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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: Jeffery Foster on September 01, 2014, 05:03:43 PM
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I believe I know the answer to this, but I just want to see it in writing from people smarter than me so that I'll quit second-guessing.
A NEMA 14-50 receptacle wired to a dual-pole 50 amp breaker. A distro connected to this that tried to pull 30 amps per leg simultaneously will indeed trip the OCPD, correct?
Thank you in advance for your knowledge!
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I believe I know the answer to this, but I just want to see it in writing from people smarter than me so that I'll quit second-guessing.
A NEMA 14-50 receptacle wired to a dual-pole 50 amp breaker. A distro connected to this that tried to pull 30 amps per leg simultaneously will indeed trip the OCPD, correct?
Thank you in advance for your knowledge!
No. The 50A breaker upstream is protected to 50A on both legs. The distro downstream that is asking for 30A/leg will not trip the 50A/leg breaker. It will have 20A/lef still available.
-Ray
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No. The 50A breaker upstream is protected to 50A on both legs. The distro downstream that is asking for 30A/leg will not trip the 50A/leg breaker. It will have 20A/lef still available.
-Ray
Ray, I've always admired your input to the boards. Thanks for the info. You seem very confident in the correct answer, does some else want to disagree?
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Ray, I've always admired your input to the boards. Thanks for the info. You seem very confident in the correct answer, does some else want to disagree?
?? A two pole breaker rated at 50 amps can handle a two pole load of 50 amps. You're suggesting a two pole 30A load. Why would that trip a 50A breaker?
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Ray, I've always admired your input to the boards. Thanks for the info. You seem very confident in the correct answer, does some else want to disagree?
Why would 30a trip a 50a breaker?
Do you know something we don't?
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I believe I know the answer to this, but I just want to see it in writing from people smarter than me so that I'll quit second-guessing.
A NEMA 14-50 receptacle wired to a dual-pole 50 amp breaker. A distro connected to this that tried to pull 30 amps per leg simultaneously will indeed trip the OCPD, correct?
Thank you in advance for your knowledge!
Are you maybe thinking that 30amps per leg, 60 amps total, would trip a dual 50amp breaker?
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Are you maybe thinking that 30amps per leg, 60 amps total, would trip a dual 50amp breaker?
I suspect that's what he was worried about. (Says the guy who wrote "20A/lef available," whateverthehell a "lef" is. Haha.)
-Ray
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Are you maybe thinking that 30amps per leg, 60 amps total, would trip a dual 50amp breaker?
Indeed everyone, I was under the incorrect impression that a 50a dual pole breaker would trip if the *total* load presented to it (in my example, 60amps) exceeded its rating. But now I understand that it is rated per 120v leg of that system. So I could pull 40amps on one branch and 40 on the other branch and never hear the woeful *snap* of the breaker slamming open.
Thanks again for all of the excellent advice here!
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Indeed everyone, I was under the incorrect impression that a 50a dual pole breaker would trip if the *total* load presented to it (in my example, 60amps) exceeded its rating. But now I understand that it is rated per 120v leg of that system. So I could pull 40amps on one branch and 40 on the other branch and never hear the woeful *snap* of the breaker slamming open.
Thanks again for all of the excellent advice here!
That is correct! :) Each pole is on on 'leg' of the service, and it's rated for 50A on each side. If you moved up, to 3Ø service, then you get a 3-pole breaker such as this-- in this example, you have 50A available on each of three legs (so 150A total). However, if either of the legs exceeds 50A, the whole service trips. And that's the case with your 1Ø/220V service-- if you drew 60A on one leg and 10A on the other, even though the total service is under 100A, since one side exceeded the breaker's capacity, it trips everything.
Hence the reason that balancing your load is very important...
-Ray
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Ray, I've always admired your input to the boards. Thanks for the info. You seem very confident in the correct answer, does some else want to disagree?
Ray is 100% correct. There are no electrical connections between the legs of a multi-pole breaker. There's only a mechanical connection in the handle so that if any single pole trips, then it mechanically trips the spring loaded latches and opens up the other pole(s). The reason for requiring all poles to trip is that a 240-volt load with only a single tripped pole would back-feed current through the now non-operating 240-volt appliance through the tripped phase. That could be very dangerous for something like a sub-panel which is fed by a double-pole breaker but then breaks out into both 240-volt and 120-volt appliances.
Also, a 3-phase motor with one leg opened up won't be able to spin up properly and will probably just sit there and overheat. Plus a non spinning motor with voltage on two the legs could be a shock hazard to anyone replacing it. Yeah, they should use a meter, but you know that's not done a lot in places like farm environments.
But back to your original question. Yup, 30+30 amps won't trip a double-pole 50-amp breaker. Nor will 40+40 or even 50+50 amps trip it. However, 60+10 amps will trip the one 50 amp pole, which will then mechanically trip the other pole even though it's only passing 10 amps on that leg.
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Thank you Mike and Ray. How a "ganged breaker" works has been puzzling to me for a long time.
Please emphasize that you should NEVER use 2 adjacent (single) breakers instead of a 2-pole when breaking out to two 120V circuits (using 4-wire feeder) that share common neutrals and grounds.
"The reason for requiring all poles to trip is that a 240-volt load with only a single tripped pole would back-feed current through the now non-operating 240-volt appliance through the tripped phase. That could be very dangerous for something like a sub-panel which is fed by a double-pole breaker but then breaks out into both 240-volt and 120-volt appliances. "
-Dennis
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Thank you Mike and Ray. How a "ganged breaker" works has been puzzling to me for a long time.
Please emphasize that you should NEVER use 2 adjacent (single) breakers instead of a 2-pole when breaking out to two 120V circuits (using 4-wire feeder) that share common neutrals and grounds.
"The reason for requiring all poles to trip is that a 240-volt load with only a single tripped pole would back-feed current through the now non-operating 240-volt appliance through the tripped phase. That could be very dangerous for something like a sub-panel which is fed by a double-pole breaker but then breaks out into both 240-volt and 120-volt appliances. "
-Dennis
If only 120V appliances are on the shared-neutral circuits, there should be no voltage potential on the tripped hot leg if the other hot leg is not tripped. However, if there is a 240V load connected to the two legs, then certainly there WOULD be voltage potential on the tripped leg.
The hazard of a shared neutral with two 120V legs (opposite poles) would be that someone repairing the circuit could assume that it's safe to break the neutral if only one of the legs is off. When working on a 120V circuit that shares a neutral with another 120V circuit, both circuits must be disconnected (and locked/tagged).
Some inspectors may allow shared neutral without ganged breakers. That's probably not a good idea. The idea of shared neutral is to gain capacity (say, 40A total on two 20A breakers with one neutral) while saving cost (only have to run one neutral wire instead of two), for optimum safety you need a ganged breaker. This introduces an inconvenience: an overload on one circuit will cause both circuits to trip.
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...There's only a mechanical connection in the handle so that if any single pole trips, then it mechanically trips the spring loaded latches and opens up the other pole(s)...
I want to clear up a technical error in the above. In multipole (IE: 2+ poles) circuit breakers there is an internal connection of the individual pole trip units to the other poles' trip units. A trip on any pole will trip all connected trip units (a rotating non-conductive pin, usually, only visible in 'demo' units that have a cutaway or clear side). Some DIN mount types allow access to this link, most do not.
An example you are sure to be familiar with: Square D QO (and QOB) breakers have only 1 handle, no matter how many poles they switch. They do offer handle ties for single pole units but there is no guarantee that tripping one pole will also switch the connected unit off.
HTH,
Jeff Robinson
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I want to clear up a technical error in the above. In multipole (IE: 2+ poles) circuit breakers there is an internal connection of the individual pole trip units to the other poles' trip units. A trip on any pole will trip all connected trip units (a rotating non-conductive pin, usually, only visible in 'demo' units that have a cutaway or clear side). Some DIN mount types allow access to this link, most do not.
An example you are sure to be familiar with: Square D QO (and QOB) breakers have only 1 handle, no matter how many poles they switch. They do offer handle ties for single pole units but there is no guarantee that tripping one pole will also switch the connected unit off.
HTH,
Jeff Robinson
But, a two-pole breaker is going to trip both poles if one is overloaded/triggers the circuit breaker, right?
Assuming that you are not asserting otherwise, it really doesn't matter how the second pole is tripped, just that bottom line, one leg goes, and the other does at the same time. We should be careful to not cause confusion by talking about semantics of how the internal mechanism works-- especially since with the breakers all being connected anyways, there's no chance of one leg going and the other one not.
-Ray
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But, a two-pole breaker is going to trip both poles if one is overloaded/triggers the circuit breaker, right?
Assuming that you are not asserting otherwise, it really doesn't matter how the second pole is tripped, just that bottom line, one leg goes, and the other does at the same time. We should be careful to not cause confusion by talking about semantics of how the internal mechanism works-- especially since with the breakers all being connected anyways, there's no chance of one leg going and the other one not.
-Ray
The point Jeff is making is that INTERNALLY tied breakers will always open all legs when tripped, externally handle ties may or may not be as effective.
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The point Jeff is making is that INTERNALLY tied breakers will always open all legs when tripped, externally handle ties may or may not be as effective.
Are these external handle ties as in "they do offer external handle ties," and something that someone buys? As opposed to the example picture I posted of a three-pole breaker with all three handles molded together for one?
Or is there a chance that a breaker such as the one I posted, where the three poles are connected with one handle, could trip one leg and not actually trigger the others?
The reason I am asking is that if that's the case, where one could trip one leg and not another, that's a good thing to know-- but if it's the case of someone would have to purchase a 2 or 3 pole breaker that isn't already tied together, and then they are having to buy the handle tie- that seems to be a situation that wouldn't come up as often. And if this came about from the potential of someone buying two single breakers as opposed to a 220V 2-pole breaker, and then needing to buy the tie-- hmmm.
An example you are sure to be familiar with: Square D QO (and QOB) breakers have only 1 handle, no matter how many poles they switch. They do offer handle ties for single pole units but there is no guarantee that tripping one pole will also switch the connected unit off.
The reason I started asking what I did is that a quick internetz search shows the QO breakers to be a 220V/two pole breaker that is connected together. So are you saying that this type of breaker, with the handle molded into one piece, could trip only one leg and not the other? And this extra-purchase handle tie would be required?
I hate hate hate ever saying something that questions the Wisdom of Tim, but I am trying to be clear as to what Jeff was referring to, since the mentioned products don't appear to be what he says they are.
-Ray
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Are these external handle ties as in "they do offer external handle ties," and something that someone buys? As opposed to the example picture I posted of a three-pole breaker with all three handles molded together for one?
Or is there a chance that a breaker such as the one I posted, where the three poles are connected with one handle, could trip one leg and not actually trigger the others?
The reason I am asking is that if that's the case, where one could trip one leg and not another, that's a good thing to know-- but if it's the case of someone would have to purchase a 2 or 3 pole breaker that isn't already tied together, and then they are having to buy the handle tie- that seems to be a situation that wouldn't come up as often. And if this came about from the potential of someone buying two single breakers as opposed to a 220V 2-pole breaker, and then needing to buy the tie-- hmmm.
The reason I started asking what I did is that a quick internetz search shows the QO breakers to be a 220V/two pole breaker that is connected together. So are you saying that this type of breaker, with the handle molded into one piece, could trip only one leg and not the other? And this extra-purchase handle tie would be required?
I hate hate hate ever saying something that questions the Wisdom of Tim, but I am trying to be clear as to what Jeff was referring to, since the mentioned products don't appear to be what he says they are.
-Ray
Question at will. I do!
I was thinking more of the aftermarket clips or the little piece of #14 the electrician would thread through the holes in the handles. The picture you posted uses a factory-applied metal clip which is probably much more rigid than either of the 'solutions' I was considering.
That said, the internal axle method is 100% and cannot be modified or altered by an end user.
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Question at will. I do!
I was thinking more of the aftermarket clips or the little piece of #14 the electrician would thread through the holes in the handles. The picture you posted uses a factory-applied metal clip which is probably much more rigid than either of the 'solutions' I was considering.
That said, the internal axle method is 100% and cannot be modified or altered by an end user.
Ah yes, so it's all a matter of shoddy electrical work being performed that opens up a potential for it not tripping properly. Hahaa. If someone uses the OEM multi-pole breaker like pictured, then they should be good. I was just worrying that it was being implied that the multi-pole breaker as shown (and others that one would use in their home, for example) could possibly only trip one leg and not the other-- I didn't think that was possible, so that's why I was questioning you, life, everything, and the lunch I just bought at Pita Pit while mystery shopping them. (Really!)
-Ray
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I was just worrying that it was being implied that the multi-pole breaker as shown (and others that one would use in their home, for example) could possibly only trip one leg and not the other-- I didn't think that was possible...
If the factory-installed handle tie is made of metal and securely fastened (i.e., riveted), it shouldn't be a problem. However, I have seen where the factory used a PLASTIC clip to tie the handles together, and the plastic cracks, allowing the handles to move independently so they WON'T trip in common.
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All,
I hope that this is the type of breaker I should be using when I have to create a 4-wire feed, for two 110V (20A each) circuits.
I use 4x12ga, not exceeding 50 feet.
Thanks,
Dennis
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That is correct-it is a 2 pole breaker using a single handle. No worries about not tripping both poles as necessary!
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I want to clear up a technical error in the above. In multipole (IE: 2+ poles) circuit breakers there is an internal connection of the individual pole trip units to the other poles' trip units. A trip on any pole will trip all connected trip units (a rotating non-conductive pin, usually, only visible in 'demo' units that have a cutaway or clear side). Some DIN mount types allow access to this link, most do not.
An example you are sure to be familiar with: Square D QO (and QOB) breakers have only 1 handle, no matter how many poles they switch. They do offer handle ties for single pole units but there is no guarantee that tripping one pole will also switch the connected unit off.
HTH,
Jeff Robinson
Golly guys.... I was only speaking in generalities that there's a mechanical connection between the 2 or 3 poles, so that when one trips, they all trip. Yes, there are both internal and external ways to do this, but I was only making the point that there's no electrical connections between the poles in a multi-pole breaker, only a mechanical connection that forces them ALL to trip.
This is a tough room, isn't it? ;D
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Golly guys.... I was only speaking in generalities that there's a mechanical connection between the 2 or 3 poles, so that when one trips, they all trip. Yes, there are both internal and external ways to do this, but I was only making the point that there's no electrical connections between the poles in a multi-pole breaker, only a mechanical connection that forces them ALL to trip.
This is a tough room, isn't it? ;D
Hey, I had your back!! :D
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Hey, I had your back!! :D
Yes you did. Thanks... :)
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Golly guys.... I was only speaking in generalities that there's a mechanical connection between the 2 or 3 poles, so that when one trips, they all trip. Yes, there are both internal and external ways to do this, but I was only making the point that there's no electrical connections between the poles in a multi-pole breaker, only a mechanical connection that forces them ALL to trip.
This is a tough room, isn't it? ;D
This room, more than any other, needs to be tough. Lives are on the line!
frank
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This room, more than any other, needs to be tough. Lives are on the line!
+1: They are indeed... 8)
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I just discovered the dual pole breaker for my well pump was missing the gang wire. But I've got bigger problems. The entire main panel of my house is a Zinsco panel, aka "burn your house down" panel. Apparently their breakers have a reputation for overheating and sometimes starting fires due to a design flaw. No longer made and for good reason.
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I just discovered the dual pole breaker for my well pump was missing the gang wire. But I've got bigger problems. The entire main panel of my house is a Zinsco panel, aka "burn your house down" panel. Apparently their breakers have a reputation for overheating and sometimes starting fires due to a design flaw. No longer made and for good reason.
Sounds like a lot of fun. See below:
Damage Created by Zinsco Panels
The Panels Produce Hazardous Situations
Zinsco panels may seem to work properly for years. But experts warn that these panels may present numerous problems and even hazards if and when they fail. In fact, one expert warns that as many as 25% of all Zinsco circuit breakers could fail to trip in response to an overcurrent or short circuit and create a possible hazardous situation.
Problems with certain Zinsco panels cannot be seen by the naked eye. Even after the cover of Zinsco panels has been removed, everything can seem to be in fine working order. Upon exploring its components, electricians find that breakers cannot be removed from the bus bar. They’ve welded together, which indicates that the breakers have melted. In that condition, a breaker would be unable to trip and may be allowing an unsafe amount of electricity into the home! This could lead to a potential fire.
Please, do not attempt to remove breakers from your own panel to see if they’ve melted. Only licensed electricians should. Zinsco panels can be electrical shock risks; they can appear to be shut off but are still conducting electricity!
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I just discovered the dual pole breaker for my well pump was missing the gang wire. But I've got bigger problems. The entire main panel of my house is a Zinsco panel, aka "burn your house down" panel. Apparently their breakers have a reputation for overheating and sometimes starting fires due to a design flaw. No longer made and for good reason.
Double whammy - my home's original panel is a Magnetrip (rebadged Zinsco). When the basement was added the Zinsco became a sub panel and a new service was installed: Federal Pacific.
Oy veh.
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Double whammy - my home's original panel is a Magnetrip (rebadged Zinsco). When the basement was added the Zinsco became a sub panel and a new service was installed: Federal Pacific.
Oy veh.
Federal Pacific makes 3Ø panels with cams? Cos I'd expect nothing less at your house. :-D
-Ray
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Federal Pacific makes 3Ø panels with cams? Cos I'd expect nothing less at your house. :-D
-Ray
The replacement service will have a 50 amp disconnect in the back yard. I've got a perfect spot to park a generator if I need more.
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The replacement service will have a 50 amp disconnect in the back yard. I've got a perfect spot to park a generator if I need more.
.... meh... ok.................... Haha.
On my pile of Things To Do -- I am going to pull a separate 200A service for my garage. I installed a separate panel out there, and have wired some common twist locks already-- 50A range plug for an RV, 50A inside, couple of L14-30s, couple of L5-30s... I just need to pull from the pole down the property line and to the garage.
... since I am currently living out there (long story involving my parents living here, and now my sister and her two daughters ages 3 and 7) having better power then a random 20A circuit off the hot tub panel, and a 30A 1Ø RV circuit-converted to 14-50 - to gennie twist - hard wired into the panel out there to light up one or two circuits -- would sure be nice!
-Ray
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For the past 6 years I have had a generator in the back yard with a L14-30 connection to a hard wired inlet to a 100a transfer switch. When power went out, I would go to the back yard, start the genny (at least it was electric start) then go in and manually throw the transfer switch. I had a bunch of useful stuff on a sub panel from the switch.
Fast forward to this past week... Last weekend I dug trenches with a rented excavator for a propane line and for connecting up a larger auto start standby generator.
Of course, I needed to remove the old wiring.
Today we finished laying down the sand for the propane line and plumbing in all the PVC pipe to the generator location.
I am typing this in the dark on UPS power since a thunderstorm took out power half an hour ago :-)
Sigh....
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