4000 Amp Bus Bar

[Andrew_NYC]

Good afternoon. There is an installation in NYC where there is two (2)-2500amp service switches (fused at 2500A) connected to a 4000 Amp bus. Not sure of the connected load, but the fused service switches are exceeding 4000 Amps by 1000A? Don't seem right.

 

[infinity]

All that you need to know is that the 4000 amp bus is sized for the calculated load. Adding the two servcie disconnect sizes together is not relevant.

Welcome to the Forum.

 

[Andrew_NYC]

ere is an installation in NYC w

Thanks infinity.

Does the following apply, NYC Amendments
2) Ampacity of the service-entrance conductors for services 1000 kVA and larger shall not be less than
the sum of the maximum ampere ratings of the service disconnecting means. When including fire pump
disconnects in the calculation, 125 percent of the fire pump full load amperes shall be added.
Exception: The ampacity of service-entrance conductors need not exceed the maximum demand
calculated in accordance with Article 220, up to a maximum of 4000 amps per service

????

 

[infinity]

Here is the 2008 NEC version:

VII. Service Equipment — Overcurrent Protection
230.90 Where Required. Each ungrounded service conductor shall have overload protection.
(A) Ungrounded Conductor. Such protection shall be provided by an overcurrent device in series with each un- grounded service conductor that has a rating or setting not higher than the allowable ampacity of the conductor. A set of fuses shall be considered all the fuses required to protect
all the ungrounded conductors of a circuit. Single-pole circuit breakers, grouped in accordance with 230.71(B), shall be considered as one protective device.

Exception No. 3: Two to six circuit breakers or sets of fuses shall be permitted as the overcurrent device to provide the overload protection. The sum of the ratings of the circuit breakers or fuses shall be permitted to exceed the ampacity of the service conductors, provided the calculated load
does not exceed the ampacity of the service conductors.

 

[Andrew_NYC]

Thanks infinity. Attached is a Picture of a drawing in the field. A 4000A fused Switch (actually 2500A in the field) a 2500A switch and a 600A service switch on the 4000A bus. So, the calculated load is below 4000A.