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Experience:  30 years Licensed Electrical Contractor in Illinois, Adjunct College Electrical Instructor, Former Electrical Inspector, Diploma: Digital Electronics, FCC Technician License
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# We are installing a 3000 amp mdp with 8 parallel runs of 500

### Customer Question

We are installing a 3000 amp mdp with 8 parallel runs of 500 mcm copper. This is a 480 volt 3 phase set up. Trying to confirm the size of grounding wire to be run tothe grounding pipe bushings. Size if we run a wir from each individually or all of them together and run one wire to the ground bus
Submitted: 1 year ago.
Category: Electrical
Expert:  Kevin replied 1 year ago.

Hello and welcome to Just Answer. My name is ***** ***** I will be happy to assist you with your electrical question.

1) Install (1) one contiguous bonding conductor from bushing to bushing (in a daisy chain fashion) and then land it on the ground bus.

2) Bonding jumper is sized according to Table 250.66. Since the ungrounded conductors are 500 kcm coppers, use a 1/0 copper as the bonding bushing conductor.

3) Refer to Article 250.102 Bonding Conductors and Jumpers (C)(2) Size for Parallel Conductor Installations. for explanation.

4) If you have a copy of the 2011 NEC Handbook, Exhibit 250.37 located on page 252 illustrates bonding bushing grounds/jumpers.

If you have any additional questions, just let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.

Thanks..............Kevin:)

Customer: replied 1 year ago.
Is that table 250.66 only for grounding electrode conductors. We are bonding or connecting the ground bushings on the pipes coming from the transformer Do I use 250.122 or 250. 102c of 2014 code book. Thinking that 250.66 is for grounding electrode which we already have in which we used 3/0 with all the parallels conductors
Expert:  Kevin replied 1 year ago.

1) Article 250.102 refers you to use Table 250.66 for sizing the bonding jumper on raceways. Table 250.66 is for dual purpose use...ie.........sizing the GEC and also the bonding bushing conductor.

2) Table 250.122 is for equipment grounding conductors and is not used for a bonding bushing. Article 250.122 is also for equipment grounding conductors.

If you have any additional questions, just let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.

Thanks.............Kevin:)

Expert:  Kevin replied 1 year ago.

If you have any additional questions, just let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.

Thanks.............Kevin:)

Expert:  Kevin replied 1 year ago.

If you have any additional questions, just let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.

Thanks.............Kevin:)

Expert:  Kevin replied 1 year ago.

If you have any additional questions, just let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.

Thanks.............Kevin:)

Expert:  Kevin replied 1 year ago.

If you have any additional questions, just let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.

Thanks.............Kevin:)

Expert:  Kevin replied 1 year ago.

If you have any additional questions, just let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.

Thanks.............Kevin:)