[RE-wrenches] CBI circuit breakers

[boB Gudgel]

Allan Sindelar wrote:
> Dan,
> My understanding is that CBI breakers aren't based on a temperature-related
> mechanical action, but a "magnetic-hydraulic" function. I recall that this
> was marketed (by Outback? Robin?) as superior to thermal-trip mechanisms as
> it was not prone to heat-induced nuisance tripping. boB can probably set us
> straight here.
>   
Yep.   Magnetic-Hydraulic they are indeed....

If you connect them up backwards, they don't quench the arc so well.

One thing I seem to remember is that if they are hot, the trip time 
changes somewhat.   That has to do with
the little magnetic piece that floats around inside the hydraulic fluid 
that can change viscosity (slightly) with
temperature.

Taking one of these little babies apart and looking closely at how it is 
constructed can be very educational.  Somewhere, we
have a Mag-Hyd breaker made out of clear plastic which really shows it 
all well.

And Kent....  That is very strange that it was in the "off" position...  
I don't suppose......  Nah !  Someone wouldn't have forgotten
to switch it on.?   Nahh....  PV Gremlins in the night ?   Nahh. !

boB




> Allan Sindelar
> Allan at positiveenergysolar.com
> NABCEP Certified Photovoltaic Installer
> EE98J Journeyman Electrician
> Positive Energy, Inc.
> 3201 Calle Marie
> Santa Fe, New Mexico 87507
> 505 424-1112
> www.positiveenergysolar.com
>
> -----Original Message-----
> From: re-wrenches-bounces at lists.re-wrenches.org
> [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Exeltech
> Sent: Monday, July 27, 2009 11:03 PM
> To: RE-wrenches
> Subject: Re: [RE-wrenches] CBI circuit breakers
>
>
> Wrenches,
>
> An assembly of thoughts:
>
> Circuit breakers operate on a bi-metallic temperature-related mechanical
> action.  They are rated to hold a specific current at a specific ambient
> temperature.  If the ambient temperature exceeds the breaker specification
> for a given current, the breaker will open at a lower current than expected.
>
> If breakers mounted on one or both sides of a suspect breaker are themselves
> running warm, this can raise the effective ambient temperature for that
> adjacent breaker and cause it to open at a current below the trip rating,
> especially if it's near its max current spec.
>
> Though crimp connections to stranded wire may be tight in of themselves, how
> about the connection between the cable lug and breaker?  Breaker hardware
> has torque specs that must be observed.  If it's not torqued properly, it
> will run warm at higher current, and transfer some of that heat to the
> internal mechanisms of the circuit breaker, which may cause an early trip.
>
> As a test, use a good DVM set to a millivolt DC scale.  With the maximum
> current flowing in the circuit, probe across each connection.  Check wire to
> lug; lug to breaker stud, and even across the breaker itself.  You should
> measure low millivolts at any connection or location - the lower the better.
> Several tenths of a volt drop across any two points with maximum current
> flowing in the circuit indicates a bad connection.
>
> If you measure what you feel is an excess voltage drop across a circuit
> breaker, and the circuit current isn't excessive, try replacing the breaker
> with a new one (preferably from a different batch or mfgr, but of an
> identical trip rating) and re-measure the voltage drop across the new
> breaker.  If both breakers have a substantially similar drop for the same
> current, it's likely the first breaker was ok.
>
> Most of you also know the breakers used for PV-side protection must have a
> DC voltage rating greater than the VOC rating of all the PV in that circuit.
> If a breaker is being used in a circuit that provides more voltage than the
> breaker ratings, repeated opening of the breaker will cause damage to the
> internal breaker contacts, leading to a premature trip condition.
>
> Once a breaker trips .. it takes fractionally less current the next time it
> trips due to stress and wear of the connecting elements inside the breaker.
> If a breaker trips often enough, or if the circuit voltage is near (or
> above) the breaker rating when it trips .. it damages the breaker contacts
> each time the breaker is opened - both "trip" or manual open.  When this
> happens, all bets are off as to the current at which the breaker will open
> the next time.
>
> Then again .. there's still a possibility the breakers are defective.
>
> Hope this helps.
>
>
> Dan
>
>
>
>
>       
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