tapping a bus in service equipment

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mollydodger

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I have an engineer who has designed a job and he is requiring me to "tap" a bus inside a 2000 ampere service enclosure. The "tap" is to feed a new 800 ampere disconnect that will provide power to a new motor control center. The 800A disconnect is at least 50 feet from the service bus enclosure. The 2000A service equipment is old and has no available spaces to add an 800A section with fuses/breaker. I do not believe the NEC allows me to "tap" a service equipment bus and exit the enclosure without overcurrent protection where the conductors recieve thier supply. I have reviewed all the "tap rules and find none that permit such a tap. Please comment. :confused:
 
mollydodger said:
I have an engineer who has designed a job and he is requiring me to "tap" a bus inside a 2000 ampere service enclosure. The "tap" is to feed a new 800 ampere disconnect that will provide power to a new motor control center. The 800A disconnect is at least 50 feet from the service bus enclosure. The 2000A service equipment is old and has no available spaces to add an 800A section with fuses/breaker. I do not believe the NEC allows me to "tap" a service equipment bus and exit the enclosure without overcurrent protection where the conductors recieve thier supply. I have reviewed all the "tap rules and find none that permit such a tap. Please comment. :confused:
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I would say that tap would have to meet 230.6(1) and (2) unless I missed something big time.
 
You need to get overcurrent protection within 25' of the tap.

I assume this tap is after the service disconnect so 240.21(2) would apply.

Also keep in mind the EGC with this tap will be based on the 2000 amp main.
 
dcspector said:
Bob this may be a tap ahead of main from what I read. Typical in gear.
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It could be. :)

But if it is, the problem that could not be overcome is having the service disconnects 50' apart. The conductors could be concrete encased but there is no way around grouping. :)
 
tom baker said:
We are assuming the design covers AIC. I am not sure if this voids the UL listing of the gear or not.
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Tom that is a good point, in the past we have always made are own taps, now I think it is better to have a panel shop design a means to tap the bus.
 
service bus tap

service bus tap

The tap is to be made on the main bus INSIDE the service equipment. There is NO single main disconnect and the gear already has six means of disconnect. Aside from the requirement to group all the service disconnects if this one is added, I do not believe the NEC permits a tap of a bus and then exiting the service enclosure WITHOUT an OCPD at the tap. It does allow for, under specific conditions, taps for transformers feeders and branch circuits, busways etc. but it does NOT mention tapping a bus bus INSIDE service equipment and then leaving the enclosure nor does it set any perameters for such a tap. At least I do not find a reference. Thanks for the replies so far. More comments welcome!!
 
As an inspector, I recently had 2 jobs similar to this.

1. I requested the contractor to provide a letter from the manufacturer of the equipment to say that the tapping of the bus as proposed would be acceptable by the manufacturer.
The manufacturer's response was that they would not permit the tap as per their specifications to the bus and would not support the equipment if the taps were made. The property owner decided that they did not want to go that way, a new service was installed.

2. Another job, the contractor installed additional conductors to existing lugs installed by the manufacturer, and left the enclosure. We required concrete encasement...which they are performing as I write.
 
tom baker said:
We are assuming the design covers AIC. I am not sure if this voids the UL listing of the gear or not.
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Every field "addition" needs to be re-evaluated (even those done by the manufacturer's techs), especially if the factory did not include provisons when the equipment was built. The question is: will the AHJ require a UL field evaluation.
 
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