We have a commercial building project that was originally drawn for a main breaker transfer switch and an outdoor 1200 amp MLO MDP. The customer removed the generator and transfer switch from the scope so we are left with a MLO MDP with 5 switches that has underground secondary conductors ran from a utility owned transformer. I understand we only have 5 switches and that is under the six switch rule but does the 2021 NEC require overcurrent protection for the secondary conductors coming from the transformer? First time using this forum and I appreciate the help.
Six Switch Rule vs Main Breaker
- Thread starter mopar1x39
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Electromatic
Senior Member
- Location
- Virginia
- Occupation
- Master Electrician
I'm not on the 2020 NEC, but my understanding is that the big change in that edition requires that the up-to-six disconnects now need to be in separate enclosures or an enclosure that somehow partitions off each switch/breaker. I don't know of any particular changes to the overcurrent protection of the service conductors.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Are you saying you have a 1200 amp main lug panel with 6 disconnects in the panel? If so that is not compliant with the new rules of 2020 nec
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
What is the thinking on this change?
hillbilly1
Senior Member
- Location
- North Georgia mountains
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- Owner/electrical contractor
The only thing I can think of, is maybe reducing arc flash exposure?
To your point, Yes the service conductors do require overcurrent protection for the secondary side of the transformer.
This is usually taken care of at the Service disconnecting means which is to be located at or near the nearest point of entry of those conductors to the building or structure.
The 6 movement rule is a separate issue which has changed in recent cycles of the code.
JAP>
In this case this MDP panel is the service disconnecting means so it would not be the six switch rule? or are you saying NEC says secondary conductors require Overcurrent protection? In the past we have seen AHJ's not require a main breaker in for instance a 4 bank meter center on a multifamily building.
texie
Senior Member
- Location
- Fort Collins, Colorado
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- Electrician, Contractor, Inspector
It seems you don't understand why you being asked if you are on the 2020 NEC. This is crucial as this would be permitted under the NEC prior to the 2020 edition. In the 2020 edition this is not compliant. What you have is compliant under NEC 217 and prior. Each of the 5 breakers is a service disconnect and is the required OCPD.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I believe it is to ensure that the buss bar is de-energized. If you have a main then you can work more safely in the panel. I blew up a trany once working on a 200 amp 12 circuit panel with no main. Got distracted and turned with screwdriver in hand. It hit the buss across both hot legs and BOOM.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
You knew better than that Dennis,,,, anyone who's been in the field long enough has witnessed a "BOOM" in one way or another.
I'm glad you're ok and I'm sure you had on your PPE at the time ......
JAP>
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
They are not supposed to be working in a live cabinet anyway.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Yes but reality is what it is. I have never met a resi guy who owned ppe.... In fact most small commercial companies don't use it either.
The requirement for a single main disconnecting means will enhance the safety of facilities. The six disconnect rule 230.71 (A) creates many problems for Electricians and Engineers in adding new electrical power distribution for new loads in an existing facility. A single main disconnect allows for the addition of new feeder devices without having to re-configure the service. Also, the single main disconnect is far safer as it allows the First Responder/Fire Department personnel or Electrician to easily disconnect power to the entire facility. Also, the new 2017 UL 67 Requirement for New Service Entrance Panelboards (NEC Article 408.3 (A)(2) requires that with the service disconnect in the off position, no ungrounded uninsulated live part is to be exposed to inadvertent contact by persons while servicing any load terminal, including a neutral load terminal, a branch circuit equipment grounding terminal, or the neutral disconnect link. The six handle rule has been used to avoid compliance with the GFCI protection for main disconnects of 1000 Amps or higher (230.95)
I cant see a single disconnecting means enhancing the safety of a facility.
Yes the 6 disconnect rule does hinder adding new loads if you're already at a max of 6 movements.
A single main does not allow for the addition of new feeder devices if the services is not built to handle the additional load in the first place.
I would agree the single main is a quicker way to disconnect power from a structure in case of an emergency.
Yes a main that is off may reduce a hazard on the load side of it, but, the hazard, or inadvertent contact still remains inside the panel on the line side so that is nothing more than a false sense of security.
I don't know of anyone who would service a load terminal or a neutral disconnect link without shutting the power off anyway.
Never really thought about using the 6 disconnect rule to avoid compliance with GFI protection, but, why is that not a genius way of thinking?
NEC made the rule on the 1000 amp and above rule to begin with. If they didn't want that rule bypassed they should have lowered the amperage requirement on services above 240 volts.
Point is, the panel should actually be completely shut down if working inside of it.
Just my 2 cents worth.
JAP>
I cant see a single disconnecting means enhancing the safety of a facility.
Yes the 6 disconnect rule does hinder adding new loads if you're already at a max of 6 movements.
A single main does not allow for the addition of new feeder devices if the services is not built to handle the additional load in the first place.
I would agree the single main is a quicker way to disconnect power from a structure in case of an emergency.
Yes a main that is off may reduce a hazard on the load side of it, but, the hazard, or inadvertent contact still remains inside the panel on the line side so that is nothing more than a false sense of security.
I don't know of anyone who would service a load terminal or a neutral disconnect link without shutting the power off anyway.
Never really thought about using the 6 disconnect rule to avoid compliance with GFI protection, but, why is that not a genius way of thinking?
NEC made the rule on the 1000 amp and above rule to begin with. If they didn't want that rule bypassed they should have lowered the amperage requirement on services above 240 volts.
Point is, the panel should actually be completely shut down if working inside of it.
Just my 2 cents worth.
JAP>
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