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Suplying a load from two different circuits #98935
06/27/06 11:15 AM
06/27/06 11:15 AM
T
tdhorne  Offline OP
Member
Joined: Mar 2001
Posts: 345
Maryland, USA
I'm hoping that those of you with a better memory might be able to point me to the code section that forbids supplying a load from two different circuits. I tried a search but I didn't use the right search terms to get what I needed. I am aware of 300.3 (B) but I was hoping for something more on point. The load in question takes its ungrounded conductor from a 240 volt circuit and its grounded conductor from a 120 volt circuit. Thanks in advance for any help.
--
Tom Horne


Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use" Thomas Alva Edison
2017 / 2014 NEC & Related Books and Study Guides
Re: Suplying a load from two different circuits #98936
06/27/06 12:00 PM
06/27/06 12:00 PM
H
hbiss  Offline
Member
Joined: Dec 2003
Posts: 886
Hawthorne, NY USA
Don't think you're going to find one. I've seen equipment that use 208/3 phase and a separate 120 volt circuit for the controls.

-Hal

Re: Suplying a load from two different circuits #98937
06/27/06 12:35 PM
06/27/06 12:35 PM
C
Creighton  Offline
Member
Joined: Jan 2002
Posts: 59
Hayward, CA
What you describe is not permitted. See 210.4(A). "All conductors shall originate from the same panelbord." Although this applies to multiwire circuits I believe it to be a good rule to follow in any case.
Creighton

Re: Suplying a load from two different circuits #98938
06/27/06 01:16 PM
06/27/06 01:16 PM
J
Jonno  Offline
Member
Joined: May 2006
Posts: 20
I would go so far as to say that it is fine and sometimes needed to suply equipment from multiple sources, 600v motors with 120v control as an example, or anything with mixed AC/DC.

This strikes me as more of an issue of conductor bundeling.

It is necissary to keep all of the conductors (grounded and non) in a circuit bundled to ensure a ballanced current flow, which reduces the inducatnce of the wire run, prevents stray EMF, and prevent conduit heating. That bundle should be continuous to the panel (hense originatng for the same pannel) wher it is consoldated and then continues bundled to the POCO.

I don't know the code section off hand, and bing a Canadian I'm not sure it would help. I know this has ben dicused in other threads.

To sum up all conductors on the same circuit (ie feeding the same load) must run in the same conduit (be it cabtire, romex, EMT etc.)

Hope this helps,
Jon

Re: Suplying a load from two different circuits #98939
06/27/06 01:32 PM
06/27/06 01:32 PM
J
Jonno  Offline
Member
Joined: May 2006
Posts: 20
This may help, it is a thread on bundeling conductors: https://www.electrical-contractor.net/ubb/Forum4/HTML/000975.html

With two ciurcuts using the same grounded conductor, I am also concerned about overcurrent protection, which is normaly provided by the non-gronded conductor's protection

Re: Suplying a load from two different circuits #98940
06/27/06 09:02 PM
06/27/06 09:02 PM
HotLine1  Offline

Member
Joined: Apr 2002
Posts: 6,997
Brick, NJ USA
Tom:
Are you saying that one leg of a 240 volt circuit is 'tapped' and using the neutral of another circuit??

With all due respect to Creighton, you didn't state coming from multiple panels (sources) distinctly.

Is this a control circuit (120 volt) for a motor/machine??

Good practice would be 2 hots for 240 v; 1 hot-1 neut for 120 plus grounds as required.

As to an NEC Article?? I'll have to look tommorow; or bring this up at the Assoc. meeting Wed Nite.

John

PS: Almost forgot...I have labels stating "More then one source of power within this enclosure/equipment/cabinet"


[This message has been edited by HotLine1 (edited 06-27-2006).]


John
Re: Suplying a load from two different circuits #98941
06/29/06 11:52 PM
06/29/06 11:52 PM
E
e57  Offline
Member
Joined: May 2003
Posts: 2,876
S.F.,CA USA
An example of where it is allowed to have 2 or more can be found in 430.113. 620.52. Otherwise it can depend on the type of equipment.... Whats the example?

Either way I think its a bad idea to have a neutral from a different circuit used, as it may over-load the neutral....


Mark Heller
"Well - I oughta....." -Jackie Gleason
Re: Suplying a load from two different circuits #98942
07/01/06 07:59 AM
07/01/06 07:59 AM
E
earlydean  Offline
Member
Joined: Dec 2003
Posts: 751
Griswold, CT, USA
Look at 300.3(B). This section requires that all conductors of a circuit be contained in the same cable or raceway.
Using the 'hot' from a 240 volt branch circuit used for other purposes and returning on the neutral from another is bad for two reasons. One is the stray EMF you build by having the circuit conductors separated; two is the possibility of shock to some poor electrician who is trying to work on the circuit having the "pirated" neutral connection. He turns the CB "off", then checks for voltage at the receptacle box. Finding none, he proceeds to tear into the wiring, only to get caught up on the open neutral, which is carrying the return current from our "pirated" connection. Ouch!
I once got caught on the return from a 277 volt lighting circuit. Hurts for days.


Earl
Re: Suplying a load from two different circuits #98943
07/01/06 08:10 AM
07/01/06 08:10 AM
I
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Quote
Look at 300.3(B). This section requires that all conductors of a circuit be contained in the same cable or raceway.


Not always.

Look at 300.3(B)(3).

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Re: Suplying a load from two different circuits #98944
07/01/06 08:22 PM
07/01/06 08:22 PM
E
earlydean  Offline
Member
Joined: Dec 2003
Posts: 751
Griswold, CT, USA
Good point!

By using the neutral from one branch circuit, with the hot from another branch circuit, you have made a multiwire branch circuit.
Section 210.4(C) requires a multiwire branch circuit to feed only line to neutral loads, unless you use a CB that open all hots.
You have a 240 volt CB with a 240 volt load and you have another 120 volt load as parts of this multiwire branch circuit. Nor are these CBs tied together.

[This message has been edited by earlydean (edited 07-01-2006).]


Earl
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