This being a rather diverse group, lemme throw one out here.
High Voltage (OK, Medium - 13.8kv) room containing network protectors, switchgear, and transformers, liquid and dry.
Air - Positive or negative pressure? Arguments are - Negative and all the dust comes into your room, Positive and in case of fire all the fumes blow into your egress hallways. Natural ventilation is highly impractical, or not possible.
I can find no code pointing to either. Does anyone have any info on if it should be positive or negative? Article 450 quotes an ANSI document C57.12.00-1993 but I don't have it, and can't even find it on ANSI's website.
George - I can't cite a code reference for you - sorry - even looked in the Fire Codes - But I'll bet you dollars-to-donuts that your Fire Marshall has an opinion (that he'll want enforced) about this; and one other source I've experienced has a final say-so is the company's insurance underwriters. I manage construction projects for a Fortune 500 company and we've found belatedly that the insurance underwriters through their engineering dept. have made demands above and beyond the codes...thus we've learned to run a few things by them first.
Re: Transformer rooms#12945 08/22/0211:20 AM08/22/0211:20 AM
The Low Voltage / VA ones I have dealt with [600 VAC and lower, 750 KVA and down] which were installed inside of a Designated "Electrical Room", normally would have supply air blowing in 24/7, and maybe a very small return air register / grill [if any!].
Some came directly from the cold air supply of HVAC systems, others were connected to like a "Dedicated Cold Air Supply For Equipment" Plenum, others just blew in outside air.
Don't recall seeing any that were negative pressure [return air only], probably due to the fact that the Buildings used ceiling space for return air [AKA Plenum Ceilings], and this would really "Suck" [no pun intended] for cooling transformers!
Now as for the PoCo's Transformer Vaults, they are normally Passive Cooled with noticeable vent stacks popping up from the vaults.
On one project in Westwood Village [on Wilshire Blvd. just down the street from Beverly Hills], the meters and MSB's were in the basement next to the PoCo's 34.5 KV Transformer Vault [separated by a locked explosion and fire resistant door]. This vault was only ventilated at the street, but did have a blower to move air. So did the gear room, since it had a bunch of transformers inside. This area was positive pressure, but not ducted for return.
Scott " 35 " Thompson Just Say NO To Green Eggs And Ham!