Do two 20's make a 40?

[olc]

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.

 

[qcroanoke]

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.

No. 310.4

 

[Smart $]

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.

The following section applies...

240.8 Fuses or Circuit Breakers in Parallel. Fuses and circuit breakers shall be permitted to be connected in parallel where they are factory assembled in parallel and listed as a unit. Individual fuses, circuit breakers, or combinations thereof shall not otherwise be connected in parallel.

 

[kwired]

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.

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.

 

[Dennis Alwon]

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 don't know your situation but is it possible that the max overcurrent protection device (OCPD) is 50 amps and the minimum circuit ampacity is 30 amps or less? In this case you can use #10 with a 50 amp OCPD

 

[stew]

see 310.10 (I) in the 2011. must be 1/0 or larger to run in paralell

 

[Smart $]

No. 310.4

see 310.10 (I) in the 2011. must be 1/0 or larger to run in paralell

Technically, conductors are not paralleled unless they connect together at both ends. As I interpret the OP, the supply ends of the conductors terminate on different breakers.

 

[wirenut1980]

Technically, conductors are not paralleled unless they connect together at both ends. As I interpret the OP, the supply ends of the conductors terminate on different breakers.

But the breakers connect to the same bus bar, right? How is that not connecting in parallel?

 

[jusme123]

Technically, conductors are not paralleled unless they connect together at both ends. As I interpret the OP, the supply ends of the conductors terminate on different breakers.

its a parallel circuit, and non compliant the way he is running it.

1/0 is the min. for ll ckts

310.4 Conductors in Parallel. Aluminum, copper-clad
aluminum, or copper conductors of size 1/0 AWG and
larger, comprising each phase, polarity, neutral, or
grounded circuit conductor, shall be permitted to be connected
in parallel (electrically joined at both ends).

 

[infinity]

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.

Short answer no, as mentioned the minimum size is #1/0.

 

[Smart $]

But the breakers connect to the same bus bar, right? How is that not connecting in parallel?

its a parallel circuit, and non compliant the way he is running it.

1/0 is the min. for ll ckts

310.4 Conductors in Parallel. Aluminum, copper-clad
aluminum, or copper conductors of size 1/0 AWG and
larger, comprising each phase, polarity, neutral, or
grounded circuit conductor, shall be permitted to be connected
in parallel (electrically joined at both ends).

The distinguishing criteria between parallel circuitry and parallel conductors is highlighted in the quote above. Connecting "through" two breakers and panelboard bussing do not qualify as electrically joining two conductors in this context. The "electrically joined" requirement does not mean "through" equipment having a main function other than connection. Now if you connect those two wires to a single breaker and together at the load end, then that is conductors in parallel.

 

[olc]

Thanks.
It looks like the answer is no if under 1/0.
(The question was - parallel conductors connected at each end?)

 

[jusme123]

Technically, conductors are not paralleled unless they connect together at both ends. As I interpret the OP, the supply ends of the conductors terminate on different breakers.

...........please explain how the ckt breakers trip on a fault when 2 (of the same phase) are not 'handle tied,' as you propose? :slaphead::happyno:

 

[kwired]

...........please explain how the ckt breakers trip on a fault when 2 (of the same phase) are not 'handle tied,' as you propose? :slaphead::happyno:

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.

 

[Smart $]

...........please explain how the ckt breakers trip on a fault when 2 (of the same phase) are not 'handle tied,' as you propose? :slaphead::happyno:

I'm not proposing it. I'm saying when each of two wires are connected an individual circuit breaker, and also connected together at the load terminal, they are not conductors in parallel... in the context used by the NEC. And as such, parallel conductor requirements do not apply. Please refer to post #3.

Also note that OP'er has clarified the intent was to connect the conductors in [NEC] parallel, so continuing this discussion is moot.

 

[iwire]

The distinguishing criteria between parallel circuitry and parallel conductors is highlighted in the quote above. Connecting "through" two breakers and panelboard bussing do not qualify as electrically joining two conductors in this context.

In my opinion the above is entirely an opinion and not really backed with code.

The "electrically joined" requirement does not mean "through" equipment having a main function other than connection.

I am interested where I can find that in the NEC.

 

[Smart $]

In my opinion the above is entirely an opinion and not really backed with code.

I am interested where I can find that in the NEC.

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???

 

[kwired]

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???

I am not going to get into this argument again, last time almost everyone ganged up on me. Even had someone tell me I had no business understanding electrical theory because I'm not an engineer Lets just say there is a difference between conductors that are just parallel to each other and conductors connected "in parallel - effectively making them one". What we are talking about in this thread IMO is somewhat of an attempt to combine the two.

 

[Smart $]

I am not going to get into this argument again, last time almost everyone ganged up on me. Even had someone tell me I had no business understanding electrical theory because I'm not an engineer Lets just say there is a difference between conductors that are just parallel to each other and conductors connected "in parallel - effectively making them one". What we are talking about in this thread IMO is somewhat of an attempt to combine the two.

A hybrid, of sorts.

Additionally, to accept the notion the two wires, each connected to a different breaker and supplying the same load terminal, are "conductors in parallel" is predicated upon accepting the notion circuit breakers are NEC-defined conductors... which they are not.

 

[busman]

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