Can't quite figure this out.....?????

[cadpoint]

realolman has a point. You really would have a parallel feed at any point of the circuit. AC current isn't really directional. We like to think of it as hot and return because that makes things simple but that's not really correct. It's not going to matter very much where they are tied together.

I'm really glad this subject got posted because I have never given it much thought before now ( stuff happens )...

ME too... :roll: (Even though I've read; had to read it several times)

No one had talked about the neutrals here, till now.

Only a few circuits are technically called out as required for a house, why not keep them totally isolated! ? (And not a Code requirement! - IE it's not stated to keep neutrals separated - BUT it sure will show up with AFCI's)

I've said before I don't a whole lot of residential, but have run MWBC's and have kept the neutral's separated. Like a 12/4 w/ ground or a 12/6. Now I know a 12/4 isn't required for the 2 circuit kitchen application. But if you really think about it makes a real strong case for it, for all the modern things going into these grand kitchens.

But I can only think that it might well matter to keep any circuit isolated in this case (the Kitchen). One certainly wouldn't want to hang off the neutral of a MWBC or even bring more together, outside the panels neutral bar.

I don't want to argue about a manufactured bundled MWBC being a circuit, that's a thread line for another day.

 

[realolman]

.....I've said before I don't a whole lot of residential, but have run MWBC's and have kept the neutral's separated......

Isn't it necessary to use a common neutral in order to have a MWBC?

 

[yucan2]

I'd like to make sure that I'm understanding this correctly.

Is it being implied that 30 amps could flow thru the entire circuit including both ungrounded conductors or simply 30 amps allowed to flow from the point of the inadvertent splice to and thru the load and thru the grounded conductor?

In other words, upstream of the splice will never see more than the individual breaker capacity. Is this correct?

 

[iwire]

Anywhere on the line side of the two 15 amp breakers will have 30 amps available.

 

[Volta]

I'd like to make sure that I'm understanding this correctly.

Is it being implied that 30 amps could flow thru the entire circuit including both ungrounded conductors or simply 30 amps allowed to flow from the point of the inadvertent splice to and thru the load and thru the grounded conductor?

In other words, upstream of the splice will never see more than the individual breaker capacity. Is this correct?

Thirty amps can flow to any point in the circuit. Once 'the' inadvertant splice is made, that particular point is no longer relevant, and there is no longer an 'upstream' direction. That splice (and all the others) are now at some point in a level canal, so to speak.

 

[yucan2]

Thirty amps can flow to any point in the circuit. Once 'the' inadvertant splice is made, that particular point is no longer relevant, and there is no longer an 'upstream' direction. That splice (and all the others) are now at some point in a level canal, so to speak.

I appreciate the response, but its not clicking. Maybe because the dog is begging to go out is distracting me? When I return I'll try and digest it. :-?

 

[iwire]

I appreciate the response, but its not clicking. Maybe because the dog is begging to go out is distracting me? When I return I'll try and digest it. :-?

Draw a quick and dirty circuit on paper and you will see it.

 

[yucan2]

Draw a quick and dirty circuit on paper and you will see it.

Attached is what I'm getting.

 

[growler]

Attached is what I'm getting.

OK so now go back and attach a load to any point along one of the conductors where you are showing a current draw of 15A. Once you complete the path to either ground or neutral you have 30A potential because current will be flowing through the two breakers. A parallel path.

 

[LarryFine]

It seems to me that the circuit will allow twice as much to any part of the line side of the two circuits as it would not being tied together....

I think , disregarding breaker time / trip characteristics, two 15 a breakers would allow 30 amps to any point of the line side of either branch circuit.

Yes, but that current would still be limited to 15a on each leg of the parallel paths by the individual breakers.

 

[LarryFine]

Will it take 30 amps to trip this circuit?

Yes, or close to it without a doubt.

The total circuit, yes, until the breaker supplying the lower-impedance side trips first (or either one at random with identical impedances), and the second will trip very soon after.

The real issue is whether any conductor will be subject to overload. For the ungrounded conductors, only a section after the two paths join together could be at risk for overload.

As for the grounded conductors, if the impedances match the ungroundeds, the same possibility as above. Otherwise, possibly so, because there are no OCPD's in them.

 

[LarryFine]

Is it being implied that 30 amps could flow thru the entire circuit including both ungrounded conductors or simply 30 amps allowed to flow from the point of the inadvertent splice to and thru the load and thru the grounded conductor?

The former for most posters, the latter for me. Only a 'tangent' from the loop is at risk.

In other words, upstream of the splice will never see more than the individual breaker capacity. Is this correct?

That's my take. I believe the breakers will still protect the individual parallel legs.

 

[LarryFine]

Anywhere on the line side of the two 15 amp breakers will have 30 amps available.

At (or beyond) a single point, yes, but not through both legs of the loop.

 

[LarryFine]

Attached is what I'm getting.

Yes, and only the section labeled 30a, the extention, the 'tangent' off of the loop, is subject to overload.

But, that overload would then have to come from a load (or comb. of loads) too great for one 15a circuit, just as with any over-fused circuit.

It's still wrong, of course.

 

[iwire]

At (or beyond) a single point, yes, but not through both legs of the loop.

Larry, reread what I said, I stand by it.

I also do not disagree with your point but it is a different point and has no bearing on what I said.

 

[LarryFine]

OK so now go back and attach a load to any point along one of the conductors where you are showing a current draw of 15A. Once you complete the path to either ground or neutral you have 30A potential because current will be flowing through the two breakers. A parallel path.

Agreed, but the two legs of the parallel path are each still protected at their rated ampacities. From the 'tap' on the loop, your point of load attachment, you definitely have the 30a potential.

 

[LarryFine]

Larry, reread what I said, I stand by it.

I agree with your statement. Any point on that loop would have 30a available. But, it's coming from two, 15a-capable paths.

I also do not disagree with your point but it is a different point and has no bearing on what I said.

What would stop each breaker from protecting its conductor? Certainly not additional current between the load and a parallel source.

 

[e57]

What would stop each breaker from protecting its conductor?

The other breaker connected to the load side of it in parallel.

 

[iwire]

Yes, and only the section labeled 30a, the extention, the 'tangent' off of the loop, is subject to overload.

Or any of the devices or equipment connected at any point in the circuit.

Lets not forget supplying an appliance designed for 20 amp supply with 30 amps is a violation and could be dangerous if the appliance has a fault.

But yes the conductor 'loop' from one breaker to the other can only have about 15 amps in each direction.

 

[iwire]

What would stop each breaker from protecting its conductor? Certainly not additional current between the load and a parallel source.

Nothing and I have not said otherwise.

The OPs question was if there was 30 amps 'available' and that is the direction I am coming from.

You are focused on the current each individual condutor running back to the breakers will carry.

Neither of us is wrong but IMO they are unrelated topics.