For new electrical service boxes:
Are they "generally" constructed to take either two of the half-thickness
breakers or a single full
thickness one ? I guess I am asking if the slot positions are generally
designed for either the two, or one, but you don't have an option ?
How about the older ones; how were they designed ?
Is there any disadvantage to the half-thick circuit breakers ?
It varies by manufacturer. There is usually a label inside the panel or the
panel cover stating what breakers the panel is approved for. If you are
shopping for an electrical panel you might see a designation on the box that
reads 20/24 or 30/40 or something like that. In the case of a 30/40 it
would interpret as 30 full size breakers total or if you want 40 circuits
you can use 20 full size breakers with 20 thin or 10 tandem (Twin) breakers.
I tend to like the full size breakers because they usually fit into the
panel with less trouble.
yeah most boxes will take the thin breakers but I dont believe they are
as durable. my old boxes have. thru 2 or 3 homes. thin breakers cost a
if your upgrading to a new service get the biggest cabnet you can with
200 amp service. it will leave room for expansion.
200 amp usually has more slots than 100 amp
The boxes aren't designed to fit the breakers, the breakers
are designed to fit the boxes. Specifically,
a duplex breaker is designed to fit in a single slot in
the panel, and serve two hots, independantly.
The only drawback (other than cost) is that the enclosure
itself is only rated for a certain number of connections,
so you can't just keep swapping duplex breakers for
normal ones until you run out of space.
If you're lucky, the upper limit is written on the box
somewhere. It does NOT appear to be related to the
number of open spaces on the ground and nuetral bars,
which are always undersized. (Can anyone explain
why that is?)
Depending upon the manufacturer, some panels can use either full or half
sized breakers in all buss locations, some buss locations or not at all. For
example if a panel is designed to use 40 full sized breakers, it won't use
any half sized breakers as the maximum amount of poles allowed in any panel
is 42. Some panels will use 20 full sized or 40 half sized, or any variables
with a max of 42
Aside from the other points. A double breaker might be connected to the
same phase or opposite phases in the panel. If they are on the same phase,
you need seperate branch conductors each with its own neutral but if the two
poles of the double breaker are on different phases, you can use a 3
conductor cable to feed two branches with one common neutral.
In my new square D homeline panel, double breakers use one phase but on my
old panel double breakers were fed from both phases. It just depends on the
box and design.
I think your talking about two separate things. There are splits or half
size breakers, some are tandem and some are not, but regardless, the two
breakers occupy one section of panel buss. Then there are double pole splits
and quads, which occupy two sections of panel buss and are for 240 volt
In their standard for panels UL limits the number of 'poles' that can be
installed in a panel (a 220V breaker is 2 poles). The maximum number of
poles in a 100A 120/240V panel is 20. (In a 200A panel 40.) If a 100A
panel has positions for 16 full sized poles it could have 4 more poles
and stay under the 20 limit. These can be installed as 8 120V
half-thickness breakers (12 full + 8 half = 20). To prevent more than 8
half-thickness breakers from being installed, the breakers have a
feature at the bus end or the rail end that only allows them to be
installed in special positions. In this case only 8 panel positions can
allow this feature and half-thickness breakers will only fit in those
positions. These breakers are called class CTL (circuit limiting). (A
100A panel may be designed so fewer than 20 total poles can be
installed.) Previous to the class CTL panels, half-thickness breakers
did not have a limiting feature and in most panels could be installed in
any position (or all the positions). Last I heard these non-CTL breakers
were still available for use in non-CTL panels. The panel, on its label,
should have a list of the number and type of breakers that can be
installed in that panel. A class CTL panel will not have non-CTL
breakers on the list and it is a code violation to install a breaker
that is not on the list.
(A 100A service disconnect breaker/fuse could feed 2 200A main lug
panels for 80 poles.)
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