Kim wrote:
"J. Clarke" wrote in message
...
Kim wrote:
"LRod" wrote in message
...
On Wed, 16 Mar 2005 10:40:45 -0800, "Kim" wrote:
Geez, where do you guys get this stuff?
IEEE, NEC, short circuit and load flow studies, breaker/device
coordinations.
You can blindly claim all the initialed documents you want, but cite
just one specific paragraph in any reputable regulatory document that
supports your statement: "[m]aximum breaker size 15A as your motor is
only about 8A at 220V."
That's pure nonsense, and I'll be the first to apologize ot you were
you to come up with something. Of course that's a safe promise,
because you not only can't, but you won't.
Local AHJs don't count as their specific requirements are not germane
to the discussion, but I'd be happy to see them if they do exist.
--
LRod
Master Woodbutcher and seasoned termite
Shamelessly whoring my website since 1999
http://www.woodbutcher.net
Here is a portion of your statement in context as related to the above:
"Maximum breaker size 15A as your motor is only about 8A at 220V.
Where do you get that from? And if there were some sort of
relationship to breaker size and load demand, why would 15A breaker
with an 8A load be okay but not 20A or 30A breaker?"
NEC Table 430-152, dependent on the motor type, the inverse time
breakers
could go either 150%, 200% or 250% of motor load. In other words, if the
motor has no code letter, for example, you could go up to a 20A breaker
based on 8A motor running nameplate load. If the restriction falls on
200%
or 150%, then 15A CB only. But as a general practice the lowest breaker
setting should be used, hence 15A. There is no reason why, from a
protection point of view, you would want to use an 20A, 30A or larger
breaker where a 15A breaker would do. 15A CB is what I would use.
I think you're confusing code requirements for permanently installed
machinery with code requirements for portable tools.
OK you got me, but the information Table 430-152 should apply, although
not mandatory for portable tools as you suggested, as motor and breaker
characteristic don't change or care if the installation is permanent or
not.
No, they don't. But unless you are going to put some kind of exotic plug on
that tool there is no way to guarantee that it is always going to be
plugged into the outlet that has your special breaker and the guy who plugs
his dryer into that outlet is going to be really ****ed when the breaker
pops for no good reason other than that you decided to makes it undersized
to protect a tool that is now plugged in somewhere else.
For sure motor inrush current was one of the reasons for this table
perhaps also fire and electrical faults from over sized breakers - who
knows what the historical reasons were for the NEC panel decisions but you
can be sure it has much to do with safety. Don't throw out the baby with
the bath water. All I'm saying was the best protection for this motor is a
15A circuit breaker based on the OP's situation. (I've used "maximum' and
perhaps that was a wrong word choice.)
The BEST protection for this motor is a purpose made contactor with
overcurrent protection designed specifically for the purpose of protecting
motors, not a general purpose breaker stuck in a breaker panel.
If there is a hole in the wall into which a cord is to be plugged, then the
breaker on the circuit to which that hole is connected should be sized to
protect the wiring--the architect, the engineer, the inspector, the
electrician, and everyone else involved have NO control over what gets
plugged into that outlet.
There is no reason, from a protection point of view, why you would want
to call an electrician and have him remove a perfectly good 30 amp
breaker and
the associated 30 amp receptacle and replace it with a 15 amp breaker and
15 amp receptacle just because you are plugging in a saw instead of a
dryer
for example.
Sure from a protection point of view a 30A breaker doesn't see the same
long time overcurrent or instantaneous trip points as a 15A breaker. In
other words, the 30A breaker doesn't see the 1hp motor as well as a 15A
breaker and, therefore, you get better protection with a smaller breaker.
If your purpose is to protect the motor on a tool that is plugged into a
receptacle, then PUT THE PROTECTION ON THE TOOL because there is no
guarantee that it is always going to be plugged into the same receptacle.
Just a question, not an argument: don't you still need to change the 30A
breaker to GFI if its now used for both dryer and portable tool(s)?
Generally speaking the code does not address anything that happens beyond
the receptacle. There is certainly no requirement in any code I've ever
heard of that one change existing work just to plug in a tool.
If there is a requirement for a GFI on the receptacle then it will be
required regardless of what you plan to plug into it.
--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)
--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)