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Old 10-06-2009, 10:36 PM   #1
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Subpanels Nightmare in Baltimore


My 1875 historic house has been used for the past 50 years as 2 apartments. After doing major work, the electrical inspector made it impossible to keep it that way, so I have 3 new panels (100A, 100A and 60A) which I need to combine under one meter, as a single family home. My questions are:

1. Do the main panels qualify as sub-panels? Do they just just get wired to a BIGGER panle with 3 breakers, each having the rating of the sub-panel it is connected to?

2. Do the breakers have to be 100A, 100A and 60A? I have 2 AC units, 2 water heaters, one kitchen, electrical dryer --- a 3 bedroom, 3 bathroom setup.

3. What hardware is used for this> a regular 200A pannel sufficient? or does it have to be equal to the sum of the individual panels ($260A)?

BTW, my electrician is suggesting that one of the 100A panels be replaced with a 200A, and the 2 other panels be connected htough it uisng 100A and 60A breakers. Someting quationable abou it!!! please advice. Thank you,

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Old 10-06-2009, 10:55 PM   #2
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Subpanels Nightmare in Baltimore


1. The term subpanel does not appear in the National Electric Code so far as I know the term is a branch wire circuit. However, for us mortals, I believe that each of the panels could be wired as a "subpanel" off of a main disconnect. I believe the code allows up to six "subpanels" off of a single main disconnect.

2. If you mean the breakers in the new main disconnect (the main panel), they should be equal in size to the breaker in each subpanel. If you mean the breakers in the subpanels, they cannot exceed the rating of the panel or the feeder wire, i.e. if you are going to wire a subpanel as a 100A panel, you will need to feed two #4 Cu hots (or possibly #3 Cu depending on the interpretation of the local electrical code official), a #4 or #3 Cu neutral (may be allowed to use a #6 Cu, again depending on local official), plus a #6 Cu independent equipment ground.

3. A 200A panel will be fine, you might as well get one with a 200A breaker, assuming your service is rated for 200A. From the sounds of it, you are getting a new meter, might as well install a 200A service while you are at it. The total load on a service is determined by load calculations set out in the NEC, but it seems very unlikely that you would come close to 200A load for a single family house, so a 200A service should be just fine.

As for the electrician's advice to replace one of the 100A panels with a 200A panel, that sounds pretty reasonable, as it would leave you with a 200A main panel, probably with 40 positions or so, plus a 60A subpanel and a 100A subpanel, should be more than adequate for a single family house. Can't really imagine you would need 2 100A subpanels plus a 60A subpanel plus a 200A main panel, but hey, maybe you have lots of electrical toys.

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Old 10-07-2009, 01:39 AM   #3
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Originally Posted by Daniel Holzman View Post
If you mean the breakers in the subpanels, they cannot exceed the rating of the panel or the feeder wire

Why not? Say I put a 50A breaker in my main panel and then I run #6 to the subpanel. Why can't I use a 100A main breaker panel as that subpanel? The 100A breaker will never trip as the 50A in the main panel will trip first and protect the #6 wire. The 100A breaker is effectively a local disconnect and not a OC device. Obviously (and maybe this is what you're saying) I now have a 50A subpanel and I can't put 100A of load on it.
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Old 10-07-2009, 07:36 AM   #4
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Thank yiou Daniel, and thanks Walden. This makes it simpler, but the part I am still confused about is the breaker in the disconnect box. If the 3 sub-panels are fed in parallel, does that mean that I need 3 disconnects with 3 breakers? and what hardware is used for that?

Now, to downgrade the capacity of a panel, say for example I am using 60A on a 100A panel, do I just replace the main disconnect inside that panel to 60A?

At this point, feeding one panel from another seems to get me same results, with less wiring, but will complicate the ""leveling" of the load (in a big 200A panel, plenty of devices to go on/off keep the load steady), but in a smaller setup fluctuates wildely. Should this be a concern for the option of not running the sub-panels in parallel?

Thanks again.
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Old 10-07-2009, 07:40 AM   #5
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Quote:
Originally Posted by AJ1962 View Post
1. Do the main panels qualify as sub-panels? Do they just just get wired to a BIGGER panle with 3 breakers, each having the rating of the sub-panel it is connected to?
The two panels that will become sub-panels will just have to have the grounds and neutrals separated and the bonding jumper removed.



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Originally Posted by AJ1962 View Post
3. What hardware is used for this> a regular 200A pannel sufficient? or does it have to be equal to the sum of the individual panels ($260A)?
A new 200A service will be fine feeding two other sub-panels.



Quote:
Originally Posted by AJ1962 View Post
BTW, my electrician is suggesting that one of the 100A panels be replaced with a 200A, and the 2 other panels be connected htough it uisng 100A and 60A breakers. Someting quationable abou it!!! please advice. Thank you,
Sounds fine.



Quote:
Originally Posted by Daniel Holzman View Post
1. The term subpanel does not appear in the National Electric Code so far as I know the term is a branch wire circuit.
So WHAT??? EVERYONE uses the term "sub-panel". Every electrician I know and every inspector.
And no, there is no term "branch wire circuit".



Quote:
Originally Posted by Daniel Holzman View Post
However, for us mortals, I believe that each of the panels could be wired as a "subpanel" off of a main disconnect. I believe the code allows up to six "subpanels" off of a single main disconnect.
NO, you can have as many sub-panels as you like. Some industrial setting have dozens of them.
You can have up to six MAIN panels though.



Quote:
Originally Posted by Daniel Holzman View Post
2. If you mean the breakers in the new main disconnect (the main panel), they should be equal in size to the breaker in each subpanel. If you mean the breakers in the subpanels, they cannot exceed the rating of the panel or the feeder wire, i.e. if you are going to wire a subpanel as a 100A panel, you will need to feed two #4 Cu hots (or possibly #3 Cu depending on the interpretation of the local electrical code official), a #4 or #3 Cu neutral (may be allowed to use a #6 Cu, again depending on local official), plus a #6 Cu independent equipment ground.
Completely wrong. You can feed a 200A sub-panel with 40A if you like.
The feeder breaker protects the feeder conductors


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Answers based on the 2008 & 2011 NEC.
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Old 10-07-2009, 12:45 PM   #6
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Subpanels Nightmare in Baltimore


I have one thing to add. Check to make sure that there are no old 3 wire (hot, hot, neutral) range or dryer circuits that originate at the 2 main panels that are gonna get converted to subpanels. The three wire circuits cannot originate at a subpanel. Not a big deal if all the panels are right next to each other, (you can move them to the main panel) but could be a pain if they are on the other side of the house or a different floor.
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Old 10-07-2009, 05:58 PM   #7
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Quote:
Originally Posted by Daniel Holzman View Post
1. The term subpanel does not appear in the National Electric Code so far as I know the term is a branch wire circuit. However, for us mortals, I believe that each of the panels could be wired as a "subpanel" off of a main disconnect. I believe the code allows up to six "subpanels" off of a single main disconnect.

2. If you mean the breakers in the new main disconnect (the main panel), they should be equal in size to the breaker in each subpanel. If you mean the breakers in the subpanels, they cannot exceed the rating of the panel or the feeder wire, i.e. if you are going to wire a subpanel as a 100A panel, you will need to feed two #4 Cu hots (or possibly #3 Cu depending on the interpretation of the local electrical code official), a #4 or #3 Cu neutral (may be allowed to use a #6 Cu, again depending on local official), plus a #6 Cu independent equipment ground.

3. A 200A panel will be fine, you might as well get one with a 200A breaker, assuming your service is rated for 200A. From the sounds of it, you are getting a new meter, might as well install a 200A service while you are at it. The total load on a service is determined by load calculations set out in the NEC, but it seems very unlikely that you would come close to 200A load for a single family house, so a 200A service should be just fine.

As for the electrician's advice to replace one of the 100A panels with a 200A panel, that sounds pretty reasonable, as it would leave you with a 200A main panel, probably with 40 positions or so, plus a 60A subpanel and a 100A subpanel, should be more than adequate for a single family house. Can't really imagine you would need 2 100A subpanels plus a 60A subpanel plus a 200A main panel, but hey, maybe you have lots of electrical toys.
This is a mistake a lot of laymen (Lay persons, really. To be Politically Correct.) are making. They tend to think the sum of the loads is additive.
I had a customer (1-Family Home) who argued with the Utility rep. about increasing the size of the Service above 200 Amps. (The Max per residential customer). His thought process was that all the loads (capacity) is/are additive. I had a hard time convincing that "a reasonable person does not put all the lights and all other appliances on at the same time"! Eliminate Confusion Through Education!!!

Last edited by spark plug; 10-07-2009 at 06:00 PM. Reason: Clarification of statement
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Old 10-07-2009, 06:06 PM   #8
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Subpanels Nightmare in Baltimore


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Originally Posted by WaldenL View Post
Why not? Say I put a 50A breaker in my main panel and then I run #6 to the subpanel. Why can't I use a 100A main breaker panel as that subpanel? The 100A breaker will never trip as the 50A in the main panel will trip first and protect the #6 wire. The 100A breaker is effectively a local disconnect and not a OC device. Obviously (and maybe this is what you're saying) I now have a 50A subpanel and I can't put 100A of load on it.
Precisely. Cutler Hammer has that Caution on all Twin Breakers. "This Breaker is not CTL and is for replacement Only"! (No matter what) Don't Drink and Drive, Ever!!!
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Old 10-07-2009, 06:07 PM   #9
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What's "CTL"?
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Old 10-07-2009, 06:12 PM   #10
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OK Speedey, let me rewrite #2 a little more clearly. If you want to have a 100A capacity subpanel, you need to feed it from upstream with 100A capacity wire, plus you need a 100A breaker upstream. While you certainly can feed a 100A subpanel with 40A wire and breaker, it wouldn't be a 100A capacity subpanel. It would be a 100A rated panel with a maximum capacity of 40A, in the sense that as soon as you loaded it to 40A the upstream breaker would trip. So what I was trying to say was that it would not make a lot of sense to put a lower ampacity breaker upstream of a 100A subpanel.

Second, I was trying to indicate that the maximum size breaker you can put in a subpanel is limited by the smaller of:

* the maximum rating of the subpanel or
* the maximum allowable ampacity of the downstream wire (which I mistakenly referred to as the feeder wire)

So if you have 60A rated wire downstream of a subpanel, you cannot use larger than a 60A breaker in the subpanel.
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Old 10-07-2009, 06:17 PM   #11
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Originally Posted by Speedy Petey View Post
The two panels that will become sub-panels will just have to have the grounds and neutrals separated and the bonding jumper removed.



A new 200A service will be fine feeding two other sub-panels.



Sounds fine.



So WHAT??? EVERYONE uses the term "sub-panel". Every electrician I know and every inspector.
And no, there is no term "branch wire circuit".



NO, you can have as many sub-panels as you like. Some industrial setting have dozens of them.
You can have up to six MAIN panels though.



Completely wrong. You can feed a 200A sub-panel with 40A if you like.
The feeder breaker protects the feeder conductors


.
But the opposite way. If you're going to put a 160 Amp, load on a 100Amp. subpanel, which is fed by a 200Amp. feeder, you'll burn up the sub.
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Old 10-07-2009, 06:30 PM   #12
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Daniel, I'm with you on the first paragraph, you've limited your 100A subpanel to be a 40A subpanel. But I'm confused by your second point. When you say "downstream" do you mean between the main panel and the subpanel, or between the subpanel and the branch circuits.

Say you've got a main panel with a 40A breaker. That 40A breaker feeds #6 wire to a subpanel that's rated at 100A. The subpanel has a 100A "main" breaker, and then feeds 5 20A branch circuits. Assuming the load calc says the combined load is < 40A I don't see a problem. The 100A breaker isn't a code violation, nor is it unsafe. It's simply a big on/off switch. The OC device is the 40A breaker in the main box. Right?
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Old 10-07-2009, 06:36 PM   #13
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You can have a 100a main breaker sub & feed it with a 60a breaker in the main panel

You CAN'T have a 60a subpanel & feed it with a 100a breaker in the main panel
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Old 10-07-2009, 07:58 PM   #14
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You can have a 100a main breaker sub & feed it with a 60a breaker in the main panel

You CAN'T have a 60a subpanel & feed it with a 100a breaker in the main panel
I brought up that second, Hypothetical example. But in reality, any job done professionally, (whether by DIY or Professional electrician) will match the protection in the main panel to the projected load in the subpanel. But sometimes, provisions are made for when someone goofs up, things still should not burn or explode. (No matter what)Don't Drink and Drive, Ever!!!
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Old 10-08-2009, 12:23 AM   #15
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What's "CTL"?
Circuit Limiting.

Breaker boxes are generally manufactured to physically reject more circuit breakers than they are designed to hold.

The use of "tandem" breakers can allow one to install more circuits than a panel has spaces for, so they make "Class CTL" to comply with UL requirements.

A panel will reject CTL breakers if one attempts to install them in a non-tandem slot.

The use of non-CTL breakers circumvents these requirements. This is why they are labeled "for replacement use only"

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