Limitation in Number of circuit breakers in a Lighting / Power Panel

[NickParker]

I remember reading something about a change in the limit to number of CB's in panel? if the limit was/is 42 why do most manufacturers make 40 space panels? Where did the number "42" come from? Why not 48 or 50?

 

[waross]

36 x 15 Amps / 3 = 180 Amps
42 x 15 Amps /3 = 210 Amps
200 Amp panel size limit.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[mparenteau]

Same quantities of A, B and C phase circuits, so 24, 30, 42. Never saw a 40 circuit panel...uneven 3 phase circuits. I don't know what originally made the 42 circuit panel the limit for one can.

Mike

 

[davidbeach]

Single phase panels stop at 40 so that there are 20 on A and 20 on B. Three-phase panels put 14 on each phase. 45 wouldn’t make sense because the two sides wouldn’t be equal and 48 would be too much. Applies only to Lighting and Appliance (or some such, defined in the code) Panels, not all panels.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[NickParker]

NEC 408. 36 Exception No.2:
Exception No. 2: [highlight #73D216]Individual protection shall not be required for a panelboard protected on its supply side by two main circuit breakers or two sets of fuses having a combined rating not greater than that of the panelboard.[/highlight] A panelboard constructed or wired under this exception shall not contain more than 42 overcurrent devices. For the purposes of determining the maximum of 42 overcurrent devices, a 2-pole or a 3-pole circuit breaker shall be considered as two or three overcurrent devices, respectively.

I do not understand the Green highlighted. Can anybody tell me exact interpretation?

 

[waross]

Can you copy the text of rule 408.36 ?

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[NickParker]

Hi Waross, find below the snippet of 408.36

 

[dpc]

IIRC, the NEC was modified some years ago (2008??) regarding the 42 circuit limit. There used to be a distinction between "power panelboards" and "lighting and appliance" panelboards. I believe this distinction is no longer in the NEC. For new panel, I don't think the 42 pole limit applies any longer provided the panel is protected by a single main breaker.

Google is probably your friend here.