House breakers accidently in paralell?

[plumsolly]

The story goes like this: We had a smoking light switch in the bathroom of our apartment a few weeks ago. I went to go flip the breaker in order to take the switch out. We are on the second floor and the breakers are in the basement and I found they were unlabeled. My girlfriend went down to flip breakers on and off until the lights went out in the bathroom. She cycled through each breaker and the lights never went off. Is there another breaker box? No. We finally figured out that two breakers had to be switched off at the same time in order to cut the power to this circuit. The way I figure it, the only way this could happen is if the circuit is wired through two breakers in parallel. If that is the case, that means that instead of breaking at the 20A the individual breakers are rated, it wont break until the circuit is drawing 40A. This seems awfully dangerous. So I told our landlord, who said she spoke with her electrician who said that it would be a major hassle to track down the fault, and it wasn't dangerous anyway. So I called the electrical code office, who said it wasn't their job. Then someone from the fire department came by for a routine check, and when I asked him he said there was nothing he could do, but if the apartment burned down, it wasn't my fault. So I have mostly given up, but I thought I'd see if anybody here had any thoughts.

Best, Ben

 

[owel]

, that means that instead of breaking at the 20A the individual breakers are rated, it wont break until the circuit is drawing 40A.

I believe they'll still trip at 20A. (think of the fuses as just wires, and not as resistors or load)

 

[Speedskater]

Parallel fuses will trip at some point between the rating of the smallest fuse and the sum of all the fuses. Why? Because there is nothing to force an even distribution of current. They divide current like very low value resistors in parallel, but each one will have a slightly different cold resistance. The fuse with the lowest cold resistance will carry the most current, As they heat up each fuse resistance will change with temperature. Huge fuses are made of multiple matched elements in parallel. 

 

[zebra50]

I had the same issue - upstairs & downstairs rings were wired in parallel to two 30A breakers at the distribution board. We found the problem last year, after living with it for 13 years!

It was simply a crossed wire at the distribution, and it only took my electrician a couple of minutes to track it down once he'd realised the problem.

 

[JohnRoberts]

If you have to turn two breakers off to break the circuit... only turn one back on...

There I fixed it for you...  ;D

JR

 

[plumsolly]

, that means that instead of breaking at the 20A the individual breakers are rated, it wont break until the circuit is drawing 40A.

I believe they'll still trip at 20A. (think of the fuses as just wires, and not as resistors or load)

They still have to split the current, though.

Parallel fuses will trip at some point between the rating of the smallest fuse and the sum of all the fuses. Why? Because there is nothing to force an even distribution of current. They divide current like very low value resistors in parallel, but each one will have a slightly different cold resistance. The fuse with the lowest cold resistance will carry the most current, As they heat up each fuse resistance will change with temperature. Huge fuses are made of multiple matched elements in parallel. 

Right - that makes sense. I erroneously assumed that the resistance would be directly tied to the amp rating, so they would be the same.

If you have to turn two breakers off to break the circuit... only turn one back on...

There I fixed it for you...  ;D

JR

You sir, are a brilliant man! That might put a lot of outlets/loads on one 20A breaker but that is certainly preferable to the alternative. Why the f@#$ didn't I think of that?!

Best, Ben

 

[sodderboy]

That still is not safe!  If you were to add any wiring or anything you could have trouble.
Just this sitch is a cry for help, and there must be other bad things around.
You should use a "circuit sniffer" to ID all circuits, and use a test plug to verify all live-neutral-grounds correct.
Mike

 

[JohnRoberts]

Using only one breaker for two branches should not be inherently unsafe, but if it starts tripping too frequently there will be a temptation to return to the unsafe two in parallel mode.

it is worthwhile figuring out how/where the two branches got shorted together and fix that..

I am surprised by what some electricians think is safe... Not surprised by landlords, but it's their property that burns down so they should be concerned too.

It's hard to imagine an innocent way to connect two branches together, or good reason, but stuff happens. 

The next question is what other mistakes may be found.

I hope you have a smoke detector.

JR

 

[Butterylicious]

I'm a master electrician and I've seen this numerous times.  IMO it is not safe.  The quick fix (which I discourage) is to isolate both home runs at the panel, then disconnect the hot & neutral of one of them.  This is still bad because now you have what's known as a back feed in the panel, and some poor unsuspecting inexperienced electrician could easily get the crap knocked out of them because normally power leaves the load center.  It's a "shocking" surprise when you find a back feed.  Furthermore, if either of the home runs are are 12/3 (shared neutral 2 circuit) you could create a 240V series circuit by disconnecting the wrong neutral.  It's also possible that it was intended to be 2 circuits, so disconnecting 1 breaker could leave you with an overload.  Parallel breakers do double the available current which is in excess of what the wire is rated for.  Under normal operating conditions it's fine, but that's not what you care about when dealing with over current protection devices.

The right fix
Your electrician is lazy.  Forever is a long time in a lonely place.  You can sniff it out yourself in an hour or less with no special tools, beyond linemen pliers, strippers, a screw driver, and a test light.  A jam box is a good substitute for a test light when working by yourself.

1st, turn off every breaker except for the 2 parallel breakers in question.  Now wander around your house and map out all the lights and receptacles that are still hot.  Assuming it's #12 wire on a 20 amp circuit, you should expect to fine 10 - 12 plugs and lights if it was supposed to be 1 circuit originally, or 20 - 25 plugs and lights if it were supposed to be 2 circuits.  If the breakers are 15A and the wire is #14AWG, reduce those expected quantities by 20ish%.  Now take into consideration if something should be a dedicated (solo) circuit such as a refrigerator, washer, etc.  If that's the case, shut off the power, pull that plug, and disconnect 1 set of wires and cap them off with wire nuts.  If it all appears to be general purpose, you're gonna wanna break the circuit somewhere in the middle.  Typically one wires in a linear fashion, meaning you leave the panel and wire in a shortest distance possible, or room by room.  Look at your map, I'd bet you see some sort of circle.  Pick a plug at the furthest point from the panel, shut off the breakers, disconnect and cap 1 set of wires, fire up just 1 of the breakers and retrace your map.  You're looking for balanced quantities, but it doesn't have to be exact.  If you have 9 plugs on one circuit and 12 on the other, that's good enough.  It's considered good etiquette to leave a note in a box with a dual feed where you've split the load.

If yo get cold feet, find a different electrician.  If you want to do it yourself, but want more internet guidance, then go ahead and map out the circuit in question and post back with a diagram.  I'll talk you through it.  Take pictures.  Approximately when was the apartment built?  What is the wire and breaker size?

-Richard

 

[PRR]

I had that in my last house. Congrats for understanding the problem.

> It's hard to imagine an innocent way to connect two branches together

In my case: there were light-circuits in the kitchen, then the required toaster-circuit was added by using bigger boxes and putting the outlet in with the light switches.

Black wire, black wire..... which is which? A logical approach might lead to a correct solution, but that didn't happen.

The next question is what other mistakes may be found.

Yes. When I went in I already knew 60% of outlets were white/black reverse and ungrounded. The ground wires were there, neatly cut back so they did not get in the way while doing the white and black wrong. In the adjacent room there was lamp-cord through the ceiling and down the outside wall to those outlets. Upstairs were splices without boxes (also without wire-nuts or now-banned solder, just twist-splice).

I like JR's "leave one breaker off" as a trial-fix. If you don't run toasters, heaters, microwaves in that area, it may be "OK". The code requires 3(?) Watts per square foot. 120V*15A is 600 square feet or 24'x24'.

There is the risk that the cross-connect is not a good screw-joint but some pinched insulation letting both black conductors "touch". Inspecting each box is the best way to find a hard-connect; if not found, be very suspicious. You could also run the 1,400 Watt heater until it flickers dim and smoke happens inside a wall.... don't try this at home. Anyway you have to try this destructive test both ways (one breaker then the other).

As Richard notes, this is NOT the long-term fix. That breaker will get turned-on again. And with both breakers, as Kevin says the trip-point is uncertain but surely in excess of wire rating. _I_ would consider disconnecting, trimming, wire-capping, and taping-up the "extra feed". This gives future electricians a clue that something is very ODD here. It might be more legal to pull the feed out of the fusebox, but then you MUST terminate it inside a box. Maybe better to have a loose-end inside the "non user servicable" fusebox than a loose wire on the wall above or a mystery junction-box with a surprise inside.

Better would be to TURN OFF, map, then open the most likely cross-connect boxes. See how many and which way the wires run. With luck they go in the obvious directions; more luck if you can trace them in basement or attic. But working inside wall-boxes is an acquired skill: I'm a wire-guy yet I asked Richard for tips to make good clean long-term safe outlet boxes. Working with someone else's mess is often worse than making a from-scratch (new room) mess as I was doing.

> it only took my electrician a couple of minutes

There are many practical advantages to ring-mains. Not counting dedicated appliances, I have like 13 circuits in a 2-floor (plus basement) house. That's about 120 more ways to cross-connect. (Except 60 of those will short across the 120V+120V legs and blow-fuse instantly.)

 

[zebra50]

Not counting dedicated appliances, I have like 13 circuits in a 2-floor (plus basement) house. That's about 120 more ways to cross-connect. (Except 60 of those will short across the 120V+120V legs and blow-fuse instantly.)

Wow, that's a lot of circuits.

My old place had just 4 -  2 x 30A ring main and 2 x 10A lighting (easy, but still wrong!), and my new house (3 floor town house) has 3 x lights, 3 x mains, plus a separate supply for the cooker. We're 240V over here of course, so more power per unit copper.

 

[johnR]

I once found a frightening example of this. A family member had just bought a house and asked me to check the electrics. There was a fairly new breaker panel that had obviously been installed by a non-electrician. The live conductors for the whole house had been connected into it entirely at random. There were two parallel 32A breakers feeding thin lighting circuit wires and other horrors. It took quite a while to fix it.

 

[okgb]

Don't forget the split recepticals in kitchens
where one outlet is broken for two different circuits
[ which then also go to another outlet ]
to aid in not blowing circuits by plugging in too many taosters

 

[SSLtech]

One other way to look at it is to try and find out which OTHER circuit is being affected by the same pair of breakers... for example, if you have bedroom 2 on one breaker, and bedroom three on another, and then bedroom 2 and 3 live connections somehow get acquainted, you 'll have both breakers controlling both rooms in parallel.

If that were to be the case, the closest-approach (where black wires bet confused and twisted together inside a wire nut for example) would be any common wall separating the two.

It's not a guaranteed way to trace the problem, but it's a useful way to look at the problem in a 'usual suspect' kind of way.

Keith

 

[JohnRoberts]

While this may be a variant on ideas already suggested,, With breaker number one on, make some quick spot measurements of outlet voltages. The again with only breaker number two on. Any voltage trends revealed should suggest where branches connect to the fuse box (highest voltage), and perhaps each other (mid way to lowest voltage each way).

Clearly there needs to be some loads on the branches to develop some useful voltage drop.

There may be some normal variation in mains voltage, so these measurements may need to be repeated and averaged, but if trends show up, this could narrow down where to look for the shunt connection. 

JR

 

[Butterylicious]

>Don't forget the split recepticals in kitchens where one outlet is broken for two different circuits

This is one reason I asked the age of the house.  Assuming the house was wired to code originally, knowing the approximate age will help determine how it should have been wired.  Split circuit receptacles in a kitchen was ousted in the early 70's in lieu of 2 completely separate small appliance circuits, shortly there after was the implementation of GFCI protection.

>We had a smoking light switch in the bathroom

This raises a few questions:  If it's smoking, it's likely to be pulling excessive current.  Shouldn't the breaker have tripped?  Maybe.... maybe not.  Obviously not with parallel feeds.  If it were a "true" parallel, meaning the circuit paralleled on one end and dead ending on the other, the ampacity would be 40 amps for a pair of 20 amp breakers, but since this is a loop, or bidirectional feed, it's a matter of which way the current decides to flow.  certainly > than 20A and probably closer to the 40A thang.  Unless there is a very long length, or a very large load, I wouldn't expect to see much easily measurable voltage drop.  Knowing that the culprit is in the bathroom, again the age matters.  I believe it was 1996 when bathrooms were supposed to be on their own circuit.  Before that, it was acceptable to put the lighting on a general use circuit and put all the garage, bathroom, and exterior receptacles on a single GFCI circuit.  Another question is, are there any obvious signs of remodel or rewiring?

>if you have bedroom 2 on one breaker, and bedroom three on another, and then bedroom 2 and 3 live connections somehow get acquainted, you 'll have both breakers controlling both rooms in parallel.

Good example and actually what the current codes are alluding to w/o coming right out and saying, "put each room on it's own circuit."  The key to figuring out this puzzle is to map out the offending circuit.  Next analyze the map by location and load.  I bet if you sketch a floor plan and depict the devices served by the offending circuit, you'll quickly see a pattern and have a pretty good idea where the mid point is.  Obviously it'll be a little hit-n-miss, but again, it's not critical that the circuits match exactly.  Hopefully you can make the split in a receptacle box instead of a switch box because there are less variables.  You do want to disconnect both the hot and neutral so you completely break the path.  I'd leave the ground looped.  This is an apartment, not a piece of audio gear.

One thing that does cross my mind is that the loop may have been a bandage to a nicked wire where just the neutral was broken.  That can be a brain teaser.  You'll realize this after you split the circuit if part of it does not come back up.  It's professionally embarrassing to say but a lot of electricians cut corners.  I doubt this is the case, but it's worth tossing out there.  Assuming this is an apartment as in "an apartment complex," they're usually roped by huge teams of rookies and an extra jumper seems most likely.

 

[plumsolly]

Thanks for all the insight. You guys are amazing. Our apartment is one of 5 that were created out of a turn-of-the-century mansion. There are 8 or so circuits for the entire building, and only one breaker box. I don't think I would be welcome to go poking around with the wiring. So I think that I'll switch one of the breakers off for now (we'll have to see how often the remaining breaker flips) and try to convince the landlord to address the problem. It's frustrating that, as a tenant, I have no recourse. As far as I can tell, this constitutes a blatant violation of electrical code - But once the electrical system has been installed,modified, or whatever it was that they had to get a permit for, there is no body that can enforce that it stays up to code - even with a specific complaint.

Thanks again and all the best,

Ben

 

[sodderboy]

Now it's time to tell the landlord about the smoking switch.  You can check what kind of legal responsibility he has, and put the squeeze on.  Embellish a little.
No one want's a fire.  The real way to wire that situation is to have separate sub-boxes in each flat. 

I am off the charts for about 30 min in the morning.  I have to juggle a choice of 3 appliances in the kitchen- drip coffee, electric kettle, toaster, microwave, and fridge compressor.  My missus is still waiting for that extra circuit. . . 

I am sure the landlord wants to fix this.  If he does not, then a lawyer can hold your rent payments in escrow until the problem is corrected.  Again, check what kind of rights you have as a tenant.  In NYC tenants have all the rights, and "rightly" so.
Mike 

 

[Emperor-TK]

Colorado has a law called The Warranty of Habitability Act passed in 2008 which addresses a tenant's right to a safe and habitable rental.  It considers a house legally uninhabitable if  "the premise is in condition that is materially dangerous or hazardous to the tenant's life, health or safety".  Fire and shock hazards seem like they would apply here.  If nothing else, bringing up the law might scare the crap out of your landlord to do something about the wiring.  I own four rental units, and any safety issue gets addressed immediately, regardless of cost, but not all landlords are like me.

-Chris

 

[Mbira]

back feed in the panel

Wow, that is scary.  Never heard of that, and I sure as heck wouldn't ever think to look for such a thing!