A 1600-A, 3-phase, 208/120-volt service is supplied with five parallel sets of 500 kcmil ungrounded conductors. What is the minimum size for the main bonding jumper?

A 1600-A, 3-phase, 208/120-volt service is supplied with five parallel sets of 500 kcmil ungrounded conductors. What is the minimum size for the main bonding jumper?

• A. 350
• B. 3/0
• C. 4/0
• D. 250

Answer: (A)

Main bonding jumper size is driven by the service rating. The neutral must be bonded to the equipment grounding conductor at the service disconnect, and the jumper that does this must be large enough to carry the fault-current path implied by the service rating. Here, five parallel sets of 500 kcmil ungrounded conductors are supplying a 1600 A service. Each 500 kcmil conductor has an ampacity well above 1600 A when you sum the five parallel paths (even using the lower 60°C rating, 380 A per conductor × 5 = 1900 A). So the service is effectively rated at 1600 A, and the main bonding jumper must be sized for that rating. For a service of 1000–1999 A, the minimum copper main bonding jumper size is 350 kcmil. Among the given options, 350 kcmil is the smallest size that meets that requirement; the AWG options (3/0, 4/0) and 250 kcmil are all smaller and would not meet the minimum. So the minimum main bonding jumper size is 350 kcmil copper.

Main bonding jumper size is driven by the service rating. The neutral must be bonded to the equipment grounding conductor at the service disconnect, and the jumper that does this must be large enough to carry the fault-current path implied by the service rating.

Here, five parallel sets of 500 kcmil ungrounded conductors are supplying a 1600 A service. Each 500 kcmil conductor has an ampacity well above 1600 A when you sum the five parallel paths (even using the lower 60°C rating, 380 A per conductor × 5 = 1900 A). So the service is effectively rated at 1600 A, and the main bonding jumper must be sized for that rating.

For a service of 1000–1999 A, the minimum copper main bonding jumper size is 350 kcmil. Among the given options, 350 kcmil is the smallest size that meets that requirement; the AWG options (3/0, 4/0) and 250 kcmil are all smaller and would not meet the minimum.

So the minimum main bonding jumper size is 350 kcmil copper.