Ring Main / Ring Wiring Method

mpillow

Member
Location
Ohio
Occupation
Business Owner
Hello. Some of my UK coworkers are suggesting we use the ring wiring technique in an industrial application (product to be installed in the US). I was hoping someone could help me identify the area of the NEC that would address this proposal. Thanks for your input.
 
Hello. Some of my UK coworkers are suggesting we use the ring wiring technique in an industrial application (product to be installed in the US). I was hoping someone could help me identify the area of the NEC that would address this proposal. Thanks for your input.
Could you elaborate on the setup and what exactly you mean? Generally ring circuits are not used in the US for wiring under the NEC.
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
Hello. Some of my UK coworkers are suggesting we use the ring wiring technique in an industrial application (product to be installed in the US). I was hoping someone could help me identify the area of the NEC that would address this proposal. Thanks for your input.
Get everyone together, and give each a complete copy of 310.10 H and talk through the meaning of the words.
 

mpillow

Member
Location
Ohio
Occupation
Business Owner
Single line link. 310 says we need to follow a method, and the relevant one would be parallel, but requires conductors to be in the same raceway etc and terminated together at both ends.
 

GeorgeB

ElectroHydraulics engineer (retired)
Location
Greenville SC
Occupation
Retired
... (product to be installed in the US). I was hoping someone could help me identify the area of the NEC that would address this proposal.
WITHIN the product, it is unlikely that the NEC will apply. As @electrofelon said, Could you elaborate on the setup and what exactly you mean?
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Maybe he meant 110.8?
Nope - I meant 110.9.

Ring systems can have fault contributions from multiple directions and the fault interrupting requirement is calculated by the current available from all directions at the "line side" of the interrupter. Non-fault interrupters only have to be rated for the current they are expected to interrupt.
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
Single line link. 310 says we need to follow a method, and the relevant one would be parallel, but requires conductors to be in the same raceway etc and terminated together at both ends.
The challenging part of the 310.10 H rule is in the limit to 1/0 AWG, and larger, conductor sizes. If your single line diagram is the assembly you are inquiring about, your largest wire gauge is a lot smaller than 1/0.
 

mpillow

Member
Location
Ohio
Occupation
Business Owner
WITHIN the product, it is unlikely that the NEC will apply. As @electrofelon said, Could you elaborate on the setup and what exactly you mean?
The wiring proposed is 1/0. There are a string of subpanels that are daisy chained together, each with breakers for downstream equipment. Proposal is to run the 1/0 cable to each end of the string from a UPS that has a single circuit breaker.
 

mpillow

Member
Location
Ohio
Occupation
Business Owner
The challenging part of the 310.10 H rule is in the limit to 1/0 AWG, and larger, conductor sizes. If your single line diagram is the assembly you are inquiring about, your largest wire gauge is a lot smaller than 1/0.
The smaller gauges would not be part of the circuit being discussed, they are downstream of the ring main.
 

mpillow

Member
Location
Ohio
Occupation
Business Owner
One other thought we had was that since we are designing the entire 'ring', we could ensure that the wire lengths are the same. There would just be a series of terminal blocks between the "start" and "end" of what we are calling a parallel run. Thanks for everyone's thoughts.
 

mpillow

Member
Location
Ohio
Occupation
Business Owner
Question is what advantage will this will give you?

-Hal
Hal, good question. The problem is that we would have to use 300amp rated wire, and even more importantly the daisy chain wires would have to be the same size. This would make it impossible for us to use the entire setup. Root cause is the single 300amp breaker on the UPS.
 

mpillow

Member
Location
Ohio
Occupation
Business Owner
Hal, good question. The problem is that we would have to use 300amp rated wire, and even more importantly the daisy chain wires would have to be the same size. This would make it impossible for us to use the entire setup. Root cause is the single 300amp breaker on the UPS.
Here is a picture of the daisy chain. If the wire sizes were doubled we would not be able to hold the spacing.

picture of daisy chain wire interconnect
 
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