Do two 20's make a 40?

[kwired]

Parallel means electrically joined at both ends.

Then you have "paralleled conductors" that are joined at both ends effectively making them a single conductor.

Just the word parallel is not specific enough. All the loads in your house are parallel to each other and to the power source. If they were not parallel they would have to be connected in series. If they were connected in series you would have a different amount of voltage drop across each one, they would all have to be in the "on" state or you would have an open circuit and nothing would work.

 

[tyha]

2 - 20's does make a 40 but there is not likely to be NEC compliant.

As far as needing 50 amp circuit for a conensing unit you need to consider a few more things. If the minimum circuit ampacity is 30 or less the 10 AWG NM cable is fine even if the unit calls for a 50 amp breaker.

Please give me the code reference that states you can connect a #10 to any CB higher than a 30 amp. We always just made sure the breaker was sized in between the min ckt amps and the max fuse and choose the wire according to what the breaker size ended up being. what code reference states i can connect the min ckt amps (wire) to the Max fuse size. I cant beleive I have been wasting all that wire.

my edit ( I didnt think about you were implying he use a a 30 amp breaker rather that the 50)

 

[kwired]

Please give me the code reference that states you can connect a #10 to any CB higher than a 30 amp. We always just made sure the breaker was sized in between the min ckt amps and the max fuse and choose the wire according to what the breaker size ended up being. what code reference states i can connect the min ckt amps (wire) to the Max fuse size. I cant beleive I have been wasting all that wire.

my edit ( I didnt think about you were implying he use a a 30 amp breaker rather that the 50)

How about we start in table 240.3. Anything mentioned in that table may vary from the general rules set in 240. Motors is probably just about the number one place where branch circuit overcurrent device is rated higher than required conductor ampacity. Rules for airconditioning in 440 refer you to rules in 430. Running through rest of table some appliances could have this situation, capacitors usually do, cranes and hoists - probably, welders could, elevators - probably, fire pumps - they want them to still hold overcurrent device indefinately when locked rotor current is encountered, industrial machinery - very likely, transformers - it does happen - usually with conditions.

 

[Smart $]

Parallel means electrically joined at both ends. This simply means that there is more than one path for the electrons to get from point A to point B. In this case from the busbar in the panel to the terminals of the equipment. It doesn't matter what they pass thru in between (circuit breakers, fuses, splices, receptacles, etc.) they are still parallel if there are two current conducting paths.

Just one man's interpretation.

Mark

Consider parallel paths is not the same as Conductors in Parallel...

Just the title and scope of Article 310 should be a clue.

A clarification might be, two or more equivalent [wire] conductors connected together at their ends and serving in lieu of one larger conductor.

 

[iwire]

You won't find it spelled out explicitly... but consider the alternative if you open the contextual meaning to allow electrically joined through equipment other than functionally simple connecting means. Every splice in a circuit would then be considered a conductor in parallel. For example, one home run spliced to two or more runs supplying two or more loads. These spliced-in conductors are electrically connected through the load equipment in parallel. Are you going to start calling them conductors in parallel. How many violations would that make in existence???

Well in my opinon being connected through a load does not make them in parallel. If it did that would be known as a short circuit.

 

[iwire]

Consider parallel paths is not the same as Conductors in Parallel...

I agree and have no idea why the path was brought into this thread.

 

[B4T]

I have seen plenty of kitchen guys who take a 10/3 cook top and a 10/3 wall oven and turn it into a 50 amp. circuit for a self cleaning free standing oven..

I was called "picky" by the kitchen guys when I mentioned it to the HO while doing a service change..

Most of these guys feel qualified to do their own wiring these days..

 

[Smart $]

Well in my opinon being connected through a load does not make them in parallel. If it did that would be known as a short circuit.

Well it's not imo either, so why do you believe it applies through breakers?

 

[jusme123]

Handle tie means nothing, they may not trip at same time but enough current will be drawn that they both will trip. 20 amp breaker with ground fault of well over 100 amps and likely at least 1000 amps should have no trouble tripping both. Not saying this is code compliant but will work. If both paths are same impedance each path will carry half the total current.

......they are required to trip at the same time. Just realized your second comment (not code compliant), its covered in the international book of hacks.

 

[jusme123]

....just one more question, would you consider the neutrals paralleled?

 

[kwired]

......they are required to trip at the same time. Just realized your second comment (not code compliant), its covered in the international book of hacks.

Handle ties do not assure that there will be common trip. Common trip breakers do. For the improper install being discussed here you will not find a common trip breaker to use anyway. The only purpose for handle ties is to assure all poles are operated when manually shutting it off.

 

[K_Buz]

Asked by a client:
For example if there are two 20A (#12) romex or MC cables installed but a 40 amp circuit is required can the two circuits be combined in parallel for the circuit?
Actually I think 2 30A (#10) circuits were installed for future condensing units but a 50A circuit is needed.

I haven't seen it addressed yet, but if we are assuming that there are 2 12/2 cables existing and he want's to splice them together (in parallel) to create a 40A circuit, how can you be sure that the cables are exactly the same length?

 

[iwire]

Well it's not imo either, so why do you believe it applies through breakers?

Because the section says electrically connected, not physically connected.

 

[Smart $]

Because the section says electrically connected, not physically connected.

Actually, it says "electrically joined".

If you have the pdf version of the NEC, search the term "join". Throughout the body, join, joint, and variations thereof, have the contextual meaning of connecting like with like directly. In most cases, physically abutted... sometimes using other "parts" to accomplish such. Yet nowhere is it implied, when not abutted, these additional "part(s)" can be two or more breakers and bus, nor that the joint is formed indirectly.

As I said earlier, conductors in parallel mean two or more equivalent conductors serving in lieu of one larger conductor. Would you connect one conductor to two breakers? Besides, as I pointed out very early in the thread, using parallel breakers is a violation of 240.8.

 

[kwired]

OK looking at title of thread I can't keep it back any longer.

If I have two 20 year old girlfriends, does that make one 40 year old?:lol:

 

[iwire]

Actually, it says "electrically joined".

OK, I went from memory. I see no differance in either wording.

If you have the pdf version of the NEC, search the term "join". Throughout the body, join, joint, and variations thereof, have the contextual meaning of connecting like with like directly. In most cases, physically abutted... sometimes using other "parts" to accomplish such. Yet nowhere is it implied, when not abutted, these additional "part(s)" can be two or more breakers and bus, nor that the joint is formed indirectly.

Interesting but IMO not relevant.

As I said earlier, conductors in parallel mean two or more equivalent conductors serving in lieu of one larger conductor. Would you connect one conductor to two breakers?

No I would not but that was the question in the OP.

Besides, as I pointed out very early in the thread, using parallel breakers is a violation of 240.8.

I agree, but IMPO the parallel conductor rule would also be broken.

Why are we still talking about it? Because that is what we do here.

 

[Smart $]

OK, I went from memory. I see no differance in either wording.



Interesting but IMO not relevant.



No I would not but that was the question in the OP.




I agree, but IMPO the parallel conductor rule would also be broken.

Why are we still talking about it? Because that is what we do here.

Well, talk no more. I can see you are not open-minded on the matter :happyyes:

 

[tyha]

How about we start in table 240.3. Anything mentioned in that table may vary from the general rules set in 240. Motors is probably just about the number one place where branch circuit overcurrent device is rated higher than required conductor ampacity. Rules for airconditioning in 440 refer you to rules in 430. Running through rest of table some appliances could have this situation, capacitors usually do, cranes and hoists - probably, welders could, elevators - probably, fire pumps - they want them to still hold overcurrent device indefinately when locked rotor current is encountered, industrial machinery - very likely, transformers - it does happen - usually with conditions.

I know all all of those articles but where does it state the ocpd can be rated higher than the branch circuit. all it states is the branch circuit is to be selected from the table or from the nameplate which states "Minimum" branch circuit selection. I dont see anywhere in article 440 (which is where it would need to be) that the ocpd can be higher than the rated current capacity stated in 310.15 for the choosen branch circuit. it does state the ocpd must be rated at least 115% above the minimum branch circuit selection but it doesnt state that it can be rated higher than the branch circuit you select. IM not aruing, I am wanting to agree with you and be able to size the wire smaller than the CB but I need a definetive code reference that states I can do that.

 

[infinity]

I know all all of those articles but where does it state the ocpd can be rated higher than the branch circuit. all it states is the branch circuit is to be selected from the table or from the nameplate which states "Minimum" branch circuit selection. I dont see anywhere in article 440 (which is where it would need to be) that the ocpd can be higher than the rated current capacity stated in 310.15 for the choosen branch circuit. it does state the ocpd must be rated at least 115% above the minimum branch circuit selection but it doesnt state that it can be rated higher than the branch circuit you select. IM not aruing, I am wanting to agree with you and be able to size the wire smaller than the CB but I need a definetive code reference that states I can do that.

Take a look at 430.52 which will direct you to some other sections.

430.52 Rating or Setting for Individual Motor Circuit.
(A) General. The motor branch-circuit short-circuit and ground-fault protective device shall comply with 430.52(B) and either 430.52(C) or (D), as applicable.

 

[kwired]

I know all all of those articles but where does it state the ocpd can be rated higher than the branch circuit. all it states is the branch circuit is to be selected from the table or from the nameplate which states "Minimum" branch circuit selection. I dont see anywhere in article 440 (which is where it would need to be) that the ocpd can be higher than the rated current capacity stated in 310.15 for the choosen branch circuit. it does state the ocpd must be rated at least 115% above the minimum branch circuit selection but it doesnt state that it can be rated higher than the branch circuit you select. IM not aruing, I am wanting to agree with you and be able to size the wire smaller than the CB but I need a definetive code reference that states I can do that.

The general rule is that conductors need protected at their rated ampacity ? or next higher standard size overcurrent device. As I pointed out 240.3 list several other articles that may have exceptions to the general rule.


For the air conditioning equipment you mention we go to Art 440.


Three different parts of 440 come into play here.

1. Branch-Circuit Short-Circuit and Ground-Fault Protection
2. Branch-Circuit Conductors

VI. Motor-Compressor and Branch-Circuit Overload Protection


Each part tells us the requirements for that particular item and does vary from what is generally required in chapters 2 and 3.


When all three of these parts are applied you still end up with a conductor large enough to supply the load without overheating, you have short circuit and ground fault protection, and you have overload protection, so the conductor is protected from overcurrent and the resulting overheating, it is just done so with more than one device. Article 430 for motors accomplishes the same thing in a similar fashion in many installations.


Almost any equipment that has an inrush current when energized will have similar requirements.
There are instances that are more specialized like a fire pump. With a fire pump they want short circuit and ground fault protection but want the motor to run even if overloaded as the purpose of the pump running is likely more important than having it shut down because it is overloaded.

Hope this helps you understand. This could get lengthy to tell all the places where higher size overcurrent device than general rules allow may exist but the idea is about the same with most of them.