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sparkjumper
If you wanted two seperate 20A circuits to share the same neutral would you put the lineside wires on two seperate single pole 20A breakers or use a 2 pole 20A breaker?
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madpenguin
Member
2 pole breaker.
We just had a big discussion about this a few days ago. I think you might have even posted on that thread if I'm not mistaken.:smile:
Both hot's would need to be in the same cable/raceway (as well as the neutral). ie - 12/3 romex, otherwise you'll get inductive heating. Each hot conductor on a different phase otherwise you'll get an overloaded neutral. Neutrals firmly wire nutted and pigtailed otherwise a potential for 240v exists when soley using the yoke connections (loose neutral).
We just had a big discussion about this a few days ago. I think you might have even posted on that thread if I'm not mistaken.:smile:
Both hot's would need to be in the same cable/raceway (as well as the neutral). ie - 12/3 romex, otherwise you'll get inductive heating. Each hot conductor on a different phase otherwise you'll get an overloaded neutral. Neutrals firmly wire nutted and pigtailed otherwise a potential for 240v exists when soley using the yoke connections (loose neutral).
madpenguin
Member
Oh.... And both hot conductors in the panel need to be zip tied together or grouped in a similar method to indicate that they belong to the same circuit.
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sparkjumper
I'm a little confused.You say they belong to the same circuit but they are two different 120V circuits sharing the same neutral.Lets say one circuit fed the receptacles in one room while the other circuit fed the receptacles in another room.Both circuits share a common neutral.Grandma has her heart machine hooked up in one room.In the other a horny grandpa uses an air compressor to blow up his sexdoll inadvertantly overloading the circuit and tripping the breaker.This in turn cuts power to grandma's heart machine and off she goes.If they had been on two seperate single pole 20A breakers my grandma would be alive today!
M
micro gro
Funniest electrical illustration ever.
madpenguin
Member
Dedicated life support equipment shouldn't be ran on a MWBC anyway.... :smile:
Yes, that can surely happen but you are required to have an internal common trip mechanism that kills both ungrounded conductors at once for the safety of servicing personnel and to just plain de-energize the entire circuit when the breaker is tripped. It is called a Multi Wire Branch Circuit (singular) after all, so both hot conductors need to be killed by the same fuse.
I don't make the rules, I just follow them..... :wink:
It IS vitally important that both ungrounded conductors be fed from opposite phases otherwise your neutral wire is liable to catch on fire due to overload conditions. If you stabbed both hots on the same phase and each hot was pulling 16A then your neutral wire will be seeing 32A worth of current when it's only rated to carry 20A non-continuous or 16A continuous. Talk about a melt down.
The double pole breaker also ensures that this will be a non-issue. Using opposite phases in the above situation would mean that your neutral will see 0A worth of current, not 32A.
Yes, that can surely happen but you are required to have an internal common trip mechanism that kills both ungrounded conductors at once for the safety of servicing personnel and to just plain de-energize the entire circuit when the breaker is tripped. It is called a Multi Wire Branch Circuit (singular) after all, so both hot conductors need to be killed by the same fuse.
I don't make the rules, I just follow them..... :wink:
It IS vitally important that both ungrounded conductors be fed from opposite phases otherwise your neutral wire is liable to catch on fire due to overload conditions. If you stabbed both hots on the same phase and each hot was pulling 16A then your neutral wire will be seeing 32A worth of current when it's only rated to carry 20A non-continuous or 16A continuous. Talk about a melt down.
The double pole breaker also ensures that this will be a non-issue. Using opposite phases in the above situation would mean that your neutral will see 0A worth of current, not 32A.
madpenguin
Member
Look at what I've bolded. That makes it one circuit. :smile: Just as a 240v appliance that uses some 120v functions (kitchen range) is considered one circuit. You really only need both hots for the oven to heat up and work but without the neutral, you can't use the timer or inside light to check your food. Not really a whole lot different than a MWBC. Well, it is... But still. It's one circuit.
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sparkjumper
I know when I used to hook up modular furniture using 3 phase power,we would have to use a 3 pole breaker so that makes sense.I spent yesterday in a xanax haze.Friday afternoon my best friend in this world was electrocuted working in live switchgear.He had about 20 years experience too.I cant believe it.I havent worked with my tools since 2001 when I took OG to heart,and I think I hate electricity more than anything in the world right now.This person so appreciated the erb and just had a good heart.I can think of so many others that deserve to be fried but it had to happen to him.I dont have the details yet as I spent yesterday comatose,but I better not find out he was pressured to work live switchgear just to save time or something.
madpenguin
Member
Wow.. I'm really sorry to hear that. This happens all the time and usually it IS because people are forced to work on hot equipment, whether it was a necessity or just a time saver thing. I've been fired before for refusing to work on High Voltage equipment when we could have just came back at night and shut everything down.
Spark, I'm sure you don't want to watch this but this kind of thing happens almost everyday somewhere in the US... (for others who may be reading).
http://www.youtube.com/watch?v=4bBvmPRqfmo
PPE is vital when working on equipment like that. Proper rated nomex gloves, suit, face shield, ear plugs, the whole works.
As I said in a previous thread a few days ago, I shorted out a hot phase on a ground rod (with a drill bit as the intermediary
) in an external disconnect last week. It was only 120v (unfused) and I pulled back quick so just got away with a little singed hair but if that had happened on Higher Voltage, I probably wouldn't be here right now... I was also lucky it was only a #2 XHHW-2 conductor. The arc flash completely incinerated the hot wire by the time my brain registered what was happening. I was lucky all around.
Hope you sort this out OK upstairs and can feel better soon.
Spark, I'm sure you don't want to watch this but this kind of thing happens almost everyday somewhere in the US... (for others who may be reading).
http://www.youtube.com/watch?v=4bBvmPRqfmo
PPE is vital when working on equipment like that. Proper rated nomex gloves, suit, face shield, ear plugs, the whole works.
As I said in a previous thread a few days ago, I shorted out a hot phase on a ground rod (with a drill bit as the intermediary
) in an external disconnect last week. It was only 120v (unfused) and I pulled back quick so just got away with a little singed hair but if that had happened on Higher Voltage, I probably wouldn't be here right now... I was also lucky it was only a #2 XHHW-2 conductor. The arc flash completely incinerated the hot wire by the time my brain registered what was happening. I was lucky all around.Hope you sort this out OK upstairs and can feel better soon.
