Electrical clearance in existing building

[alanb]

I am reviewing a public agency project were a replacement air handling unit (AHU) has been installed in an existing mechanical room. The mechanical room has no other equipment except the 120V AHU control panel and a water heater. The AHU is rated 480V and has two VFDs and a disconnect ahead of the VFDs. The clearances for the VFDs and disconnect are between 30"-40".

Customer recommended solution: The customer would like to relocate the disconnect such that the clearance is greater than 42" (but not 30" wide), and post signs that the electrical equipment cannot be opened or maintained unless deenergized, and the work can only be performed by qualified personnel. A sign can be posted at each entrance door and on each disconnect/VFD.

Any recommendations concerning the suggested solution?

 

[charlie b]

Re: Electrical clearance in existing building

I don't think the AHJ will buy it. I wouldn't. No sign is going to stop some management person from insisting that someone do live work "because we can't afford to shut it down at this time." I don't think it is ever right to scrimp on working clearance.

 

[tom baker]

Re: Electrical clearance in existing building

I had a clearance problem once with a 480 V MCC It needed 42" to a grounded surface, which was 12" water pipe. But only 36" to an insulated surface. My solution was to have an insulated pipe cover made, the AHJ accepted this.

 

[pierre]

Re: Electrical clearance in existing building

As an electrical engineer, you should realize there are not many requirements in the NEC that are there to protect the electrician - this is one of them. Lets give the electrician THE BARE MINIMUM REQUIRED CLEARANCES and require the building owner to give up some of his precious space to possibly save a life.

I know that I never, never would sign a special permission to give up this SAFETY requirement.

 

[tom baker]

Re: Electrical clearance in existing building

I reread the orginall post, I would not allow an exception from the 30". VFD's have to be worked on while energized.
Go to plan B

 

[alanb]

Re: Electrical clearance in existing building

Thanks for the info. If the disconnect and VFDs are moved, does the working space headroom requirement apply?

 

[derf48]

Re: Electrical clearance in existing building

110.26 Working space is what I call non-negotiable! It is a life safety item, and as stated here, a bare minimum. A simple way to teach the space to the non electrical personnel is to give it a real object comparison. I teach it as if it were a large refrigerator, everyone knows what that is and can visualize it. No, it is not exact, but the larger the voltage, the larger the frig.

Fred