Current Indicator Circuit Breaker

[jollyrgr]

I've checked Square D but no luck. I'm looking for a cheap way to monitor the current on every circuit breaker in a standard three phase 42 breaker load center. Has anyone ever seen a circuit breaker with an LED or LCD display that indicates the current through the breaker? I have a clamp on current meter that I monitor the breakers in our data center about every three to six months. (When new servers arrive not everyone pays close enough attention and sometimes too many devices are connected to one circuit.)

I was taking my readings before a major switchover and the life safety officer noticed I was inside the panels. Apparently regulations require that I be in a Arc Flash suit if I break the plane of the panel front for any reason. (The Arc Flash suit resembles the radiation suit of Marty McFly in Back to The Future.) In the next few weeks we will be activating 45 new servers and thus I'll be donning this suit more often than I'd like. For the future panels we will be installing I'd like to get circuit breakers with a display on them indicating the current. For the extra five to ten bucks a breaker I'd consider this to be a worthy investment. Any such animal exist? No luck so far but someone has got to have thought of this before me.

[Janitor Tzap]

jollyrgr,

Is this what you are looking for?

http://www.crouzet-usa.com/catalog/_hdi.shtml


Signed: janitor Tzap

[Smoke_Maker]

I use a load bank to test 100k generators and the machine has three analog meters on the front panel that are connected to current sensing rings that are fitted over the three input wires. This might be a little harder to install but I haven't seen anything like what your looking for.

Something like this
http://www.dentinstruments.com/CurrentTransformers.htm

[jollyrgr]

I know about panel meters and those would be fine for a machine of some sort. What I need is a common Square D service panel breaker. These are typically found in places like your home. Here are some two pole and dual breaker examples:


I'm looking for a breaker like the one in the center of the picture above for single pole circuits. The two pole and three phase circuits are very difficult to overload as they typically connect to one device and have only one outlet. The 120V breakers go to duplex outlets that have multi-outlet "power strips" connected to them. A large number of servers can then be connected to these strips accidentally. What I'm looking for is a single pole breaker in the Square D profile that has a small LCD or LED display and indicates 0 to 20 amps.

[dacflyer]

jollyrgr >>> that would be an awsome device, even better is if it had an alarm to notify you if your approaching the trip point..
but i think that all that neet idea wouldn't be possible to fit inside a breaker
they are already pretty full inside them.. i have seen one time a breaker that had a led that lit up after it was tripped..
but i think you might be out of luck here on this great idea..
but who knows....lots are being done these days with micro electronics...

[ecerfoglio]

You may order a bigger pannel with some extra space, and place a current transformer on each output circuit.

I don't know if they make current transformers in the format of the american breakers, but I've seen them built to fit in the european "DIN" format. (Here in Argentina we use mostly DIN format breakers since some 20 or 30 years ago, but before that time the american format ones where common).

The secondaries of all the current transformers (low current ~ 1 A, low voltage if you ground one wire of each secondary) could be wired to a multi pole swich that selects which circuit you measure and to a single panel ammeter.

Warning: Unused current transformer secondaries should be shorted. That complicates the selector swich (one pole per circuit?), but it should be cheaper that putting one meter per circuit.

[Chris Smith]

This could get quite complex which is why I would simply add in some Lcd ammeters and shunts to each circuit.

In a lot of cases you can do this for under $20.00 a circuit. [depending on total load]

You can house all of the numbered LCDs in another box.

[Lenp]

Check out www.crmagnetics.com They have small CT(current transformer) coils and meters that may be what you need. Some of their CTs drive an LED if the current is within a certain range and others that have outputs for metering at 0.5% accuracy. If they were used with a switched meter the cost may not be too bad. Since their outputs are quite accurate the possibility of an alarm also exists using a simpl threashold detector. I won't get into the NEC aspects of you installing these into a distribution panel since your organization seems to be a little itchy about safety.

A while back I used their LED driver CTs to turn on an optoisolator that started a Lithium powered LCD counter and timer. It monitored the cycling and run time of lighting circuits to evaluate lamp life in commercial buildings. The package was compact, and was slipped right into the panel, when nobody was watching, so there was no indication that the circuits were being monitored.

We proved that the lighting was on much longer time than the building was occupies, with average on cycle of over 30 hours. The lamp life was really exceeding the manufacturer's best life estimate. Case closed.

Len

[Externet]

Make 'em !
Find 115 or 230V surplus solenoids/relays you can salvage the coil, insert the breaker wire in it as a current transformer, rectify to power a LM3914 in dot mode and use up to 10 efficiency leds as you want to display the scale, running at 2 miliamperes.

If you find those tiny ~3/8" Ø galvanometer type battery indicator from the seventies (I have seen them advertised at some surplus store) you will have a simpler analog, smaller display.

Do you know what formula applies for current transformers?
For 1 Ampere AC to yield 1 Volt AC, how many turns are needed?

Miguel

[ecerfoglio]

Do you know what formula applies for current transformers?
For 1 Ampere AC to yield 1 Volt AC, how many turns are needed (Externet)

Current transformers are just that: Current transformers. . You obtain current, not voltage.

If you have a turns ratio of, say, 25 to 1, and you have 25 amperes in the primary winding, you will obtain 1 ampere in the secondary.

If you leave the secondary open you will obtain some voltage, but the transformer's core will saturate, it won't be linear and it may oveheat.

If you look at a current transformer's specs you will find:
>> Primary current
>> Secondary current (or turns ratio)
>> Frecuency
>> Accuracy (% of allowed error)
>> Power rating in VA (VoltAmperes)

Example: 25/1 Ampere, 50/60 Hz, 0.5%, 10 VA


What you may do is shunt the current transformer's output with a low value resistor, say 1/10 ohm. You may then measure up to 100 mv (AC) across the resistor, which will mean 1 amp in the secondary and 25 amps in the primary.

The resistor will dissipate up to (1A)^2 x 0.1 ohm = 100 mW, and the transformer will give an (aparent) power of 100 mV x 1 A = 100 mVA << 10 VA.

[Externet]

Gracias, ecerfoglio.
Still have difficulty grabbing some concepts.
Yes, the ratio yields the current; but for such induction to be of use, must have capability to produce a voltage to operate a circuit. If the circuit takes -say 6 AC volts- to run, at a minimum current trough the inductor air core, there has to be a minimum number of turns to come up with the 6 VAC tension.

The keyword as you say is VA voltamperes. But of no use if the voltage does not fill the requierements.

I was reading this:
http://www.mmgca.com/apps/ctdesign.pdf

And have not clear, if I want to run a circuit that takes 6VAC and 0.1 A AC (~0.6VA); from a weak 1 AC Ampere flowing on half a turn (just passing trough the core) in series to the breaker; what would be the minimum number of turns to achieve this?

A 0.6 VA may supply the power, but does not mean the circuit will work if there is not 6V AC at that 0.1A AC load.
Can you shine more light?

Miguel

[dyarker]

Current transformers are for measuring the current through the primary, not for providing power on the secondary side. The load on the secondary must be fixed to make consistant measurements.

Of course there is a voltage on the secondary, but it varies directly with the current through the primary.

Here is spec sheet for a 15A current transformer:
http://rocky.digikey.com/WebLib/Amveco- ... AC1015.pdf

For example: The 12AWG wire from the load side of a circuit breaker in the power panel would pass through the hole in the center of the transformer once then go to the outlet or lights or equipment cabinet. With a 100 Ohm load resistor, a DMM would read 1V if the AC mains load is drawing 10A; 1.5V for a 15A AC mains load; and 0V for zero AC load. Power for the measuring circuitry must be supplied separately, like the battery in a DMM.

Cheers,

[Externet]

Good ! , Dale. Thanks.
That link has it. A chart of amperes VS volts at several loads. Period, no complications.
A measuring circuit can run self powered by the current transformer to display the AC.
Miguel

[rick.curl]

You can get these current transformers: http://rocky.digikey.com/WebLib/Amveco- ... AC1025.pdf for about six bucks each from Digi-Key. Put a 100 ohm resistor across each one and bring the pins out to a couple of tip jacks on a panel, and you're done. I would think that as small as these are, you could find room on most breaker panels to add them without getting too crowded.

-Rick

[Robert Reed]

Don't forget, that on the pass thru styles, you can wrap the primary several times thru it and increase output voltage. This is sort of linear up to a point and will vary some with different transfomers. I have done this several times to get enough voltage output to reliably operate PN junctions.