A/C Current & Circuit Breakers - Page 1
Forum section: electronics / general

author: daveyk
author_rank: Frequent Contributor
timestamp: May 17, 2017, 09:01:04 pm
content: Hello there,I am not real knowledgeable on A/C Mains as it has been about 37 years since I studied A/C in school.A little background. About 15 years ago, we had a four season sun porch built. I did all the electrical wiring with good heavy 12 gauge wire. At the time we were no planning on living in it. So I only sent three circuits to it:#1: Industrial Vent controlled my a humistat and thermostat, 20AMP breaker#2: Ceiling track lights and ceiling fan. 20 AMP breaker (6 spotters and 4 lights in the ceiling fan all LED now!!)#3: One looping line for power outlets along all the walls. 20 AMP BreakerWe are now spending a lot more time in it than intended. Last year I installed one of those vertical air conditioner units and built it in one of the large horizontally sliding windows. Insulated it and all real well..Well today, I came home from work. The 46" TV was running and my wife had a small clamp fan running blowing on her. She wanted the Air conditioner started. I plugged it in, cleaned the filter and set it to 79 degrees. It ran for about 5 minutes, the compressor kicked in and the air started to get cool and then <POP> goes the 20 amp breaker.The breaker box is down stairs and in the garage. I came down reset the breaker and it's been okay since then. I attached the A/C clamp meter from Fluke 43B around the wire feeding that circuit. It seems to be drawing about 12 amps (TV and Air Conditioner, little fan not running). I am letting it record transients so on its scope display it shows what looks like a thick current traces (almost oscillations). I have it set for continuous record. I am seeing no reason why the breaker tripped.Now that breaker and a few others right close to it shows signs of corrosion around the wire clamp screw. I don't know if it is just garage dew/humidity or if water got in the box.I've had this expensive Fluke 43b for many years and never really learned how to use it. In transient record mode is it measuring A/C amps or A/C RMS Amps? Is there a difference? If that meter is measuring RMS amps, does that mean the actual current draw is higher? Does a breaker trip on peak or RMS if it's rated at 20 AMPS?I was measuring the voltage drop across the breakers. Most have virtually 0 volt drop, but remember all the house lighting is now LED. This breaker had close to one volt drop across it, but it was also supplying 12 amps. Also, I need to check if I was scraping through the corrosion.I might switch the outlet line in to the light breaker and the lights line in to the outlet breaker and see if that works better. The problem may have just been a bad breaker. I don't think the 20 amp lines was over loaded. My wife has fixed sweeper cords herself when the dog chewed them and so there has been shorts and this breaker has been tripped many times due to that. I am thinking that the breaker is just worn out.I am looking for thoughts on this and someone with knowledge of those Fluke 43B type meters.Thanks much.Dave

author: BradC
author_rank: Super Contributor
timestamp: May 17, 2017, 10:41:14 pm
content: Just a wayward aside but I recently had to swap out a 16A breaker that was tripping on a 3A load when the switchboard got exposed to 40C ambients. So it's not unheard of for breakers to develop faults. Rare, but possible.

author: tautech
author_rank: Super Contributor
timestamp: May 17, 2017, 10:54:00 pm
content: Quote from: daveyk on May 17, 2017, 09:01:04 pmYep, it will be tired.Sparky mate regularly replaces breakers that have had lots of trip events.He's on the ground doing this stuff for a living and knows what he's talking about.You can install motor rated breakers if the circuit is exposed to regular high loads or surges, they give a longer duration at a certain % overload before tripping.D curve breakers have the best ratings for this use but you need to ensure the sub-main circuit cabling is sufficiently heavy to handle the short term overloads that D curve breakers allow.

author: Electro Detective
author_rank: Super Contributor
timestamp: May 17, 2017, 11:06:15 pm
content: I'm also voting to swap out the breaker, they can go weird especially after few years and or exposed to hot/cold outdoor conditionsassuming it's a correct curve breaker to begin withSame deal for RCD/GFCIs, their test switches can seize up/not work even though the unit trips on a fault.The clamp meter you'll have to brush up on how it it's capture and logging modes work.Get a fan heater or hairdryer and get familiar capturing min max avg peak on off inrush etcthen have a go at the breaker boardMy bet is on a dicky breaker that trips off too easily on low to higher current drawDon't rule out a fault as well (twofer!) from the air con to the breaker eitherGood luck, and no shame to call in an experienced sparky or HVAC jedi to sort it out

author: Red Squirrel
author_rank: Super Contributor
timestamp: May 18, 2017, 05:10:16 am
content: Is the clamp meter true RMS? The reading might be off if it's not accounting for power factor. Though I would expect a portable AC unit to draw no more than 15 amps so there is still 5 amps to spare, I doubt the TV and fan use more than 5.Though you said you set the AC to 79F which is 26C, that's quite hot to set an AC at, what is the actual temp? If it's very hot where the panel is, that may potentially cause the breakers to trip prematurely as they work based on temp.I would go ahead and replace the breaker just to see if it clears the issue though, but don't throw out the old one yet as it might not be the problem, but worth trying.

author: Gregg
author_rank: Super Contributor
timestamp: May 18, 2017, 06:08:16 am
content: The air conditioner compressor may have had much higher than normal starting current if most of the oil had drained back into the compressor over the winter.The connection between the breaker and the mains bus in the breaker panel may be corroded. This could cause both heat and a voltage drop; a lower voltage would make the compressor need more current on startup. Most breakers are heat sensitive.The internal breaker contact may have some moisture damage that caused the problem and now that it is reset the contacts wiped away some or most of the corrosion temporarily alleviating the problem.What brand is the breaker / breaker panel? If it is a Federal Pacific brand you should consider replacing the whole breaker panel. Enclosed is a picture of a breaker for an air conditioning unit that failed just because it was located in a hot electrical room.

author: Zero999
author_rank: Super Contributor
timestamp: May 18, 2017, 10:28:41 am
content: One thing to note about breakers; there are two different methods of sensing the current: thermal (current flowing through a resistor, heats up a thermally activated switch to cut off the current) and magnetic (current flows through a coil, generating a magnetic field which activates switch to cut off the current). If the breaker reacts slowly to overloads, then it'll be thermal, if it's fast blow, then it'll be magnetic. There are also breakers which combing thermal and magnetic sensing methods and will trip very rapidly if subjected to a heavy overload and slowly if lightly overloaded.

author: sibeen
author_rank: Frequent Contributor
timestamp: May 18, 2017, 11:56:29 am
content: This is where some care needs to be taken when advice is given on this subject. As a point, and tautech I'm not having a go at you here; but t reccomended that the installation of a D curve circuit breaker may be a good idea. Now this probably is not the worst idea I've ever heard, but in this case it is useless.There is a wide, great chasm of a divide in the electrical world, and hardly do the twain ever meet. One side of the canyon consists of those who live in the IEC regulated part of the world; Europe, Asia, Oceania etc. We'll call this the sane part of the world just for clarities sake. The other side of the chasm is the IEEE world (the dark side). USA, Canada, rest of Americas etc.In the IEC (sane) side, a D Curve circuit breaker at the miniature circuit breaker (MCB) is a standard device. Over on the nutters side they've never heard of such an animal. They just don't use the B, C, D nomenclature that the sane size uses nor do they have an equivalent....and yes I'm taking the piss about sane vs nutter etc. But the point does stand. What goes on in IEC world does not translate to IEEE world, and vice versa.

author: Ampera
author_rank: Super Contributor
timestamp: May 18, 2017, 01:58:18 pm
content: Be lucky you got 20 amp breakers. In my house everything is 15 amp, and when you have an American kitchen, that sucks. The microwave uses power, the AC uses power, the coffee machine uses power, the Kettle uses power, the pressure cooker uses power, the dishwasher uses power. The only thing that doesn't use much power is the gas stove.And because it's an American house, the circuit wiring was done by syphilitic gibbons. If one runs the microwave, A/C, or coffee pot at the same time (Might just be the microwave and the AC or coffee pot) then the 15 amp breaker trips. So, what does it trip? Well it trips all the lights on the third floor. The kitchen is on the second floor. What if you overload the other circuit by running the water kettle and pressure cooker at the same time? Well, as far as I know a third of the bedroom used as a computer room trips.I mean how does someone build a house circuit that breaks the upstairs lights as well as the kitchen, but not the lights to the room that has the breakers in it? Oh yeah, the breakers aren't right in the obvious either. You have to go upstairs, open a door, go downstairs through a strange auxiliary stairwell, and access the breakers, all in the dark because the lights have tripped. There are also a whole of two windows on the entire floor. fun.Anyways the part of this pointless rant that helps the conversation is that this has happened so many times over the past years that I wouldn't be surprised if the breaker is a bit worn. If the power was a bit older and we still had fuses for everything, we'd probably run a few hundred dollars in fuses alone. We have noticed that things that would normally be fine together, like the coffee pot and the microwave, no longer stay on. So maybe our breaker is a bit worn.

author: tautech
author_rank: Super Contributor
timestamp: May 18, 2017, 04:10:13 pm
content: Quote from: sibeen on May 18, 2017, 11:56:29 amGotcha, thanks for pointing this out, I had no idea the US was constrained in this way.Glad to know we're on the sane side.Back to breakers again................ they wear out.

author: HoracioDos
author_rank: Frequent Contributor
timestamp: May 19, 2017, 07:54:39 pm
content: Quote from: sibeen on May 18, 2017, 11:56:29 amI'm far from being an expert and perhaps I got it wrong but a MCB is the standard device in most countries in the southern cone of South America including Brazil. Most of them are IEC members.http://www.iec.ch/dyn/www/f?p=103:5:0

author: jmelson
author_rank: Super Contributor
timestamp: May 19, 2017, 08:48:23 pm
content: I recently have had 3 breakers that tripped for no discernable reason. At least one time, the breaker was very CLEARLY warm to the touch. A momentary short would not warm the breaker. So, what I think happened is the breakers had been on for YEARS, and the contacts slowly became oxidized. Finally the resistance started to go up, and turning some larger load, like a laser printer, on created enough heat to trip the breaker on the thermal function. I just reset the breakers, and there has been no repeat. So, I guess the contacts need to be cleaned by tripping and resetting the breakers every few years.Jon

author: Monkeh
author_rank: Super Contributor
timestamp: May 19, 2017, 08:51:00 pm
content: If the contacts are able to oxidize then the breaker is faulty by design - contact pressure should be far too high for that to happen.

author: rstofer
author_rank: Super Contributor
timestamp: May 19, 2017, 08:58:40 pm
content: Quote from: tautech on May 18, 2017, 04:10:13 pmWe do have high-magnetic molded case breakers for handling high inrushhttp://www.schneider-electric.us/en/faqs/FA96714/These are usually 1pole 15A or 20A although there are some 2 pole breakers also rated as High Magnetic.All of our molded case breakers have both thermal and magnetic trip elements. In fact, we can't eliminate the instantaneous trip (magnetic) until we use an open frame breaker like the GE AK series

author: Electro Detective
author_rank: Super Contributor
timestamp: May 20, 2017, 02:40:09 am
content: Speaking from past and very recent experience, I would strongly suggest to members here, who don't need any extra PITAS in their lives,to exercise ALL breakers at least once a year, and anything with a switch at the board!i.e. switch off the mains, and flick the breakers on and off a few times,leave them off,and give the mains switch a few on/offs as well.The idea is to work the switches and maintain NO POWER going in to your appliances as they won't like this on/off 'workout'It's also THE best opportunity to do same with the RCD/GFCI switches, and run some checks with an external trip device at the furthest power points, so you can be sure that it 'should' work during a real event.Whenever there have been unexplained board behaviour at various jobs, this routine gets everything back to normal, and or quickly isolates any problem breaker or wiring,before considering getting medieval with a megohm insulation tester or 30 amp 'breaker basher' load

author: BradC
author_rank: Super Contributor
timestamp: May 20, 2017, 08:45:57 am
content: Quote from: Electro Detective on May 20, 2017, 02:40:09 amIf you need to do this, have your breakers replaced with quality units. You should *never* have to perform this ritual. Testing RCDs I can get on board with, but operating switches and breakers as some form of preventative is lunacy. Quality units get turned on and not touched for 25 years.

author: Electro Detective
author_rank: Super Contributor
timestamp: May 20, 2017, 09:23:05 am
content: Quote from: BradC on May 20, 2017, 08:45:57 amYou must be kidding, leaving switches untouched in less than ideal environments for25 yearsPRAYING the mechanism will PHYSICALLY trip,and not seize up for too many reasons, including Murphy?The average cost cutting ignorant owner and his cash grab installer isn't interested in 25 year 'quality' units, just the bottom line and getting the electrical inspector to tick his clipboard.Which brand are 'quality' units btw, who tests them to failure nowadays,where are the curve charts, and WHERE are these 'quality' ones made?Any chance most are made in china and rebranded ? lol

author: HoracioDos
author_rank: Frequent Contributor
timestamp: May 20, 2017, 05:29:44 pm
content: Quote from: BradC on May 20, 2017, 08:45:57 amI don't test the RCD at home because I'm always fixing something. AFAIK users must test them every month. See attached pics.The second one is exactly my unit.

author: rstofer
author_rank: Super Contributor
timestamp: May 20, 2017, 06:49:23 pm
content: Quote from: Electro Detective on May 20, 2017, 09:23:05 amUL has standards and if a company doesn't follow them, they are out of business. Check what happened to Federal Pacific. They were a HUGE supplier until they lost their UL rating and not of just residential equipment:https://www.angieslist.com/articles/are-federal-pacific-circuit-breaker-panels-safe.htmSquare D is a pretty good brand and trip curves are EASY to find for all major brands. Google is your friend!http://static.schneider-electric.us/docs/Circuit%20Protection/Miniature%20Circuit%20Breakers/QO-QOB%20Circuit%20Breakers/730-3.pdfGE is a pretty good brand and trip curves are also easy to find:http://apps.geindustrial.com/publibrary/checkout/GES-9884?TNR=Time%20Current%20Curves%7CGES-9884%7CPDF&filename=GES-9884.pdfI found most of the information for Cutler-Hammer (Eaton) but I only got as far as the main breaker. I'm sure the branch breaker trip curves are out there but I got bored. NOBODY in the residential business pays any attention to trip curves and at the industrial/commercial level, everybody is using a computer with breaker libraries to coordinate tripping.Some factories do indeed perform regular maintenance on large circuit breakers. Almost nobody does any more than an IR scan of small loadcenters. In 36 years, I have never done any maintenance on residential panels. I did have our 12kV and 115kV equipment serviced annually. The generators and transfer switches were exercised from time to time. Usually after hours...

author: Monkeh
author_rank: Super Contributor
timestamp: May 20, 2017, 07:02:22 pm
content: Quote from: rstofer on May 20, 2017, 06:49:23 pmAnd why the *bleepity* *bleep* *bleeping* *bleep* are those different? Standards too much effort?

author: rstofer
author_rank: Super Contributor
timestamp: May 20, 2017, 07:16:50 pm
content: Quote from: Monkeh on May 20, 2017, 07:02:22 pmDo you want to guarantee your breakers in a panel made by others? Or, do you want to guarantee your panel with breakers made by others? Where's the upside in that?There is some interchangeability at the Cutler-Hammer level but GE doesn't fit in C-H - on purpose! And I'm pretty sure there is no interchangeability with Square-D as well.Yes, there is a difference between the pick-up points for the instantaneous trip but the time overcurrent isn't all that much different. At 2x, the Square D trips inn 8 seconds and the GE in about 12.One could surmise that GE thinks their breakers can withstand a little more fault current than does Square-D.

author: Electro Detective
author_rank: Super Contributor
timestamp: May 20, 2017, 11:49:22 pm
content: LOL, for 25 or 250 year maintenance free GUARANTEED circuit breakers that WILL break the circuit,with zero concern about electro-mechanical trip FAIL due to switch mechanism inactivity coupled to internal aging effects, lube fail, OL bake fatigue, and shifted threshold sensitivity etc etc etc (x1000000...)then source and fit a vintage switchboard with ceramic plugins, and screw in the correct ratedFUSE WIRE.Decades later it's still the ultimate DIY WYSIWYG circuit breaker,even better if the fuse wire packaging has UL listing!Add a master RCD/GFCI (that may never be tested 'monthly') and you have a great old school meets new tech switchboardthat will take out the fuse wire,and not your devices or premisesAnd if you're one of the few that actually gas, fit some RCD/GFCI sockets and or powerboards (that can be tested 'monthly' or ANY TIME and every time) with thermal OL switches, inside the premisesand MAYBE your equipment, employees, partner and children have half a chance to avoid serious consequences resulting from faults or blunders.If you don't agree with any of the above I wish you and the people around you good health, and the BEST of luck when using electricity.Me? I make my own 'luck' and give the switches a good physical 'workout' AND a smell test for any stray nano releases of magic smoke

author: IanB
author_rank: Super Contributor
timestamp: May 20, 2017, 11:57:55 pm
content: In industrial settings anything safety related gets tested at regular intervals like once per year. The last thing you ever do is to hope and pray that your safety device will work when needed if you haven't looked at it or touched it for ten years.

author: daveyk
author_rank: Frequent Contributor
timestamp: May 28, 2017, 01:43:12 pm
content: So I need to find a square d QO20HM? I'll ask at Lowe's.Thanks.P.S. I picked up a second hand encasement window type A/C unit to replace the three year old Fridgedair junker.Sent from my iPhone using Tapatalk

author: Gregg
author_rank: Super Contributor
timestamp: May 29, 2017, 07:32:02 pm
content: Square D, QO breakers only fit in Square D breaker panels that are designed to use them. There should be a sticker on your panel that tells you what breakers are compatible. If not, you might want to take your old breaker to Lowes to match up with a replacement that will fit your specific breaker panel.You may also want to clean the contact area between the breaker and the panel bus bar with some fine ScotchBrite and probably use some anti oxide coating on the joint like Noalox or Oxguard (should be available at Lowes).This might also be a good time to make sure all connections in your breaker panel are in good shape. If you have aluminum entrance wire that is connected with setscrew connectors, the aluminum deforms over time from it being soft and thermal cycling leading to loose connections.

author: daveyk
author_rank: Frequent Contributor
timestamp: May 29, 2017, 07:56:48 pm
content: Quote from: Gregg on May 29, 2017, 07:32:02 pmIt's a Square D 200 amp panel not the Square D Homeline. On Lowe's web site, they don't appear to have the HM type but I'll have to look in person. There may be a Granger in State College about 40 mins away if necessary. I can see if they have them. I bought a replacement A/C unit. Between that and the breaker, the problem Shaw be solved. I will bring to bad one down to the shop. Our other Fridadair 220v a/c unit was three years old when the blower fan start up cap melted (literally) in to a pile of mush. Maybe this one will need start up caps too, along with some control board repair replacement.Sent from my iPhone using Tapatalk