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

[220/221]

Never underestimate the power of the hacks!

It is actually an easy mistake to make.

Two rooms, different circuits, sharing a common wall. Someone puts a jumper where it shouldn't be and, there you go. They end up on the same leg and it may be a while before someone catches it.

I've seen it a few times. I usually find it in a troubleshoot when I can't get a circuit to turn off. I found it a couple times on a service change when the circuits ended up on opposite legs.

 

[e57]

Of course, if the splice is open, we are back to a 15 amp circuit, overloaded as it may be.

Not quite - depending on where that open is and on what conductor... You could end up with a 30a neutral... As you would if double feeding a 3-wire...

 

[e57]

It is actually an easy mistake to make.

Two rooms, different circuits, sharing a common wall. Someone puts a jumper where it shouldn't be and, there you go. They end up on the same leg and it may be a while before someone catches it.

I've seen it a few times. I usually find it in a troubleshoot when I can't get a circuit to turn off. I found it a couple times on a service change when the circuits ended up on opposite legs.

I find it in K&T buildings where someone cared little when they made the building a 120/240 service as opposed to a 120 only service.

 

[Volta]

Not quite - depending on where that open is and on what conductor... You could end up with a 30a neutral... As you would if double feeding a 3-wire...

Hmmm, maybe. I'll have to draw that out.

 

[realolman]

You could have installed a 15 a. circuit perfectly correctly that contained a j-box with a tap...

I come in and incorrectly hook two circuits together, clear on the other end of the place...

Although the two #14 circuits that are fed from each breaker would never be overloaded, the tap conductors from that j-box ( that I was never near, or knew anything about ) certainly could be.

That is why I thought it might be a good idea to point out that the 30 a. could be allowed by the two 15 a. breakers at any point in either circuit... not just after the point where they were hooked together.

 

[LarryFine]

... though once again acknowledging that upstream of the splice will never see more than 15 amps.

That is, on the ungrounded conductor. The grounded will carry the full load.

Actually, two of them will, and proportionately to the hots, if all of the connections, etc., happen to have the same impedances as the hots they accompany.

 

[LarryFine]

... the 30 a. could be allowed by the two 15 a. breakers at any point in either circuit... not just after the point where they were hooked together.

Yes, 30a in total, but again, the individual breakers should protect the individual line conductors.

 

[realolman]

Yes, 30a in total, but again, the individual breakers should protect the individual line conductors.

Not that tap from the j-box that you theoretically installed in my post... that I never went near.... That's subject to 30 A.

I called it a tap... I didn't know how else to easily describe one part of a branch circuit fed from a splice in a j-box.

 

[Volta]

Actually, two of them will, and proportionately to the hots, if all of the connections, etc., happen to have the same impedances as the hots they accompany.

Uh, yeah. I forgot that this circuit has two non-parallel grounded conductors. I was visualizing a shared neutral . . .

When drawing it out, I see that we simply have two (poorly) paralleled 14 awg 'hot' conductors, and I don't see how any point will substantially have more than 15 amps flowing. Thirty amp total, sure, but basically split onto two wires.

 

[LarryFine]

Uh, yeah. I forgot that this circuit has two non-parallel grounded conductors. I was visualizing a shared neutral . . .

I took it as a given that the whites were tied together where the blacks were. If not, each will carry the total currents of the loads connected to it.

When drawing it out, I see that we simply have two (poorly) paralleled 14 awg 'hot' conductors, and I don't see how any point will substantially have more than 15 amps flowing. Thirty amp total, sure, but basically split onto two wires.

That's how I see it, too. Generally speaking, the main ring of wire is protected at 15a, but the loads (and any taps or pigtails) are not.

Granted, more than 15a could flow through any section, but either breaker will step in when its conductor carries more than its share.

 

[realolman]

I think everyone pretty well gets this by now, but I will give the dead horse one more shot, because I think the words taps and pigtails give the impressions of only small portions of the circuit not being protected. Taps are also a seperate subject.

It could in fact be extensive portions... even the majority of both circuits that are subject to 30 amps and could be far away and seemingly unrelated to the original connection point of the two circuits... at ANY point in EITHER circuit... not just the portion on the load side of the connection.

In this picture the two black circuits are connected at the blue connection and the blue portion is subject to 30 a.. However the red portions are also subject to 30 a.

I believe I'm done now... thank you.... thank you very much.

 

[ptonsparky]

Can not remember which mfgs, but didn't one or two make a 200 amp panel that paralleled two 100 amp cbs?

 

[mcclary's electrical]

Can not remember which mfgs, but didn't one or two make a 200 amp panel that paralleled two 100 amp cbs?

GE, among others, good point, but installed in that manner,they balance automatically

 

[growler]

I think everyone pretty well gets this by now, but I will give the dead horse one more shot, because I think the words taps and pigtails give the impressions of only small portions of the circuit not being protected. Taps are also a seperate subject.

Want to have some real fun??? Try explaining this problem to a homeowner and that it really is worth his spending some of his hard earned money to correct this problem when everything appears to be working just fine.

It really gets to be fun if the circuits are connected in a junction box buried in the wall of his newly remodeled living room or behind some book shelves or molding.

 

[LarryFine]

In this picture the two black circuits are connected at the blue connection and the blue portion is subject to 30 a.. However the red portions are also subject to 30 a.

I agree with you 100%. All three of those are electrically identical, qualify as the taps I was talking about, and are subject to overload.

But, each of the two breakers will still protect their respective home runs just as they would without the accidental inter-connection.

Again, for the overload to happen, a load in excess of 15a would have to be applied to each one of those taps, or branches, of the loop.

 

[LarryFine]

Can not remember which mfgs, but didn't one or two make a 200 amp panel that paralleled two 100 amp cbs?

Yes, for the main, but the paralleled portions are only an inch or so long, outside of the breakers themselves.

 

[220/221]

Want to have some real fun??? Try explaining this problem to a homeowner and that it really is worth his spending some of his hard earned money to correct this problem when everything appears to be working just fine.

Aint that the truth. Fortunately, this previous customer has complete faith in us. I just offered a basic explanation, he nodded his head and said "fix it".