On 3/2/2014 12:55 PM, Robert Green wrote:
"bud--" wrote in message
eb.com...
On 2/26/2014 4:59 AM, Robert Green wrote:
I was mostly concerned at the time
that the inspector would disallow the dual skinnies because of the
potential
to overload the panel.
Panels will have a rating something like 10/16. There are 10 full size
breaker positions and you can put 16 "poles" in it. A tandem breaker is
2 poles, so you could install up to 6 tandem breakers. The label should
tell you the rating.
Panel is a QO CAT QO BW - 20M - 100 - 5
I believe that the 20 refers to the max # of breakers and the 100 is the max
current. Otherwise the catalog number don't seem to agree with the listing
in the PDF. No idea what BW means. It's hard to read the label because
it's a) faded, b) upside down and c) obscured by neutral and ground wires.
I agree with 20 and 100. M means it has a main breaker. (As in your link
below.)
I don't know what BW is either. Need a real old catalog.
I would read "20" as not allowing tandem breakers. "2024" would allow
tandems in 4 positions. But it is an old catalog number.
Seems like UL had maximum number of poles depending on the panel rating.
I think a 100A panel had a max of 20 poles and 200A had a max of 40 or
42 poles. That makes it harder to overload a panel, but doesn't work so
good if you don't have much on each circuit (so you need more circuits).
SquareD has panels with a lot more poles ("circuits") than that now.
The panel is tested with the maximum number of poles - 16 above - and UL
does not allow installing more poles than that. That is done by only
allowing tandem breakers in certain positions (6 in the example above).
The label will indicate which positions tandem breakers can be installed
in. In a 10/20 panel it is all positions. It may also be no positions. A
SquareD tandem breaker has a bar on the bottom that has to fit into a
slot through the gutter rail, which exists only in the positions where
tandem breakers are allowed. These are class CTL panels and breakers
(circuit limiting) and they have been around a long time.
This has to be a pre 1985 panel and I haven't found it yet although I found
a few like it in this PDF:
www.farnell.com/datasheets/1626663.pdf
The inspector wants to know that tandem breakers were installed in
positions where they are allowed.
From what I can see, that's not an issue with my panel. As I recall, the
hot bar (not sure of the technical name of the alternating metal "fingers"
running down the center) was the same from the top to the bottom - no
specialized slots for tandems (why would there be?). The replacement
breakers have a very different connection mechanism that the original ones.
The ones that came with the panel have two pronged clips that make the
connection to the rail but the replacements have a single claw-like
"grabber" - so different looking that I was sure I bought the wrong
breakers.
SquareD class CTL tandem breakers have the usual horizontal clip at the
busbar end. At the gutter rail end they have what you describe as a
claw, which fits into a slot in the gutter rail. The slot is only
present at the positions where tandem breakers are allowed.
Your farnell link has a crappy picture for a Homeline panel on page 9 of
your link.
A better picture is
http://www.circuitbreakersuperstore...._8_2_5862.html
where the gutter rail claw can be seen.
Regular breakers just have a clip at the gutter rail end, as with your
original breakers.
There are also non-class CTL tandem breakers that can be installed in
any position - for older panels that are before CTL came out. I know no
one here would ever install one of them in a class CTL panel.
I am pretty sure that at least on of the labels on the panel has the letters
CTL but if it came out after 1985, then I definitely don't have a CTL panel.
From what I can see of the PDF listed above, the breaker panels that support
special slots for tandems look quite different from the box I have which is
a series of alternating metal fingers running down the heavy black plastic
"spine" of the panel.
The difference is only in the gutter rail.
http://en.wikipedia.org/wiki/Circuit_total_limitation
Talks about CTL being in place since 1969 and replacement breakers being
non-CTL. Even if the panel ends up "dangerously overloaded" isn't the main
breaker supposed to trip before anything bad happens?
Yes.
I don't entirely agree with the limit on circuits. If I watch the
connected load I might install tandems where you are not supposed to.
I think one reason for the limit is to limit the heat produced in the
panel. Heat can cause a breaker to trip at a lower current. Would seem
like a 100A panel would only make 100A of heat no matter how many breakers.
There is, in general, a limitation for fuses and circuit breakers of 80%
for "continuous" loads, which are loads that are on for 3 hours or more.
My understanding is this is based on panel heat, and the breaker may
trip at less than 100% if the load is on for more than 3 hours.
An exposed 20A breaker or fuse by itself is supposed to hold at 20A forever.