used. When you have exhausted your panel you start thinking about your upgrade. Sub or new service panel.
You have already mentioned two loads you plan to install. Will your existing panel allow the needed breakers for the new equipment? If the answer is yes, you do not have to do anything.

I applaud your desire to understand how this works. But it is much simpler to just look at capacity and leave the calculations alone.

Silk has explained this very well for you.

PS.....When it's time for the hot tub, call a licensed and insured electrician. Don't mess with hot tubs or pools yourself.

jamiedolan 09-07-2008 11:12 PM

Quote:

Originally Posted by J. V. (Post 155864)
Why don't you just make this easier on your part. How many spare breakers slots do you have. You can put as many breakers in your panel that it will allow. When you run out of breaker slots you can check your panel and see if slimlines or double throw single pole breakers can be used. When you have exhausted your panel you start thinking about your upgrade. Sub or new service panel.
You have already mentioned two loads you plan to install. Will your existing panel allow the needed breakers for the new equipment? If the answer is yes, you do not have to do anything.

I applaud your desire to understand how this works. But it is much simpler to just look at capacity and leave the calculations alone.

Silk has explained this very well for you.

PS.....When it's time for the hot tub, call a licensed and insured electrician. Don't mess with hot tubs or pools yourself.


HI;

My panel is Full. I need to add 2 -240 30 Circuits, and at least 3 or 4 20A Circuits. The double breakers will not give me room for the 240's I need, and they are very expensive for the pushmatic box, around $70 each.

Here she is, the old pushmatic box:

http://www.dolanhosting.net/jamiedol...atic_panel.JPG

Before you comment: The second breaker from the bottom is double wired, I never do this, and have turned this breaker off and am just living with the outlets being disabled for the moment. Also the neutral for one of the wires on that second from the bottom break is slightly burned, another reason I turned the breaker off. -- Mind you I know this was all done by licensed electricians.
There are a couple other breakers off due to remodeling, but the are active circuits.
Directly about the 100A main, there are lugs for attaching wire, just before the main. So they are always hot. There are currently wires on them, they go to a small box next to the panel, I felt this setup was incorrect (as several here confirmed), and there is nothing hot in the box anymore, I plan to pull it when the meter is off. -- However I am curious, Can anyone tell me what a legitimate / legal use of these lugs would be? Since they are before the 100A main?

RE: Hot Tub, I will have my dad help with that project, he's installed tubs before, commercial, 3phase, etc. But he has been very busy lately and I have been trying really hard to learn more myself. As well as educate myself about the current codes, as I know some things change all the time.

Thanks again for the help.
Jamie

jamiedolan 09-08-2008 01:09 AM

Directly about the 100A main, there are lugs for attaching wire, just before the main. So they are always hot. There are currently wires on them, they go to a small box next to the panel, I felt this setup was incorrect (as several here confirmed), and there is nothing hot in the box anymore, I plan to pull it when the meter is off. -- However I am curious, Can anyone tell me what a legitimate / legal use of these lugs would be? Since they are before the 100A main?
jamie


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