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#49875 03/19/05 02:34 PM
Joined: Apr 2002
Posts: 7
Junior Member
engineer designed-150 amp 3 ph circuit feeds streetlights and handhole boxes in sidewalks for taps for city events.the end of the circuit goes back to the panel and is connected to another 150 amp brkr.yes a 360 degree loop.turn 1 brkr off and the circuit is still hot from the other brkr.same panel.he swears its legal.240.8 i think says no.

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#49876 03/19/05 02:54 PM
Joined: Jan 2003
Posts: 4,391
I agree with you 100%, in my opinion this is a direct violation of 240.8 as you pointed out.

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.

There could also be another violation.

240.4 Protection of Conductors.
Conductors, other than flexible cords, flexible cables, and fixture wires, shall be protected against overcurrent in accordance with their ampacities specified in 310.15, unless otherwise permitted or required in 240.4(A) through (G).

Two 150 amp breakers in parallel will provide 300 amps of current.

Are the conductors rated for 300 amps?

Is there any chance this engineer is from Europe?

Bob Badger
Construction & Maintenance Electrician
#49877 03/19/05 03:01 PM
Joined: Jan 2003
Posts: 4,391
You could probably throw this section at him also.

240.20(B) Circuit Breaker as Overcurrent Device. Circuit breakers shall open all ungrounded conductors of the circuit unless otherwise permitted in 240.20(B)(1), (B)(2), and (B)(3).

Bob Badger
Construction & Maintenance Electrician
#49878 03/19/05 03:08 PM
Joined: Jan 2003
Posts: 4,391
You got me thinking on this one.

Did the engineer do this to help lessen voltage drop?

If so and the conductors are 1/0 or larger you may be able to tie them together at the panel and land them on one breaker.

This would still be a ring circuit but would avoid the parallel breaker problems.

These ring circuits are a controversial subject some will argue it is nothing more than parallel conductors and others argue it violates 300.3(B).

Good Luck, Bob

Bob Badger
Construction & Maintenance Electrician
#49879 03/19/05 04:08 PM
Joined: May 2003
Posts: 2,876
e57 Offline
Bob's idea is a good one. Or a 6-pole breaker, they are out there, but who knows where to find one.

As for the instalation of a big loop like that... I don't know if that is a good idea. Say a connection fails at any point. How would you know? As you would probhably be using 120-N, or 208/240 between phases for the lights. (I figure this voltage as you say "Taps for city events".) Voltage from either side could feed around a bad connection. That, and how would smaller wiring be protected?

FYI: I used to work with air-field lighting, and most all of those systems are essentially a ring circuit. A single #8 can go around a whole runway, it runs through isolation transformers at each light This is all run by a HV 10 - 30+ Kw variable current transformer that acts a huge dimmer. When you had a bad connection, you knew right away - no lights.

Mark Heller
"Well - I oughta....." -Jackie Gleason
#49880 03/19/05 07:52 PM
Joined: May 2004
Posts: 50
Ring circuits are common place in the UK. In homes, offices and similar installations, socket outlet circuits are wired as rings from common breakers, but NEVER from seperate breakers.

In higher power supplies, some large installations, such as schools covering wide areas, they have high power rings from the substation, usually using 300mm csa plus SWA's and rated at 600A to 1200A (In the US similar supplies would be double due to you guys only using 120V).

However, which ever way you install a ring, the conductors should always be fed from common isolators / circuit breakers were all poles are interlinked and operate simultaneously.

[This message has been edited by FWL_Engineer (edited 03-19-2005).]

#49881 03/21/05 03:16 AM
Joined: Jan 2005
Posts: 354
pdh Offline
Carling Technologies makes 6-pole breakers. I don't know if these would serve your needs.

#49882 03/21/05 07:06 AM
Joined: May 2001
Posts: 717
This concept is called a radial loop. It is very common in medium voltage. You would normally open the circuit somewhere in the middle, but in case of failure you can feed from both directions, in this case, with full power (gotta be a BIT more cautious of that in MV).

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