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Sub Panel Install – Conflicting Recommendations

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Old 09-20-09, 06:42 PM
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Sub Panel Install – Conflicting Recommendations

I’ve done a lot of reading on this site as well as on others about how to install a load center sub-panel inside a residential home. However, I’ve run into a glitch in my understanding about a couple of aspects for the project and I could use some help in sorting things out.


A little background:
I have a close friend who’s a licensed electrician that volunteered himself to help me with my sub panel project. (I know…already sounds like trouble, huh?) I wasn’t even going to mention the project to him, but our wives “talk”.

One reason I wasn’t going to mention it is that I normally don’t like to ask for professional services from my friends. The other reason is that this fellow really doesn’t “do” residential. He’s spent most of his career doing large commercial projects with a multi-national contractor. He also readily admits he’s not “100 percent” up on residential code…something he didn’t mention until later.

At any rate, he’s insisted on helping. He came over and scouted the project and he’s told me what materials I need to get. He’s out of town on a job for the next a couple of weeks, and we’re supposed to get back together after I’ve purchased everything.


Here’s the project:
I have a Cutler Hammer BR 200 amp main panel in my 12-year-old home’s attached garage. It’s wired with 20 amp breakers, but it has only two vacant breaker spaces left (alternate legs). I wish to install four (and eventually more) dedicated circuits to feed some higher-end audio gear. Installing a sub panel appears to be the way to go. Wiring for the sub panel’s circuits will be 10/2 copper.

(I know…dedicated circuits and over-spec wire gauge probably don’t seem necessary to most folks here, but its just part of my hobby’s madness. My friend has agreed to humor me. I hope folks here will also.)

Instead of pulling several 10/2 runs back to a sub panel in the garage, plans are to instead put a sub panel in the room that houses the equipment (i.e., in the same structure as the main panel). My electrician buddy figures we’ll need about 80 feet of feeder. This feeder wire will be strung freely up into attic space above, and droped into sheet-rocked interior walls.


Now here’s where I’m a bit confused:
My buddy’s instructed me to buy a 100 amp “one-way” breaker for the main panel. I could be wrong, but I’m assuming he meant a single pole breaker?? He also told me to buy a 100 amp sub panel WITH a 100 amp breaker. In other words, I guess he’s specified that he doesn’t want to use a lug panel.

Individual breakers will be 20 amp. He’s also specified that I buy a #3 copper wire feeder cable that contains three conductors, plus safety wire.

Now…from my research, unless code specifically calls for it (and I’ve reason to believe it doesn’t in my area), it appears most installations of this type use a lug panel…or at least don’t install a main breaker in the sub panel. From what I gather, the 100-amp breaker that the feeder wire is tied to in the main panel is all that’s necessary.

However, my concern isn’t whether or not we will be using a main breaker in the sub panel. My concern has to do with the wiring phase and voltage that’s being fed to the sub panel. One of the main goals for the project is to be sure all the circuits that feed the audio equipment are wired to the same phase, or leg.

If I’ve understood my friend’s terminology correctly, and if in fact he intends for me to purchase a single pole 100 amp breaker…. what exactly will be fed to the sub panel? I assume it will be 120v…no? If so, would this mean that both sides in the sub panel will be on the same phase?

Most recommendations I’ve seen on the audio forums is to feed the sub panel 120/240v and use alternating breaker rows for the audio gear. Circuits for miscellaneous other equipment can then be put on the opposite sub panel leg. To feed 120/240v wouldn’t I need to install a double, or two-pole, breaker in the main panel?


Last question:
When he said get a three conductor #3 Cu cable, what the heck type of cable should I be looking for? I’ve worn google out searching for such a cable. Am I looking for THHN…SE…what?

Also…I assume that since I’ll be buying it as a cable, I’ll only need one 80 foot run, right? (I know the question seems obvious, but I had to ask.) Since I’m sure the big box stores wouldn’t carry it, would this be something a local electrical supply house would stock and sell by the foot? Is there any place to get it online?

Well, for all who’ve stuck with this post to read this far, you have my thanks. I’d be even more grateful if someone would be so kind to offer a little info and advice.

Thanks,

JD
 
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Old 09-20-09, 08:18 PM
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I will try to answer and then you can follow up.

I have never heard of a one-way breaker. If you were to feed the panel with a single pole you would only have a 120 panel and every other leg would not have power.

You do not need a main breaker in the subpanel as this is an attached structure. You can use one if you wish.

If you are planning on a conduit system you would use THHN and would need 4 conductors. For a cable you could use SER.

I am not an audiophile, but will make some comments. The 100 amp panel you are planning is way more than you would need for an audio system and home theater. A 50 amp sub should still be overkill.

I may have missed some points so followup.
 
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Old 09-20-09, 09:20 PM
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The only things I can add is:

Why would want (or care) if the circuits are fed off the same leg? It shouldn't matter AFAIK. Plus, you will artificially load up that one phase.

Some times a main breaker panel is cheaper or a better value than a main lug panel because manufactures toss in "free" breakers. There is nothing wrong with a main breaker panel and it can even be handy.

I think you would have a VERY hard time finding a 100 amp single pole breaker. I'm sure he ment two pole.

If you cant find the cable at a home center (which they may carry) then most electrical supply house will carry it in stock or will get it in one day.

I also agree with PCboss. Save the money and frustration and go with a 50 or 60 amp sub panel. It will be plenty big. Spend the money on some more high end gear.
 
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Old 09-21-09, 09:01 AM
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Thanks, Tolyn & PC Boss. Sounds like I probably got my wires crossed concerning his mention of a 100 amp "one-way breaker". The install won't be anything out of the ordinary, so I'm sure he didn't mean for me to try and locate a specialty item. I'll pick up a two-pole breaker and go with that.

As to amperage...I too wondered why a 100amp breaker. I'm not even sure my main panel is spec'd for this size. I'll check though, and if it's rated for something lower, that's what I'll buy.

Thanks also for the comments regarding using a main breaker in the sub panel. Thinking about it a little more, I too can see where it might be beneficial in certain cases.

Question: If I end up with using a main breaker in the sub panel, I assume it has to be the same amperage that I install in the main...right?

Also appreciate helping me out on the type of cable I'm looking for, PC Boss. I know these things are second nature to folks like yourself, so thanks for bearing with me.

And finally...
Originally Posted by Tolyn Ironhand View Post
The only things I can add is:

Why would want (or care) if the circuits are fed off the same leg? It shouldn't matter AFAIK. Plus, you will artificially load up that one phase.
In the audiophile world, clean power is a BIG deal these days. My equipment is certainly not up there with the big money boys...and I'm not sure I subscribe to all the theories about it. But basically, the idea for putting your gear (at least, your most sensitive gear..preamps, turntables, etc.) on one leg is primarily to avoid voltage variations between the two phases. Also...folks try to keep big motor and switching devices on the opposite leg in an effort to reduce noise or AC hash (i.e., fluctuations). Additionally, since the individual components will be fed from different (dedicated) circuits...but remain all connected via interconnecting cables...it's thought that having everything on one phase reduces the chance for ground loops.

Let me tell you...it's crazy what some folks are doing for clean power. Hi-end power conditioners are now reviewed in audio publications like they were another component. The top one's retail for 4 to 5 thousand dollars!

And it doesn't stop there. Take a look at this subpanel from Isoclean (wish I could post a pic). Retails out at $5,500, I believe...but the site I've linked to is offering it a bargain price of $4,998. Hmmm...wonder if that includes free shipping?

Thanks again, guys, for the info and advice. I think I have a better direction now. Hope I've brightened your day and perhaps given you a laugh by providing a glimpse into the outrageous world of hi-end audio.

JD
 
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Old 09-21-09, 09:10 AM
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Originally Posted by JD Taznor View Post
He also told me to buy a 100 amp sub panel WITH a 100 amp breaker.
I agree the 100A is huge if you're only powering home theater stuff with it (even an enormous home theater). I used to work at a small theater and we had 50A to the entire audio system for a 1000 seat venue which could easily be heard down the street at times.

One of the main goals for the project is to be sure all the circuits that feed the audio equipment are wired to the same phase, or leg.
That is not important in residential wiring as both legs are fed from the same transformer. It is only a concern in commercial three-phase systems which can be fed from transformer banks instead of a solid core multiwinding transformer. A residential service is only ever a single phase split into two legs so you really don't have to worry about harmonics between the legs.

Most recommendations I’ve seen on the audio forums is to feed the sub panel 120/240v and use alternating breaker rows for the audio gear.
You can do if you wish, but there really isn't any reason to do so other than superstition. In fact, by loading up one leg you double your voltage drop which probably has a much more detrimental effect on the equipment and overall performance.
 
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Old 09-21-09, 09:16 AM
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You will not find a main breaker smaller than 100 amps. You can feed this with a smaller breaker in the main panel without problems. At that point it is just a large on/off switch for the panel.

If you go with the smaller 50 amp panel you could use #6 NM-B cable.

You will also need proper working clearances around your subpanel. 30 inch width x 36" deep, no closet.

I have read some of the hype? regarding clean power and oxygen free cables and the like. I think most of it is snake oil. Silver plated receptacles for $50, isolated grounds in a house where there is no need etc. The human ear is only so sensitive. If the only difference is measureable with test equipment who cares? I have heard systems that were run over CAT5 wiring that sounded just as good as one using Monster cables.

You could possibly run your whole setup from 1 circuit and avoid your issues regarding noise etc.
 
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Old 09-21-09, 09:19 AM
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Originally Posted by JD Taznor View Post
If I end up with using a main breaker in the sub panel, I assume it has to be the same amperage that I install in the main...right?
No it doesn't. The breaker in the main panel protects everything downstream. The main breaker in the subpanel acts only as a disconnect, not an overcurrent protection device. You won't be able to find a main breaker less than 100A anyway because no one makes one.

Let me tell you...it's crazy what some folks are doing for clean power.
Yes it is crazy as most of those recommendations are fabricated to sell expensive equipment. Very little of it is supported by any sort of engineering or scientific analysis. Much like healing crystals and those "enhancement" pills we all see in our inboxes daily.
 
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Old 09-21-09, 11:55 AM
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Don't forget the flashing LEDs that cure everything from arthritis to cancer. Too bad they don't cure gullibility.
 
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Old 09-21-09, 03:31 PM
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Possibly the feeder conductors could terminate on a 2-pole CB it's own seperate enclosure.The 2-pole CB could protect two 2-wire, 120 volt sub-feeders to two main-lug sub-panels , one for the audio circuits , and the other for general-pupose receptacles and lighting. Each panel would need a 2-pole CB with a jumper between the terminals as a "bridge" linking the two panel buses together. ( I know, $$$$ ).

The power-capacity of each panel = 120 X the ampacity of the Feeder;
60 amp Feeder = 7200 watts , 100 amp Feeder = 12,000 watts
 
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Old 09-21-09, 03:44 PM
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Originally Posted by pcboss View Post
If you go with the smaller 50 amp panel you could use #6 NM-B cable.
#6 NM-B may be protected by a 60 amp breaker. (55 amps on the 60 degree column bumped up to 60 due to no 55 amp breaker available) IMO - 60 amps is the way to go.

Originally Posted by pcboss View Post
You will also need proper working clearances around your subpanel. 30 inch width x 36" deep, no closet.
A closet is OK as long it is NOT a clothes closet. If the closet is for the equipment AND the clearances above are maintained in front of the panel, then you should be OK.

Question: If I end up with using a main breaker in the sub panel, I assume it has to be the same amperage that I install in the main...right?
I think this was answered but I will reiterate: The breaker in the main panel protects everything down stream from there. You need to size the breaker according to the wire you run.
IE: If it is #6 NM-B (romex) than you must use no larger than a 60 amp breaker. If it is #3 THHN in conduit, then you can use no larger than a 100 amp breaker.

The sub panel you choose must be rated equal or greater than the breaker that you install in the main panel.
IE: You can have a 60 amp in the main panel and a 100 amp sub panel but you can't have a 100 amp in the main panel and a 60 amp sub panel.
 
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Old 09-21-09, 06:56 PM
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Originally Posted by Tolyn Ironhand View Post
#6 NM-B may be protected by a 60 amp breaker. (55 amps on the 60 degree column bumped up to 60 due to no 55 amp breaker available) IMO - 60 amps is the way to go.
As of right now, going with a 60 amp CB in the main panel would sure make things easier on my end. I checked with the big box stores as well as a couple of nearby small electrical supply places, but no one stocks #3 Cu SER cable. Can't locate it online either (which I find surprising)...at least not cut in a length I would need it.

A closet is OK as long it is NOT a clothes closet. If the closet is for the equipment AND the clearances above are maintained in front of the panel, then you should be OK.
Understand, but no...the sub panel won't be going in a closet and will have the necessary clearance.

I think this was answered but I will reiterate: The breaker in the main panel protects everything down stream from there. You need to size the breaker according to the wire you run.
IE: If it is #6 NM-B (romex) than you must use no larger than a 60 amp breaker. If it is #3 THHN in conduit, then you can use no larger than a 100 amp breaker.

The sub panel you choose must be rated equal or greater than the breaker that you install in the main panel.
IE: You can have a 60 amp in the main panel and a 100 amp sub panel but you can't have a 100 amp in the main panel and a 60 amp sub panel.
Got it. Makes perfect sense, and I appreciate you spelling it out.

And PATTBAA...what can I say? It sounds like you've done some creative thinking on this one. A little over this layman's head, but I appreciate the idea for a different approach.

At this point, I'm thinking I'll wait until I can talk to my electrician friend before I purchase anything. I want to tactfully suggest we use a 60amp breaker in the main panel. From the feedback I've received here I can't imagine he would have an objection. However, he is the pro on this job I want to get his buy-in.

Thanks again everyone.
 
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Old 09-21-09, 10:38 PM
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Originally Posted by JD Taznor View Post
no one stocks #3 Cu SER cable. Can't locate it online either (which I find surprising)...at least not cut in a length I would need it.
Just to be clear on the 100A option, if you used SER cable it would need to be #2 copper (probably 2-2-2-8 or 2-2-4-8). THHN copper in conduit could be #3-3-3-8. I know it's confusing but the different wiring methods have different maximum temperature ratings, so sizes must be adjusted accordingly. That's probably why you're having trouble finding #3 SER.

The 60A option would be wired with #6/3g NM-B "Romex" cable.
 
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Old 09-22-09, 10:27 AM
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Thanks. I really appreciate you taking the time to detail out the fine points for what to use as a feeder cable.

I've done some additional reading about how wire is specified in the trade and found it quite interesting. A bit confusing at first as you say, but I think some of it is starting to gel. Actually, I've enjoyed reading and learning about all the aspects of residential electric power. My hat is off to the pros that work in this field. There are so many factors to be aware of, and even a small mistake can turn out to be deadly.
 
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Old 09-22-09, 11:25 AM
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If you're interested in further reading, article 310 "Conductors for General Wiring" of the NEC (National Electric Code, NFPA 70) is where this all comes from. It's a little dense to use as teaching material, but you can learn all you want about wiring sizing if you read through it. Specifically table 310.16 gives the allowable ampacity for various size wires at various temperature ratings. Generally speaking, cables such as NM-B "Romex", SER and UF-B are restricted to 60°C, conductors in conduits are restricted to 75°C, and the 90°C column is reserved for special uses only. I say "generally", because there's a lot of give and take which can adjust the ampacities based on the situation.
 
 

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