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Old 11-15-2011, 07:41 PM   #1
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combining 2 220v circuits


I have a dilema and a question. I am replacing my drop-in cooktop and electric range with a stand alone range. the problem is that there are 2 separate 220v drops, one for the old cooktop and another for the range. both are 220v with 30AMP breakers. The new range draws around 60amps. Can I tie both 220 lines together as one and use that circuit without any modification or does a new line need to be run. If it is ok, do I need to change the breakers to a lower amperage. This is a 2 story home with no real way to run another new line. Is this configuration ok or do I need to bite the bullet and have new line run..

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Old 11-15-2011, 07:47 PM   #2
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combining 2 220v circuits


A new properly sized circuit must be installed. The wiring in place now is too small to parallel.

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Old 11-15-2011, 07:53 PM   #3
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combining 2 220v circuits


I read the specs on the range and what I stated earlier was incorrect. They were generic KW values.. The KW rating for this model is 11.9 KW 240v so it would be 49 amp max current draw.

Last edited by idaman; 11-15-2011 at 10:07 PM. Reason: Correction
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Old 11-15-2011, 10:22 PM   #4
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combining 2 220v circuits


The current sharing between wires depends on the connection resistance at the wire ends and will be difficult to control. In general, these resistances will not be equal and may change over time.

The likely outcome for current draw over 30A is that one breaker will trip, then all of the current will go through the other cable, then the other breaker will immediately trip. You may see this outcome immediately or after some time interval.
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Old 11-15-2011, 10:26 PM   #5
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combining 2 220v circuits


You are not permitted to parallel wires under #6 gauge. You must run a new circuit with 6/3 cable.
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Old 11-16-2011, 06:18 AM   #6
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combining 2 220v circuits


Quote:
Originally Posted by joed View Post
You are not permitted to parallel wires under #6 gauge. You must run a new circuit with 6/3 cable.

under #0, you mean..
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Old 11-16-2011, 07:17 AM   #7
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combining 2 220v circuits


Joed, under the NEC you cannot parallel less than 1/0.
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Old 11-16-2011, 12:47 PM   #8
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combining 2 220v circuits


I should know better than to post a reply without drawing out the equivalent circuit and running the numbers.

For two parallel cables, how much different would the resistance of one, plus end connections, have to be from the other? Assuming I've made no reasoning or arithmetic errors, for a 30/19 amp split the answer is that one cable plus connections should have 30/19 ths the resistance of the other one.

In the special case of 50' of #10 copper Romex and two perfect end connections this lower resistance path is 0.10 ohm, so the other cable path is allowed to be 0.16 ohm.
For the other cable, assuming one perfect end connection, the last remaining connection which is assumed to be bad is allowed 0.06 ohm. This bad connection gives the uneven split.

To put this in perspective, I once found a badly installed wirenut - one of the wires did not have score marks from the coil spring inside the nut. This measured 0.5V at 10A, so 0.05 ohms.

I now say this particular parallel setup would probably work if you pay attention to the end connections.

Whether an electrical code allows this depends on their risk aversion and what they can expect, day to day, from their electricians.

Last edited by Yoyizit; 11-16-2011 at 12:59 PM.
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Old 11-16-2011, 01:11 PM   #9
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combining 2 220v circuits


Quote:
Originally Posted by Yoyizit View Post
I now say this particular parallel setup would probably work if you pay attention to the end connections.

Whether an electrical code allows this depends on their risk aversion and what they can expect, day to day, from their electricians.
It does not matter since what the OP proposed to do is strictly prohibited against by the NEC. Are you saying this could be safely done with enough conductors from phone cables if you made careful connections? Many thing are therohetically possible, but the intent is to give code compliant information to people that may not be able to discern theory from actual code compliant methodology.

You also ignored the specific conditions in which the rules about paralleling can be used including conductor length, materials etc.

Please stop giving advice that is in violation of the rules, regardless of your feeling af risk aversion. The rules are in place to protect life safety.
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Last edited by Jim Port; 11-16-2011 at 01:52 PM. Reason: added theory vs reality comments
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Old 11-16-2011, 01:47 PM   #10
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combining 2 220v circuits


Thank you Mr. Port. Safety first guys! Let's all follow the (common sense) rules and try to stay alive, OK?
Just because something CAN be done, does NOT mean it can be DONE!

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Old 11-16-2011, 10:00 PM   #11
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combining 2 220v circuits


Quote:
Originally Posted by Yoyizit View Post
I should know better than to post a reply without drawing out the equivalent circuit and running the numbers.

For two parallel cables, how much different would the resistance of one, plus end connections, have to be from the other? Assuming I've made no reasoning or arithmetic errors, for a 30/19 amp split the answer is that one cable plus connections should have 30/19 ths the resistance of the other one.

In the special case of 50' of #10 copper Romex and two perfect end connections this lower resistance path is 0.10 ohm, so the other cable path is allowed to be 0.16 ohm.
For the other cable, assuming one perfect end connection, the last remaining connection which is assumed to be bad is allowed 0.06 ohm. This bad connection gives the uneven split.

To put this in perspective, I once found a badly installed wirenut - one of the wires did not have score marks from the coil spring inside the nut. This measured 0.5V at 10A, so 0.05 ohms.

I now say this particular parallel setup would probably work if you pay attention to the end connections.

Whether an electrical code allows this depends on their risk aversion and what they can expect, day to day, from their electricians.


WTH, do you even own a NEC?
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Old 11-16-2011, 10:04 PM   #12
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combining 2 220v circuits


Quote:
Originally Posted by DangerMouse View Post
Thank you Mr. Port. Safety first guys! Let's all follow the (common sense) rules and try to stay alive, OK?
Smart fella, isn't he. He talks, I listen.

Quote:
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Old 11-16-2011, 10:15 PM   #13
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combining 2 220v circuits


Quote:
Originally Posted by idaman View Post
I read the specs on the range and what I stated earlier was incorrect. They were generic KW values.. The KW rating for this model is 11.9 KW 240v so it would be 49 amp max current draw.
This is a start....

Quote:
Originally Posted by joed View Post
You are not permitted to parallel wires under #6 gauge. You must run a new circuit with 6/3 cable.
Correct on the first statement. Not necessarily so on the second statement. While installing a range circuit using #6/3 cable is permissible, it is not required in this instance, in the US.

Table 220.55 of the NEC allows one range of 12 kW or less to have a maximum demand factor applied of 8 kW when figuring branch circuit loads.

A 40 Amp circuit, fed with a #8/3 copper cable is more than adequate for such an appliance.

Also note that section 210.19(A)(3) requires a minimum 40 Amp circuit for any range rated over 8-3/4 kW. This prevents the OP from using either of those existing 30 Amp circuits
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Last edited by kbsparky; 11-16-2011 at 10:17 PM.
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Old 11-16-2011, 10:20 PM   #14
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combining 2 220v circuits


Quote:
Originally Posted by kbsparky View Post
This is a start....



Correct on the first statement. Not necessarily so on the second statement. While installing a range circuit using #6/3 cable is permissible, it is not required in this instance, in the US.

Table 220.55 of the NEC allows one range of 12 kW or less to have a maximum demand factor applied of 8 kW when figuring branch circuit loads.

A 40 Amp circuit, fed with a #8/3 copper cable is more than adequate for such an appliance.

Also note that section 210.19(A)(3) requires a minimum 40 Amp circuit for any range rated over 8-3/4 kW. This prevents the OP from using either of those existing 30 Amp circuits
Nice.
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Old 11-16-2011, 10:42 PM   #15
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combining 2 220v circuits


I was thinking 60 amps sounded a bit high.

but ya, run some new grounded 6/3. doubling them up is not something I'd do, and I probably have a significantly under developed sense of fear about electricity.

If you just cant do it the right way, just put a range receptacle on your current line and don't use more than 2 burners or 1 burner and the range at a single time. Worst case is you trip your breaker.

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Last edited by forresth; 11-16-2011 at 10:46 PM.
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