NEC question - Roofing over outdoor Primary Subs 1

[nsbelectrical]

Is there any NEC regulation on putting an awning over a 34.5KV - 4160V outdoor transformer and switchgear? Required height, material, etc..?
NOTE: awning is to prevent large amounts of rain building up on transformer pad

Be Safe.

 

[rbulsara]

None that I know of.

The equipment enclsoure itself has to be rated for NEMA 3R(outdoor) or better application.

To your NOTE: How would water "build-up" on a "pad"? You provide proper drainage to avoid that, not a awning.

 

[BJC]

Outdoor equipment is rain proof as long as the doors are closed. Of course the doors never have to be opened during rainy weather and fuses only blow on sunny days. You can buy walkin gear or build a shelter.
One thing to consider about shelters is birds. The right kind of structure encourages them to nest and/roost over your gear. It can get very messy.
rbulsara is correct, pads should be sloaped to drain water away form gear.

 

[nsbelectrical]

To rbulsara,

We had a situation where the entire area flooded over the pad and water went through conduit to basement areas causing damage to drives and motors over $500,000 worth... so we have put walls on the pad with valve drains in case the area floods again, and the awning would prevent large amounts of rain entering pad.

Be Safe.

 

[davidbeach]

A better solution would be to correct the problem that allows water in the conduits to cause damage. All underground conduits should be assumed to contain water. It is not unreasonable to install drains to take care of water coming out of conduits to prevent damage.

 

[nsbelectrical]

Davidbeach I agree,

Those measures have been taken along with sump pumps. The awning is more a precautionary measure to help prevent damage in the event that sump pumps and drains do not do the job or fail. A large reason for this precautionary measure is b/c it so expensive to fix when this problem does occur.

Be Safe.

 

[dpc]

I'd be a little careful about putting an awning over an outdoor oil-filled transformer. Not sure what the fire marshal or your underwriter might think about that. Might depend on the type of construction used and proximity to any buildings. Transformers can turn into fireballs - rarely, but it does happen.

 

[rbulsara]

nsbelectrical:

Awning is certainly not an answer to the problem you describe. It sound like the sub is installed in undesireable (flooding) location. As davidbeach said too..take measure to seal the conduits, provide drains in conduits if need be, also provide U bends in conduit (with holes)or cables or break conduits between the entry point in the building and the first equipment it feeds so that any water in conduit do not get to the expensive equipment.

As for avoiding flood at the pad, seek advise of a geotech people.

Better yet, if the problem is so acute, look at the wholesale change to the design and equipment location.

 

[nsbelectrical]

Thanks rbulsara I will look into those options.

If those measures have been taken and we cannot move the sub, do you think an awning would help? Note the awning will probably be about 15 ft above the top of the transformer.

Be Safe.

 

[tinfoil]

Transformers are only as good as their ability to get rid of heat. Putting a roof over them, or decreasing their ventilation in any way, and you run the risk of having to derate the capacity of the transformers.

My utility installed a 'fake house' around three walls of an urban substation, with the 'roof' completely open, and still had to install forced air ventilation in the facade of the structure to keep things cool.


Rule #1 of digging: water will eventually find its way into every hole below local grade. Better to deal with that reality than to try to somehow stop it. If the entire area floods, I am unclear what teh awning is going to acomplish.

 

[rbulsara]

I doubt very much. But again I have limited knowledge of the ground realities.

An awning (if properly built)will only help, if the water getting in counduit is all coming thru top of the pad (that is getting below the pad through cable holes) and no where else. I doubt very much that this is the case, even if it sounds counterintuitive. Most flood water below a pad etc., comes from the ground water and seepage around the edges of pad. This gets a little complex, hence I advise to seek help of geotech people and they can tell you where exactly the water is coming from. You will be surprised.

 

[davidbeach]

With your wall around the transformer, you will only slow down the ingress of water. Once the soil is saturated, water will come up through the pad, particularly if the openings around the conduits are not sealed. Conduits running through saturated soil will (eventually) carry water from the saturated area into your building. Your scheme may well reduce the amount of water and the frequency of water ingress, but it will not eliminate the problem you had before. The only true solution is to accept that you will have water coming in through the conduits and keep the water from making it to the gear.

 

[nsbelectrical]

I will look into getting geotech people to asses where the water is coming from. So that we can be sure that if we stop most water from getting on the pad that it will eliminate our problem in the basement.

This post adapted to things I was not planning on discussing I would like to get back to the electrical application of this project as it is not really my job to decide whether or not the walls/awnings are effective but rather how they effect the electrical system (heat) and if they are legal...
I am considering putting complete walls on 2 or 3 sides of the pad leading up to the awning. Does this violate NEC code / fire code? Tinfoil touched on this some and I realize we will need forced air ventilation.

Thanks and



Be Safe.

 

[waross]

Have you installed seals on the conduits where they enter the building? It is improbable that the conduits can be kept dry in wet weather. It may be possible to prevent water in the conduits from entering the building.
respectfully

 

[davidbeach]

waross, you shouldn't be giving false hope. ;-)

It is far better to assume that the conduits will bring water into the building and deal with that then it is to assume that there is a way of preventing water from entering in the first place.

One project I did, I installed the medium voltage service equipment 3 floors below grade (generally not allowed by the utility), but arranged the installation such that the conduits entered pits below the gear, and provided drains for the pits. Beyond that water would have had to get at least 3 inches above floor level to begin to be a problem (secondary connections to the MV breakers, power connections much higher), and I had 30 or 40,000 sf of parking garage to absorb that water, assuming the sump pumps failed.

Again, far better to assume water in the conduits, regardless of any measures taken to slow down that water, than to assume that water can be kept out of the conduits.

 

[bigbillnky]

nsbelectrical

Goodevening.
Maybe I can help answer your specific question. I find no specific article in code that would prohibit an awning over a transformer. Code does require that adequate ventilation is provided to prevent the transformer from exceeding the max temperature rise as stated on the nameplate. It would probably be best to seek assistance from the transformer manufacturer's sales rep, or better yet, their application engineer, to ensure that the necessary ventilation is provided.

I would also suggest that provisions are made to allow for the replacemant of the transformer should it fail. Code also requires drains installed if you completely enclose the transformer with dike walls. Refer to the NEC, Articles 110, 450, and 490 for more information.

One other thing I will suggest is to follow all the good advice mentioned above. An ounce of prevention...........!!




Bigbillnky,C.E.F.....(Chief Electrical Flunky)

 

[nsbelectrical]

Thanks for the suggestions. To clear up a few things about this particular post.

We do assume water will get in the basement. We have drains and sump pumps. What we dont assume is that there is free flowing water into the basement (this was the case). We had over 5 ft. of water in a 60,000 sq. ft. basement. Flood water had gone over the conduits at the 2 of the primary subs and was free flowing through the conduit into the basement. We have filled the conduits with foam, dikes around the subs, and most likely will put an awning over them to prevent this from ever happening again.

Thanks bigbillnky for acknowledging my orginal question.

Be Safe.

 

[TestBeforeTouch]

If case you do decide to install an awning I would like to share some issues we have had with them.
Over the past 20+ years my plant has installed awnings on 8 substations. These substations are constructed with 15KV metal enclosed gear. The first couple of awnings were installed to eliminate water leaks into the gear from rust holes and worn out gaskets that caulking, sealant and replacing gaskets did not seem to fix.
In 1994 and 2004 we had large snowstorms (12+ inches of snow) that caused about half the awnings to collapse. These metal awnings were not very expensive and look identical to a residential or commercial carport.
The last awning that that the plant installed was designed so that the roof could withstand snow loading and hurricane force winds. It is constructed of I-beams and looks like it could support the weight of an army tank. My understanding is that the wind-loading requirement was the main reason for the size of the steel beams.
The awnings do prevent water from falling directly on the roof of the gear if the wind is not strong, however, for the size awning we have, the gear and the pad still get soaked during a strong storm.
The installers of the awning are probably not aware of the clear working space requirements in the NEC. In one of our installations the support post was too close (less than 6 feet at 15kv) to the gear and had to be relocated after it was installed.

 

[nsbelectrical]

Do you have removable roofs to change out the gear?

Be Safe.

 

[TestBeforeTouch]

Yes, the roofs are removable. The carport style roofs are raised by jacks, moved into place and attached to the preinstalled posts. The I-beam supported roof has removable panels.