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Tapping Busbar Considerations

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This UL publication is from the April 2010 issue of Electrical Connections, and it may not reflect changes that have occurred since its original publication.

Many code authorities have encountered situations in which installers wish to tap busbars to accommodate the installation of fire pumps or to connect renewable energy sources such as photovoltaic systems.

This raises several questions, including the following:

  • Does this field modification affect the UL Listing of the panelboard or deadfront switchboard?
  • Are there any available guidelines for tapping the busbar?
  • What are the concerns regarding this practice?

Panelboards and deadfront switchboards are not Listed to have their busbars tapped unless there are existing holes in the busbars marked with the word “Tap” adjacent to the holes. Other holes in the busbar that are not marked with the word “Tap” are intended for the connection of overcurrent devices, other device’s as identified by the product markings and in the installation instructions or other uses identified by the manufacturer.

When the electrical equipment Listing does not include product markings or instructions for tapping busbars, code authorities often ask what can be done to approve such modifications. This situation should be treated like any other field modification of Listed equipment.

Click here to download and read the paper.

For more information, visit www.ul.com

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  • Mike:

    Any such modification to the equipment in question is VERY dangerous and poses serious risks to the equipment involved. Namely: 1) Any such modification to the equipment without prior direct approval and permission from the equipment manufacturer can affect the integrity and reliability of said equipment. 2) Any such modification to the equipment would require the direct authorization of the Local AHJ. 3) Coordination between the Available Short Circuit Current availability and the WIC of the equipment (fire pump or pumps) MUST be preformed and approved by both of the manufacturers of the equipment involved. 4) Reliability of the power source feeding the equipment in question must be investigated and approved by the Local AHJ, including the local fire inspector. 5) Ditto for the fire insurance company involved. 6) The affect of the intended new load (fire pump or pumps) on the equipment in question must be investigated and approved by the equipment manufacturer as well as the local AHJ and the insurance company. E.G. what risks to the equipment in question would be involved by connecting said fire pump or pumps. 7) The starting method used by the fire pump controller or controllers is very important to said coordination studies. 8) This especially since even reduce voltage (current) starting methods in the fire pump controller(s), such as wye-delta, autotransformer, part winding, soft-start, & etc. will still impose a Full Voltage, Locked Rotor load on the equipment when the fire pump(s) are either started Manually, -- by uses of the Manual Mechanical Operator means on the fire pump controller(s) -- will always impose Lock Rotor Current on the equipment in question. 9) Ditto if, for any reason, power to the equipment in question is interrupted and the fire pump controller(s) are locked via the aforementioned Manual Mechanical Operator. 10) Coordinating with the equipment manufacturer may involve going thru several layers of contractor and/or sub-contractors; but, is nonetheless essential. 11) In general then, any such proposed connection must be fully engineered and approved by both manufactures, the insurance company, and the Local AHJ.

    James S. Nasby  January 28 2019, 12:59 am EST
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