Allowed or no?

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hardworkingstiff

Senior Member
Location
Wilmington, NC
Does the NEC allow (rather prohibit) running two circuits of the same ampacity to multiple loads and connecting the two circuits together at the end of the run?

Example. Pull a 100-amp rated cable to power center A that has two 50-amp (240-volt) shore power receptacles, then loop out of this power center to the adjacent one (B) (configured the same) and then back to the panel. Both cables in the panel will be connected to separate breakers (phasing maintained).

My 1st reaction is no way. Then, I thought about it and did not know the reason why. I don't see how a fault could put more ampacity on the conductor than it was rated for, and the power centers have their own OCD for their outlets.

Thoughts?
 

iwire

Moderator
Staff member
Location
Massachusetts
Re: Allowed or no?

That is the same as a English ring circuit, but with their ring circuit they put OCP at each outlet.

Without the OCP at the outlet in your example you would have 100 amps available at the 50 amp outlet.

I agree with Mike that it puts the OCP in parallel and therefore is a violation, but there is disagreement on this.

Be prepared for a long thread. :cool:
 

roger

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Location
Fl
Occupation
Retired Electrician
Re: Allowed or no?

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.
Roger

[ November 13, 2005, 11:07 AM: Message edited by: roger ]
 

roger

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Fl
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Retired Electrician
Re: Allowed or no?

Hardworkingstiff, I apologize, I was editing my post to include the wording of 240.8 when you posted.

Roger
 

john m. caloggero

Senior Member
Re: Allowed or no?

I drew a diagram including the bus arrangement in the supplying panelboard. I detect three Code violations as follows:

(1) Section 240.8: The two 50 amp breakers are in parallel for a total of 100 amps to the receptacles.

(2) Table 21.24: A 50 amp receptacle is not allowed on a branch circuit greater than 50 amps.

(3) Section 310.4: The supply conductors are in parallel due to the interconnection between the load distribution panels. The conductors do not satisfy the minimum size of 1/0 and the conductor lengths would be un-equal.
 

pierre

Senior Member
Re: Allowed or no?

Parallel conductors.
electrically joined at both ends.
If there are two sets of overcurrent devices, then this would not comprise a parallel installation.
Am I understanding this installation properly?

Also, take a peak at 240.8.

[ November 13, 2005, 10:39 PM: Message edited by: pierre ]
 

hardworkingstiff

Senior Member
Location
Wilmington, NC
Re: Allowed or no?

john,

Based on your response, I believe we did not obtain accurate communication. These conductors are not branch circuits, rather they are feeders. I say this because the power centers have breakers in them for the receptacles they serve. It is not uncommon to have 2 50-amp and 2 30-amp receptacles on each power center and feed it with a 100-amp feeder. This would negate your point number 2.

On point 3, the wiring method discussed is different in that the two separate (as originating at the panel) circuits are not connected to the same overcurrent device. Both feeders would be rated at 100-amps and both would have OCP at 100-amps. I don't see how either feeder could become overloaded.

Pierre makes an excellent point about switching off one breaker and having the other still energized, a real safety problem. I believe this may be able to be rectified with a handle tie, but larger hurdles exist.

Pierre also brings up the question of the definition of parallel circuits. While this is an interesting question, I don't believe we can dispute that in the wiring method described the breakers would be connected in parallel and therefore would not be allowed per 240.8.
 

charlie b

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Location
Lockport, IL
Occupation
Retired Electrical Engineer
Re: Allowed or no?

Originally posted by pierre: Parallel conductors. electrically joined at both ends. If there are two sets of overcurrent devices, then this would not comprise a parallel installation.
The words "electrically joined at both ends" (from 310.4) are not relevant to this situation. Those words are explaining "parallel conductors." The conductors are not parallel in this situation. But the breakers are in parallel. I agree with the statement that this is a violation of 240.8.
 
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