Circuit breakers/fuses in parallel
 

I have been looking for a 30 AMP circuit breaker to add to my rebuild
of switch panel on Herodotus.

I had often wondered if two 15 AMP ones in parallel would work and be
equivalent to a single 30 AMP one but thought "No, thats dumb - too
simple a solution" It sounded so ignorant of electricity that I was
too afraid to ask lest I be the object of ridicule.

Today the local electronics technician recommended that path to me as
the ones I wanted only went up to 25 AMPs. Showed me commercial, high
end car audio equipment with parallel circuit breakers.

May be useful information to someone else.

However wait a while to see if Larry blows me out of the water and
proves me wrong.

Larry????

cheers
Peter

Circuit breakers/fuses in parallel
 

My only question would be. Will the current divide evenly between the
two paths? If there is corrosion on one path that would "force" all
the current to the other.

Circuit breakers/fuses in parallel
 

On Jun 26, 9:11 am, Herodotus wrote:
I have been looking for a 30 AMP circuit breaker to add to my rebuild
of switch panel on Herodotus.

I had often wondered if two 15 AMP ones in parallel would work and be
equivalent to a single 30 AMP one but thought "No, thats dumb - too
simple a solution" It sounded so ignorant of electricity that I was
too afraid to ask lest I be the object of ridicule.

Today the local electronics technician recommended that path to me as
the ones I wanted only went up to 25 AMPs. Showed me commercial, high
end car audio equipment with parallel circuit breakers.

May be useful information to someone else.

However wait a while to see if Larry blows me out of the water and
proves me wrong.

Larry????

cheers
Peter

It'll be OK. I won a bet 30 years ago amongst my peers, 20
electronics techs, did a demonstration, all that.

What tiny problem arises is with the timing. Two 10 Amp fuses in
parallel pop a little sooner than one 20 Amp.

Terry K

Circuit breakers/fuses in parallel
 

Paul wrote:
My only question would be. Will the current divide evenly between the
two paths? If there is corrosion on one path that would "force" all
the current to the other.
You are correct, corrosion on the contacts of one of the fuses will
upset the balance. The current will be evenly divided only if the
resistance (contacts, fuses, wires) in each leg is absolutely equal.
This is unlikely to be the case and a slight difference in resistance
will exist but won't be of much consequence. Even two identical fuses
will have a slight difference.
So just make sure that both current paths have good contacts and wires.
Boeland

Circuit breakers/fuses in parallel
 

"Paul" wrote in message
...
My only question would be. Will the current divide evenly between the
two paths? If there is corrosion on one path that would "force" all
the current to the other.

'Fail safe' then, in that case

Circuit breakers/fuses in parallel
 

On Thu, 26 Jun 2008 07:44:39 -0700 (PDT), Terry K
wrote:



It'll be OK. I won a bet 30 years ago amongst my peers, 20
electronics techs, did a demonstration, all that.

What tiny problem arises is with the timing. Two 10 Amp fuses in
parallel pop a little sooner than one 20 Amp.

Terry K

Hi Terry,

Will the "little sooner" be much of a problem practically?

Peter

Circuit breakers/fuses in parallel
 

On Fri, 27 Jun 2008 05:03:22 +1000, Herodotus
wrote:

On Thu, 26 Jun 2008 07:44:39 -0700 (PDT), Terry K
wrote:



It'll be OK. I won a bet 30 years ago amongst my peers, 20
electronics techs, did a demonstration, all that.

What tiny problem arises is with the timing. Two 10 Amp fuses in
parallel pop a little sooner than one 20 Amp.

Terry K

Hi Terry,

Will the "little sooner" be much of a problem practically?

Peter

I would have said that the fuses would blow at somewhat less than the
sum of the rated currents - that is, two 10 amp fuses in parallel may
blow at 18 amps rather than the expected 20.

This is because the resistances in the two paths are unlikely to be
identical, so path will carry a little more than half the current,
causing that fuse to blow when the total current is less than the
total rating. (Of course, a fuse will not blow instantly at exactly
its rated current, even for fast-blow types, and the fuse rating
should always be somewhat more than the expected maximum current, so
this discussion may be somewhat academic...)

--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

Circuit breakers/fuses in parallel
 

On 2008-06-26 08:11:48 -0400, Herodotus said:

I have been looking for a 30 AMP circuit breaker to add to my rebuild
of switch panel on Herodotus.

I had often wondered if two 15 AMP ones in parallel would work and be
equivalent to a single 30 AMP one but thought "No, thats dumb - too
simple a solution"

I wonder about the original premise, as I have a 50 amp breaker. It's
not in the panel, in fact it protects the panel, but they exist. As I
recall, it mounts through a 1/4 or 3/8" hole, a simple push-button.

--
Jere Lull
Xan-à-Deux -- Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/

Circuit breakers/fuses in parallel
 

On Jun 26, 4:03 pm, Herodotus wrote:
On Thu, 26 Jun 2008 07:44:39 -0700 (PDT), Terry K

wrote:

It'll be OK. I won a bet 30 years ago amongst my peers, 20
electronics techs, did a demonstration, all that.

What tiny problem arises is with the timing. Two 10 Amp fuses in
parallel pop a little sooner than one 20 Amp.

Terry K

Hi Terry,

Will the "little sooner" be much of a problem practically?

Peter


No. Thermal effect equalize the current sharing. If one fuze carries
a little more, it gets warmer and it's resistance increases, balancing
the load.

Without hi speed photography, I cannot say they fused at exactly the
same time, but it looked close, and niether blew until it seemed a
fuse rated at the sum of all fuses must pop.

Terry K

Circuit breakers/fuses in parallel
 

On Fri, 27 Jun 2008 01:53:57 GMT, Jere Lull wrote:

On 2008-06-26 08:11:48 -0400, Herodotus said:

I have been looking for a 30 AMP circuit breaker to add to my rebuild
of switch panel on Herodotus.

I had often wondered if two 15 AMP ones in parallel would work and be
equivalent to a single 30 AMP one but thought "No, thats dumb - too
simple a solution"

I wonder about the original premise, as I have a 50 amp breaker. It's
not in the panel, in fact it protects the panel, but they exist. As I
recall, it mounts through a 1/4 or 3/8" hole, a simple push-button.

The shop - Jaycar, a nation wide store in Australia similar to what
Radioshacks used to be like did not had the push buttom type you write
of in 50 AMPs but not in 30 in their rather extensive catalogue.

Peter