Sure, but why is that wire less susceptible to a short than a wire not feeding a motor? If the OCD is there to protect the wire, it doesn't matter what fails on the other end of it.
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6 years ago
nuisance trip central vac breaker
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6 years ago
On 13-Nov-17 12:06 PM, snipped-for-privacy@notreal.com wrote: ...
It isn't, but a short is by definition a high-current event so the size of the breaker is essentially immaterial.
The amperage rating of the breaker protects against continuous overcurrent; the motor is different in that the high current only lasts for a few msec at most; the current draw is well within the ampacity of the wire otherwise.
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6 years ago
Uh huh, sure. You know what you're talking about.
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6 years ago
Is that a quote from a previous post?
Who are you and what did you do with Iggy? (Not that we mind if you made him go away)
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6 years ago
That's not my point. Forget the motor operation. What happens when it, or the outlet itself, shorts?
Again, not the point. OCDs are there to protect the wiring during a failure. Motors, or devices with motors never fail?
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6 years ago
replying to DerbyDad03, Iggy wrote: Come on, it's the 3rd time I did it for you and the last.
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6 years ago
Au contraire, IS the point and why there's a difference in NEC for dedicated motor circuit...
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6 years ago
The SHORT circuit protection is still there. short is an instantaneous very high current spike that will still trip the breaker IMMEDIATELY
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6 years ago
It's OK to admit that you did it in error.
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6 years ago
OK, why? The fault that the OCD is there to safe is still there.
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6 years ago
But that is *not* why the OCD is there. Are you saying that motors can never fail?
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6 years ago
No, I'm saying motors have built-in thermal protection, and a "motor failure" will increase current by 5 amps pretty darn quick - so the circuit breaker will still protect the wire. I wouldn't go stupid and install a 30 (or heaven forbid a 40) amp breaker.
I'm pretty sure the high-mag breaker will do the job anyway, given the symptoms and amp draw readings I'm getting.
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6 years ago
What's the difference? Nothing can go wrong.
This sounds like a much better option.
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6 years ago
On 14-Nov-17 8:32 PM, snipped-for-privacy@notreal.com wrote: ...
Precisely _because_ it is a motor circuit and motors are different and NEC understands that.
It's all in Section 430 but short story is as outlined above; ampacity of the wire is determined for FLA of the motor; the breaker/fusing is sized to allow to be able to handle inrush starting current and the LRA or similar _continuous_ overcurrent protection is _NOT_ provided by the breaker but the _REQUIRED_ thermal protection for the motor (and thereby the wiring as well).
IOW, there's a second layer of protection besides the branch circuit breaker of a "normal" branch circuit you're used to that isn't in the lighting/general use circuit which relies on the one device for both functions.
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6 years ago
On 15-Nov-17 8:53 AM, dpb wrote: ...
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And, if the thermal protection is built into/comes with the motor, that's allowable; larger motors of the woodworking-shop class generally have "heaters" located in the starter enclosure that can be simply inline fusible links that serve the purpose or the "thermal reset" button in a motor that is just a circuit breaker or there are similar resettable heaters as well.
Doesn't matter _where_ the device is, specifically, but must be there by Code.