paralleling a 2 pole breaker

[charlie b]

If your choosing to follow the NEC then IMO your proposed installation violates 240.8.

Bob, what is your opinion of the question I posed at the end of my post #11?

Looking at the first sentence of 240.8, can it be said that twoskinsoneman is the ?factory,? and that this usage is indeed ?factory installed,? so that the proposed installation is therefore allowable?

 

[iwire]

Bob, what is your opinion of the question I posed at the end of my post #11?

I actually agree with you. :smile:

But I am confused what the OP is looking for, on one hand he wants to comply with the NEC even though he does not have to.


So as far as 240.8 I agree as a factory he can choose to ignore 210.8.

 

[Twoskinsoneman]

I actually agree with you. :smile:

But I am confused what the OP is looking for

So as far as 240.8 I agree as a factory he can choose to ignore 210.8.

Why are you confused? I had simple question you answered. I then asked why something was dangerous, in response to someone stating it was without any offered reasoning.

Also I feel like you are continuing to poke at me by stating "he wants to comply with the NEC even though he does not have to"?

I guess what I have to do is food for thought.
I can choose not to follow the NEC, but if the owner of my company catches on I may get fired. I may also get sued if there is ever a problem with my work and it comes back that I signed a contract with a gov agency to do the work a certain way and ignored it (certainly plossible if someone is hurt).

Why do you follow the NEC even though you don't have to?
Sure there are consequences if you don't but the same goes for me.

 

[iwire]

Also I feel like you are continuing to poke at me by stating "he wants to comply with the NEC even though he does not have to"?

I have absolutely no idea why you feel that way.


Sorry I ever looked in on this thread. :roll:

Follow the NEC, don't follow the NEC, I really don't give a rats behind.

 

[petersonra]

I guess what I have to do is food for thought.
I can choose not to follow the NEC, but if the owner of my company catches on I may get fired. I may also get sued if there is ever a problem with my work and it comes back that I signed a contract with a gov agency to do the work a certain way and ignored it (certainly plossible if someone is hurt).

Why do you follow the NEC even though you don't have to?
Sure there are consequences if you don't but the same goes for me.

The point is that the type of equipment he is making just plain is not covered by the NEC. Its like arguing that a guy in CA ought to follow the traffic laws of Illinois. They just don't apply.

Now if the thing has to meet some other standard, what is proposed might be a violation of that standard.

I would point out that this is a far less egrious problem than if someone were to put two relay contacts in parallel. If the load is above the rating of either contact, one of the contacts will see more load than it is rated for on power up, and one will have to break more load on power off.

A CB is a little different. If you are running 50 amps through two parallel 15 amp breakers it will eventually trip one of them first. The other one will see the full load and it will also trip. The second CB is not harmed more by this than if it (a 15A breaker) saw a 50A load and tripped because of that. Keep in mind circuit breakers are designed to take inrush currents far exceeding their thermal trip rating, so it is not much of an issue on power up either, other than the potential for a trip on power up due to excess inrush.

Even so there is generally no reason to do this for small breakers.

 

[Twoskinsoneman]

I have absolutely no idea why you feel that way.


Sorry I ever looked in on this thread. :roll:

Follow the NEC, don't follow the NEC, I really don't give a rats behind.

Fair engouh.

 

[Twoskinsoneman]

The point is that the type of equipment he is making just plain is not covered by the NEC. Its like arguing that a guy in CA ought to follow the traffic laws of Illinois. They just don't apply.

Now if the thing has to meet some other standard, what is proposed might be a violation of that standard.

I would point out that this is a far less egrious problem than if someone were to put two relay contacts in parallel. If the load is above the rating of either contact, one of the contacts will see more load than it is rated for on power up, and one will have to break more load on power off.

A CB is a little different. If you are running 50 amps through two parallel 15 amp breakers it will eventually trip one of them first. The other one will see the full load and it will also trip. The second CB is not harmed more by this than if it (a 15A breaker) saw a 50A load and tripped because of that. Keep in mind circuit breakers are designed to take inrush currents far exceeding their thermal trip rating, so it is not much of an issue on power up either, other than the potential for a trip on power up due to excess inrush.

Even so there is generally no reason to do this for small breakers.

I think this is kinda the way I felt also. It seems to make sense. That's why I questioned it being dangerous. I also agree it serves no useful purpose.

 

[LarryFine]

I would point out that this is a far less egrious problem than if someone were to put two relay contacts in parallel. If the load is above the rating of either contact, one of the contacts will see more load than it is rated for on power up, and one will have to break more load on power off.

Since you brought it up...

Placing relay contacts in series, not parallel, helps them last longer when subject to high loads. Paralleling decreases contact resistance, yes, but since one contact will always open last, that one gets worn from pitting the most. Placing them in series has the same effect as the contacts opening twice as fast, minimizing arcing.

 

[grich]

Looks like a small TV truck panel, a bit fancier than the ones I work on.

What's your 40A 120V load going to be, or is that breaker going to be a main?

 

[Twoskinsoneman]

Looks like a small TV truck panel, a bit fancier than the ones I work on.

What's your 40A 120V load going to be, or is that breaker going to be a main?

We do a fair amount of TV trucks. This panel was from something else. Gov agency. Communications support vehicle

OP was purely hypothetical. I wasn't going to use the paralleled 40amp. It that what your asking? Or are you talking about something you see in the pic?

 

[grich]

OP was purely hypothetical. I wasn't going to use the paralleled 40amp. It that what your asking? Or are you talking about something you see in the pic?

Just referring to the OP, not the picture.

We do a fair amount of TV trucks. This panel was from something else. Gov agency. Communications support vehicle

That explains why it looks fancier than the TV trucks I work with...it's a guv-mint truck. Figured it was a good guess, since our trucks have some combination of masts, dishes, leveling jacks, gensets and inverters.