Current leakage on residential service

[wptski]

I've search the net and this forum for information on what would be normal, if there is such a thing for the "net current leakage"/"ground or neutral current leakage on a residential 120V/neutral/120V service. Although I've found some interesting threads, none are for residential, so far!

It appears that the applied loads aren't setup very well, meaning there are two fridges and the furnace blower motor on one side. At the POC into the home, one side is drawing .5A but the other side as much as 14A at times. The net current leakage for the two 120V wires plus neutral is 5.4A and 9A on the neutral alone. I'm wondering if this all becuase on the imbalance?

The garage where there's a good sized air compressor is on the same side as the bigger loads. If the compressor is turned ON, the neautral current increases to 15A.

Another odd thing is that at the POC, the .5A side is showing 80% THD with the other side just a few percent. Most if not all of these wires are impossible to get a current clamp around in the fuse panel in this 50 year old home!

EDIT: Managed to get my AEMC F25 around the service coming from the meter, figured out which side is which and figured out which branch circuit the distortion was coming from. The closer you get to the source the greater it is, way over a 100% at the branch! I put a scope on it and it's your typical SMPS current distortion. It's on a receptical with a TV, DVD/VCR Player and a very old Radio Shack antenna amplifier which I think is the culprit!

 

[jim dungar]

...the .5A side is showing 80% THD with the other side just a few percent.

It is normal for lightly loaded circuits to have very high THD. In your case, the THD is probably from switched mode power supplies and fan motors.

There is nothing wrong with having current on the neutral of a standard 120/240V residential service.

I am wondering, why are you doing all of this investigation?

 

[wptski]

It is normal for lightly loaded circuits to have very high THD. In your case, the THD is probably from switched mode power supplies and fan motors.

There is nothing wrong with having current on the neutral of a standard 120/240V residential service.

I am wondering, why are you doing all of this investigation?

Jim:

I'm not a electrician, I'm a machine repairman by trade in the auto industry but a ex-Navy electronics tech who got interested in power quality, etc. I decided to get a clamp meter although I have several probes to look at PF for one. I got a AEMC F05 which lead to a F25 and 565. Here I am!

A few weeks ago, I discover a problem with a 30A breaker on my air conditioner compressor circuit while just poking around too.

 

[Pierre C Belarge]

How does one reference harmonics on a single phase system?

On a 120V circuit, the neutral conductor will carry the same current as the phase conductor.
Your post asks about leakage current...I do not believe you are reading leakage current.

 

[mdshunk]

Some small amount of current will always be returning to the POCO transformer via the GECs to the rods and water pipes, as well as any CATV braids and messengers. That current will appear to have "leaked" from the neutral, as it will be "missing" from the actual neutral current measurement when compared with the current measured on the hots.

I don't know if this is what you were asking about, but that's what I decided to talk about right now.

 

[LawnGuyLandSparky]

What is the electrical problem?

I've search the net and this forum for information on what would be normal, if there is such a thing for the "net current leakage"/"ground or neutral current leakage on a residential 120V/neutral/120V service. Although I've found some interesting threads, none are for residential, so far!

It appears that the applied loads aren't setup very well, meaning there are two fridges and the furnace blower motor on one side. At the POC into the home, one side is drawing .5A but the other side as much as 14A at times. The net current leakage for the two 120V wires plus neutral is 5.4A and 9A on the neutral alone. I'm wondering if this all becuase on the imbalance?

The garage where there's a good sized air compressor is on the same side as the bigger loads. If the compressor is turned ON, the neautral current increases to 15A.

Another odd thing is that at the POC, the .5A side is showing 80% THD with the other side just a few percent. Most if not all of these wires are impossible to get a current clamp around in the fuse panel in this 50 year old home!

EDIT: Managed to get my AEMC F25 around the service coming from the meter, figured out which side is which and figured out which branch circuit the distortion was coming from. The closer you get to the source the greater it is, way over a 100% at the branch! I put a scope on it and it's your typical SMPS current distortion. It's on a receptical with a TV, DVD/VCR Player and a very old Radio Shack antenna amplifier which I think is the culprit!

 

[wptski]

How does one reference harmonics on a single phase system?

On a 120V circuit, the neutral conductor will carry the same current as the phase conductor.
Your post asks about leakage current...I do not believe you are reading leakage current.

What do you mean by "reference"?

Right, they cancel each other out but what's left over or read on the meter is leakage or so I have read. You can clamp around 3-phase wires, four wire 3-phase or two phases. Some things I've read say not to include ground but others state that you can be you'll read the unintended path to ground current.

On 120V appliciances with three wire grounded cords, the current read from all three wires is normally or mostly the current on the ground conductor added to what you'd read around the phase and neutral conductor. So far, the majority of the current has been on the ground conductor.

 

[wptski]

What is the electrical problem?

Maybe none, that's why I asked what's normal!

 

[don_resqcapt19]

Bill,

On 120V appliciances with three wire grounded cords, the current read from all three wires is normally or mostly the current on the ground conductor added to what you'd read around the phase and neutral conductor. So far, the majority of the current has been on the ground conductor.

First what are you calling the "ground" conductor? There is a grounded conductor and a grounding conductor. There is not a ground conductor. On a 3 wire appliance cord the net current with the amp clamp around all of the conductors should always be zero. Unless there is some problem with the appliance the current will always be on the grounded and ungrounded conductors...not on the grounding conductor.
Don

 

[wptski]

Bill,

First what are you calling the "ground" conductor? There is a grounded conductor and a grounding conductor. There is not a ground conductor. On a 3 wire appliance cord the net current with the amp clamp around all of the conductors should always be zero. Unless there is some problem with the appliance the current will always be on the grounded and ungrounded conductors...not on the grounding conductor.
Don

Don:

On a three prong apploance there isn't a ground wire? Maybe you don't call it a conductor but in this article http://support.fluke.com/find-sales/Download/Asset/2788368_6115_ENG_A_W.PDF they refer to it as a ground conductor. Most all appliances I checked have some leakage current either by clamping with or without the ground wire or whatever you want to call it. Now it may be only 10-20 microamps!

 

[iwire]

Bill in the interests of clarity and so we are all using the same terminology the NEC does....

Grounded conductor = white conductor and sometimes neutral used for a circuit conductor.

Grounding conductor = bare or green used for fault current

Ungrounded conductor = other than bare, green or white (often black) used as a circuit conductor

 

[wptski]

Bill in the interests of clarity and so we are all using the same terminology the NEC does....

Grounded conductor = white conductor and sometimes neutral used for a circuit conductor.

Grounding conductor = bare or green used for fault current

Ungrounded conductor = other than bare, green or white (often black) used as a circuit conductor

Bob:

Thanks! Okay, I'm refering to clamping around the phase, grounded conductor and grounding conductor. That may be around 5ma but when clamped around the phase and grounded conductor is may be around 2-4 microamps. The highest I've seen is 5ma with most being 2-4 microamps clamped either way.

 

[jim dungar]

Most all appliances I checked have some leakage current either by clamping with or without the ground wire or whatever you want to call it. Now it may be only 10-20 microamps!

There are only two current paths from an appliance: one is through the conductors of the power cord and the other an unintended path.

If you put your clamp-on meter around all of the power cord conductors and you do not read 0A, you have one of two situations. Your meter does not have a true zero reading. Or, you have an unintended current path in which case the appliance needs to be removed from service immediately and repaired/destroyed.

If you are saying that you are reading microAmps (.000001A) with a clamp-on meter, you are mistaken. It is unlikely that your clamp-on meter can even accurately measure milliAmps (.001A).

 

[wptski]

There are only two current paths from an appliance: one is through the conductors of the power cord and the other an unintended path.

If you put your clamp-on meter around all of the power cord conductors and you do not read 0A, you have one of two situations. Your meter does not have a true zero reading. Or, you have an unintended current path in which case the appliance needs to be removed from service immediately and repaired/destroyed.

If you are saying that you are reading microAmps (.000001A) with a clamp-on meter, you are mistaken. It is unlikely that your clamp-on meter can even accurately measure milliAmps (.001A).

Jim:

This is what I'm using: http://www.tequipment.net/AEMC565.html. True, most current clamp meters won't read that low but this one is made for that. You had better look again as there are many current clamp meters out there that'll measure that low! It actually has a physical/electrical contact where the jaws close with five mating contacts on each side.

Could it be defective? Sure? There are current leakage specs for medical equipment that give a 5ma limit but I believe that it can't be compared to standard appliances and the test euipment/procedure used is special also.

Most often it states to contact the manufacturer for specs on power cord current leakage.

 

[jim dungar]

You are correct that your specific meter is capable of reading as low as 10 microAmps.

However, there still should be 0amps of current if you surround all of the power cord conductors. All of the current flowing "into" the appliance must "exit" through one of the power cord conductors unless there is an unintended path (of course if the frame of the appliance is bonded it may not be possible to surround all of the intended current paths), because current can only flow in a closed loop.

 

[brian john]

I own and utilize this meter in addition to at least 7-8 other clamp ons, below 1 Amp I would not trust the readings and or resolution.

 

[wptski]

I own and utilize this meter in addition to at least 7-8 other clamp ons, below 1 Amp I would not trust the readings and or resolution.

Brian:

Your profile states that you are a contractor. You have 7/8 current clamp meter that you don't trust below 1A!:-? Reading a branch circuit, my AEMC 565, F25 and MeterMan CT238 probe all show around .4A.

I'm not sure if there's a way test a RMS meter for zero as they are going to flicker a bit on the last digit with nothing clamped.

 

[wptski]

You are correct that your specific meter is capable of reading as low as 10 microAmps.

However, there still should be 0amps of current if you surround all of the power cord conductors. All of the current flowing "into" the appliance must "exit" through one of the power cord conductors unless there is an unintended path (of course if the frame of the appliance is bonded it may not be possible to surround all of the intended current paths), because current can only flow in a closed loop.

Jim:

Fluke makes one that'll read lower than 10 microamps too.

That's exactly what the PDF that I linked states, a unintended path. Isn't the point of current leakage testing to determine if you have current flow in the insulation? Can there "really" be a reading of a perfect zero?

 

[jim dungar]

Isn't the point of current leakage testing to determine if you have current flow in the insulation?

No, at 60Hz, current does not flow in the insulation of standard conductors. The purpose of leakage current testing is to "predict" insulation failure in a device or set of conductors.

Normally, current is not supposed to flow on the grounding conductor. If you put your clamp-on only around the grounded (white) and the ungrounded (black) you may be able to measure the leakage current of the appliance. This current should be flowing on the grounding (green) conductor. A large amount of ground current (i.e. >3mA) might indicate a "weakening" of the insulation internal to the appliance.

Can there "really" be a reading of a perfect zero?

If you measure all of the possible current paths you should get a zero reading. But, not all meters can display a true zero current (your meter is only good down to .01mA).

 

[iwire]

Brian:

Your profile states that you are a contractor. You have 7/8 current clamp meter that you don't trust below 1A!:-? Reading a branch circuit, my AEMC 565, F25 and MeterMan CT238 probe all show around .4A.

Bill I have some nice clamp meters and I will not trust the accuracy at those low levels.

As far as Brian, he makes a living running an electrical testing company and I bet he has at least 20 years of experience doing so.

Do what you want but you have a couple of guys with at least 40 years experience between them telling you that your method may be flawed.