JBC wrote:
HorneTD Wrote:

OK......well and good for someone knowing the code and all. But, in-
regular do-it-yourself language....how can I tell if a breaker box is
OK with a tandem breaker?-

If that breakers model/part number is not listed on the label in the
panel cabinet and that panel's model/part number is not listed on a
list
that is packed with the breaker then you cannot use that breaker in
that
panel.
--
Tom H


The Breaker container has no mention of any panel. I can't see where
the panel mentions any breaker type either. They are both QO
(SquareD), and the type of clips that holds it in and makes electrical
contact are the same. I'm just wondering why there is a problem. It's
hard to find breakers for my panel, most I've seen have this hook
looking type of clip

The only thing I can think of, is that 40 versus 20 amps could
effectively be pulled though the breakers incoming hot rail connection
point, that's it. And since the rail clips for both single and tandem
breakers are exactly the same width, one can only conclude that a panel
made for tandem breakers must have a rail that's more conductive.
That's the only reasoning I can see. Is it supposed to start a fire as
it sparks from 40 amps running across the connection? I just don't get
it!

Is there an engineer handy?

Obviously I don't want to start a fire. The only other solution I have
is to have a new service put in, which is beyond my abilities, not to
mention the steep price tag.

Is it actually safer to have the single 20 amp breaker trip
periodically? The wiring dates back to 1957 (not the Panel I believe,
It would have fuses right) so the circuit covers several rooms, which
draws more current than the 20 amp breakers limit? I figure it's
better to add a 20 amp tandem and run wire for the second side, than to
increase the breaker to 30 amps because the existing wire gage might not
be able to handle 30 amps.

My plan is to increase the service rating (the MAIN breaker is 100 amps
at this point) and rewire the entire house eventually.

So what's my course of action in the interim?



(I seem to be missing the start of this thread in case this post isn't
entirely appropriate.)

UL, as I understand it, in their standard for panels limits the number
of 'poles' that can be installed in a panel. (a 220V breaker is 2 poles,
a 12V breaker is 1 pole, a 120V tandem breaker is 2 poles.) The maximum
number of poles in a 100A 120/240V panel is 20. (In a 200A panel 40.) If
a 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 4 120V tandem
breakers. To prevent more than 4 tandem breakers from being installed, a
tandem breaker has a hook to install it on the panel rail instead of the
normal SquareD U shaped clips. Only 4 positions on the rail can have a
slot to accept the hook. 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 tandem breakers had
the normal U shaped clip and could be installed in any position (or all
the positions). Last I heard these non-CTL breakers were still
available. As indicated in the quoted post, a panel on its label should
have a list 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.

While I can understand how a panel can wind up with breakers for more
load than the panel can handle, I don't see what the difference in
installing a breaker for a subpanel and adding the subpanel breakers in
the main panel (asuming available neutral positons and adequate side
gutter space). I suppose it is a question of enforcing a reasonable limit.

I assume someone said going to a 30A breaker is not safe.

bud--