NEC 110.26 Workig Clearance Requirements

[enverd]

Reviewing 110.26.A.1 and associated table the working space depth is clear on its requirements.
However I have been told that if you have two switchboards facing each other at 600V where one of the boards is 3000A and the other is 800A, you have to double the working clearance. As for the reasoning I was directed to 110.26.2.b and associated Exhibit 110.19 but after reviewing the information I just don't agree because the Exhibit clearly shows that both switchboards need to be 1200A or more for the working space to be doubled.

Thoughts please?

Thanks in advance.

 

[rcw retired EE]

My interpretation is that working space depth is only doubled if there is only one egress from the space. If there is an exit path at boths ends of the aisle between the two pieces of equipment, the aisle width can be the single depth given in the table.

BUT, I would never use the minimum clearance on a 3000A board. It is just too small a space for safe maintenance, especially with the appropriate arc flash hazard protective clothing.

Note that the "Exhibits" you refer to are explanatory material from NEC Handbook and are not a part of the Code.

 

[enverd]

Thanks for the input rc,

I agree that it is doubled when you have only one egress door but that also depends on the Amp size of the switchgear doesn't it? It seems as if 110.26.2.b is not very clear on that? Or I might be misreading it.

I completely agree with you on the subject of always providing enough space for the safe maintenance, however this is an existing situation and it was just brought up for the discussion. So even though I don't agree how it was done during the original construction neglecting good practice I am trying to completely understand if the install is per code or not.

 

[dpc]

I would never use the minimum clearance on a 3000A board

On many commercial buildings, we have to fight architects tooth and nail to even get an electrical room at all and bare minimum NEC clearances. It's nice to have a big room with a lot of space, but that just isn't reality in many situations - at least in my world.

 

[enverd]

DPC,

I completely agree, we are having great deal of trouble in that regard as well.
As a matter of just on the last Medical Office Building we designed, the size of the room actually got small as the design went on so we had to get very inovative.

 

[dpc]

The architects like to talk about electrical "closets".

 

[rbalex]

Section 110.26(C)(2)(b) applies to either or both switchgears where 110.26(A)(1), Condition 3 exists. That is, only one of them must be 1200A or greater since it alone still must have entrance/egress from the workspace at each end or meet 110.26(C)(2)(b). [110.26(C)(2)(a) is virtually impossible to achieve in Condition 3.]