For a 200-amp load center used because that feeding charging tools that is around 400 ft from key switchboard, what dimension of bonding wire is required? — T. C.

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Answer

The question appears to deal with a voltage-drop situation, but information is missing. I will certainly answer the concern by inserting the minimum crucial information. The first item come clarify is the terminology. I presume you space referring come the size of the equipment grounding conductor v the feeder and not a bonding wire which is unknown by the NEC. The next little bit of information needed is the dimension of the ungrounded step conductors intended come be set up for this feeder. Note: if a voltage-drop calculate is performed for this 400-ft feeder, climate the device voltage and phase configuration of the feeder are crucial for the voltage-drop calculation. I will certainly answer the inquiry without the voltage-drop calculation information due to the fact that this info is missing.

First, the concern is restructured together follows:

What is the minimum size devices grounding conductor compelled for a feeder (400 feet in length) supplying a panelboard because that charging equipment?

For a 200-ampere feeder, a 3/0 copper conductor is generally required by the minimum demands of the NEC. The minimum size devices grounding conductor required for a 200-ampere feeder is not less than 6 AWG copper (see 250.122 and Table 250. 122). Currently if the feeder ungrounded conductors have been raised in size from 3/0 copper to 250 kcmil copper (for example) because that voltage autumn reasons, climate the required devices grounding conductor must also be raised in dimension proportionately . This is done as adheres to using Table 8, thing 9 that the NEC:

Using Table 8, chapter 9Required size 3/0 AWG = 167,800 cmAdjusted dimension 250 kcmil = 250,000 cm

Adjusted dimension phase conductor ÷ compelled phase conductor size = 250,000 ÷ 167,800 = 1.49The multiplier is 1.49. The size of the ungrounded circuit conductors has been raised 149%; therefore, the devices grounding conductors have to be enhanced 149% as well, every 250.122(B).

Required tools grounding conductor = 6 AWG copper (Table 250.122 based on 200 ampere overcurrent defense for the feeder)

Using Table 8, chapter 96 AWG = 26,240 cm × 1.49 = 39,097.6 cm

According come Table 8, a 4 AWG copper is compelled = 41,740 cm

The minimum size tools grounding conductor because that this 200-ampere feeder is a 4 AWG copper conductor. The prize is based on NEC-2008, sections 250.122, Table 250.122, and Chapter 9, Table 8 (conductor properties).

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I hope this helps with you questions worrying sizing equipment grounding conductors because that feeders. As always, above the local authority having actually jurisdiction for any type of local electric code rules that might be crucial in enhancement to the minimum requirements of the NEC. — Michael J. Johnston, CMP-5


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Michael Johnston is NECA’s executive director that standards and safety. Prior to his place with NECA, Mike was director of education codes and also standards because that IAEI. Mike holds a BS in organization Management native the college of Phoenix. Mike is the chairman the the NEC Correlating Committee. He offered on NEC CMP-5 in the 2002, 2005, and chair of CMP-5 representing NECA because that the 2011 NEC cycle. Among his obligations for managing the codes, standards, and also safety features for NECA, Mike is secretary of the NECA Codes and also Standards Committee. Johnston is a member the the IBEW and also is an energetic member of ANSI, IAEI, NFPA, SES, ASSE, ANSI-EVSP and ANSI-ESSCC, and the UL electrical Council, the nationwide Safety Council and vice chair of the NFPA electrical Section.