Circuit breaker question- quick - Page 2 - AVS Forum
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post #31 of 53 Old 07-08-2013, 12:20 PM
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Originally Posted by Glimmie View Post

And you had all the equipment on the same phase? While I have seen some small facilities in split phase systems, the majority of broadcast plants are three phase. And the idea that different equipment on different phases causes hum is an audiophile myth.

Certainly not in a large plant. They usually use 3-phase power distribution. The best practice is to have a common ground point as close as possible to the equipment. I was careful to say "some experts", since it can also depend on the type of power supplies you are feeding (linear or switching), whether your signals are analog or digital, etc.

PDX asked a simple question, which I tried to answer, that's all.
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post #32 of 53 Old 07-08-2013, 05:15 PM
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Frankly, I don't think anybody in the thread made any gross misstatements (other than amp wattage correlating to AC wattage).

I'm not sure what the issue with greg is-- what he said may have been stated clearer, but none of it was incorrect. He basically said the same thing as everybody else.

I've always referred to circuit breakers as quad, tandem, 2-pole or single pole. A 240v breaker is a 2-pole that must be common disconnect and common trip. A MWBC must be common disconnect. A 2-pole CB can be used for a MWBC or 240v. Handle ties are only for MWBC and I would not say a handle tie creates a 2-pole breaker in the sense that everybody in the trade that I have met uses the term.

Improper grounding will cause hum. I've never heard from a reliable source that having equipment on different legs creates hum, but if anybody fitting that description would like to comment to the contrary, I would certainly be open to that.

Using a MWBC assures that the path to ground is the same for both circuits, which is a good thing. Beware the AFCI.

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post #33 of 53 Old 07-08-2013, 06:03 PM
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This thread seems to be a collection of individual statements. Most by themselves are correct, but each may apply to a different situation than some others.

This is a Middle Atlantic paper on the subject:

"Integrating Electronic Equipment and Power into Rack Enclosures"
'Optimized Power Distribution and Grounding for Audio, Video and Electronic Systems'

http://www.middleatlantic.com/pdf/PowerPaper.pdf
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post #34 of 53 Old 07-08-2013, 07:31 PM
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Originally Posted by Colm View Post

No qualified electrician will do that. You cannot have a MWBC if the two hots are on the same leg. The definition of a MWBC in the NEC includes a voltage between the hots, IOW the two hots are on different legs in a typical residential single phase 3-wire system.

I hate to say it , but this statement is somewhat false . I've seen hundreds of installations that do exactly this , done by journeymen electricians , as well as licensed contractors in residential , commercial and industrial applications. In regard to MWBC you are correct , that it does not meet the definition of MWBC , but that does not mean it violates code . In this instance it is two individual circuits that share a common , as a MWBC by definition has to have voltage between the conductors or it is not MWBC . There is nothing wrong with multiple conductors of the same phase traveling together , the problem is sharing the common between circuits on the same phase. It is not rare to see contractors trying to save a few bucks on material and forgetting some basic tenants of electrical installation.
Back on topic , none of this , or any installation will inherently introduce interference or "hum" . I have dealt with almost every conceivable wiring anomaly and have never had to troubleshoot "hum" in a residential application . The rats nest of power cords and communication cables behind our gear is more likely to introduce interference.

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post #35 of 53 Old 07-08-2013, 08:09 PM
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Originally Posted by scubasteve2365 View Post

You're not correct.

1) There is a time domain element.
2) the purpose of the circuit breaker is to protect the wire, not the equipment or load the wire is servicing.
3) you will likely never see a transient 1600W draw.
4) breakers are rated for amperage, not wattage.

Signed,
EE

The max wattage of a breaker is determined by the base volts times the amp of the break to give you the total watts. Sure they may be Amp rated, but there is a direct correlation to the wattage draw.

My amps are rated by Rotel with a max draw of 800 watts each. Sure that is driving them 100% which is unlikely. But I am not going to chance putting 3 of them on a single 15amp breaker. If all 3 pull even 80% of their max load I will be overloading the circuit.

Coupled with the fact that you should never be running your circuit at much more than 80% of the total watts it can handle, putting 2 of these amps on one 15amp breaker is already nearing the 80% mark.

This is before you take into account ALL my other equipment in a theater.

All I am saying is that Greg's comments about having "too much" equipment is ridiculous, especially when most of us running a 7.1 system are already nearing or exceeding what is recommended for a 15amp breaker.

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post #36 of 53 Old 07-08-2013, 09:18 PM
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The max wattage of a breaker is determined by the base volts times the amp of the break to give you the total watts. Sure they may be Amp rated, but there is a direct correlation to the wattage draw.

Theoretically this is correct , but in application it doesn't always hold true . Circuit breakers , put bluntly , suck at doing their jobs . That's why outlets burn out and hair dryers melt , and occasionally houses burn down. I've tested circuits where 15a breakers were feeding over 35a without tripping. I've set up tests where if the load is gradually increased ( using both lights on dimmers and variable speed motors) I could easily exceed the amp rating of a breaker , sometimes more than double. Fuses are far more reliable to truly limit current , unless there's a penny behind it or tin foil wrapped around it.
I agree that it would be foolish to run your amps on one 15a circuit hoping for the best , and that saying someone has "too much equipment" is ridiculous , unless they have to sit on their porch to enjoy their HT because there's no room inside for them to sit , or it's too hot when all the amps are running.

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post #37 of 53 Old 07-08-2013, 09:34 PM
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Originally Posted by acras13 View Post

I hate to say it , but this statement is somewhat false
Only if you choose to take it out of context.

FWIW the idea of installing a MWBC in this case seems ludicrous to me. All the OP wants is an additional circuit, on the same leg as an existing circuit. A tandem breaker will replace a single pole breaker. The simplest thing would be to just pull the wire for a separate circuit.
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post #38 of 53 Old 07-08-2013, 11:14 PM
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Originally Posted by Colm View Post

Only if you choose to take it out of context.

FWIW the idea of installing a MWBC in this case seems ludicrous to me. All the OP wants is an additional circuit, on the same leg as an existing circuit. A tandem breaker will replace a single pole breaker. The simplest thing would be to just pull the wire for a separate circuit.

Wasn't taken out of context , and the I stand by my statement that your comment was somewhat false . Many " qualified" electricians will share a common on 2 circuits of the same phase . When a tandem breaker is installed to provide 2 new circuits , quite often the electrician will pull 12/3 romex for the new runs , especially in a case like the OP's where they are going to basically the same place , but there is no need for 240v.
Further , where did you read that he wanted 1 additional circuit on the same leg as an existing circuit? That was not the OP's question. He's adding 2 20a circuits and had read about interference if they were the same phase.

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post #39 of 53 Old 07-09-2013, 09:09 AM
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Originally Posted by acras13 View Post

Wasn't taken out of context , and the I stand by my statement that your comment was somewhat false . Many " qualified" electricians will share a common on 2 circuits of the same phase . When a tandem breaker is installed to provide 2 new circuits , quite often the electrician will pull 12/3 romex for the new runs , especially in a case like the OP's where they are going to basically the same place , but there is no need for 240v.
Further , where did you read that he wanted 1 additional circuit on the same leg as an existing circuit? That was not the OP's question. He's adding 2 20a circuits and had read about interference if they were the same phase.

I just thought I'd throw out that a local home builder in my area is running 14/3 (pretty sure its 14 and not 12), to a two pole 15A breaker, with a shared neutral to feed a Dishwasher and Disposal.

I'm sure that lots of builders will do a shared neutral in cases like this, it saves them money, and it's code compliant. I won't say I'm in love with it, but when you have some load diversity, it works.

Now, that might change with the 2014 NEC, where the push is to AFCI almost everything....... and a shared neutral makes that hard.
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post #40 of 53 Old 07-09-2013, 10:08 AM
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Originally Posted by acras13 View Post

I hate to say it , but this statement is somewhat false . I've seen hundreds of installations that do exactly this , done by journeymen electricians , as well as licensed contractors in residential , commercial and industrial applications. In regard to MWBC you are correct , that it does not meet the definition of MWBC , but that does not mean it violates code . In this instance it is two individual circuits that share a common , as a MWBC by definition has to have voltage between the conductors or it is not MWBC . There is nothing wrong with multiple conductors of the same phase traveling together , the problem is sharing the common between circuits on the same phase. It is not rare to see contractors trying to save a few bucks on material and forgetting some basic tenants of electrical installation.
Back on topic , none of this , or any installation will inherently introduce interference or "hum" . I have dealt with almost every conceivable wiring anomaly and have never had to troubleshoot "hum" in a residential application . The rats nest of power cords and communication cables behind our gear is more likely to introduce interference.

I don't see where Colms statement is wrong. You cannot have two conductors on the same phase sharing a single neutral. Of course you can have two hots on the same phase with two neutrals even in the same cable or conduit.

Same goes for three phase. Here you can get three 120v circuits to a single neutral. However there is an exception in most local codes for technical power systems. In this age of switch mode power supplies, the high frequency harmonic current does not cancel and therefore shared neutrals can become seriously overloaded. There are stories of cherry red neutral buss bars in panels feeding large data center loads. Overloaded neutrals on three phase systems are nothing new. There was always an minor issue with large fluorescent lamp loads as they have a nonlinear current draw. But it';s the switchmode power supply revolution in the 1980s that brought this problem to the surface.

Also there is a case with running conductors of the same phase together. In larger commercial installations you can't get a big enough wire to handle the current needs. So you parallel several smaller wires to get the current rating. In three phase systems, when you do this, the wires must be three phases to a conduit. This is so the field will cancel within the conduit. Example, say you need to run three MCM250 wires per phase. Each conduit will need a wire from each of the phases. Doing otherwise will cause heating of the conduits.

Of course when we are talking about three phase, we are well out of residential concerns.

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post #41 of 53 Old 07-09-2013, 10:13 AM
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Originally Posted by acras13 View Post

Wasn't taken out of context , and the I stand by my statement that your comment was somewhat false . Many " qualified" electricians will share a common on 2 circuits of the same phase . When a tandem breaker is installed to provide 2 new circuits , quite often the electrician will pull 12/3 romex for the new runs , especially in a case like the OP's where they are going to basically the same place , but there is no need for 240v.

This is WRONG. And I doubt it's legal in an local codes. Look at it from an EE perspective. If I am pulling 35amps (assume 12ga wire) between those tow hots, the neutral will be overloaded. Sure it works most of the time because household loads are very light.

This is a hack. No true professional electrician would do this. And if a fire ever resulted, the electrician would be liable.

But your statement that many do this is true. My last house was wired this way, that is red and black to a tandem breaker. And it seems to have passed inspection too. I fixed it in short order!

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post #42 of 53 Old 07-09-2013, 10:14 AM
 
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They will just start using the AFCI outlets at that point, or Double Pole AFCI breakers will become more common. See http://forums.mikeholt.com/showthread.php?t=134400 from 2011. This is from 2006 http://www.ecmag.com/section/miscellaneous/multiwire-branch-circuits-afcis-and-more From 2013 http://forums.mikeholt.com/showthread.php?t=151432 2010 white paper http://w3.usa.siemens.com/us/internet-dms/btlv/Residential/Residential/docs_AFIC%20Circuit%20Protection/SIE_BR_2poleCAFCI%20Resi%20applications.pdf Another 2013 article http://m.csemag.com/index.php?id=2832&tx_ttnews%5Btt_news%5D=86039&cHash=ef74da76e78cd6ab0b4075d71f8e8070 NECPlus article http://www.necplus.org/Features/Pages/AFCIRulesCouldExpandProtectionforBranchCircuits.aspx?sso=0

ECMMag, Mikeholt.com & NECPlus are about the best resources to keep up on this. You can get on the list for keeping up with the changes, by signing up for the NFPA newsletter, also keeping an eye on the three sites listed at the beginning of this paragraph. Really the one thing that the use of AFCI breakers in residential settings, is that the whole structure is now going to be covered by having the breakers or outlets in them. No longer is it just bedrooms or living spaces. You can now get the outlets from Leviton, but they cost as much as the circuit breakers do.
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post #43 of 53 Old 07-09-2013, 10:25 AM
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Originally Posted by gregzoll View Post

They will just start using the AFCI outlets at that point, or Double Pole AFCI breakers will become more common. See http://forums.mikeholt.com/showthread.php?t=134400 from 2011. This is from 2006 http://www.ecmag.com/section/miscellaneous/multiwire-branch-circuits-afcis-and-more From 2013 http://forums.mikeholt.com/showthread.php?t=151432 2010 white paper http://w3.usa.siemens.com/us/internet-dms/btlv/Residential/Residential/docs_AFIC%20Circuit%20Protection/SIE_BR_2poleCAFCI%20Resi%20applications.pdf Another 2013 article http://m.csemag.com/index.php?id=2832&tx_ttnews%5Btt_news%5D=86039&cHash=ef74da76e78cd6ab0b4075d71f8e8070 NECPlus article http://www.necplus.org/Features/Pages/AFCIRulesCouldExpandProtectionforBranchCircuits.aspx?sso=0

ECMMag, Mikeholt.com & NECPlus are about the best resources to keep up on this. You can get on the list for keeping up with the changes, by signing up for the NFPA newsletter, also keeping an eye on the three sites listed at the beginning of this paragraph. Really the one thing that the use of AFCI breakers in residential settings, is that the whole structure is now going to be covered by having the breakers or outlets in them. No longer is it just bedrooms or living spaces. You can now get the outlets from Leviton, but they cost as much as the circuit breakers do.

Yeah, Mike Holt is a great resource. Lets take this idea of "MWBC off a tandem breaker" over to his forum and see what he thinks. rolleyes.gif

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post #44 of 53 Old 07-09-2013, 10:33 AM
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Originally Posted by homeav View Post

I just thought I'd throw out that a local home builder in my area is running 14/3 (pretty sure its 14 and not 12), to a two pole 15A breaker, with a shared neutral to feed a Dishwasher and Disposal.

I'm sure that lots of builders will do a shared neutral in cases like this, it saves them money, and it's code compliant. I won't say I'm in love with it, but when you have some load diversity, it works.

Now, that might change with the 2014 NEC, where the push is to AFCI almost everything....... and a shared neutral makes that hard.

If the two pole breaker is a double wide type, that is a 240v breaker, that what they are doing is fine and code compliant. But if the breaker is a tandem, that is two breakers in a single slot, it's not OK and with a 15a circuit feeding a dishwasher and disposal, you are in the area where overheating of the neutral could easily occur if shared and not split phase.

I'm not sure but I thought some codes require 20amp circuits in all residential kitchens? I would do that anyway.

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post #45 of 53 Old 07-09-2013, 01:06 PM
 
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Originally Posted by Glimmie View Post

If the two pole breaker is a double wide type, that is a 240v breaker, that what they are doing is fine and code compliant. But if the breaker is a tandem, that is two breakers in a single slot, it's not OK and with a 15a circuit feeding a dishwasher and disposal, you are in the area where overheating of the neutral could easily occur if shared and not split phase.

I'm not sure but I thought some codes require 20amp circuits in all residential kitchens? I would do that anyway.
Again, there is no such thing as a 240VAC breaker. You have Single Pole, Double Pole, Quad Pole, Tandem Single Pole, type breakers.

There are two types of Tandem breakers. There is the Single slot and double slot form factor, depending on the manufacturer and panel. The Double slot can have a handle tie on it, to tie both handles together, same goes for the Quad pole breaker. You remove the handle tie, and you have a single unit with two separate poles that can allow you to control two individual circuits that are not Multi-wire branch., or you can use it to control a device that is 240vAC or MWBC, by keeping the handle tie in place.

A single slot can only be used for MWBC or a 240vAC circuit, if you have two in two single slots, and tie the handles in a way, that the two middle handles are tied together. A Single slot Tandem is not the best way to create a MWBC circuit or sistering with another breaker next to it in another slot on the other leg, because they were not intended for that.

The only way to properly use OCPD (Over Current Protection Device), is using the proper product for what you are doing.

Suggest you read up on electrical methods or take a class at a local trade school regarding electrical service and performing the duties of a licensed professional electrician Glimmie. Giving out the information that you have on this thread, not only endangers others, but has been a lot of misinformation in how to handle what the OP is wanting to do.
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post #46 of 53 Old 07-09-2013, 05:10 PM
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Originally Posted by gregzoll View Post

Again, there is no such thing as a 240VAC breaker. You have Single Pole, Double Pole, Quad Pole, Tandem Single Pole, type breakers.

There are two types of Tandem breakers. There is the Single slot and double slot form factor, depending on the manufacturer and panel. The Double slot can have a handle tie on it, to tie both handles together, same goes for the Quad pole breaker. You remove the handle tie, and you have a single unit with two separate poles that can allow you to control two individual circuits that are not Multi-wire branch., or you can use it to control a device that is 240vAC or MWBC, by keeping the handle tie in place.

A single slot can only be used for MWBC or a 240vAC circuit, if you have two in two single slots, and tie the handles in a way, that the two middle handles are tied together. A Single slot Tandem is not the best way to create a MWBC circuit or sistering with another breaker next to it in another slot on the other leg, because they were not intended for that.

The only way to properly use OCPD (Over Current Protection Device), is using the proper product for what you are doing.

I know that. I was just trying to make it clear to the poster that in order to have a MWBC, you must take up two full slots in the panel. Getting into quad tandem breakers would further complicate this and only make it more confusing.
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Suggest you read up on electrical methods or take a class at a local trade school regarding electrical service and performing the duties of a licensed professional electrician Glimmie. Giving out the information that you have on this thread, not only endangers others, but has been a lot of misinformation in how to handle what the OP is wanting to do.

That comment is uncalled for. I hold a BSEE as well as 25 years experience in designing large communications facilities. I work with UPS systems in the 500kw plus range. So don't lecture me on codes. There is nothing in my posts that is incorrect. Perhaps I and others may have used the wrong inner circle electrician terms but then again I don't hang out and socialize at electrical supply houses. I hang out with electrical PE's. I bet I can throw out a few terms that will send you for a spin.

Show me exactly where I gave out unsafe advice. You are all hung up on these terms. The point here is that you cannot share two hots on the same phase with a single neutral. Any combination of breakers that allows that is not to code and dangerous.

P.S.
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Again, there is no such thing as a 240VAC breaker. You have Single Pole, Double Pole, Quad Pole, Tandem Single Pole, type breakers.
You forgot three pole breakers. Ever see one of those? They are very common on commercial and industrial.

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post #47 of 53 Old 07-09-2013, 06:57 PM
 
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Glimmie a Three pole Breaker is for use on Three phase service. As for the BSEE, anymore it is no better than having a Associates. You learn from experience of doing stuff over time, or talking about it. Don't think I am busting your chops, it is just that at times it gets frustrating when you go back and forth about this stuff on forums. The only time I really get pissed, is when you have the types on here and other boards that outright attack someone because the person being the attacker feels that they are above others.

As for clearing stuff up for the OP, I think that if we could have all agreed from the beginning about why there is hum on circuits, which is caused by poor grounding, not by gear being on opposite legs. As for noise from electrical equipment, the only way to really get around that is with Isolation transformers, or through a UPS or Battery Bank that would smooth out the waveform before it gets out to the equipment.

Onboard our ship, we had more gear on Isolation transformer banks, than most people would think, because even though we could keep the waveform at 60 cycle or 400 cycle, we still would have glitches or odd cycles. Especially if we hooked up to shore power in Europe or Asia, and had to deal with 50 cycle shore power, we still had to go through the hassle of making sure gear was able to stay online and not release the magic smoke if something goes wrong.

I have seen everything from 400 amp three phase Shore power lines turn into a bonfire, without the breaker tripping onboard the ship or on the dock, to even seeing a 400 amp Three Phase breaker get a huge hole blown out the side, along with a Bus bar get melted in half from the surge, when the afore said breaker blew out.

As for my home setup, I have made sure that everything is within code, and that grounds are good and tight, incoming telephone NID is properly grounded to Earth ground, and main panel is bonded to the Cold water pipe to make sure that is up to code.

This time of year, a lot of people forget about going out and pouring at least 5 gallons of water where their ground rod is, when there has been no rain for days, and the moisture starts getting sucked out of the ground, due to the heatwave. The last thing you want, is a ground rod in dry earth, which is no better than not having one at all.

Really Glimmie, I think that if we could just see eye to eye, and just work together, and add on to or clarify what someone states, it does help others out. So I would say if something is mashed up or too technical, I agree with you to bring it down a bit. I do tend to be more on the technical side, due to growing up around electronics and what I did in the Navy, along with dealing with electrical circuits on a weekly basis, doing side work for people when they have a problem, or even with networking setups. Being around this stuff all my life for over 40 years, you tend to look at stuff in a different viewpoint than someone that has not grown up around it, and has not really gotten hands on, but only seen most of this stuff in the books.
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post #48 of 53 Old 07-09-2013, 07:23 PM
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Originally Posted by gregzoll View Post

..... As for the BSEE, anymore it is no better than having a Associates.
And how would you know that? Just because an EE can't always walk into Home Depot and know the difference between a tandem and double pole breaker is hardly grounds for such a comment. Can you calculate neutral current on a three phase system taking into account harmonic current?
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Really Glimmie, I think that if we could just see eye to eye, and just work together, and add on to or clarify what someone states, it does help others out. So I would say if something is mashed up or too technical, I agree with you to bring it down a bit. I do tend to be more on the technical side, due to growing up around electronics and what I did in the Navy, along with dealing with electrical circuits on a weekly basis, doing side work for people when they have a problem, or even with networking setups. Being around this stuff all my life for over 40 years, you tend to look at stuff in a different viewpoint than someone that has not grown up around it, and has not really gotten hands on, but only seen most of this stuff in the books.

You think you are the only one who has a life long experience with electronics. I hear that "EE's are book theory only" all the time from technicians. While sometimes true, it's hardly the norm. Take a look at my HT site. You call that lack of practical experience? Note my house wide balanced power system installation. That's a DIY install by me. To say I need a local trade school course in electrical systems is ridiculous
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This time of year, a lot of people forget about going out and pouring at least 5 gallons of water where their ground rod is, when there has been no rain for days, and the moisture starts getting sucked out of the ground, due to the heatwave. The last thing you want, is a ground rod in dry earth, which is no better than not having one at all.
Huh? What is this supposed to accomplish? Want to tell us the engineering theory behind this?

And you still didn't show us where I gave unsafe electrical advice. OK so technically "a 240 volt breaker" is not a proper term. But in a residential setting with a UL listed panel, any double pole breaker will have 240v across it won't it? And I'll bet I can walk into any electrical supply house and ask for a 240v breaker and be handed the proper double pole type.
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post #49 of 53 Old 07-09-2013, 08:47 PM
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Originally Posted by gregzoll View Post

As for the BSEE, anymore it is no better than having a Associates..

Except no one will hire you as an engineer.

It's always funny when maintanence and techs chime in and after the fact "hindsight" engineer ****. Engineers develop solutions within constraints. Not just solutions. When you're installing something that an EE designed and wonder why they made choices they made, realize that things are the way there are for budget, lead time, or other policy reasons. I've not once had the luxury of doing things 100% the way I'd do them from my ideal development perspective. It's the engineers job to work within those constraints. That silly branch circuit you're installing, it's because the facility won't let the EE power down the distribution panel because the Union will lose the TV in the break room. That #250 cable you're pulling is because corporate moved up the installation window and the lugs you needed for the breaker had too long a lead time to run parallels. That silly obscure part your installing, instead of the off the shelf part, is because some slick salesmen took the director out for steak and titties and got him to agree to an exclusivity deal.

Just today I had some tech question about 8 decisions I made in a 5 minute period, "why didn't you do this, that would've been better, so and so manufacturer does this". My reply," if you can do that for 100k and a 6 day lead time ill put the overalls on and do your job."

electricians, techs and the like never see such constraints and should consider such when critiquing the work of others.
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post #50 of 53 Old 07-09-2013, 08:59 PM
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Originally Posted by cofn42 View Post

The max wattage of a breaker is determined by the base volts times the amp of the break to give you the total watts. Sure they may be Amp rated, but there is a direct correlation to the wattage draw.

My amps are rated by Rotel with a max draw of 800 watts each. Sure that is driving them 100% which is unlikely. But I am not going to chance putting 3 of them on a single 15amp breaker. If all 3 pull even 80% of their max load I will be overloading the circuit.

Coupled with the fact that you should never be running your circuit at much more than 80% of the total watts it can handle, putting 2 of these amps on one 15amp breaker is already nearing the 80% mark.

This is before you take into account ALL my other equipment in a theater.

All I am saying is that Greg's comments about having "too much" equipment is ridiculous, especially when most of us running a 7.1 system are already nearing or exceeding what is recommended for a 15amp breaker.

No. Breakers don't have little amp meters in them. They are, most commonly magnetic or thermal devices within the time domain. X threshold exceeded for x period of time results in a trip. Your amplifiers will spend the majority their time, unless your listening to sine wave test frequencies, drawing a very small percentage of their max or RMS capability. Those high peak transient moments likely won't occur long enough to trip the common household breaker.

The 80% mark you refer to is standard derating for breakers and applies to continuous loads. A continuous load is defined as something with a steady consumption over 3 hours IIRC, not a subwoofer blurb from war of the worlds. Non-continuous loads need not worry about the 80% derate.

That being said, multiple circuits are probably best for transient voltage drop issues in your situation.

The rabbit hole goes deeper than simple ohms law.
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post #51 of 53 Old 07-10-2013, 12:07 AM
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Originally Posted by Glimmie View Post

This is WRONG. And I doubt it's legal in an local codes. Look at it from an EE perspective. If I am pulling 35amps (assume 12ga wire) between those tow hots, the neutral will be overloaded. Sure it works most of the time because household loads are very light.

This is a hack. No true professional electrician would do this. And if a fire ever resulted, the electrician would be liable.

But your statement that many do this is true. My last house was wired this way, that is red and black to a tandem breaker. And it seems to have passed inspection too. I fixed it in short order!

Glimmie , I'm assuming you are refering to the action being wrong , not my comment about seeing this countless times . Correct me if I'm wrong in my assumption.My comment to Colm about being partially incorrect was limited to the part about "qualified electricians" not the technical aspects of his statement.
"Professional" electrician is subjective here . One who is responsible , thorough , and concerned about a quality , safe installation , no , they would not. Someone who is certified , licensed , or paid as an electrician , yes , plenty of them do. I just passed inspection on a house I took over after the licensed electrical contractor was fired , had several instances of what we're discussing , not to mention that he took out the AFCI breakers that are required by 2011 code because he couldn't get them to work with 12/3 and 14/3 because of the shared neutral . He was nice to the homeowner about it , charged the price of the AFCI's (@50ea) , cut the pigtails off of the ones he left to render them useless , then installed $5 breakers , of the wrong type so they had to be replaced as well. This is mild compared to some of the hack jobs I get to correct these days , done by legitimate , licensed "professional" electricians. I carry the information on how to lodge a complaint against a contractor in my state with me to give to homeowners , I'm seriously thinking about having the info printed on my invoices. I work both for myself and union in California , and can say that many of the big contractors have the same poor ethic , as long as the work lasts 1 year and 1 day they don't care about anything else , thats all they are obligated to warranty most of the time.


From Gregzoll : I do tend to be more on the technical side, due to growing up around electronics and what I did in the Navy, along with dealing with electrical circuits on a weekly basis, doing side work for people when they have a problem, or even with networking setups.



There are two types of Tandem breakers. There is the Single slot and double slot form factor, depending on the manufacturer and panel. The Double slot can have a handle tie on it, to tie both handles together, same goes for the Quad pole breaker. You remove the handle tie, and you have a single unit with two separate poles that can allow you to control two individual circuits that are not Multi-wire branch., or you can use it to control a device that is 240vAC or MWBC, by keeping the handle tie in place.

Technically , I don't know of a manufacturer who refers to them as "tandem" , and for an example , Murray ( Crouse-Hinds) refers to theirs as duplex, triplex and quadplex , so there are 3 types from them.


Quote : A single slot can only be used for MWBC or a 240vAC circuit, if you have two in two single slots, and tie the handles in a way, that the two middle handles are tied together. A Single slot Tandem is not the best way to create a MWBC circuit or sistering with another breaker next to it in another slot on the other leg, because they were not intended for that.

First off , the first statement , HUH? A single slot in no way or form can be used for anything except HALF of a MWBC. Secondly , are you saying that the outer , linked , common trip handles of a quadplex can not be classified as providing MWBC ? You also say "tie the handles in a way..." insinuating linking them yourself , then you say "sistering" is not the right way to do it , but if you tie handles together to achieve a MWBC the only way to do it would be to "sister" , otherwise , how would you achieve voltage between the load wires ? A single slot duplex can not create a MWBC because it is drawing from a single stab , or slot on the buss. Just buy the right breaker for the job , If you need MWBC , then get a triplex or quadplex ( or whatever the manufacturer calls theirs). Working on obsolete panels , there is sometimes need to "sister" with the proper handle tie , either the bracket type or the pin type , but if breakers are still readily available , get the right tool for the job. I do agree that sistering is not preferred , but sometimes you have to set aside your preferences , but never safety, for the benefit of the client.
Saying "there is no such thing as a 240v breaker" is foolish when you yourself use nicknames for electrical equipment. walk into ANY Home Depot , Lowes , local hardware store , or electrical supply house and ask for a xx amp 240v breaker and guess what happens, they will put one in your hand. You might get a pompous ass who feels like correcting your terminology every once in a while , but you still get the same damn part that you asked for . I'm rusty on this point and don't feel like opening the book , but I believe that breakers are UL listed , and modifying a device negates it's UL listing , so a 2 pole common trip breaker installed in a split phase residential panel can only supply 240v , so it is in effect a 240v breaker. Remove the handle tie , you have a non-compliant device in the panel that you are liable for.

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post #52 of 53 Old 07-10-2013, 12:27 AM
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People tend to have various definitions of what is a professional. I think the dictionary defines a professional as one who is paid for their work?

But in my vocabulary, any electrician that ties two hots to the same phase and only supplies a single neutral with those two hots is not a professional.

It's just that simple.
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post #53 of 53 Old 07-10-2013, 11:19 AM
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Originally Posted by Glimmie View Post

People tend to have various definitions of what is a professional. I think the dictionary defines a professional as one who is paid for their work?

But in my vocabulary, any electrician that ties two hots to the same phase and only supplies a single neutral with those two hots is not a professional.

It's just that simple.

Agreed, and unfortunately a "professional" (dictionary definition) can make that mistake, and even worse, hundreds of times, and there is NO provision to take away their certification or license. If an inspector catches it ( and some don't) then they just have to correct that one, most likely will continue doing it wrong.
I wish there was a reporting and documenting system for inspections, too many failed inspections and the state reviews your license or certification. If they see a pattern of short cuts or poor craftsmanship, you have to take classes or lose your cert. Major property damage or loss of life because of gross negligence in the installation, lose license or cert. and criminal charges. The only way to improve the industry is to have consequences for our actions, there are none now. 2 years ago I could have wired a house in every city around me that I can think of , 12/3 2 circuits same phase, and I would have over a 70% chance of passing inspection. AFCI requirements negate that chance now, mostly, but I guarantee I could do a commercial panel and get it passed.

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