Thermal-magnetic c'bkrs are designed to carry 100% of name plate
rating on a continuous basis in free air.
Mount the c'bkr in an enclosure and a 20% thermal de-rate applies.
A load center (panel) is considered an enclosure.
Thus the following applies:
15A c'bkr will carry 15(80%) = 12Amps continuous
20A c'bkr will carry 20(80%) = 16Amps continuous
30A c'bkr will carry 30(80%) = 24Amps continuous
No magic involved, just basic engineering.
Understand that start up is greater than running speed however it seldom
tripped a 15 amp breaker in my old home when it came on and a 15 amp
router, dust collector, and radio were all already running on the same
circuit. Come summer time that was another story.
"One a week when both would come on at the same time the breaker
The one starting while the other was running (or worse, both starting
simultaneously) was enough to trip the breaker. Both running is not. I would
expect this sort of behavior. The breaker in your old house may not have been
working at all.
I'm no electrical engineer and I'm just thinking out loud.....
Summer months are high load months for the electric company, so maybe
there is a slight voltage drop during those times.... ie: from 125+ down
to 115- ????
"Playing is not something I do at night, it's my function in life"
Circuit breakers do not measure amperage so to speak, they measure
temperature in the breaker. If the amperage draw is too high it gets hot
and trips. In the summer it is already warm and the added load trips the
breaker more quickly. During the cooler months the breaker has to warm up
more before it trips. We are only talking momnets but it only takes moments
for a motor to start up. Think of a circuit breaker as a reusable fuse.
Only partially true.
C'bkrs found in buildings are thermal-magnetic devices.
The magnetic portion of the c'bkr measures the inrush current and
responds instantaneously to a fault condition independent of
If a c'bkr trips when a load such as a motor is first turned on, the
magnetic portion of the c'bkr is responding to the inrush conditions.
Mean while the thermal portion of the c'bkr responds to the long term
conditions of the circuit such as when an overload on a continuous
Circuit conditions maybe be such that it may take several minutes for
the thermal portion of the c'bkr to trip.
Overload current vs. thermal trip time is an inverse ratio.
This explains why you can temporarily overload a table saw during a
cut and not trip the c'bkr, if you do it quickly enough.
The above correctly describes only the functioning of the thermal
portion of a c'bkr.
The above describes only the magnetic portion of a functioning c'bkr
in a round about way and should not be confused with the thermal
function of a thermal-magnetic c'bkr.
All of this discussion helps to explain why 15A c'bkrs protecting #14
AWG wiring are basically a total waste of time in today's buildings,
and especially in the shop.
The electrical demands of today are much higher than they were 50
years ago and 15A ckt's are simply inadequate in today's world.
Aw, c'mon, Leon. You three -gush- over Festools, every time.
I am familiar with the products. They just didn't let the vendors plug
anything in outside the store that day, so I can't judge performance.
I'm good at judging the quality (or lack thereof) of tools from their
feel and action, even unplugged, so I was disappointed when I didn't
feel the silky smoothness of Festool when I did pick them up and run
them through their ranges of motion and such. I couldn't tell any
difference from their Bosch, DeWalt, Ridgid, or Makita counterparts,
and that really surprised me. THAT is why I say "Festering" when I
see their prices.
From what you converts say, they probably perform much better with
power. I wish I knew someone local who would let me play with their
agro-colored toys sometime.
"A patriot must always be ready to defend his country
against his government." --Edward Abbey
Don't know where you're located, but there's a number of hands on classes
for Festool in the US. As well, I've heard of several dealers that let
customers try out a few tools. Maybe you should call around. And finally,
Festool does have a 30 return policy.
I like Festool, I get no benefit from any one buying one.
Ignorance guides your thought process. You think you are good at judging
quality. Untill you actually use the tool you don't know squat about how
well that tool operates. Results, day in and day out are what count.
I wish I knew someone local who would let me play with their
Any one that sells them should let you try them, even if you mail order you
have 30 days to decide.
I should hope so, but will it last 15~20 years like the old stuff did? I
have a 22 year old PC right angle ROS that I retired 3 years ago, it still
runs as good as it did when new although I have worn out the pad 3 or 4
times, same goes for my old PC SpedBloc. The SpedBloc however did poop out
about 5 years ago and I replaced it with the same model but unfortunately it
is not the same tool. That was my last PC purchase. My type 1 557 plate
joiner still works well as did its belt driven predecessor.
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