Bus Size and Frame Size

[zam]

On an electrical panelboard schedule, what does the bus size mean? The bus size (in amps) is usually written after the main circuit breaker size on the panel schedule. The standard circuit breaker sizes are found in the NEC section 240.6. What are the standard bus sizes? With regards to the frame size in a distribution panel, what are the standard frame sizes? Thank you.

 

[Smart $]

Frame size is the panelboard rating, typically the bus rating. An example is a panelboard (with enclosure) rated 225A and a 200A MCB. An example where this could be an issue is 240.21(C)(1)(b). Another is 705.12(D).

 

[iwire]

In my experaince

Bus size = rating of bus in amps. This rating may be the same as the over current device or larger

Frame size = the maximum rating in amps of breakers with rating plugs or fusable disconects. For example a breaker with a 200 amp frame size with a 150 rating plug.

 

[zam]

Re: Bus Size and Frame Size

On an electrical panelboard schedule, what does the bus size mean? The bus size (in amps) is usually written after the main circuit breaker size on the panel schedule. The standard circuit breaker sizes are found in the NEC section 240.6. What are the standard bus sizes? With regards to the frame size in a distribution panel, what are the standard frame sizes? Thank you.

30A, 60A, 100A, 200A, 400A, 600A, 800A, 1200A, 1600A, 2000A are the standard disconnect switch sizes. Do you what are the standard bus sizes and standard frame sizes? Also what actually is a bus in a panelboard?

 

[Smart $]

...Do you [know?] what are the standard bus sizes and standard frame sizes?

I believe 400A and above is same as disconnects... but uncertain if it is actually a standard rather than commonplace. You'd likely have to refer to NEMA standards to make that determination.

Also what actually is a bus in a panelboard?

In a typical MCB panelboard the conductors between the MCB and the either the branch breakers or the "fingers" to which they connect. Same for MLO but substitute main lugs for MCB. Also any "in between" grounded conductor supply and load terminations that is not wire.

 

[m sleem]

IMO, the bus size always refers to the breaker frame rating, but i had a project where one of the suppliers has a panel schedule dedicated for his system & shows information for bus size means that the busbar model not rating.