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Discussion Starter · #1 ·
Here's a question for you electrical experts / contractors. I did a brief search through the NEC and couldn't find anything prohibiting this. Anyway, here it goes:


I'm helping my neighbor design his media room and he has 200 amp service at his service panel on one end of the house in the garage. On the other end of the house down in the basement, the house has a 100 amp sub-panel installed in the HVAC/utility room, which is almost full (2 slots open, enough for 2 breakers or 4 circuits using skinnies). The HT equipment room is not going to be too far from this HVAC room, and the walls and ceiling joists between the two are unfinished. I would say there is probably 90' of 2SER cable connecting these two panels (big nasty stuff which is needed for 100A).


While we could probably get by with 4 circuits, both he and I agree that we don't want to fill up the panel leaving no room for expansion since more of the basement will need refinishing later. Another option is to replace the subpanel with a larger one (why the original builder spent over $100 in 2SER cable and then put on a $20 panel is beyond me). However, the solution we both think that the ideal option labor-wise would be to just daisy chain to another subpanel either mounted on the same service board in the util room, or run right to one in the equipment room.


In summary, you would have the main service panel (200A) feeding a 100A subpanel, which would in turn have a 50A or 100A breaker in it feeding yet another 50A or 100A subpanel. I've never seen this done before, and can't find anything in the NEC prohibiting it (unless I overlooked something), and if done properly I can't think of any reason as to why it would be unsafe; but the fact that I've never seen this before bothers me a bit (thus the reason for the post).


Does anybody know if there are any issues with this?
 

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There is absolutely no problem doing this. Just remember to continue the practice of separate neutrals (insulated grounded conductors) and grounds (bare grounding conductors). The neutral and ground are always separate past the first main disconnect (exceptions aside).


The existing #2 feeder should have an insulated neutral and a bare ground, and the sub-panel should have a neutral bus insulated from the panel, and a grounding bus tied to the enclosure. You should continue this with your new feeder and panel.


Unless you're going to install an incredible AV system and lighting system, a 30-amp sub-panel should be more than enough. You can feed four or six single 120-volt circuits from a 240-volt 30-amp panel with no problem; the main doesn't need to equal the sum of the circuits.


(When I say 30 amps, I'm referring to the circuit size; the panel you buy will probably have a 125-amp rated capacity, but as long as the breaker protects the wire (#10 for 30 amps), that's what determines the circuit rating.)
 

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I just installed exactly as Larry just explained in my own theater. There was a subpanel right on the other side of one of my walls with room in it to handle the Ht but I have to go outside to get to it (utility room) in the event of a trip. I decided to go with very small sub panel right in the HT. 30 amps feeding four positions but I could add to it with split breakers.
 

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Larry, not an issue for this thread but isn't there something in the code about no more than six disconnecting means on a circuit? I read that as no more than six breakers or disconnect switches between the device or outlet and the service enterance.


My guees is that it has something to do with voltage drop across each breaker which we all know happens.
 

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Discussion Starter · #5 ·
Thanks for the answers folks, I figured it was ok, but it doesn't hurt to ask.
 

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Well, Glimster, let me start here: The '96 NEC (still in force here), Art. 230-71, says, in part:


"The service disconnecting means...shall consist of not more than six switches or six circuit breakers..." The idea is that an entire service can be disconnected "with no more than six operations of the hand."


If your panel doesn't have a main breaker, then there is one (or two) breaker(s) that is labeled 'main' and will de-energize the lighting/receptacle circuits, and the rest of the 240-volt breakers are heavy-appliance circuits, and a maximum of six breakers will disconnect the entire house.


That's the only reference to 'six' I could find, other than no more than six services grouped together (like a strip-mall or apartment-building electric service). These all refer to parallel connections, not series.


If anyone else knows of a reference to a limit on the number of panels a circuit may be powered through, I'd be interested to know.
 

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Quote:
Originally posted by Larry Fine
Well, Glimster, let me start here: The '96 NEC (still in force here), Art. 230-71, says, in part:


"The service disconnecting means...shall consist of not more than six switches or six circuit breakers..." The idea is that an entire service can be disconnected "with no more than six operations of the hand."


If your panel doesn't have a main breaker, then there is one (or two) breaker(s) that is labeled 'main' and will de-energize the lighting/receptacle circuits, and the rest of the 240-volt breakers are heavy-appliance circuits, and a maximum of six breakers will disconnect the entire house.


That's the only reference to 'six' I could find, other than no more than six services grouped together (like a strip-mall or apartment-building electric service). These all refer to parallel connections, not series.


If anyone else knows of a reference to a limit on the number of panels a circuit may be powered through, I'd be interested to know.
Ah, now I think I get it. You must be able to totally disconnect a building with no more that six breaker or disconnect operations. This is what the pro's must mean by the old phrase "six throws of the hand".


So there is really no limit to how many disconnects may in SERIES to a device or panel?
 

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None that I'm aware of. There is no "series resistance" that breakers are rated with.
 

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I think the only thing you need to watch out for is voltage drop. A 2% maximum drop on a feeder is typical, I think. With two feeders in series, if both were at 2%, that would be 4% just from the feeders, plus whatever is in the branches themselves.


You just need to run the calculations for the distances you're running, and maybe go to a larger guage wire if necessary.
 
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