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#1
Posted to rec.woodworking
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electrical question (wood shop)
Finished wiring the wood-shop area. All in conduit, 12 quadplex wall outlets, and four fluorescent lights on three way switches. Also a 220V feed to the air compressor. New sub-panel in wood shop is fed by an other sub-panel 3 feet away on the other side of a wall. Feeder panel has a 50amp breaker feeding the wood shop sub panel. All wiring within conduit is #12 except the 220 which is #10.
Question: As I installed each of the quad (gang of four) outlets, I would go to the breaker, turn it on and check the outlet with a clamp lamp and then turn off the breaker for further work. When I was installing the outlet group # 11, the wires shifted withing the conduit and the hot wire in # 12 touched the metal box. (Yes, I didn't cap the wires while I was working, I simply bent them out of each other's way. Stupid) Anyway, the question is "why did the 50 amp breaker feeding my sup panel break instead of the 20 amp breaker withing the sub panel"? Later, after wrestling my large air compressor into it's closet the same thing happened. I dislodged the safety shield on the belt, the fan blade could not turn and ergo the motor drew too many amps on start-up. Again, instead of the 30 amp circuit feeding the compressor breaking, it's the 50 amp feeding the panel that broke. Note: 50 amp breaker is used. 30 amp breaker is used. 20 amp breaker is new. Is the 50 amp breaker simply too sensitive? I could live with the above, except when the 50 amp breaker trips I lose everything and am left in the dark. Have to get a flashlight, go outside one building and into another to access the other side of the wall. All comments and advise appreciated. Ivan Vegvary |
#2
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electrical question (wood shop)
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#3
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electrical question (wood shop)
Ivan Vegvary wrote in
: [...] Anyway, the question is "why did the 50 amp breaker feeding my sup panel break instead of the 20 amp breaker withing the sub panel"? [...] Is the 50 amp breaker simply too sensitive? Well, it's *more* sensitive, anyway. That doesn't mean, necessarily, that it's *too* sensitive (i.e. more sensitive than it's supposed to be). It could be that way by design. |
#4
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electrical question (wood shop)
On 8/31/2012 11:21 AM, Doug Miller wrote:
Ivan wrote in : [...] Anyway, the question is "why did the 50 amp breaker feeding my sup panel break instead of the 20 amp breaker withing the sub panel"? [...] Is the 50 amp breaker simply too sensitive? Well, it's *more* sensitive, anyway. That doesn't mean, necessarily, that it's *too* sensitive (i.e. more sensitive than it's supposed to be). It could be that way by design. Although I don't have Doug's electrical expertise, I was thinking that the surge was just that, a surge. It's wasn't like the turning the flow from a water faucet from low to high. It was more like turning the flow from low to "Niagara Falls"! CB'ers supposedly handle motor start-up better than fuses(don't they?), clearly due to a delay. I think it's built into the mechanics of the CB'er. Maybe this delay is a measurable feature of the 2 CB'ers involved? |
#5
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electrical question (wood shop)
Bill wrote:
Although I don't have Doug's electrical expertise, I was thinking that the surge was just that, a surge. It's wasn't like the turning the flow from a water faucet from low to high. It was more like turning the flow from low to "Niagara Falls"! Not so bad an analogy, but it does not address the real question - why did the 50A breaker trip and not the 20A. Keep working on it Bill - though admitedly, it is a bit of speculation after the fact like this. CB'ers supposedly handle motor start-up better than fuses(don't they?), clearly due to a delay. I think it's built into the mechanics of the CB'er. Maybe this delay is a measurable feature of the 2 CB'ers involved? Actually, slow blow fuses can perform better than breakers when it comes to start up current. The operative word is "can". As far as the "measurable feature of 2 CB's involved" - not even sure what that means, but the short answer is... likely, no. -- -Mike- |
#6
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electrical question (wood shop)
On 8/31/2012 12:06 PM, Mike Marlow wrote:
.... ... As far as the "measurable feature of 2 CB's involved" - not even sure what that means, ... Circuit breakers have time response curves, too; there are ones specifically for motor applications as well just as "slo-blo" fuses. It's possible one of OPs is but it'll be knowable by looking at the actual manufacturer's part no's... As for tripping a 50A breaker ahead of a 20A when the short is on that 20A circuit--that ain't the way it should operate, no. I'd suspect the 50A is the culprit here--check that it's not warm to touch when operating normally; they will fail w/ age and that's often a clue. -- |
#7
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electrical question (wood shop)
On 8/31/2012 12:06 PM, Mike Marlow wrote:
Bill wrote: Although I don't have Doug's electrical expertise, I was thinking that the surge was just that, a surge. It's wasn't like the turning the flow from a water faucet from low to high. It was more like turning the flow from low to "Niagara Falls"! Not so bad an analogy, but it does not address the real question - why did the 50A breaker trip and not the 20A. Keep working on it Bill - though admitedly, it is a bit of speculation after the fact like this. CB'ers supposedly handle motor start-up better than fuses(don't they?), clearly due to a delay. I think it's built into the mechanics of the CB'er. Maybe this delay is a measurable feature of the 2 CB'ers involved? Actually, slow blow fuses can perform better than breakers when it comes to start up current. The operative word is "can". As far as the "measurable feature of 2 CB's involved" - not even sure what that means, but the short answer is... likely, no. We have a new home and had a problem with a breaker, it clearly was rated high enough to perform the task. The electrician that came out to replace the breaker indicated that the typical modern breaker is designed to blow up at up to 20% below the rating. BS or not, this is not the first time I have heard this. In my old shop I was running a compressor and freezer on the same circuit. If I added my router and fan the 15 amp breaker would some times trip. In the new house on a 20 amp dedicated circuit the breaker often tripped with only the compressor and freezer. So now the freezer runs on a separate 15 amp circuit and the compressor and drum sander run on the 20 amp. No more problems. |
#8
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electrical question (wood shop)
Leon lcb11211@swbelldotnet writes:
We have a new home and had a problem with a breaker, it clearly was rated high enough to perform the task. The electrician that came out to replace the breaker indicated that the typical modern breaker is designed to blow up at up to 20% below the rating. BS or not, this is not the first time I have heard this. IIRC, the code requires that a circuit be loaded to no more than 80% ampacity, derated by temperature and raceway loading. As for the OP, if the 50 is upstream of the 20, and the 50 blows first on a dead short, the 20 should be replaced ASAP. scott |
#9
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electrical question (wood shop)
On 8/31/2012 1:16 PM, Scott Lurndal wrote:
.... As for the OP, if the 50 is upstream of the 20, and the 50 blows first on a dead short, the 20 should be replaced ASAP. .... Excepting (unless he mistyped) the 20A is supposedly a brand new breaker while the 50A is used. I'm suspecting the 50A (or something else isn't kosher that's totally impossible to diagnose from here). -- |
#10
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electrical question (wood shop)
dpb wrote:
On 8/31/2012 1:16 PM, Scott Lurndal wrote: ... As for the OP, if the 50 is upstream of the 20, and the 50 blows first on a dead short, the 20 should be replaced ASAP. ... Excepting (unless he mistyped) the 20A is supposedly a brand new breaker while the 50A is used. I'm suspecting the 50A (or something else isn't kosher that's totally impossible to diagnose from here). Not to mention that if I recall correctly, there were more than on sub panel breakers that exhibited this same symptom - so, both of them passed the current to the sub-panel feed. That would seem to point to the sub-panel feed. -- -Mike- |
#11
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electrical question (wood shop)
On 8/31/2012 1:02 PM, Leon wrote:
.... We have a new home and had a problem with a breaker, it clearly was rated high enough to perform the task. The electrician that came out to replace the breaker indicated that the typical modern breaker is designed to blow up at up to 20% below the rating. BS or not, this is not the first time I have heard this. .... You can always go to manufacturer datasheets and see...eg, http://products.schneider-electric.us/support/technical-library/?event=detail&oid=0900892680117fff&cat=0b008926800 fd695 -- |
#12
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electrical question (wood shop)
On 8/31/2012 1:16 PM, Scott Lurndal wrote:
Leon lcb11211@swbelldotnet writes: We have a new home and had a problem with a breaker, it clearly was rated high enough to perform the task. The electrician that came out to replace the breaker indicated that the typical modern breaker is designed to blow up at up to 20% below the rating. BS or not, this is not the first time I have heard this. IIRC, the code requires that a circuit be loaded to no more than 80% ampacity, derated by temperature and raceway loading. Well that would support the design of modern breakers to enforce that code. ;~) As for the OP, if the 50 is upstream of the 20, and the 50 blows first on a dead short, the 20 should be replaced ASAP. Now that is a logical safe first step to diagnosis. |
#13
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electrical question (wood shop)
dpb writes:
On 8/31/2012 1:16 PM, Scott Lurndal wrote: ... As for the OP, if the 50 is upstream of the 20, and the 50 blows first on a dead short, the 20 should be replaced ASAP. ... Excepting (unless he mistyped) the 20A is supposedly a brand new breaker while the 50A is used. I'm suspecting the 50A (or something else isn't kosher that's totally impossible to diagnose from here). Assuming everything was wired correctly, and the 20 isn't a delayed trip device, perhaps the 50 trips more quickly. But I agree with the "totally impossible to diagnose from here". scott |
#14
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electrical question (wood shop)
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#15
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electrical question (wood shop)
Bill wrote in
: Although I don't have Doug's electrical expertise, I was thinking that the surge was just that, a surge. It's wasn't like the turning the flow from a water faucet from low to high. It was more like turning the flow from low to "Niagara Falls"! CB'ers supposedly handle motor start-up better than fuses(don't they?), clearly due to a delay. I think it's built into the mechanics of the CB'er. Maybe this delay is a measurable feature of the 2 CB'ers involved? It's possible that the current drawn would exceed the current ratings of both circuit breakers, and in that case there would be a race condition to see which one trips first. The used 50A breaker might move easier, so it would tend to win that race. Replacing the 50A breaker might let the 20A breaker "win the race" more often. This doesn't eliminate the race condition, so the main might go first on a dead short every now and again. Puckdropper -- Make it to fit, don't make it fit. |
#16
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electrical question (wood shop)
On Thu, 30 Aug 2012 21:04:39 -0700 (PDT), Ivan Vegvary
wrote: Finished wiring the wood-shop area. All in conduit, 12 quadplex wall outlets, and four fluorescent lights on three way switches. Also a 220V feed to the air compressor. New sub-panel in wood shop is fed by an other sub-panel 3 feet away on the other side of a wall. Feeder panel has a 50amp breaker feeding the wood shop sub panel. All wiring within conduit is #12 except the 220 which is #10. Question: As I installed each of the quad (gang of four) outlets, I would go to the breaker, turn it on and check the outlet with a clamp lamp and then turn off the breaker for further work. When I was installing the outlet group # 11, the wires shifted withing the conduit and the hot wire in # 12 touched the metal box. (Yes, I didn't cap the wires while I was working, I simply bent them out of each other's way. Stupid) Anyway, the question is "why did the 50 amp breaker feeding my sup panel break instead of the 20 amp breaker withing the sub panel"? Later, after wrestling my large air compressor into it's closet the same thing happened. I dislodged the safety shield on the belt, the fan blade could not turn and ergo the motor drew too many amps on start-up. Again, instead of the 30 amp circuit feeding the compressor breaking, it's the 50 amp feeding the panel that broke. Note: 50 amp breaker is used. 30 amp breaker is used. 20 amp breaker is new. Is the 50 amp breaker simply too sensitive? I could live with the above, except when the 50 amp breaker trips I lose everything and am left in the dark. Have to get a flashlight, go outside one building and into another to access the other side of the wall. All comments and advise appreciated. You don't say whether all the breakers are the same manufacturer. Actually had that happen in a computer center where a 125 amp breaker would trip before the 30 amp parking area breaker. Of course it always led to a 2AM call out so we found that problem quickly. Anyway you have two variables which is the short circuit trip time and the overload trip time. Possible this was the result of the dead short so you might not have to do anything. Possible a defective breaker, most likely the one tripping to fast. A possible problem of a poor ground path to the first breaker. Mike M |
#17
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electrical question (wood shop)
Puckdropper wrote:
It's possible that the current drawn would exceed the current ratings of both circuit breakers, and in that case there would be a race condition to see which one trips first. The used 50A breaker might move easier, so it would tend to win that race. No race condition at all if both breakers are working at rated capacities. At rated capacities, a 20A breaker will trip before a 50A breaker. By your own statement above... " It's possible that the current drawn would exceed the current ratings of both circuit breakers", which should result in the 20A op3ning first. Obviously, there is a problem, because this is not happening. But - to throw black magic at it is no solution to the problem. "Maybe, kinda sorta" stuff has no place in this kind of conversation. Replacing the 50A breaker might let the 20A breaker "win the race" more often. This doesn't eliminate the race condition, so the main might go first on a dead short every now and again. Do you understand electricity at all? -- -Mike- |
#18
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electrical question (wood shop)
Somebody wrote:
The used 50A breaker might move easier, so it would tend to win that race. ----------------------------------- All bets are off. A thermal-magnetic, molded case, plug-in cbk'r is a single use device. They are a single use device that provides inrush (magnetic) or inverse time delay (thermal) protection. These cbk'rs only have to clear a fault ONCE to meet design spec. There is no such thing as a USED cbk'r that you can trust. Lew |
#19
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electrical question (wood shop)
It happens that Mike M formulated :
On Thu, 30 Aug 2012 21:04:39 -0700 (PDT), Ivan Vegvary wrote: Finished wiring the wood-shop area. All in conduit, 12 quadplex wall outlets, and four fluorescent lights on three way switches. Also a 220V feed to the air compressor. New sub-panel in wood shop is fed by an other sub-panel 3 feet away on the other side of a wall. Feeder panel has a 50amp breaker feeding the wood shop sub panel. All wiring within conduit is #12 except the 220 which is #10. Question: As I installed each of the quad (gang of four) outlets, I would go to the breaker, turn it on and check the outlet with a clamp lamp and then turn off the breaker for further work. When I was installing the outlet group # 11, the wires shifted withing the conduit and the hot wire in # 12 touched the metal box. (Yes, I didn't cap the wires while I was working, I simply bent them out of each other's way. Stupid) Anyway, the question is "why did the 50 amp breaker feeding my sup panel break instead of the 20 amp breaker withing the sub panel"? Later, after wrestling my large air compressor into it's closet the same thing happened. I dislodged the safety shield on the belt, the fan blade could not turn and ergo the motor drew too many amps on start-up. Again, instead of the 30 amp circuit feeding the compressor breaking, it's the 50 amp feeding the panel that broke. Note: 50 amp breaker is used. 30 amp breaker is used. 20 amp breaker is new. Is the 50 amp breaker simply too sensitive? I could live with the above, except when the 50 amp breaker trips I lose everything and am left in the dark. Have to get a flashlight, go outside one building and into another to access the other side of the wall. All comments and advise appreciated. You don't say whether all the breakers are the same manufacturer. Actually had that happen in a computer center where a 125 amp breaker would trip before the 30 amp parking area breaker. Of course it always led to a 2AM call out so we found that problem quickly. Anyway you have two variables which is the short circuit trip time and the overload trip time. Possible this was the result of the dead short so you might not have to do anything. Possible a defective breaker, most likely the one tripping to fast. A possible problem of a poor ground path to the first breaker. Mike M Can you explain what part a ground plays in a simple 2 terminal breaker? -- John G |
#20
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electrical question (wood shop)
Problem solved! Thanks for all the help.
Scrounged around for another breaker and found a 40 amp double (240 volt). Replaced the suspect 50 with the 40 and all is O.K. If I force a short in the 20 amp circuit the 20 amp now breaks and the upstream 40 amp holds. Obviously the 50 amp breaker was bad. (proved it by putting it back in and forcing a short) BTW, I force a short by plugging in a shorted power cord. (Doesn't everybody in this group cut off the power cord on a tool prior to throwing it away?) Thanks again, you guys are wonderful! Ivan Vegvary |
#21
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electrical question (wood shop)
On Fri, 31 Aug 2012 23:21:50 -0700 (PDT), Ivan Vegvary
wrote: Problem solved! Thanks for all the help. Scrounged around for another breaker and found a 40 amp double (240 volt). Replaced the suspect 50 with the 40 and all is O.K. If I force a short in the 20 amp circuit the 20 amp now breaks and the upstream 40 amp holds. Obviously the 50 amp breaker was bad. (proved it by putting it back in and forcing a short) BTW, I force a short by plugging in a shorted power cord. (Doesn't everybody in this group cut off the power cord on a tool prior to throwing it away?) Thanks again, you guys are wonderful! Ivan Vegvary Jeeze, Ivan. We usually remove the plug from the outlet before cutting the cord. "Forcing a short" indeed! -- I have the consolation of having added nothing to my private fortune during my public service, and of retiring with hands clean as they are empty. -- Thomas Jefferson, letter to Count Diodati, 1807 Too bad -none- of the current CONgresscritters are willing to do that. -LJ |
#22
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electrical question (wood shop)
"Mike Marlow" wrote in news:45b12$504180ab
: Puckdropper wrote: It's possible that the current drawn would exceed the current ratings of both circuit breakers, and in that case there would be a race condition to see which one trips first. The used 50A breaker might move easier, so it would tend to win that race. No race condition at all if both breakers are working at rated capacities. At rated capacities, a 20A breaker will trip before a 50A breaker. Not necessarily, Mike -- it depends on the speed with which the breaker reacts to the overcurrent. If the overcurrent is, say, 40A, of course the 20A breaker should trip first, because the 50A breaker should not trip at all. But a dead short may result in a brief current of well over 50A, in which case the breaker that trips will be the one that reacts fastest. In this case, with a used 50A breaker and a new 20A breaker, one would expect the 50A breaker to trip a little faster when subjected to a current of, say, 100A. Even if they're both brand-new, and even if both have the same *design* trip speed, they still won't respond at *exactly* the same speed, simply due to normal statistical variability in the manufacturing process. Suppose the breakers are designed to trip within 10ms +/- 0.5% when an overcurrent occurs -- if the actual trip delay is 9.95ms for the 50A breaker, and 10.05ms for the 20A, they're both within design specifications, but on a 100A overcurrent the 50A breaker will go first every time. By your own statement above... " It's possible that the current drawn would exceed the current ratings of both circuit breakers", which should result in the 20A op3ning first. No, it should not. It should result in the fastest-reacting breaker opening first. The reaction speed of a breaker is *not* dependent on its amperage rating. Obviously, there is a problem, because this is not happening. But - to throw black magic at it is no solution to the problem. "Maybe, kinda sorta" stuff has no place in this kind of conversation. Replacing the 50A breaker might let the 20A breaker "win the race" more often. This doesn't eliminate the race condition, so the main might go first on a dead short every now and again. Do you understand electricity at all? I think you owe Puckdropper an apology for that. He's more nearly right than you are. |
#23
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electrical question (wood shop)
On 8/31/2012 10:21 AM, Doug Miller wrote:
Ivan Vegvary wrote in : [...] Anyway, the question is "why did the 50 amp breaker feeding my sup panel break instead of the 20 amp breaker withing the sub panel"? [...] Is the 50 amp breaker simply too sensitive? Well, it's *more* sensitive, anyway. That doesn't mean, necessarily, that it's *too* sensitive (i.e. more sensitive than it's supposed to be). It could be that way by design. Any consideration given to the 20AMP being defective? |
#24
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electrical question (wood shop)
Doug Miller wrote:
I think you owe Puckdropper an apology for that. He's more nearly right than you are. Point taken on the speed of each breaker affecting which will open first. I will offer that apology to Puckdropper, however I wouldn't go so far as to say more nearly right. You are - as is he, correct that the speed of each breaker is the factor, but there is a 50/50 chance on either one of them being faster just based on manufacturing limitations. Well taken point Doug. -- -Mike- |
#25
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electrical question (wood shop)
On 9/1/2012 7:47 PM, Mike Marlow wrote:
.... ... but there is a 50/50 chance on either one of them being faster just based on manufacturing limitations ... Well, only if the two responses are nominally identical...which wouldn't be necessarily so at all. -- |
#26
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electrical question (wood shop)
Unquestionably Confused wrote in news:50428439$0$15608
: On 8/31/2012 10:21 AM, Doug Miller wrote: Ivan Vegvary wrote in : [...] Anyway, the question is "why did the 50 amp breaker feeding my sup panel break instead of the 20 amp breaker withing the sub panel"? [...] Is the 50 amp breaker simply too sensitive? Well, it's *more* sensitive, anyway. That doesn't mean, necessarily, that it's *too* sensitive (i.e. more sensitive than it's supposed to be). It could be that way by design. Any consideration given to the 20AMP being defective? While certainly possible, I'd consider it to be pretty unlikely -- the OP stated that the 20A breaker is new, and the 50A is used. |
#27
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electrical question (wood shop)
On 9/2/2012 6:34 PM, Doug Miller wrote:
Well, it's *more* sensitive, anyway. That doesn't mean, necessarily, that it's *too* sensitive (i.e. more sensitive than it's supposed to be). It could be that way by design. Any consideration given to the 20AMP being defective? While certainly possible, I'd consider it to be pretty unlikely -- the OP stated that the 20A breaker is new, and the 50A is used. I agree that it is unlikely, but we BOTH agree that it is possible. Quality Control isn't always controllingg Logically, it's worth looking at and swapping out the breaker to make certain that is NOT the case, especially when a dead short on that circuit won't trip the 20A breaker but will flip the 50A. |
#28
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electrical question (wood shop)
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#29
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electrical question (wood shop)
J. Clarke wrote:
In article , says... On 9/1/2012 7:47 PM, Mike Marlow wrote: ... ... but there is a 50/50 chance on either one of them being faster just based on manufacturing limitations ... Well, only if the two responses are nominally identical...which wouldn't be necessarily so at all. How much load on the upstream breaker? Let's say you have a load center with a 50 amp main breaker and four 20 amp circuits. Now, let's also say that three circuits have 15 amp loads on them already, and you put a 10 amp load on the fourth. What happens? You trip the 50 amp breaker without tripping any of the 20s. Not saying that's what happened in this case--not enough information was given. But it's something to think about. Correct, but that's a different set of conditions from what the OP presented. -- -Mike- |
#30
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electrical question (wood shop)
On Sat, 01 Sep 2012 15:55:42 +1000, John G
wrote: It happens that Mike M formulated : On Thu, 30 Aug 2012 21:04:39 -0700 (PDT), Ivan Vegvary wrote: Finished wiring the wood-shop area. All in conduit, 12 quadplex wall outlets, and four fluorescent lights on three way switches. Also a 220V feed to the air compressor. New sub-panel in wood shop is fed by an other sub-panel 3 feet away on the other side of a wall. Feeder panel has a 50amp breaker feeding the wood shop sub panel. All wiring within conduit is #12 except the 220 which is #10. Question: As I installed each of the quad (gang of four) outlets, I would go to the breaker, turn it on and check the outlet with a clamp lamp and then turn off the breaker for further work. When I was installing the outlet group # 11, the wires shifted withing the conduit and the hot wire in # 12 touched the metal box. (Yes, I didn't cap the wires while I was working, I simply bent them out of each other's way. Stupid) Anyway, the question is "why did the 50 amp breaker feeding my sup panel break instead of the 20 amp breaker withing the sub panel"? Later, after wrestling my large air compressor into it's closet the same thing happened. I dislodged the safety shield on the belt, the fan blade could not turn and ergo the motor drew too many amps on start-up. Again, instead of the 30 amp circuit feeding the compressor breaking, it's the 50 amp feeding the panel that broke. Note: 50 amp breaker is used. 30 amp breaker is used. 20 amp breaker is new. Is the 50 amp breaker simply too sensitive? I could live with the above, except when the 50 amp breaker trips I lose everything and am left in the dark. Have to get a flashlight, go outside one building and into another to access the other side of the wall. All comments and advise appreciated. You don't say whether all the breakers are the same manufacturer. Actually had that happen in a computer center where a 125 amp breaker would trip before the 30 amp parking area breaker. Of course it always led to a 2AM call out so we found that problem quickly. Anyway you have two variables which is the short circuit trip time and the overload trip time. Possible this was the result of the dead short so you might not have to do anything. Possible a defective breaker, most likely the one tripping to fast. A possible problem of a poor ground path to the first breaker. Mike M Can you explain what part a ground plays in a simple 2 terminal breaker? Simple you can have a line to line short, or a short to ground. If it is a short to ground and you have a poor ground path the breaker may sense it more as an overload then a short and not trip or take longer to trip. |
#31
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electrical question (wood shop)
On Mon, 03 Sep 2012 08:49:35 -0700, Mike M
wrote: On Sat, 01 Sep 2012 15:55:42 +1000, John G wrote: It happens that Mike M formulated : On Thu, 30 Aug 2012 21:04:39 -0700 (PDT), Ivan Vegvary wrote: Finished wiring the wood-shop area. All in conduit, 12 quadplex wall outlets, and four fluorescent lights on three way switches. Also a 220V feed to the air compressor. New sub-panel in wood shop is fed by an other sub-panel 3 feet away on the other side of a wall. Feeder panel has a 50amp breaker feeding the wood shop sub panel. All wiring within conduit is #12 except the 220 which is #10. Question: As I installed each of the quad (gang of four) outlets, I would go to the breaker, turn it on and check the outlet with a clamp lamp and then turn off the breaker for further work. When I was installing the outlet group # 11, the wires shifted withing the conduit and the hot wire in # 12 touched the metal box. (Yes, I didn't cap the wires while I was working, I simply bent them out of each other's way. Stupid) Anyway, the question is "why did the 50 amp breaker feeding my sup panel break instead of the 20 amp breaker withing the sub panel"? Later, after wrestling my large air compressor into it's closet the same thing happened. I dislodged the safety shield on the belt, the fan blade could not turn and ergo the motor drew too many amps on start-up. Again, instead of the 30 amp circuit feeding the compressor breaking, it's the 50 amp feeding the panel that broke. Note: 50 amp breaker is used. 30 amp breaker is used. 20 amp breaker is new. Is the 50 amp breaker simply too sensitive? I could live with the above, except when the 50 amp breaker trips I lose everything and am left in the dark. Have to get a flashlight, go outside one building and into another to access the other side of the wall. All comments and advise appreciated. You don't say whether all the breakers are the same manufacturer. Actually had that happen in a computer center where a 125 amp breaker would trip before the 30 amp parking area breaker. Of course it always led to a 2AM call out so we found that problem quickly. Anyway you have two variables which is the short circuit trip time and the overload trip time. Possible this was the result of the dead short so you might not have to do anything. Possible a defective breaker, most likely the one tripping to fast. A possible problem of a poor ground path to the first breaker. Mike M Can you explain what part a ground plays in a simple 2 terminal breaker? Simple you can have a line to line short, or a short to ground. If it is a short to ground and you have a poor ground path the breaker may sense it more as an overload then a short and not trip or take longer to trip. This may be true in a GFI (ground fault interrupter) circuit breaker, but in 120/240v standard breakers, there IS no ground lead. -- The most powerful factors in the world are clear ideas in the minds of energetic men of good will. -- J. Arthur Thomson |
#32
Posted to rec.woodworking
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electrical question (wood shop)
On 9/1/2012 2:21 AM, Ivan Vegvary wrote:
Problem solved! Thanks for all the help. Scrounged around for another breaker and found a 40 amp double (240 volt). Replaced the suspect 50 with the 40 and all is O.K. If I force a short in the 20 amp circuit the 20 amp now breaks and the upstream 40 amp holds. Obviously the 50 amp breaker was bad. (proved it by putting it back in and forcing a short) Good job. Before the woodworkers are done here, they will be plotting things out on a Cray supercomputer, and fighting for government approval of some sort of new electrical code. BTW, I force a short by plugging in a shorted power cord. Works, but I'm sure it violates a gov't code somewhere, and if you kill yourself, neighbors, family pets, your insurance company will certainly deny all claims. (Doesn't everybody in this group cut off the power cord on a tool prior to throwing it away?) I thought I was the only one, I have a giant box of them. I tend to save all sorts of stuff on the way to the trash. ****es the wife off when she catches me, until she needs me to fix something she broke. -- Jack Add Life to your Days not Days to your Life. http://jbstein.com |
#33
Posted to rec.woodworking
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electrical question (wood shop)
On Mon, 03 Sep 2012 09:27:50 -0700, Larry Jaques
wrote: On Mon, 03 Sep 2012 08:49:35 -0700, Mike M wrote: On Sat, 01 Sep 2012 15:55:42 +1000, John G wrote: It happens that Mike M formulated : On Thu, 30 Aug 2012 21:04:39 -0700 (PDT), Ivan Vegvary wrote: Finished wiring the wood-shop area. All in conduit, 12 quadplex wall outlets, and four fluorescent lights on three way switches. Also a 220V feed to the air compressor. New sub-panel in wood shop is fed by an other sub-panel 3 feet away on the other side of a wall. Feeder panel has a 50amp breaker feeding the wood shop sub panel. All wiring within conduit is #12 except the 220 which is #10. Question: As I installed each of the quad (gang of four) outlets, I would go to the breaker, turn it on and check the outlet with a clamp lamp and then turn off the breaker for further work. When I was installing the outlet group # 11, the wires shifted withing the conduit and the hot wire in # 12 touched the metal box. (Yes, I didn't cap the wires while I was working, I simply bent them out of each other's way. Stupid) Anyway, the question is "why did the 50 amp breaker feeding my sup panel break instead of the 20 amp breaker withing the sub panel"? Later, after wrestling my large air compressor into it's closet the same thing happened. I dislodged the safety shield on the belt, the fan blade could not turn and ergo the motor drew too many amps on start-up. Again, instead of the 30 amp circuit feeding the compressor breaking, it's the 50 amp feeding the panel that broke. Note: 50 amp breaker is used. 30 amp breaker is used. 20 amp breaker is new. Is the 50 amp breaker simply too sensitive? I could live with the above, except when the 50 amp breaker trips I lose everything and am left in the dark. Have to get a flashlight, go outside one building and into another to access the other side of the wall. All comments and advise appreciated. You don't say whether all the breakers are the same manufacturer. Actually had that happen in a computer center where a 125 amp breaker would trip before the 30 amp parking area breaker. Of course it always led to a 2AM call out so we found that problem quickly. Anyway you have two variables which is the short circuit trip time and the overload trip time. Possible this was the result of the dead short so you might not have to do anything. Possible a defective breaker, most likely the one tripping to fast. A possible problem of a poor ground path to the first breaker. Mike M Can you explain what part a ground plays in a simple 2 terminal breaker? Simple you can have a line to line short, or a short to ground. If it is a short to ground and you have a poor ground path the breaker may sense it more as an overload then a short and not trip or take longer to trip. This may be true in a GFI (ground fault interrupter) circuit breaker, but in 120/240v standard breakers, there IS no ground lead. I don't know what code book your using but you'll never pass a NEC inspection if the entire system isn't grounded. Your thinking of the nuetral or identified conducter. Mike M |
#34
Posted to rec.woodworking
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electrical question (wood shop)
"Jack" wrote BTW, I force a short by plugging in a shorted power cord. Only thing with that is that it melts the plug contacts a bit. Plug the cord in then short the ends together, or my favorite is a u shaped piece of wire against the sides of the plug's hookup screws. Even better, they make plug testers that you plug in and push a button. Not too expensive, and tells you if you have all of the wires hooked up correctly all the way back to the breaker box. Jim in NC |
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